JP2005101765A - Method and apparatus for processing image, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for processing an image which processes the image based on a stored attribute by extracting an amount of features of image data by preliminarily scanning, judging the attribute of an original from the extracted amount of the features, and storing the attribute and to provide an image forming apparatus. <P>SOLUTION: The apparatus for processing the image includes an original classification judging unit 10; a base level judging unit 50 and a number-of-general halftone dot line judging unit 60 which extract the amount of the features of the original from the image data of the original read by the preliminarily scanning, and judge the classification of the original, the base level and the attribute of the original of the level of the number of the halftone dot lines from the extracted amount of the features; and store the attribute of the judged original in a storage unit 20. The image data read by this scanning are compressed by an image compressing unit 21, and stored in a storage unit 22. The image data recovered by an image recovering unit 23 are processed by input gradation correction processing, color correction processing, black generation base color removal processing, a space filter processing, output gradation correction processing, gradation reproduction processing, etc. based on the attribute of the original. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides an image processing method for reading image data of a document by pre-scanning and main scanning, extracting a feature amount of the document from the read image data, and performing image processing of the read image data based on the feature amount, The present invention relates to an image processing apparatus that executes an image processing method and an image forming apparatus including the image processing apparatus.

  Due to the recent progress of digital image processing technology and the digitization of information due to the high penetration rate of networks, image forming apparatuses such as digital color copiers or color digital multifunction peripherals that reproduce color images with high image quality have been commercialized.

  When copying a plurality of originals using these image forming apparatuses, image processing is performed after temporarily storing the read images in a storage device in order to process a large number of originals at high speed. In addition, since a plurality of originals having different image characteristics such as character images or photographic images are mixed, it is necessary to perform image processing with good reproducibility according to the characteristics of these images. For this reason, the feature amount of the document read by scanning the document is extracted, and image processing is performed based on the extraction result.

  For example, when a plurality of originals are copied by performing a reduced layout that reduces them to one printing sheet, the plurality of originals are pre-scanned, the read image data is stored in a storage device, and each of the originals is stored. A luminance signal is extracted from the read image data of the image and a histogram is created by adding the number of pixels of the same luminance signal level. From the generated histogram, an image of an image such as the brightest signal level, the darkest signal level or the most frequent level is displayed. Extracts feature values, creates a brightness / density conversion table according to the feature values, and uses this table to perform automatic density conversion processing (hereinafter referred to as AE processing) of image data read by the main scan. A method has been proposed (see Patent Document 1).

  Also, the image data read by scanning the document is encoded and stored, and a histogram indicating the luminance distribution of the document is created from the encoded data, and the brightest level, the darkest level, etc. of the image are generated from the created histogram. There has also been proposed a method of detecting feature amounts and performing AE processing based on the feature amounts (see Patent Document 2).

According to another conventional example, the image data read by the main scan is temporarily stored in the storage device as it is, and is read from the storage device before performing image processing based on the extracted feature amount. .
JP-A-8-84247 JP 9-93438 A

  However, since the method according to Patent Document 1 stores all pre-scanned image data, enormous storage capacity is required to store high-resolution image data, and a reduction in storage capacity is desired. It was.

In the method according to Patent Document 2, a density histogram of an image is created from encoded image data, and density information such as the number of peaks above a certain frequency and the frequency of the peaks, the brightest level, and the darkest level is obtained. Since density conversion processing is performed based on this, only the original is recognized as a normal image, a reverse image, and a gradation image, and image processing with higher image quality has been desired.
Further, since all of the scanned image data is stored, a large storage capacity is required even for an encoded image.

  Further, in the other conventional example, since the image data read by the main scan is stored in the storage device as it is, in order to store the image data with high resolution, a huge storage capacity is required, and the storage capacity is reduced. It was desired.

  The present invention has been made in view of such circumstances, and extracts the feature amount of the document from the image data of the document read by the preliminary scan, determines the attribute of the document from the extracted feature amount, and determines the determined Provided is an image processing method, an image processing apparatus, and an image forming apparatus provided with the image processing apparatus capable of reducing the storage capacity by storing the attributes of the original document as compared to storing the read image data as it is. There is.

  Another object of the present invention is to compress and store the image data read by the main scan, and perform image processing after restoring the stored image data, so that the read image data is stored as it is. An object of the present invention is to provide an image processing method, an image processing apparatus, and an image forming apparatus including the image processing apparatus that can reduce the storage capacity.

  Another object of the present invention is to determine an original composition area such as a character area, a halftone dot area, and a photographic paper area from image data read by preliminary scanning, and based on the original composition area, a character original, print An object of the present invention is to provide an image processing method, an image processing apparatus, and an image forming apparatus including the image processing apparatus that can perform image processing according to the type of the original by determining the type of the original such as a photo original.

  Another object of the present invention is to provide an image processing method, an image processing apparatus, and an image processing method capable of performing image processing according to the background level of the document by determining the background level of the document from the image data read by the preliminary scanning. An object of the present invention is to provide an image forming apparatus provided with a processing device.

  Another object of the present invention is to determine the halftone line number level of an original from image data read by preliminary scanning for image reading, thereby enabling image processing according to the halftone line number level of the original. A processing method, an image processing apparatus, and an image forming apparatus including the image processing apparatus are provided.

  An image processing method according to the present invention extracts a feature amount of image data of a read original and performs image processing on the read image data based on the extracted feature amount. Extracting the feature amount, determining the attribute of the document from the extracted feature amount, storing the determined attribute of the document, and performing image processing on the image data read by the main scanning based on the stored attribute of the document It is characterized by that.

  The image processing method according to the present invention is characterized in that, in the above-described invention, the image data read by the main scan is compressed and stored, and the image processing is performed after the stored image data is restored.

  In the image processing method according to the present invention, in the above-described invention, the attribute of the document is a document type, the document configuration area is determined from the feature amount, and the document configuration area is determined based on the determined document configuration area. The type is determined.

  The image processing method according to the present invention is characterized in that, in the above-mentioned invention, the document attribute is a background level of the document.

  The image processing method according to the present invention is characterized in that, in the above-mentioned invention, the document attribute is a halftone line number level of the document.

  An image processing apparatus according to the present invention includes an extraction unit that extracts a feature amount of image data of a read original, and an image processing unit that performs image processing on the read image data based on the extracted feature amount. In the apparatus, an extraction unit that extracts a feature amount of image data by preliminary scanning, a determination unit that determines an attribute of a document from the extracted feature amount, a storage unit that stores the determined attribute of the document, and a storage And image processing means for performing image processing on the image data read by the main scanning based on the attribute of the document.

  In the image processing apparatus according to the present invention, in the above-described invention, a compression unit that compresses image data read by the main scan, a storage unit that stores the compressed image data, and an image process that restores the compressed image data. And a restoring means for restoring the compressed image data.

  In the image processing apparatus according to the present invention, in the above-described invention, the determination unit that determines the attribute of the document is a determination unit that determines a type of the document, and a determination unit that determines a document configuration area from the feature amount. And determining means for determining the type of the document based on the document configuration area.

  The image processing apparatus according to the present invention is characterized in that, in the above-mentioned invention, the determination means for determining the attribute of the document is a determination means for determining the background level of the document.

  The image processing apparatus according to the present invention is characterized in that, in the above-mentioned invention, the determination means for determining the attribute of the original is a determination means for determining the halftone line number level of the original.

  An image forming apparatus according to the present invention includes any one of the image processing apparatuses according to the above-described invention, and further includes an image forming unit that forms an image based on image data processed by the image processing apparatus. Features.

  According to the present invention, the entire image data of the read document is stored in order to determine the attribute of the document from the feature amount of the document extracted from the image data of the document read by the preliminary scanning and store the attribute of the document. Compared to the case, the storage capacity can be reduced.

  Further, in the present invention, the image data read by the main scan is compressed and stored, and the stored image data is restored and then subjected to image processing, thereby storing the read image data as it is. The capacity can be reduced.

  Further, in the present invention, a document composition area such as a character area, a halftone dot area, and a photographic paper area is determined from image data read by preliminary scanning, and based on the document composition area, a character document, a printed photograph is determined. By determining the type of document such as a document, image processing can be performed according to the type of document, even if the document is a mixture of text, printed photographs, or photographic paper photographs, and good image formation is possible. It becomes.

  In the present invention, the optimum background removal processing according to the background level of the document is determined by determining the background level indicating the presence / absence of the background of the document and the density classification of the background level from the image data read by the preliminary scanning. Therefore, it is possible to form a good image.

  In the present invention, it is possible to perform optimum filtering by determining the presence / absence of halftone dots and the level of the number of halftone dots indicating the level of the number of halftone dots from the image data read by the preliminary scanning. Improvement and the formation of a good image without moire.

