JP4958626B2 - Image processing method, image processing apparatus, image forming apparatus, computer program, and recording medium - Google Patents

Description

  The present invention relates to an image processing method, an image processing apparatus, an image forming apparatus, a computer program, and a recording medium that can change an ACS criterion according to a document type.

  In addition to the conventional analog type, digital type is widely used as an image forming apparatus such as an electronic copying machine, and with the advancement of digital image processing technology, a full-color digital copying machine that reproduces color images with high image quality is available. It has been commercialized. In general, a full-color digital copying machine performs color reproduction using a plurality of toners. Also, it has a monochrome mode using only black toner. Since copying in the monochrome mode uses only black toner, the cost is lower and the required time is shorter than color copying in which a plurality of toner images are sequentially superimposed.

  Therefore, an ACS (Auto Color Selection) function for determining whether the original is a color original or a monochrome original and setting a copy mode corresponding to the original has been put into practical use (see, for example, Patent Document 1). This function is particularly useful when a large number of documents are copied using an ADF (automatic document feeder). There is no need for the user to distinguish between color originals and monochrome originals. If a plurality of originals are set in the ADF and the start key is pressed, color copying is performed for color originals and monochrome copying is performed for monochrome originals.

For example, in the image processing apparatus described in Patent Document 1, a brightness histogram of an original and a histogram of achromatic dots in the original are obtained, and a chromatic histogram of the original is calculated from a difference between these histograms. Next, based on the ratio between the number of chromatic pixels and the number of achromatic pixels, it is determined whether it is a color document or a black and white document. Based on this result, a histogram is analyzed, and a black and white photo document, a black and white standard document, There are five types of originals: full-color photographic originals, color standard originals with white background, and color standard originals with background color. Then, appropriate background adjustment, black character discrimination processing, gradation reproduction processing, and the like are performed according to the document type.
JP-A-8-251402

  However, in the case of a halftone photo original printed with a color material, it is determined to be a color original when the original type is determined by the above-described method even though it looks monochrome. Often.

  Further, in the case of a photographic paper photographic original, even if the original original is a black-and-white photograph, there is a problem that when a black-and-white copy is made, the tone gap is conspicuous and the image quality is liable to be deteriorated. .

  Furthermore, in the case of a photograph with a small number of color pixels (for example, a photograph taken of a night scene), there is a problem that image deterioration is likely to occur as in the case of the above-described black-and-white photograph.

  Further, conventionally, regardless of the pixel region attribute (whether it belongs to a plurality of regions including a character region or a halftone dot region), the chromatic / achromatic determination of the pixel is performed, and the result is used for the color document. Since the monochrome document is discriminated, the discrimination accuracy is poor and the image quality may be lowered. For example, a document including color characters with low saturation may be determined as a monochrome image, or a document composed only of mixed color gray may be determined as a color image.

  The present invention has been made in view of such circumstances, and a criterion for determining whether or not a document includes a chromatic color is set based on the document type, and a document including a chromatic color based on the set criterion. By determining whether the image is present and performing image processing according to the determination result, the color / monochrome determination accuracy of the document can be improved, and by performing appropriate image processing according to the determination result An object is to provide an image processing method, an image processing apparatus, an image forming apparatus, a computer program, and a recording medium that can improve image quality.

  In the present invention, a criterion for determining whether or not the document includes a chromatic color is set based on the document type, and whether or not the document includes a chromatic color is determined based on the set criterion. Since the image processing is performed according to the determination result, the determination criterion as to whether or not the document is a chromatic color can be changed according to the document type, and the determination accuracy as a whole increases. Further, image quality can be improved during copying by performing appropriate image processing depending on whether or not the color is chromatic.

  In the present invention, when the document type is a photographic paper photo document, a determination criterion is set so that it is easy to determine that the document is a document including a chromatic color. When a photographic paper photograph is output as a monochrome copy, there are many cases in which image quality deterioration such as tone gap generally occurs and dots are conspicuous and graininess is noticeable. Therefore, even black-and-white photographs are output as color copies as much as possible to improve image quality.