  According to the present invention, the attribute of the document is determined from the feature amount of the document extracted from the image data of the document read by the preliminary scanning, the attribute of the document is stored, and image processing is performed based on the attribute of the document. Regardless of the resolution of the input image data, it is not necessary to increase the storage capacity, and the storage capacity can be reduced as compared with the case where the entire image data of the read original is stored. An image can be formed according to the attribute.

  Further, according to the present invention, the image data read by the main scan is compressed and stored, and the stored image data is restored, and the image processing is performed, so that the read image data is stored as compared with the case where the read image data is stored as it is. The capacity can be reduced.

  In addition, according to the present invention, a document area such as a character area, a halftone dot area, and a photographic paper area is determined from image data read by preliminary scanning, and a character document or a printed photo document is determined based on the document structure area. By determining the type of original, such as a text original, a printed photographic original, or a photographic paper photographic original, it is possible to perform image processing according to the original type and form a good image. Is possible.

  In addition, according to the present invention, the optimum background removal processing according to the background level of the document is determined by determining the background level indicating the presence / absence of the background of the document and the density classification of the background level from the image data read by the preliminary scanning. Therefore, it is possible to form a good image.

  In addition, according to the present invention, it is possible to perform optimum filtering by determining the presence / absence of halftone dots and the halftone dot number level indicating the level of halftone dots from the image data read by the preliminary scanning, and the edge filtering. It is possible to improve and form a good image without moire.

  FIG. 1 is a block diagram showing a main configuration of a digital color copying machine which is an image forming apparatus according to the present invention. The digital color copying machine includes a color image input device 1, a color image processing device 2, a color image output device 3, and an operation panel 26.

The color image input apparatus 1 includes a scanner unit including a CCD (Charge Coupled Device) and a lens, a document conveying unit, a sensor for detecting the size of the document, and the like. Pre-scanning and main scanning for reading an image of a document are performed in a main scanning direction that is the direction in which the CCDs are arranged and a sub-scanning direction that is a direction orthogonal to the main scanning direction.
The document transport unit transports a document placed on a document table, and the sensor detects the size of the document (for example, A4, A3, etc.), and reflects light from the document according to the detected paper size. Is reduced or enlarged by the lens of the scanner unit so as to fit the width in the main scanning direction and the sub-scanning direction, and only the image of the entire document is RGB (R: red, G, G) by the CCD with reference to the position of one corner of the document. : Green, B: blue) are read as analog signals and output to the color image processing apparatus 2.

  The color image processing device 2 includes an image processing IC 4, storage devices 20 and 22, an image compression unit 21, an image restoration unit 23, a CPU 24, and a ROM 25, and an image input from the color image input device 1. Image processing is performed on the data, and the processed image data is output to the color image output device 3.

  The image processing IC 4 includes an A / D (analog / digital) conversion unit 8, a selector 9, a document type determination unit 10, a background level determination unit 50, a total halftone line number determination unit 60, a density conversion unit 11, and a region separation processing unit. 12, an input tone correction unit 13, a color correction unit 14, a black generation and under color removal unit 15, a scaling unit 16, a spatial filter processing unit 17, an output tone correction unit 18, and a tone reproduction processing unit 19. The CPU 24 controls the operations of the image processing IC 4, the storage devices 20 and 22, the image compression unit 21 and the image restoration unit 23, and the ROM 25 stores a program executed by the CPU 24.

The color image output device 3 outputs the image data output from the color image processing device 2, and is a photosensitive drum corresponding to each color of CMYK (C: cyan, M: magenta, Y: yellow, K: black), A tandem system equipped with a developing device is used.
The operation panel 26 is used to set the operation of the digital color copying machine, and includes a liquid crystal display unit and operation buttons such as enlargement / reduction settings or color / monochrome settings.

Next, the color image processing apparatus 2 will be described.
The A / D converter 8 converts the RGB analog signal input from the color image input device 1 into an RGB digital signal and outputs it to the selector 9.
The selector 9 outputs the input RGB signals to the document type determination unit 10, background level determination unit 50, and total halftone line number determination unit 60 when the document is pre-scanned.

The selector 9 switches the output destination of the input RGB signal according to a signal from the color image input device 1 when a plurality of originals are scanned. That is, when copying a plurality of originals, RGB signals input from the color image input device 1 are sent to the image compression unit 21. In other cases, the RGB signals are directly sent to the density conversion unit 11. Output.
The RGB signals sent to the image compression unit 21 are stored in the storage device 22 after being compressed. The compressed image data is restored by the image restoration unit 23 and sent to the density conversion unit 11 when an attribute such as the type of document stored in the storage device 20 is read.

  Based on the RGB signals input from the selector 9, the document type determination unit 10 determines the number of pixels determined as a character area, a dot area, a photographic paper area, or a background area for the entire document, and a preset threshold value. Are compared with each other to determine the document type such as a text document or a printed photo document, and the determination result is stored in the storage device 20.

The background level determination unit 50 determines the background level based on the RGB signals input from the selector 9 and stores the determination result in the storage device 20.
The total halftone line number determination unit 60 determines whether each pixel of interest in the input image is a halftone dot region based on the RGB signal input from the selector 9, and based on the counted number of pixels. The halftone line number level is determined and stored in the storage device 20.

  The density conversion unit 11 performs processing for removing various distortions generated in the optical system of the color image input apparatus 1 on the RGB signal input from the selector 9 or the image restoration unit 23, and performs RGB processing after processing. Are output to the region separation processing unit 12, converted into CMY signals suitable for image processing, and the converted signal is output to the region separation processing unit 12.

  The region separation processing unit 12 outputs the RGB signal input from the density conversion unit 11 as it is to the input tone correction unit 13 at the subsequent stage, and based on the CMY digital signal input from the density conversion unit 11, It is determined whether each target pixel in the input image of the original read in the scanning belongs to a character area, a halftone area, a photographic paper area, or a background area, which is an original constituting area. Based on the determination result, an area identification signal indicating which area the pixel belongs to is output to the black generation and under color removal unit 15, the spatial filter processing unit 17, and the gradation reproduction processing unit 19.

  Note that the area separation process in the area separation processing unit 12 is the same as the process for determining the document configuration area in the document type determination unit 10 described later.

The input tone correction unit 13 converts the RGB signal input from the region separation processing unit 12 into a signal obtained by inverting the complementary color, and sets a density conversion table based on the background level determination result in the background level determination unit 50. The tone corrected signal is output to the color correction unit 14.
The color correction unit 14 realizes faithful color reproduction of the signal input from the input tone correction unit 13 and performs a process of removing color turbidity to prevent color misregistration due to a difference in color material of the document. The CMY signals after color correction are output to the black generation and under color removal unit 15.

The black generation and under color removal unit 15 generates a black signal from the color-corrected CMY signal input from the color correction unit 14 and reproduces a good achromatic color, and subtracts the black signal to generate a new CMY signal. By generating a signal, the CMY signal is converted into a CMYK signal and output to the scaling unit 16.
The black generation / under color removal processing in the black generation / under color removal unit 15 includes a method of generating black by skeleton black. In this method, the input / output characteristics of the skeleton curve are y = f (x), the input signals are C, M, and Y, and the minimum values of the input signals C, M, and Y are min (C, M, Y). If the UCR (Under Color Removal) rate is α (0 <α <1), the output signals C ′, M ′, Y ′, and K ′ are expressed by the following equations.

K ′ = f {min (C, M, Y)}
C ′ = C−αK ′
M ′ = C−αK ′
Y ′ = C−αK ′

The scaling unit 16 performs processing such as image enlargement or reduction on the CMYK signal input from the black generation and under color removal unit 15 based on a signal operated by a setting button provided on the operation panel 26. And output to the spatial filter processing unit 17.
The spatial filter processing unit 17 performs spatial filter processing using a digital filter on the CMYK signal input from the scaling unit 16 and corrects the spatial frequency characteristics to prevent image blurring and graininess deterioration. Processing is performed, and the CMYK signal after the spatial filter processing is output to the output tone correction unit 18.

The output tone correction unit 18 performs an output tone correction process for converting the CMYK signal input from the spatial filter processing unit 17 into a halftone dot area ratio which is a characteristic value of the color image output device 3, and outputs The CMYK signal after the gradation correction processing is output to the gradation reproduction processing unit 19.
The tone reproduction processing unit 19 performs tone reproduction processing (halftone generation) on the CMYK signal input from the output tone correction unit 18 so that the tone of the read image can be reproduced. The image is output to the image output device 3.

  The storage device 20 stores the document attributes determined by the document type determination unit 10, the background level determination unit 50, and the total halftone line number determination unit 60. The image compression unit 21 compresses image data read by the main scanning. As a method used for image compression, JPEG (Joint Photographic Experts Group) compression can be mentioned, but other methods may be used. The storage device 22 stores the image data compressed by the image compression unit 21. The image restoration unit 23 restores the image data read from the storage device 22 when performing processing for each document. The restored image data is output to the density conversion unit 11.

  The document attributes determined by the preliminary scan are stored in the storage device 20 in the order of the read documents, and the image data read by the main scan is also stored in the storage device 22 in the order of the read documents. According to the storage order stored in each storage device, it is possible to perform image processing on image data read based on the type of document.

  Next, a process for determining a document configuration area by determining a document type from a feature amount of image data read by preliminary scanning, a process for determining a background level of a document, and a process for determining a halftone line number level of a document. explain.

  The determination of the document configuration area and the determination of the halftone line number level of the document are performed for each 15 × 7 pixel block unit centering on the target pixel as shown in FIG. 2 in the order of the image data of the document read by the preliminary scanning. It is stored in a line memory for seven lines in the sub-scanning direction (not shown), and is performed by the document type determination unit 10 and the total halftone line number determination unit 60 for each target pixel.

When the document type is determined by preliminary scanning, the scanning speed is faster than when image data of the document is read by main scanning, so the document type is read at a low resolution.
In the figure, the main scanning direction determination area is a pixel only in the main scanning direction including the target pixel, and the sub scanning direction determination area is a pixel only in the sub scanning direction including the target pixel.
The background level of the document is determined by the background level determination unit 50 based on the RGB signals output from the selector 9 in the order of the image data of the document read by the preliminary scanning.

  First, a process for determining a document configuration area from a feature amount of image data read by preliminary scanning will be described. The document configuration area is a character area, a halftone dot area, a photographic paper area, and a background area, and the determination of the document configuration area determines which area the target pixel is.

FIG. 3 is a block diagram of the document type determination unit 10 of the color image processing apparatus according to the present invention. The document type determination unit 10 includes a determination block unit 101, a main scanning direction determination unit 30, a sub-scanning direction determination unit 40, a signal determination unit 104, an overall determination unit 105, and a document configuration area determination unit 106.
The RGB signals output from the selector 9 are stored in a line memory for seven lines in the sub-scanning direction (not shown) for each pixel block, and are held until the processing for each pixel block is completed.
The determination block unit 101 reads out a pixel block including the target pixel from the line memory.

The main scanning direction determination unit 30 reads out pixel data in the main scanning direction (main scanning direction determination region) including the target pixel from the pixel block stored in the determination block unit 101, and the target pixel constitutes a document configuration for each RGB signal. It is determined whether the area belongs to a character area, a halftone dot area, a photographic paper area, or a background area, and an area identification signal indicating a document constituting area is output to the signal-specific discrimination unit 104.
The sub-scanning direction determination unit 40 reads out pixel data in the sub-scanning direction (sub-scanning direction determination region) including the target pixel from the image block stored in the determination block unit 101, and is similar to the main scanning direction determination unit 30. Processing is performed and an area identification signal is output to the signal-specific discrimination unit 104.

When the area identification signal in the main scanning direction and the sub scanning direction is different from the area identification signal for each RGB signal input from the main scanning direction determination unit 30 and the sub scanning direction determination unit 40 In addition, the region identification signal of the pixel of interest is determined with priority given to the region identification signal in the main scanning direction, and the region identification signal for each RGB signal is output to the comprehensive determination unit 105.
Since the discrimination result input from the signal discrimination unit 104 may differ for each RGB signal, the overall judgment unit 105 determines which of the RGB signals is to be prioritized based on a preset priority order. Thus, an area identification signal indicating the document configuration area is output to the document configuration area determination unit 106.

  Based on the region identification signal for each pixel of interest input from the overall determination unit 105, the document configuration region determination unit 106 counts the ratio of the number of pixels for each region to the total number of pixels of interest, and the document configuration region determination unit 106 By comparing with preset threshold values (T5, T6, T7, T8), the type of the document is determined, and the determination result is stored in the storage device 20.

FIG. 4 is a block diagram of the main scanning direction determination unit 30. For the pixel block input from the selector 9 and read into the determination block unit 101, the minimum density value calculation unit 301 calculates the minimum density value of the main scanning direction determination region, and the maximum density value calculation unit 302 similarly Calculate the maximum density value.
The maximum density difference calculation unit 303 calculates the maximum density difference using the minimum density value and the maximum density value.
A total density busyness calculation unit 304 calculates a total density busyness that is a sum of absolute values of density differences between adjacent pixels.

  The background photographic paper / character halftone dot determination unit 305 includes a maximum density difference threshold value setting unit 306 and a total density busyness threshold value setting unit 307, and the maximum density difference input from the maximum density difference calculation unit 303 and the maximum density difference. The maximum density difference threshold T1 set in the threshold setting unit 306 is compared, and the total density busyness input from the total density busyness calculating unit 304 and the total density set in the total density busyness threshold setting unit 307 The congestion threshold value T2 is compared to determine whether the pixel of interest is a background area / printing paper area or a character area / halftone dot area, and the determination result is used as the background / printing paper determination unit 308 and the character / halftone screen. It outputs to the point determination part 310.

  The background / photographic paper determination unit 308 includes a background / photographic paper determination threshold value setting unit 309. When the determination result input from the background photographic paper / character halftone dot determination unit 305 is the background / photographic paper region, the maximum density The maximum density difference input from the difference calculating unit 303 is compared with the background / photographic paper determination threshold value T3 (T3 <T1) set in the background / photographic paper determination threshold value setting unit 309. It is determined which is the photographic paper area, and the determination result is output to the signal-specific determination unit 104.

The character / halftone dot determination unit 310 includes a character / halftone dot determination threshold setting unit 311. When the determination result input from the background photographic paper / character halftone dot determination unit 305 is a character / halftone dot area, the total density The total density busyness input from the busyness calculation unit 304 is compared with the product of the character / halftone dot determination threshold value T4 and the maximum density difference set in the character / halftone dot determination threshold value setting unit 311. It is determined whether it is a character or a halftone dot, and the determination result is output to the signal-specific determination unit 104.
The sub-scanning direction determination unit 40 has the same configuration.

Next, the characteristics of the pixel density distribution in each region will be described. The pixel density distribution represents the density for each pixel in each scanning direction determination area.
FIG. 5 is an explanatory diagram showing an example of the pixel density distribution in the base region. The feature of the pixel density distribution of the background area is that the density change for each pixel is small, and therefore, when the maximum density difference and the total density busyness are both small, it can be determined that the background area is the background area.
FIG. 6 is an explanatory diagram showing an example of the pixel density distribution in the photographic paper region. The characteristic of the photographic paper region distribution is that the density change of the pixels is smooth, and therefore, when the total density busyness is small and the maximum density difference is large, it can be determined that the photographic paper region is a photographic paper region.

FIG. 7 is an explanatory diagram showing an example of the pixel density distribution in the halftone dot region. The characteristic of pixel density distribution in the halftone dot area is that the maximum density difference of pixel density is distributed according to the halftone dots, and the total density busyness changes by the number of halftone dots, so the ratio of the total density busyness is the maximum. If it is larger than the density difference, it can be determined that it is a halftone dot region.
FIG. 8 is an explanatory diagram showing an example of the pixel density distribution in the character area. Characteristic pixel density distribution features a large maximum density difference, and the total density busyness is large in proportion to the maximum density difference, but the total density busyness is small compared to the halftone dot area because the density change is small. Become. Therefore, when the ratio of the total density busyness to the maximum density difference is small, it can be determined that the area is a character area.

The determination of each region will be described based on the characteristics of the pixel density distribution described above.
FIG. 9 is an explanatory diagram showing an example of the distribution of the maximum density difference of pixels and the total density busyness in each region. As described above, the maximum density difference and the total density busyness are both small in the background area and the photographic paper area, and the maximum density difference is smaller in the background area than in the photographic paper area. Therefore, if the maximum density difference of the pixels is smaller than the maximum density difference threshold T1 and the total density busyness is smaller than the total density busyness threshold T2, it is determined that the area is the background / printing paper area. If the maximum density difference of the pixel of interest determined to be the background / photographic paper area is smaller than the background / photographic paper determination threshold value T3, it is determined to be the background area, and the maximum density difference is determined to be the background / photographic paper determination threshold value. If it is larger than T3, it is determined to be a photographic paper region.

When the maximum density difference of the pixel is large and the total density busyness is large, it is either a character or a halftone dot area, and therefore the maximum density difference of the pixel is larger than the maximum density difference threshold T1 and the total density busyness When the degree is larger than the total density busyness threshold value T2, it can be determined that the area is a character / halftone braille region. As described above, in the pixel density distribution of the halftone dot region, since the ratio of the total density busyness is larger than the maximum density difference, the total density busyness is determined by the product of the maximum density difference and the character / halftone dot determination threshold T4. Can be determined as a halftone dot region, and when the total density busyness is smaller than the product of the maximum density difference and the character / halftone dot determination threshold T4, it can be determined as a character region.
There is no region where the total density busyness is less than or equal to the maximum density difference.