  In the present invention, when the document type is a printed photo document, a determination criterion is set so that it is easy to determine that the document is an achromatic document. In a photograph with few color pixels, such as a night scene, there are many cases in which image quality deterioration such as tone gap occurs and dots are noticeable and graininess is noticeable. Therefore, even if it is a color photograph, if there are few color pixels, it is output as a monochrome copy to improve image quality.

The image processing method according to the present invention determines whether or not the document is a document including a chromatic color based on image data obtained by reading the document, and performs image processing on the image data according to the determination result. In the image processing method, the pixel of interest among the pixels included in the image data is determined to belong to a character region, a halftone dot region, or a third region other than the character region and the halftone dot region. When the region is a character region, a criterion for determining whether or not the pixel of interest is a chromatic color is more easily determined as a chromatic color than a predetermined criterion used when it is determined as the third region. If the determined region is a halftone dot region, a determination criterion for determining whether or not the pixel of interest is a chromatic color is a predetermined criterion used when the third region is determined. Than the criterion of The image data includes processing for setting a determination criterion that makes it easy to determine an achromatic color and determining whether the pixel of interest is a chromatic color using the predetermined determination criterion or the set determination criterion. And determining a criterion for determining whether or not the document is a document including a chromatic color based on the total number of pixels determined to be a chromatic color pixel .

  In the present invention, it is determined whether or not the document of interest includes a chromatic color based on a determination result of whether or not the target pixel belongs to at least a character area or a halftone dot area, and image processing according to the determination result is performed. Therefore, the color / monochrome determination result can be corrected based on the pixel region determination result, and the determination accuracy is improved as a whole. Further, image quality can be improved during copying by performing appropriate image processing depending on whether or not the color is chromatic. The present invention can also be applied to a scanner. In this case, since the color / monochrome determination result can be corrected based on the pixel region determination result, for example, when a monochrome image is scanned as a color image, an increase in the capacity of the image data can be prevented.

  In the present invention, when the target pixel belongs to the character area, a determination criterion is set so that it is easy to determine that the document is a document including a chromatic color. In the case of text, there are many cases in which the difference from achromatic colors such as brown is small. The accuracy of determination increases.

  In the present invention, when the target pixel belongs to the halftone dot region, a determination criterion is set so that it is easy to determine that the document is an achromatic document. In the case of composite gray (when gray is expressed by a mixed color dot of CMY), erroneous determination that the pixel of interest is a chromatic color (color) is prevented. An original formed only with mixed color gray is determined as a monochrome original.

  In the present invention, a criterion for determining whether or not the document includes a chromatic color is set based on the document type, and whether or not the document includes a chromatic color is determined based on the set criterion. Since the image processing is performed according to the determination result, the determination criterion as to whether or not the document is a chromatic color can be changed according to the document type, and the determination accuracy as a whole increases. Further, image quality can be improved during copying by performing appropriate image processing depending on whether or not the color is chromatic.

  In the present invention, when the document type is a photographic paper photo document, a determination criterion is set so that it is easy to determine that the document is a document including a chromatic color. When a photographic paper photograph is output as a monochrome copy, there are many cases in which image quality deterioration such as tone gap generally occurs and dots are conspicuous and graininess is noticeable. Therefore, even black-and-white photographs are output as color copies as much as possible to improve image quality.

  In the present invention, when the document type is a printed photo document, a determination criterion is set so that it is easy to determine that the document is an achromatic document. In a photograph with few color pixels, such as a night scene, there are many cases in which image quality deterioration such as tone gap occurs and dots are noticeable and graininess is noticeable. Therefore, even if it is a color photograph, if there are few color pixels, it is output as a monochrome copy to improve image quality.

The image processing apparatus according to the present invention determines whether or not the document is a document including a chromatic color based on image data obtained by reading the document, and performs image processing on the image data according to the determination result. In the image processing apparatus for performing the above , a means for determining whether the pixel of interest among the pixels included in the image data belongs to a character area, a halftone dot area, or a third area other than the character area and the halftone dot area; If the determined area is a character area, the determination criterion for determining whether or not the pixel of interest is a chromatic color is determined to be a chromatic color rather than a predetermined determination criterion used when it is determined to be the third region. Means for setting a determination criterion that facilitates the determination, and when the determined region is a halftone dot region, the determination criterion for determining whether or not the pixel of interest is a chromatic color is determined as the third region Predetermined to use when A means for setting a determination criterion that makes it easier to determine an achromatic color than a determination criterion, and a process for determining whether or not the pixel of interest is a chromatic color using the predetermined determination criterion or the set determination criterion Means for executing each of the pixels included in the image data, and means for setting a determination criterion for determining whether or not the document is a document including a chromatic color based on the total number determined to be chromatic pixels. It is characterized by providing.