Next, the region separation process in the main scanning direction determination unit 30 will be described. The following processing is performed in parallel for each of the RGB signals.
FIG. 10 is a flowchart showing a region separation processing procedure in the main scanning direction determination unit 30. The minimum density value calculation unit 301 calculates the minimum density value of the main scanning direction determination region from the pixel block including the target pixel stored in the determination block unit 101 (S101). Similarly, the maximum density value calculation unit 302 calculates the maximum density value of the main scanning direction determination area (S102). The maximum density difference calculation unit 303 calculates the maximum density difference based on the minimum density value and the maximum density value input from the minimum density value calculation unit 301 and the maximum density value calculation unit 302 (S103). The total density busyness calculation unit 304 calculates a total density busyness that is a sum of absolute values of density differences between adjacent pixels from the pixel block including the target pixel stored in the determination block unit 101 (S104).

The background photographic paper / character halftone dot determination unit 305 compares the maximum density difference input from the maximum density difference calculation unit 303 with the maximum density difference threshold T1 set in the maximum density difference threshold setting unit 306. The total density busyness input from the total density busyness calculating unit 304 is compared with the total density busyness threshold T2 set in the total density busyness threshold setting unit 307 (S105). When the background photographic paper / character halftone dot determination unit 305 determines that the maximum density difference is smaller than the maximum density difference threshold T1 and the total density busyness is smaller than the total density busyness threshold T2 (YES in S105). The pixel of interest is determined to be a background / printing paper area (S106), and the result is output to the background / printing paper determination unit 308.
On the other hand, when it is determined that the maximum density difference is not smaller than the maximum density difference threshold T1 or the total density busyness is not smaller than the total density busyness threshold T2 (NO in S105), the target pixel is a character / halftone dot. The area is determined (S107), and the determination result is output to the character / halftone determination unit 310.

  The background / photographic paper determination unit 308 sets the maximum density difference input from the maximum density difference calculation unit 303 and the background / photographic paper determination threshold setting based on the determination result input from the background photographic paper / character halftone determination unit 305. When the maximum density difference is smaller than the background / printing paper determination threshold T3 (YES in S108), the target pixel is the background. If the maximum density difference is not smaller than the background / photographic paper determination threshold T3 (NO in S108), it is determined that the target pixel is a photographic paper area (S111). ), And outputs a region identification signal as a determination result to the signal-specific determination unit 104.

Based on the determination result input from the background photographic paper / character halftone determination unit 305, the character / halftone determination unit 310 calculates the total density busyness, the maximum density difference, and the character input from the total density busyness calculation unit 304. The product of the halftone dot determination threshold setting unit 311 and the character / halftone dot determination threshold T4 is compared (S109), and the total density busyness is the product of the maximum density difference and the character / halftone dot determination threshold T4. If it is smaller (YES in S109), it is determined that the pixel of interest is a character region (S112), and the total density busyness is smaller than the product of the maximum density difference and the character / halftone determination threshold T4. If not (NO in S109), it is determined that the target pixel is a halftone dot region (S113), and a region identification signal as a determination result is output to the signal-specific determination unit 104.
The region separation process in the sub-scanning direction determination unit 40 is performed in the same manner.

  The signal discrimination unit 104 compares the determination result for each RGB signal input from the main scanning direction determination unit 30 with the determination result for each RGB signal input from the sub-scanning direction determination unit 40, and both determination results are obtained. If they are different, the determination result from the main scanning direction determination unit 30 is prioritized and the region identification signal as the determination result is output to the comprehensive determination unit 105. Thereby, it is possible to prevent a difference in determination results due to a difference in the size or resolution of image data in the main scanning direction and the sub-scanning direction.

  When the determination result for each of the RGB signals input from the signal determination unit 104 is different, for example, when the R signal is a background area, the G signal is a background area, and the B signal is a character area, The character area is given priority over the background area, the background area is determined to be erroneously determined, the result of the B signal is determined to be a character area, and an area identification signal indicating the document structure area is output to the document structure area determination unit 106. .

  When the above processing for the target pixel is completed, the pixel block including the next target pixel is held in the line memory, and the determination block unit 101 reads the pixel block including the target pixel from the line memory. This process is repeated until the image data is finished.

Next, document type determination processing in the document type determination unit 10 will be described. There are five types of manuscripts: a character manuscript, a printed photo manuscript, a photographic paper photo manuscript, a character printed photo manuscript, and a character photographic paper photo manuscript.
The document configuration region determination unit 106 counts the total number of pixels of interest and the number of pixels for each region from the region identification signal for each pixel of interest output from the comprehensive determination unit 105, and counts the number of character region pixels counted. The ratio of the dot area pixel number, the photographic paper area pixel number, the background area pixel number, and the total pixel number of the pixel of interest is set in advance as a character area threshold value T5, a dot area threshold value T6, and a photographic paper area threshold value T7. And the comparison with the base region threshold value T8.

The ratio of the number of pixels determined as the character area to the total number of pixels of the target pixel is larger than the character area threshold T5, and the ratio of the number of pixels determined as the halftone dot area, the photographic paper area, and the background area is respectively If it is smaller than the point area threshold T6, the photographic paper area threshold T7, and the background area threshold T8, it is determined that the document type is a character document.
The ratio of the number of pixels determined as the halftone dot area to the total number of pixels of the target pixel is larger than the halftone dot area threshold T6, and the ratio of the number of pixels determined as the character area, the photographic paper area, and the background area is respectively If it is smaller than the character area threshold value T5, the photographic paper area threshold value T7, and the background area threshold value T8, it is determined that the document type is a printed photo document.
The ratio of the number of pixels determined as the photographic paper area to the total number of pixels of the target pixel is larger than the photographic paper area threshold T7, and the ratio of the number of pixels determined as the character area, the halftone dot area, and the background area is respectively If it is smaller than the character area threshold value T5, the halftone dot area threshold value T6, and the background area threshold value T8, it is determined that the document type is a photographic paper photo document.

If the ratio of the number of pixels determined to be the character area and the halftone dot area to the total number of pixels of the target pixel is larger than the character area threshold value T5 and the halftone dot area threshold T6, the type of document is character printing. It is determined that the document is a photo original.
When the ratios of the number of pixels determined as the character area and the photographic paper area to the total number of pixels of the target pixel are larger than the character area threshold value T5 and the photographic paper area threshold value T7, the type of document is a character photographic paper photograph. It is determined that the document is a manuscript.
The determination result is stored in the storage device 20.

FIG. 11 is a flowchart showing processing for determining the document type.
The document configuration region determination unit 106 counts the total number of pixels of the target pixel from the region identification signal for each target pixel output from the comprehensive determination unit 105 (S201), and determines the number of character region pixels, the number of dot region pixels, The number of pixels, which is the number of photographic paper area pixels and the number of background area pixels, is counted (S202).
The document configuration area determination unit 106 determines the ratio of the number of character area pixels, the number of halftone dot area pixels, the number of photographic paper area pixels, the number of background area pixels, and the total number of pixels of the target pixel. Then, the dot area pixel number ratio, the photographic paper area pixel number ratio, and the background area pixel number ratio are respectively calculated (S203).

The background area pixel number ratio is compared with the threshold T8 (S204). If the background area pixel number ratio is larger than the threshold T8 (YES in S204), it is determined that the document is a background document (S205).
If the background area pixel number ratio is not larger than the threshold value T8 (NO in S204), the character area pixel number ratio is compared with the threshold value T5 (S206), and if the character area pixel number ratio is larger than the threshold value T5. (YES in S206), the dot area pixel number ratio is compared with the threshold T6 (S207).

When the dot area pixel number ratio is larger than the threshold value T6 (YES in S207), it is determined that the document is a character / print photo document (S208).
If the dot area pixel number ratio is not greater than the threshold T6 (NO in S207), the photographic paper area pixel number ratio is compared with the threshold T7 (S209).
If the photographic paper region pixel number ratio is larger than the threshold value T7 (YES in S209), it is determined that the document is a character / photographic paper photographic document (S210). If the photographic paper region pixel number ratio is not greater than the threshold value T7 (NO in S209), it is determined that the document is a character document (S211).

On the other hand, when the character area pixel number ratio is not larger than the threshold T5 (NO in S206), the halftone area pixel number ratio is compared with the threshold T6 (S212). If the dot area pixel number ratio is larger than the threshold value T6 (YES in S212), it is determined as a printed photo document (S213), and if the dot area pixel number ratio is not larger than the threshold value T6 (S213). (NO in S212), the photographic paper region pixel number ratio is compared with the threshold T7 (S214).
If the photographic paper region pixel number ratio is larger than the threshold value T7 (YES in S214), it is determined that the photographic paper region is a photographic document (S215). If the photographic paper region pixel number ratio is not larger than the threshold value T7 (S214). NO), the process is terminated.
The document configuration area determination unit 106 stores the determination result in the storage device 20.

Next, processing for determining the background level of the document from the feature amount of the image data read by the preliminary scanning will be described.
The background is the color of the paper used for the document. For example, when light gray paper such as newspapers or magazines is used, an unnatural output image will result if the color of the paper is accurately reproduced. Therefore, the background is removed.
Further, the background level represents the background in terms of density, and includes the case where there is no background.

FIG. 12 is a block diagram showing the configuration of the background level determination unit 50. The background level determination unit 50 includes a signal conversion unit 501, a histogram creation unit 502, a threshold setting unit 503, and a density category extraction unit 504.
The signal conversion unit 501 sequentially extracts RGB signals input from the selector 9 and converts them into luminance data L based on the image data of the original read by the preliminary scanning. The luminance data L is expressed by the following formula using RGB signal data.

    L = aR + bG + cB

Here, a, b, and c are coefficients experimentally obtained from human visibility characteristics for each color. In the present invention, each of a, b, and c uses a value of “1/3”. The background of the original is detected by grasping the color characteristics of the original by weakening the gradation value of the G signal and enhancing the gradation value of the B signal.
The histogram creation unit 502 divides the density into 32 sections using brightness data L ′ (L ′ = 255−L) obtained by inverting the brightness data L, and creates a density histogram representing the frequency of each density section. Then, the data is output to the density category extraction unit 504. In the density histogram, the density category 1 has the lowest density (high luminance), and the density category 32 has the highest density (low luminance).

The threshold setting unit 503 stores a first threshold T11, a second threshold T12, and a third threshold T13 (T12 <T11 <T13) set in advance. The first threshold value T11 determines the presence or absence of a background based on the magnitude of white with no color, the second threshold value T12 determines a background level candidate, and the third threshold value T13 determines the background level. For each.
The density category extraction unit 504 searches the density histogram input from the histogram creation unit 502 from the low density (high luminance) side to the high density (low luminance) side, and determines the frequency of the density histogram, the first threshold value T11, and the second threshold value. The background level is extracted by comparing the threshold value T12 and comparing the added value of the density histograms of adjacent density sections with the third threshold value T13, and the background level is stored in the storage device 20.

Next, the background level determination will be described.
FIG. 13 is a flowchart showing a background level determination procedure. The histogram creation unit 502 creates a density histogram using the luminance data input from the signal conversion unit 501 (S301).
The density category extraction unit 504 determines the background level for each density category from the density category 1 to the density category 32 based on the density histogram input from the histogram creation unit 502 (S302).

  That is, assuming that the histogram frequency of density category i (i is an integer from 1 to 32) is hist (i), if hist (i) is less than the first threshold T11 (YES in S302), the background It is determined that there is a base level candidate, and the process proceeds to the detection procedure of the background level candidate (S303). On the other hand, when hist (i) is greater than or equal to the first threshold T11 (NO in S302), it is determined that there is no background (S306), it is determined whether i has reached the density category 32 (S308), and the density category is determined. If it has not reached 32 (NO in S308), i is incremented by 1 (S309), and the same processing is performed after step S302.

If it is determined in step S302 that the background level is present, the density classification extraction unit 504 compares hist (i) with the second threshold T12, and if hist (i) is less than the second threshold T12 (S303). NO), it is determined that there is no background (S306), it is determined whether i has reached the density category 32 (S308), and if it has not reached the density category 32 (NO in S308), i is set to 1. (S309), the same processing is performed after step S302.
When hist (i) is equal to or greater than the second threshold T12 (YES in S303), the density category i is set as a background level candidate.

The frequency hist (i) of the background candidate level density classification detected in step S303 and the frequency hist (i + 1) of the classification one density higher than the classification are added (S304), and the added value hist (i) If + hist (i + 1) is equal to or greater than the third threshold T13 (YES in S305), the section i is determined as the background level (S307), the background level is stored in the storage device 20, and the process is terminated.
If the added value hist (i) + hist (i + 1) is less than the third threshold T13 (NO in S305), it is determined that there is no background (S306), and whether or not i has reached the density category 32 is determined. If it is determined (S308) and the density category 32 has not been reached (NO in S308), i is incremented by 1 (S309), and the same processing from step S302 is performed.
In step S306, it is determined that there is no background, and when i reaches the density category 32 (YES in S308), it is finally determined that there is no background, the determination result is stored in the storage device 20, and the process is terminated.

FIG. 14 is an explanatory diagram showing an example of a density histogram of a text document having a background such as a newspaper. For example, in the density categories 1 to 5, since the frequency is less than the first threshold T11 and less than the second threshold, it is determined that there is no background. Since the frequency in the density category 6 is equal to or higher than the first threshold value T11 and the second threshold value T12, the density category 6 is set as a background level candidate, and the sum of the frequency in the density category 6 and the frequency in the density category 7 is the first. If it is equal to or greater than 3 threshold value T13, the density category 6 becomes the background level.
FIG. 15 is an explanatory diagram showing an example of a density histogram of a document in which a text document having a background such as a newspaper is pasted on a blank sheet. This is the same as described above.

  FIG. 16 is an explanatory diagram showing an example of a density histogram of a photographic document in which a blank paper portion and / or a highlight portion exists. In the figure, since the frequency in the density category 1 is less than the first threshold value T11 and greater than or equal to the second threshold value T12, the density category 1 is a background level candidate. If the sum of the frequency of the density category 1 and the frequency of the density category 2 is less than the third threshold value T13, there is no background. Similarly, since the frequency in the density category 2 is less than the first threshold value T11 and greater than or equal to the second threshold value T12, the density category 2 is a background level candidate. If the sum of the frequency of the density category 2 and the frequency of the density category 3 is less than the third threshold value T13, there is no background. Furthermore, since the frequency from the density category 3 to the density category 32 is less than the first threshold value T11 and less than the second threshold value T12, it is finally determined that there is no background.

Next, processing for determining the halftone line number level of a document from the feature amount of image data read by preliminary scanning will be described.
A halftone dot is a minute dot obtained by converting the shading of an image into a large or small area, and the number of halftone dots represents the fineness of the image, for example, the number of halftone dots per inch.
The halftone line number level is represented by three levels: no halftone dot, low halftone line number, and high halftone line number.

FIG. 17 is a block diagram illustrating a configuration of the total halftone line number determination unit 60. The total halftone line number determination unit 60 includes a first halftone dot determination unit 70 and a halftone line number determination unit 80.
Pixel blocks including the target pixel in the image data read by the preliminary scanning are stored in a line memory (not shown) from the selector 9 in the order of reading.
The first halftone dot determination unit 70 reads out pixels in each scanning direction including the target pixel from the line memory, determines whether the target pixel is a halftone area, and determines whether the document has a halftone dot. The first halftone dot region pixel count scr1, which is the number of target pixels determined to be halftone dots, is counted, and the determination result and the first halftone dot region pixel count scr1 are output to the halftone dot number determination unit 80.

  The halftone line number determination unit 80 determines whether or not the target pixel is a halftone dot region using a threshold value that is larger than the threshold value used in the first halftone dot determination unit 70, and the number of target pixels that are determined to be halftone dots The second halftone dot region pixel number scr2 is counted, and a pixel number ratio scr2 / scr1 which is a ratio of the first halftone dot region pixel number scr1 to the second halftone dot region pixel number scr2 is calculated to obtain a halftone dot number level. Is determined, and the determination result is stored in the storage device 20. When it is determined that there is no halftone dot in the document, the halftone line number level is not determined.

FIG. 18 is a block diagram showing a configuration of the first halftone dot determination unit 70.
The character area determination unit 71 determines whether or not the target pixel is a character area and outputs the determination result to the first determination unit 73. Note that the processing in the character region determination unit 71 is the same as the processing in the main scanning direction determination unit 30, and thus description thereof is omitted.
The first halftone dot region determination unit 72 determines whether or not it is a halftone dot region based on the pixels in each scanning direction including the target pixel, and outputs the determination result to the first determination unit 73.

The first determination unit 73 is based on the determination result input from the character region determination unit 71 and the first halftone dot region determination unit 72 and the priority order that determines which region of the character or the halftone dot is to be prioritized. Area determination is performed, and the determination result is output to the comprehensive determination unit 74.
The overall determination unit 74 determines the presence or absence of halftone dots in the document based on the determination result input from the first determination unit 73, and outputs the determination result to the halftone line number determination unit 80.