  In the present invention, it is determined whether or not the document of interest includes a chromatic color based on a determination result of whether or not the target pixel belongs to at least a character area or a halftone dot area, and image processing according to the determination result is performed. Therefore, the color / monochrome determination result can be corrected based on the pixel region determination result, and the determination accuracy is improved as a whole. Further, image quality can be improved during copying by performing appropriate image processing depending on whether or not the color is chromatic. Based on the determination result of whether or not the target pixel belongs to the character area or the halftone dot area, it is determined whether or not the document includes a chromatic color, and image processing is performed according to the determination result. As a result, the color / monochrome determination result can be corrected, and the determination accuracy is improved as a whole. Further, image quality can be improved during copying by performing appropriate image processing depending on whether or not the color is chromatic. The present invention can also be applied to a scanner. In this case, since the color / monochrome determination result can be corrected based on the pixel region determination result, for example, when a monochrome image is scanned as a color image, an increase in the capacity of the image data can be prevented.

  In the present invention, when the target pixel belongs to the character area, a determination criterion is set so that it is easy to determine that the document is a document including a chromatic color. In the case of text, there are many cases in which the difference from achromatic colors such as brown is small. The accuracy of determination increases.

  In the present invention, when the target pixel belongs to the halftone dot region, a determination criterion is set so that it is easy to determine that the document is an achromatic document. In the case of composite gray (when gray is expressed by a mixed color dot of CMY), erroneous determination that the pixel of interest is a chromatic color (color) is prevented. An original formed only with mixed color gray is determined as a monochrome original.

  An image forming apparatus according to the present invention includes an image processing apparatus according to any one of the above-described inventions, and a unit that forms an image on a sheet based on image data subjected to image processing by the image processing apparatus. It is characterized by providing.

  In the present invention, it is possible to accurately determine whether or not the original is a chromatic color and to perform image processing according to the determination result to form an image on the sheet.

  In the present invention, a criterion for determining whether or not a document includes chromatic colors is set based on the document type, and whether or not the document includes chromatic colors is determined based on the determined criterion. Since the image processing according to the determination result is performed, the determination criterion as to whether or not the document is a chromatic color can be changed according to the document type, and the determination accuracy as a whole increases. Further, image quality can be improved during copying by performing appropriate image processing depending on whether or not the color is chromatic.

A computer program according to the present invention causes a computer to determine whether or not the document is a document including a chromatic color based on image data obtained by reading the document, and converts the image data into the image data according to a determination result. In a computer program that performs image processing, the computer determines whether a pixel of interest among the pixels included in the image data belongs to a character region, a halftone dot region, or a third region other than the character region and the halftone dot region. If the determined region is a character region, the determination criterion for determining whether or not the pixel of interest is a chromatic color is greater than the predetermined criterion used when the third region is determined. If the criterion is set so that it can be easily determined as a chromatic color, and the determined region is a halftone dot region, the criterion for determining whether the pixel of interest is a chromatic color is It is set to a determination criterion that makes it easier to determine an achromatic color than a predetermined determination criterion used when it is determined as the third region, and the target pixel is present using the predetermined determination criterion or the set determination criterion. A process for determining whether or not the image is chromatic is executed for each pixel included in the image data, and based on the total number determined to be chromatic pixels, whether or not the document is a document including a chromatic color is determined. to execute the process of setting the criteria for determining that said Rukoto.

  In the present invention, it is determined whether or not the document of interest includes a chromatic color based on a determination result of whether or not the target pixel belongs to at least a character area or a halftone dot area, and image processing according to the determination result is performed. Therefore, the color / monochrome determination result can be corrected based on the pixel region determination result, and the determination accuracy is improved as a whole. Further, image quality can be improved during copying by performing appropriate image processing depending on whether or not the color is chromatic.

A recording medium according to the present invention is characterized in that the computer program described above is recorded.

  In the present invention, the above-described image processing apparatus is realized on a computer by a program read from a recording medium.

  According to the present invention, a criterion for determining whether or not a document includes a chromatic color is set based on the document type, and whether or not the document includes a chromatic color is determined based on the determined criterion. Perform image processing according to the result. Therefore, the criterion for determining whether or not a document has a chromatic color can be changed according to the document type, and the determination accuracy for determining whether or not the document has a chromatic color can be improved. Further, image quality at the time of copying can be improved by performing appropriate image processing depending on whether or not the color is chromatic.

  According to the present invention, when the document type is a photographic paper photo document, a determination criterion is set so that it is easy to determine that the document is a document including a chromatic color. When a photographic paper photo is output as a monochrome copy, there are many cases in which image quality deterioration such as tone gap generally occurs and dots are noticeable and graininess is noticeable. By outputting, image quality can be improved.

  According to the present invention, when the document type is a printed photo document, a determination criterion is set so that it is easy to determine that the document is an achromatic document. In photographs with few color pixels, such as images of night scenes, there are many cases where image quality deterioration such as tone gaps and dots are noticeable and graininess is noticeable. When the number is small, the image quality can be improved by outputting it as a monochrome copy.

  According to the present invention, it is determined whether or not the original pixel includes a chromatic color based on the determination result of whether or not the target pixel belongs to the character area or the halftone dot area, and image processing is performed according to the determination result. Therefore, the color / monochrome determination result can be corrected by the pixel region determination result, and the determination accuracy can be improved as a whole. Further, image quality at the time of copying can be improved by performing appropriate image processing depending on whether or not the color is chromatic.

  According to the present invention, when the target pixel belongs to the character area, a determination criterion is set so that it is easy to determine that the document is a document including a chromatic color. In the case of text, there are many cases in which the difference from achromatic colors such as brown is small. The accuracy of determination can be increased.

  According to the present invention, when the target pixel belongs to the halftone dot region, a determination criterion is set so that it is easy to determine that the document is an achromatic document. In the case of composite gray (when gray is expressed by a mixed-color halftone dot of CMY), it can be prevented that the pixel of interest is erroneously determined to be a chromatic color. An original formed only with mixed-color gray can be determined as a monochrome original.

  According to the present invention, it is possible to accurately determine whether or not a document is a chromatic color, and to perform image processing according to the determination result to form an image on a sheet, thereby improving image quality during copying. it can.

  In the case of the present invention, the above-described image processing method can be realized by computer processing.

  In the case of the present invention, the above-described image processing apparatus can be realized on a computer by a program read from a recording medium.

Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
Embodiment 1 FIG.
FIG. 1 is a block diagram illustrating an internal configuration of an image processing apparatus according to the present invention. The image processing apparatus according to the present invention includes a control unit 1, an image input unit 3, an image processing unit 5, an image output unit 7, and an operation unit 9. The control unit 1 includes a ROM that stores a control program for controlling the respective hardware units, a CPU that executes the control program, and a RAM that stores various data generated during the execution of the control program.

  The image input unit 3 is a unit that optically reads an image of a document, and includes a light source that irradiates light to a document for reading, an image sensor such as a CCD (Charge Coupled Device), and the like. In the image input unit 3, a reflected light image from a document set at a predetermined reading position is formed on the image sensor, and RGB (R: Red, G: Green, B: Blue) analog electrical signals are output. . The analog electrical signal output from the image input unit 3 is input to the image processing unit 5.

  The image processing unit 5 converts the analog electrical signal output from the image input unit 3 into a digital electrical signal, and then performs image processing according to the document type to generate an output image signal. The generated image signal is output to the image output unit 7. In the present embodiment, CMYK signals (C: Cyan, M: Magenta, Y: Yellow, K: Black) are generated as image signals for output. The internal configuration and operation of the image processing unit 5 will be described in detail later.