FIG. 19 is a block diagram showing a configuration of the first halftone dot area determination unit 72. The first halftone dot region determination unit 72 includes a binarization processing unit 721, an inversion number counting unit 722, a maximum value selection unit 725, an inversion number determination unit 726, and a parameter setting unit 727.
The binarization processing unit 721 reads out the pixel block including the target pixel stored in the line memory (not shown) from the selector 9, binarizes the pixels in the pixel block using the average value calculated from each pixel value as a threshold, The binarized data is output to the inversion number counting unit 722.

The inversion number counting unit 722 includes a main scanning direction counting unit 723 and a sub scanning direction counting unit 724, and the number of inversions of the binarized data in each of the main scanning direction and the sub scanning direction input from the binarization processing unit 721. And the count result is output to the maximum value selection unit 725.
The maximum value selection unit 725 selects the maximum value from the inversion number results in the main scanning direction and the sub-scanning direction in the inversion number counting unit 722, and outputs the maximum value to the inversion number determination unit 726.
The inversion number determination unit 726 compares the maximum value input from the maximum value selection unit 725 with a threshold value TH1 (for example, “2”) set in the parameter setting unit 727, and determines whether the target pixel is a halftone dot region. It is determined whether or not, and the determination result is output to the first determination unit 73.

  FIG. 20 is a flowchart showing a processing procedure in the first halftone dot region determination unit 72. The binarization processing unit 721 binarizes the intra-block pixels including the target pixel with an average value (S401). The inversion number counting unit 722 inverts the pixels in the block binarized by the binarization processing unit 721 in the main scanning direction and the sub scanning direction, that is, from “0” to “1”, or from “1”. The number of inversions at which the pixel value is inverted to “0” is calculated (S402). The maximum value selection unit 725 selects the maximum value MaxRev from the inversion numbers calculated in the main scanning direction and the sub-scanning direction (S403), and the inversion number determination unit 726 sets parameters in advance with the inversion number maximum value MaxRev. The threshold TH1 set in the unit 727 is compared, and if the maximum number of inversion MaxRev is greater than the threshold TH1 (YES in S404), it is determined that the pixel of interest is a halftone dot region (S405), and the maximum number of inversions is reached. When the value MaxRev is equal to or less than the threshold value TH1 (NO in S404), it is determined that the target pixel is a non-halftone area (S406), and the determination result is output to the first determination unit 73.

  Since the first determination unit 73 determines whether or not there is a halftone dot region, the determination result in the first halftone dot region determination unit 72 is given priority over the determination result in the character region determination unit 71. For example, as shown in Table 1, the determination result from the character region determination unit 71 is a character region (character region determination “1”), and the determination result from the first dot region determination unit 72 is a dot region. In the case of (halftone area determination “1”), it is determined that the target pixel is a halftone area.

The overall determination unit 74 includes a character region pixel counting unit 741, a halftone dot region pixel counting unit 742, a total pixel number counting unit 743, a divider 744, and a second determination unit 745.
The character area pixel counting unit 741 counts pixels that are determined to be character areas by the first determination unit 73.
The halftone dot region pixel counting unit 742 counts the pixels determined to be the halftone dot region by the first determination unit 73 and outputs the first halftone dot region pixel count scr1 as the counting result to the divider 744.
The total pixel number counting unit 743 counts the total number of target pixels input to the first halftone dot determination unit 70.

The divider 744 calculates a ratio between the first halftone dot region pixel count scr1 input from the halftone dot region pixel counting unit 742 and the total pixel count input from the total pixel number counting unit 743, and calculates the calculation result. 2 is output to the determination unit 745.
The second determination unit 745 determines that the original has halftone dots when the ratio of the first halftone dot region pixel count scr1 to the total pixel count is larger than a threshold TH3 (eg, 0.05), and the first halftone dot is determined. The dot area pixel number scr1 and the determination signal are output to the halftone line number determination unit 80. If the ratio of the dot area pixel number to the total pixel number is equal to or less than the threshold value TH3, it is determined that the document has no halftone dots. The determination signal is output to the halftone line number determination unit 80.

FIG. 21 is a block diagram illustrating a configuration of the halftone line number determination unit 80. The halftone dot number determining unit 80 includes a second halftone dot region determining unit 81, a halftone dot region pixel counting unit 82, a halftone dot number determining unit 83, a threshold setting unit 84, and a control unit 85.
The second halftone dot region determination unit 81 includes a binarization processing unit 811, a main scanning direction counting unit 813 and a sub scanning direction counting unit 814, an inversion number calculating unit 812, a maximum value selection unit 815, an inversion number determination unit 816, and A parameter setting unit 817 is provided, and it is determined whether the target pixel is a halftone dot region, and the determination result is output to the halftone dot region pixel counting unit 82.

  Each of the binarization processing unit 811, the inversion number calculation unit 812, the maximum value selection unit 815, the inversion number determination unit 816, the parameter setting unit 817, the main scanning direction counting unit 813, and the sub scanning direction counting unit 814 has the above binary values. The processing is the same as that performed by the conversion processing unit 721, the inversion number counting unit 722, the maximum value selection unit 725, the inversion number determination unit 726, the parameter setting unit 727, the main scanning direction counting unit 723, and the sub scanning direction counting unit 724. Omitted.

The halftone dot region pixel counting unit 82 counts the number of pixels determined to be a halftone dot region based on the determination result input from the second halftone dot region determining unit 81, and the counting result (second halftone dot) The number of area pixels scr2) is output to the halftone line number discrimination unit 83.
Note that the threshold TH11 set in the parameter setting unit 817 is a value greater than TH1 (for example, “4”), so that the pixel of interest that does not have a larger maximum number of inversion MaxRev is a halftone dot region. Not judged. As a result, the halftone dot region pixel counting unit 82 of the halftone dot number determination unit 80 counts compared to the first halftone dot region pixel count scr1 counted by the halftone dot region pixel counting unit 742 of the first halftone dot determination unit 70. The second halftone dot region pixel count scr2 becomes a small value, and by calculating the ratio of these, the halftone dot number level can be determined.

The halftone dot number discriminating unit 83 calculates a pixel number ratio scr2 / scr1 which is a ratio of the second halftone dot region pixel number scr2 to the first halftone dot region pixel number scr1, and the pixel number ratio scr2 / scr1 and the threshold value setting unit 84. Is compared with the threshold value TH2 (for example, “0.25”) set to “1”.
When the pixel number ratio scr2 / scr1 is larger than the threshold value TH2, it is determined as a high halftone line number, and when the pixel number ratio scr2 / scr1 is not larger than the threshold value TH2, it is determined as a low halftone line number.

FIG. 22 is a flowchart showing a processing procedure in the total halftone line number determination unit 60.
The total pixel number counting unit 743 in the first halftone dot determining unit 70 counts the total number of pixels, and the halftone dot region pixel counting unit 742 counts the first halftone dot region pixel number scr1 (S501). 744 calculates the ratio of the first halftone dot region pixel count scr1 to the total pixel count (S502).

The second determination unit 745 compares the ratio of the first halftone dot region pixel count scr1 to the total pixel count with the threshold TH3 (S503), and the ratio of the first halftone dot region pixel count scr1 to the total pixel count is greater than the threshold TH3. If it is larger (YES in S503), the determination result that there is a halftone dot in the document and the first halftone dot region pixel count scr1 are output to the halftone dot number determination unit 80, and the process proceeds to step S505.
When the ratio of the first halftone area pixel count scr1 to the total pixel count is equal to or less than the threshold value TH3 (NO in S503), a determination result that there is no halftone dot in the document is output to the halftone dot number determination section 80. The halftone line number determination unit 80 does not determine the number of halftone lines (S504), and the determination result is stored in the storage device 20 (S510).

The dot area pixel counting unit 82 calculates the second dot area pixel count scr2 (S505).
The halftone dot number discriminating unit 83 calculates a pixel number ratio scr2 / scr1 which is a ratio of the second halftone dot region pixel number scr2 to the first halftone dot region pixel number scr1 (S506), and the pixel number ratio scr2 / scr1 and a threshold value are calculated. The threshold value TH2 set in the setting unit 84 is compared (S507). If the pixel number ratio scr2 / scr1 is larger than the threshold value TH2 (YES in S507), it is determined that the number of lines is high (S508). The halftone line number level is stored in the storage device 20 (S510), and if the pixel number ratio scr2 / scr1 is equal to or less than the threshold value TH2 (NO in S507), it is determined that the number is low (S509). Several levels are stored in the storage device 20 (S510), and the process ends.