  The image output unit 7 is a unit that forms an image on a sheet such as paper or an OHP film based on the image signal output from the image processing unit 5. Therefore, the image output unit 7 is a charger that charges the photosensitive drum to a predetermined potential, and laser writing that generates an electrostatic latent image on the photosensitive drum by emitting laser light in accordance with image data received from the outside. An apparatus, a developing device that supplies toner to the electrostatic latent image formed on the surface of the photosensitive drum to make it visible, a transfer device that transfers the toner image formed on the surface of the photosensitive drum onto paper (not shown), etc. And an image desired by the user is formed on a sheet by electrophotography. In addition to image formation by an electrophotographic method using a laser writing apparatus, an image formation may be performed by an inkjet method, a thermal transfer method, a sublimation method, or the like.

  The operation unit 9 includes various switches and buttons for accepting user instructions and selection operations.

  Although the image input unit 3 is configured as an image reading unit and the image output unit 7 is configured as an image forming unit, the image input unit 3 is configured as a unit that receives image data from the outside and a unit that transmits image data to the outside. Alternatively, a configuration in which they are appropriately combined may be used. For example, when the image input unit 3 is an image reading unit and the image output unit 7 is an image data transmission unit, the present invention operates as a scanner device (image reading device). When the data receiving unit and the image output unit 7 are image forming units, the present invention operates as a printer device (image forming device). Needless to say, the present invention can also be applied to a digital multi-function peripheral including an image reading unit, an image forming unit, and an image data transmitting / receiving unit.

  FIG. 2 is a block diagram illustrating the configuration of the image processing unit 5. The image processing unit 5 includes an AD conversion unit 51, a shading correction unit 52, a document type determination unit 53, an ACS determination unit 54, an input tone correction unit 55, a region separation processing unit 56, a color correction unit 57, and a black generation under color removal. Unit 58, spatial filter processing unit 59, output tone correction unit 60, and tone reproduction processing unit 61.

  The AD conversion unit 51 converts the RGB analog signal input from the image input unit 3 into a digital signal. The shading correction unit 52 performs a process of removing various distortions generated in the illumination system, the imaging system, and the imaging system of the image input unit 3 on the digital RGB signal output from the AD conversion unit 51. Further, the shading correction unit 52 adjusts the color balance.

  The document type determination unit 53 uses an RGB (RGB reflectance signal) from which various distortions have been removed by the shading correction unit 52 and the color balance is adjusted, such as a density signal, and is used in a color image processing apparatus. Is converted into an easy-to-handle signal, and the document type is determined. A document type determination signal output as a determination result by the document type determination unit 53 includes an ACS determination unit 54, an input tone correction unit 55, a color correction unit 57, a black generation and under color removal unit 58, a spatial filter processing unit 59, And input to the gradation reproduction processing unit 61. The determination method will be described in detail later.

  The ACS determination unit 54 determines whether the document read by the image input unit 3 is a color document or a monochrome document. The ACS discrimination signal output by the ACS discrimination unit 54 as a determination result is input to the input tone correction unit 55, the color correction unit 57, and the black generation and under color removal unit 58 in the subsequent stage. The determination method will be described in detail later.

  The input tone correction unit 55 performs image quality adjustment processing such as background density removal and contrast. The region separation processing unit 56 performs processing for separating each pixel in the input image into one of a character region, a halftone dot region, and a photographic region from the RGB signals. Based on the separation result, the region separation processing unit 56 outputs a region identification signal indicating which region the pixel belongs to, a subsequent color correction unit 57, a black generation and under color removal unit 58, a spatial filter processing unit 59, and a gradation. The output signal is output to the reproduction processing unit 61 and the input signal output from the input tone correction unit 55 is output to the subsequent color correction unit 57 as it is.

  The color correction unit 57 performs processing for removing color turbidity based on the spectral characteristics of CMY color materials including unnecessary absorption components in order to faithfully reproduce color reproduction. The black generation and under color removal unit 58 generates black (K) signals from the CMY three-color signals after color correction, and generates a new CMY signal obtained by subtracting the K signal obtained by black generation from the original CMY signals. Generate the process. By this processing, the CMY three-color signal is converted into a CMYK four-color signal.

  As an example of the black generation process, there is a method (general method) for generating black by skeleton black. In this method, the input / output characteristic of the skeleton curve is y = f (x), the input data is C, M, Y, the output data is C ′, M ′, Y ′, K ′, the UCR rate (UCR) : Under Color Removal) α (0 <α <1), the black generation under color removal processing is expressed by the following equation.

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

  The spatial filter processing unit 59 performs spatial filter processing using a digital filter on the image data of the CMYK signal input from the black generation and under color removal unit 58 based on the region identification signal, thereby correcting the spatial frequency characteristics. Processing is performed to prevent blurring and particulate deterioration of the output image.

  For example, the region separated into characters by the region separation processing unit 56 has a high frequency enhancement amount in the sharp enhancement processing in the spatial filter processing by the spatial filter processing unit 59 in order to improve the reproducibility of black characters or color characters in particular. Increased. At the same time, the tone reproduction processing unit 61 selects binarization or multi-value processing on a high-resolution screen suitable for high-frequency reproduction. Further, with respect to the region separated into halftone dot regions by the region separation processing unit 56, the spatial filter processing unit 59 performs low pass filter processing for removing the input halftone component. The output tone correction unit 60 performs output tone correction processing for converting a signal such as a density signal into a halftone dot area ratio that is a characteristic value of the color image output device, and then the tone reproduction processing unit 61 performs the final processing. Specifically, gradation reproduction processing is performed in which an image is separated into pixels and processed so that each gradation can be reproduced. In addition, regarding the region separated into photographs by the region separation processing unit 56, binarization or multi-value processing is performed on the screen with an emphasis on gradation reproducibility.

  Next, processing contents in the document type determination unit 53 will be described. FIG. 3 is a block diagram illustrating the configuration of the document type determination unit 53. The document type determination unit 53 includes a signal conversion unit 5300, a minimum density value calculation unit 5301, a maximum density value calculation unit 5302, a maximum density difference calculation unit 5303, a total density busyness calculation unit 5304, a determination area setting unit 5305, and a maximum density difference. Threshold setting unit 5306, total density busyness threshold setting unit 5307, character / halftone determination unit 5310, character / halftone determination threshold setting unit 5311, character pixel counting unit 5312, halftone pixel counting unit 5313, background / printing paper determination A unit 5320, a background / photographic paper determination threshold setting unit 5321, a background pixel counting unit 5322, a photographic paper pixel counting unit 5323, and a document determination unit 5330.

  The signal conversion unit 5300 converts the RGB signal output from the shading correction unit 52 into a CMY density signal and outputs the converted signal to the minimum density value calculation unit 5301, the maximum density value calculation unit 5302, and the total density busyness calculation unit 5304. . The minimum density value calculation unit 5301 calculates the minimum density value based on the input CMY signal, and the maximum density value calculation unit 5302 calculates the maximum density value based on the input CMY signal. The maximum density difference calculator 5303 calculates the maximum density difference using the minimum density value and the maximum density value calculated by the minimum density value calculator 5301 and the maximum density value calculator 5302.

  A total density busyness calculation unit 5304 calculates the total sum of absolute values of density differences between adjacent pixels. The determination area setting unit 5305 is calculated by the maximum density difference calculated by the maximum density difference calculation unit 5303, the threshold for the maximum density difference set by the maximum density difference threshold setting unit 5306, and the total density busyness calculation unit 5304. Are divided into a background / printing paper (photo) area and a character / halftone dot area on the basis of the threshold values for the total density busyness and the total density busyness threshold setting unit 5307.

  The character / halftone dot determination unit 5310 determines whether the pixel in the region separated into the character / halftone dot region by the determination region setting unit 5305 is a character or a halftone dot. For the determination, a threshold set by the character / halftone dot determination threshold setting unit 5311 is used. The character pixel counting unit 5312 counts pixels determined to be characters, and the halftone pixel counting unit 5313 counts pixels determined to be halftone dots.

  The background / photographic paper determination unit 5320 determines whether the pixels in the region separated by the determination region setting unit 5305 into the background / printing paper region are the background or the photographic paper. For the determination, a threshold set in the background / photographic paper determination threshold setting unit 5321 is used. A background pixel counting unit 5322 counts pixels determined to be the background, and a photographic paper pixel counting unit 5323 counts pixels determined to be photographic paper.

  The document determination unit 5330 determines the document type based on the pixel count results of each region, and outputs the document type determination signal to the subsequent ACS determination unit 54, the input tone correction unit 55, the color correction unit 57, and the black generation base. The data is output to the color removal unit 58, the spatial filter processing unit 59, and the gradation reproduction processing unit 61.