Next, image processing based on the determined document attributes will be described.
When the image restoration unit 23 reads out the image data of the original read by the main scanning from the storage device 22 and restores the image data, the area separation processing unit 12 reads the original type and halftone line number level stored in the storage device 20. The input tone correction unit 13 similarly reads the attribute of the document that is the background level, and performs the following processing based on the attribute of the document.

First, processing based on the document type will be described.
When the determined original is a text original, the processing in the area separation processing unit 12 for the image data read by the main scanning is performed based on the area identification result obtained by separating the areas as characters.
The input tone correction unit 13 converts the RGB signal output from the region separation processing unit 12 into a signal obtained by inverting the complementary color, selects a tone correction conversion table that enhances contrast, performs tone correction, and performs color correction. To the unit 14.
The color correction unit 14 performs color correction that enhances the saturation of the character color with respect to the CMY signals input from the input tone correction unit 13.

The black generation and under color removal unit 15 converts the CMY signal output from the color correction unit 14 into a CMYK signal by increasing the black generation amount so as to emphasize the black color of the character. The data is output to the spatial filter processing unit 17 via the scaling unit 16.
The spatial filter processing unit 17 includes a digital filter that can set a filter coefficient, and performs a process of correcting the spatial frequency characteristic. The spatial filter processing unit 17 selects a filter coefficient that enhances the edge of the character with respect to the CMYK signal input from the scaling unit 16, and performs a filter process to reduce the smoothing process. Output to the gradation reproduction processing unit 19.
The gradation reproduction processing unit 19 performs gradation processing on the CMYK signal input from the spatial filter processing unit 17 by multi-value processing suitable for high frequency reproduction.

When the determined original is a photographic paper original, the processing in the region separation processing unit 12 for the image data read by the main scanning is performed based on the region identification result obtained by the region separation as the photographic paper.
The input tone correction unit 13 selects a tone correction conversion table that emphasizes highlights and increases tone characteristics for the RGB signals output from the region separation processing unit 12, performs tone correction, and Output to the color correction unit 14.
The color correction unit 14 performs color correction that enhances the gradation of the CMY signals input from the input gradation correction unit 13.

The black generation and under color removal unit 15 converts the CMY signal output from the color correction unit 14 into a CMYK signal with a reduced black generation amount, and converts the converted signal to the space via the scaling unit 16. Output to the filter processing unit 17.
The spatial filter processing unit 17 selects a filter coefficient that weakens edge enhancement on the CMYK signal input from the scaling unit 16 and performs a filter process to reduce the smoothing process, thereby performing gradation The data is output to the reproduction processing unit 19.
The gradation reproduction processing unit 19 performs gradation processing by multi-value processing suitable for gradation reproduction on the CMYK signal input from the spatial filter processing unit 17.

When the determined original is a printed photo original, the process in the area separation processing unit 12 for the image data read by the main scan is performed based on the area identification result obtained by the area separation as halftone dots.
The input tone correction unit 13 selects a tone correction conversion table that emphasizes highlights and increases tone characteristics for the RGB signals output from the region separation processing unit 12, performs tone correction, and Output to the color correction unit 14.
The color correction unit 14 performs color correction that enhances the gradation of the CMY signals input from the input gradation correction unit 13.

The black generation and under color removal unit 15 converts the CMY signal output from the color correction unit 14 into a CMYK signal with a reduced black generation amount, and converts the converted signal to the space via the scaling unit 16. Output to the filter processing unit 17.
The spatial filter processing unit 17 performs low-pass filtering on the CMYK signal input from the scaling unit 16 by selecting filter coefficients that weaken edge enhancement and remove halftone components. And output to the gradation reproduction processing unit 19.
The gradation reproduction processing unit 19 performs gradation processing by multi-value processing suitable for gradation reproduction on the CMYK signal input from the spatial filter processing unit 17.

In addition, when the determined document includes a plurality of document types, the determination is performed using an intermediate parameter of parameters used for area processing of each mixed area. For example, when the determined document is a character / photographic paper photographic document, the processing in the region separation processing unit 12 for the image data read by the main scan validates the region separated as characters or photographic paper, A region separated as a halftone dot is not reflected as erroneous separation.
The input tone correction unit 13 performs highlight removal and contrast adjustment using intermediate parameters between character document processing and photographic paper photograph document processing.

The color correction unit 14 performs a color correction process so that the balance between saturation strength and gradation is not extreme.
The black generation and under color removal unit 15 adjusts the black generation amount to the extent that the output image is not affected.
The gradation reproduction processing unit 19 performs gradation processing using intermediate parameters that emphasize resolution and gradation.

When the determined original is a character / printed photo original, the processing in the area separation processing unit 12 for the image data read by the main scan validates the area separated as a character or a halftone dot as photographic paper. The region separated is not reflected as erroneous separation.
The input tone correction unit 13 performs highlight removal and contrast adjustment using intermediate parameters between character document processing and printed photo document processing.
The color correction unit 14 performs color correction processing so that the balance between the intensity of saturation and the gradation is not excessive.

The black generation and under color removal unit 15 adjusts the black generation amount to the extent that the output image is not affected.
The spatial filter processing unit 17 performs a filter process for removing halftone components using an intermediate parameter between the character document process and the printed photograph document process.
The gradation reproduction processing unit 19 performs gradation processing using intermediate parameters that enhance the resolution and gradation.

Next, background removal processing in the case of the background level will be described.
FIG. 23 is an explanatory diagram showing a density conversion table corresponding to the detected background level. As shown in the figure, when it is determined that there is no background, a conversion straight line represented by a white circle “◯” that is not corrected is selected.
In the case where the background level is the density category 1 or 2, the output density in the range of the input density from “0” to “128” is smaller than the conversion straight line represented by the white circle “◯”, and the inverted triangle “ Select the conversion curve represented by “”.
When the background level is the density category 3 or 4, the square “□” in which the output density when the input density range is “0” to “128” is smaller than the conversion curve represented by the inverted triangle “三角”. Select the conversion curve represented by.

When the background level is the density category 5 or 6, the output density is small when the input density range is “0” to “48”, and when the input density is “48” to “128”, the output density gradually increases. A conversion curve represented by an increasing triangle “Δ” is selected.
When the background level is the density category 7 or 8, the output density when the input density range is “0” to “128” is smaller than the conversion curve represented by the triangle “Δ”. Select the represented transformation curve.
In addition, after the density category 9, a conversion curve represented by a black circle “●” may be selected, or another conversion curve may be selected.

  The input tone correction unit 13 performs complementary color inversion on the RGB signal input from the region separation processing unit 12 and is set in the input tone correction unit 13 based on the background level of the original read from the storage device 20. The selected density conversion table is selected, and a tone corrected signal is output to the color correction unit 14.

  As a result, the input tone correction unit 13 outputs the input density as it is when there is no background, so the background removal is not performed. On the other hand, for example, when the density classification of the background level is 6, the density conversion is performed so that the density of the output image is smaller than the density of the input image, so that the background is removed. As a result, in the case of a document having a light gray background such as a newspaper or magazine, the background can be removed well without reproducing the light color of the background.

Next, processing in the case of the halftone line number level will be described. The region separation processing unit 12 adjusts the character / halftone dot determination threshold T9 in the region separation processing unit based on the halftone line number level read from the storage device 20, and applies the image data read by the main scanning to the image data read. Region separation processing.
That is, when it is determined that the number of high halftone lines is higher than the case where it is determined that the number of low halftone lines is high, the total density busyness in the region separation processing is increased. By adjusting T9 to a larger value, the accuracy of the region separation process in the region separation process can be improved. If it is determined that there is no halftone dot, the processing result in the region separation process is preferably a character region, and therefore the character / halftone dot determination threshold T9 is adjusted to a larger value.

The spatial filter processing unit 17 includes a digital filter that can set a filter coefficient, and performs a process of correcting the spatial frequency characteristic. The spatial filter processing unit 17 selects a filter coefficient based on the halftone line number level, and when the halftone line number level is a low line number, the edge enhancement is prevented by the filter enhancement process, and the halftone line number level is When the number of lines is high, the high frequency component of the image signal is reduced by the filter smoothing process, the contrast is weakened, and moire is prevented.
The gradation reproduction processing unit 19 selects a dither pattern based on the halftone line number level,
When the halftone line number level is a low line number, dithering is performed so as to increase the resolution, and when the halftone line number level is a high line number, a process for increasing gradation is performed.

As described above, the document type determination unit 10 determines the document type for the image data of the document read by the preliminary scan, the background level determination unit 50 determines the background level, and the total number of halftone lines. The determination unit 60 determines the level of the number of dotted lines, and stores the original attribute as a result of the determination in the storage device 20.
The image restoration unit 23 restores the image data stored in the storage device 22 for the document image data read by the main scan, and performs the above-described processing for each document based on the document attributes. As a result, it is possible to perform image processing according to the document type, background level, and halftone line number level of the document.

24 and 25 are flowcharts showing the processing procedure of the digital color copying machine according to the present invention. The color image input apparatus 1 performs a preliminary scan to read an image (S601).
The document type determination unit 10 determines the document type (S602), and the document type is stored in the storage device 20 (S605).
The background level determination unit 50 determines the background level (S603), and the background level of the document is stored in the storage device 20 (S605).
The total halftone line number determination unit 60 determines the halftone line number level of the document using the color input signal data obtained by the preliminary scanning (S604), and the halftone line number level is stored in the storage device 20 (S604). S605).

  Next, the color image input device 1 performs a main scan (S606), and the image compression unit 21 compresses the image data read by the color image input device 1 (S607), and stores the compressed image in the storage device 22. (S608). It is determined whether or not processing has been performed for a predetermined number of documents (S609). If the predetermined number of sheets has not been reached (NO in S609), the same processing is performed from step S601.

  If the predetermined number is reached in step S609 (YES in S609), the document type, background level, and halftone line level stored in the storage device 20 are read (S610). The image data stored in the storage device 22 is read (S611), and the image restoration unit 23 restores the read image data by a restoration process (S612). Depending on the document type, the region separation processing unit 12, the input tone correction unit 13, the color correction unit 14, the black generation and under color removal unit 15, the scaling unit 16, the spatial filter processing unit 17, and the output tone correction unit 18 are used. The gradation reproduction processing unit 19 sequentially performs the above-described image processing on the restored image data (S613).

It is determined whether or not the above processing has been performed for a predetermined number of documents (S614). If the predetermined number of documents has not been reached (NO in S614), the same processing is performed after step S610. When the predetermined number of documents has been reached (YES in S614), the color image output device 3 prints the image data that has been subjected to final processing in the gradation reproduction processing unit 19 (S615).
The color image output device 3 determines whether or not a predetermined number of copies have been printed (S616). If the predetermined number of copies has not been reached (NO in S616), the predetermined number of copies are printed. If the predetermined number of copies has been printed (YES in S616), the process ends.

  The document type determination process described above is performed for pixel blocks in the main scanning direction and the sub-scanning direction. However, the preliminary scanning has a higher scanning speed than the main scanning, and the resolution of the image data in the sub-scanning direction is reduced. Therefore, the determination result only in the main scanning direction may be used.

Each of the above threshold values (T1, T2, T3, T4) performs a wide range of processing by setting a plurality of values in advance in a storage medium such as a ROM and setting each threshold value setting unit under the control of the CPU 24. Is possible.
In addition, when the threshold values for the region separation determination (T1, T2, T3, and T4) are changed, the number of pixels counted for each region is different and the determination result is different. Threshold values (T5, T6, T7, and T8) for determining the document type can be set according to T1, T2, T3, and T4).
Furthermore, by setting the document type discrimination threshold values (T5, T6, T7, and T8) to a small value, it is possible to reduce the number of read pixels for discrimination without degrading the determination accuracy.

  The processing in the second halftone dot region determination unit 81 may be performed using the first halftone dot region determination unit 72, and the processing in the halftone dot region pixel counting unit 82 is performed using the halftone dot region pixel counting unit 742. May be performed. In this case, the control unit 85 needs to change the threshold value TH1 set in the parameter setting unit 727 to the threshold value TH11.

1 is a block diagram showing a configuration of a main part of a digital color copying machine according to the present invention. It is a schematic diagram which shows a 15 * 7 pixel block centering on an attention pixel. 3 is a block diagram of a document type determination unit of the color image processing apparatus according to the present invention. FIG. It is a block diagram of a main scanning direction determination part. It is explanatory drawing which shows the example of pixel density distribution in a base area | region. It is explanatory drawing which shows the example of pixel density distribution in a photographic paper area | region. It is explanatory drawing which shows the example of the pixel density distribution in a halftone dot area | region. It is explanatory drawing which shows the example of the pixel density distribution in a character area. It is explanatory drawing which shows the example of distribution of the maximum density difference of a pixel in each area | region, and total density busyness. It is a flowchart which shows the area | region separation processing procedure in the main scanning direction determination part. 6 is a flowchart illustrating processing for determining a document type. It is a block diagram which shows the structure of a background level determination part. It is a flowchart which shows the determination procedure of a background level. It is explanatory drawing which shows the example of the density histogram of the character original document which has backgrounds, such as a newspaper. It is explanatory drawing which shows the example of the density | concentration histogram of the original document which pasted the character original which has backgrounds, such as a newspaper, on the white paper. It is explanatory drawing which shows the example of the density histogram of the photographic original in which the blank paper part and / or highlight part of an edge exist. It is a block diagram which shows the structure of a total halftone line number determination part. It is a block diagram which shows the structure of a 1st halftone dot determination part. It is a block diagram which shows the structure of a 1st halftone area | region determination part. It is a flowchart which shows the process sequence in a 1st halftone area | region determination part. It is a block diagram which shows the structure of a dotted line number determination part. It is a flowchart which shows the procedure of the process in a total halftone line number determination part. It is explanatory drawing which shows the density | concentration conversion table corresponding to the detected background level. 3 is a flowchart showing a processing procedure of the digital color copying machine according to the present invention. 3 is a flowchart showing a processing procedure of the digital color copying machine according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color image input device 2 Color image processing device 3 Color image output device 4 Image processing IC
DESCRIPTION OF SYMBOLS 10 Document type determination part 11 Density conversion part 12 Area | region separation process part 13 Input gradation correction part 14 Color correction part 15 Black generation under color removal part 17 Spatial filter process part 18 Output gradation correction part 19 Tone reproduction process part 20 Memory | storage Device 21 Image compression unit 22 Storage device 23 Image restoration unit 24 CPU
25 ROM
30 Main scanning direction determination unit 40 Sub scanning direction determination unit 50 Background level determination unit 60 Total halftone line number determination unit 70 First halftone dot determination unit 72 First halftone dot region determination unit 74 General determination unit 80 Halftone line number determination unit 81 Second halftone area determination unit 83 Halftone dot number determination unit 101 Determination block unit 104 Signal-specific determination unit 105 Total determination unit 106 Document configuration region determination unit 301 Minimum density value calculation unit 302 Maximum density value calculation unit 303 Maximum density difference calculation unit 304 Total density busyness calculation unit 305 Background photographic paper / character halftone dot determination unit 306 Maximum density difference threshold setting unit 307 Total density busyness threshold setting unit 308 Background / printing paper determination unit 309 Background / printing paper determination threshold setting unit 310 Characters Halftone dot determination unit 311 Character / halftone dot determination threshold value setting unit 501 Signal conversion unit 502 Histogram creation unit 503 Threshold value setting unit 504 Density group Extraction unit

Claims (11)

In an image processing method for extracting a feature amount of image data of a read original and performing image processing on the read image data based on the extracted feature amount,
The feature amount of the image data is extracted by preliminary scanning, the attribute of the document is determined from the extracted feature amount, the determined attribute of the document is stored, and the image read by the main scanning based on the stored attribute of the document An image processing method comprising performing image processing on data.   The image processing method according to claim 1, wherein the image data read by the main scanning is compressed and stored, and the image processing is performed after the stored image data is restored.   The document attribute is a document type, wherein the document configuration area is determined from the feature amount, and the document type is determined based on the determined document configuration area. Item 3. The image processing method according to Item 2.   3. The image processing method according to claim 1, wherein the attribute of the document is a background level of the document.   The image processing method according to claim 1, wherein the attribute of the original is a halftone dot number level of the original. An image processing apparatus comprising: an extracting unit that extracts a feature amount of image data of a read document; and an image processing unit that performs image processing on the read image data based on the extracted feature amount.
Extraction means for extracting feature amounts of image data by preliminary scanning;
Determining means for determining an attribute of the document from the extracted feature amount;
Storage means for storing the determined attribute of the document;
An image processing apparatus comprising: an image processing unit that performs image processing on image data read by main scanning based on the stored original attribute. Compression means for compressing image data read by the main scanning;
Storage means for storing compressed image data;
The image processing apparatus according to claim 6, further comprising: a restoration unit that restores image data compressed to perform image processing.   The determination means for determining the document attribute is a determination means for determining a document type, a determination means for determining a document composition area from the feature amount, and a document type determination based on the document composition area. The image processing apparatus according to claim 6, further comprising a determination unit that performs the determination.   The image processing apparatus according to claim 6, wherein the determination unit that determines the attribute of the document is a determination unit that determines a background level of the document.     8. The image processing apparatus according to claim 6, wherein the determination unit that determines the attribute of the document is a determination unit that determines a halftone line level of the document.   11. An image processing apparatus according to claim 6, further comprising image forming means for forming an image based on image data processed by the image processing apparatus. Image forming apparatus.

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