  FIG. 4 is a flowchart for explaining a procedure of processing executed by the document type determination unit 53. Hereinafter, a case where determination is performed on an n × m block will be described. First, the minimum density value and the maximum density value in the n × m block including the target pixel are calculated (steps S11 and S12), and the maximum density difference is calculated using the calculated minimum density value and the maximum density value (step S13). . Next, the sum of absolute values of density differences between adjacent pixels (that is, the total density busyness) is calculated (step S14).

  Then, the calculated maximum density difference and the maximum density difference threshold are compared, and the calculated total density busyness and the total density busyness threshold are compared. Both the maximum density difference and the total density busyness are compared. It is determined whether it is smaller than the threshold value (step S15). When it is determined that the maximum density difference is smaller than the maximum density difference threshold and the total density busyness is smaller than the total density busyness threshold (S15: YES), it is determined that the target pixel is the background / printing paper region ( Step S16).

  At this time, the maximum density difference is compared with a threshold (background / photographic paper determination threshold) set by the background / photographic paper determination threshold setting unit 5321 to determine whether the maximum density difference is smaller than the background / photographic paper determination threshold. Is determined (step S17). If it is determined that the maximum density difference is smaller than the background / photographic paper determination threshold value (S17: YES), the target pixel is counted as a background area (step S18), and the maximum density difference is equal to or greater than the background / photographic paper determination threshold value. If it is determined (S17: NO), the target pixel is counted as a photographic paper region (step S19).

  On the other hand, when it is determined in step S15 that either the maximum density difference or the total density busyness is greater than or equal to the comparison target threshold (S15: NO), it is determined that the target pixel is a character / halftone dot region ( Step S20).

  At this time, the total density busyness is compared with the product of the maximum density difference and the threshold (character / halftone determination threshold) set by the character / halftone determination threshold setting unit 5311. It is determined whether it is smaller (step S21). When it is determined that the total density busyness is smaller than the product value (S21: YES), the target pixel is counted as a character area (step S22), and when the total density busyness is determined to be equal to or greater than the product value (S21). : NO), the target pixel is counted as a halftone dot region (step S23).

  Next, it is determined whether or not all the pixels have been processed (step S24). If it is determined that the processing has not ended (S24: NO), the process returns to step S11. If it is determined that all pixels have been processed (S24: YES), document discrimination is determined based on the count results in steps S18 and S19 and steps S22 and S23 (step S25). A threshold value is set for each of the background area, the photographic paper area, the halftone dot area, and the photographic paper area, and the document type can be determined by comparing the threshold value with the count result of each area.

For example, when the ratio of the character area and the ratio of the halftone dot area are equal to or greater than the threshold value, respectively, it is determined that the character / halftone original (character-printed photo original). If the detection accuracy is higher in the order of characters, halftone dots, and photographic paper photographs, when the ratio of the character area is 30% or more of the total number of pixels, the ratio of the character original and the halftone area is 20% of the total number of pixels. In the above case, when the ratio of the halftone original (printed photo original) and the photographic paper photo area is 10% or more of the total number of pixels, it is determined that the image is a photographic paper photo original. In this case, the document type is determined to be a character document, a character printed photo document, a printed photo document, a photographic paper photo document, or a character photographic paper photo document. The document type determination may be performed using image data temporarily stored in a storage unit such as a hard disk instead of performing pre-scanning.

  Next, an example of pixel density distribution in each area of the background, photographic paper, halftone dots, and characters will be described. FIG. 5 is a schematic diagram illustrating an example of the pixel density distribution in each region, and FIG. 6 is a schematic diagram illustrating a distribution according to the maximum density difference and the total density busyness in each region. FIG. 5A shows the density distribution of the background. In each of FIGS. 5A to 5D, the horizontal axis indicates the pixel, and the vertical axis indicates the density. Since the density distribution of the background region is usually small in density change, both the maximum density difference and the total density busyness are very small, and the distribution shown in FIG. 6 is obtained. Therefore, if the maximum density difference is smaller than the background / printing paper determination threshold (Th1) with respect to the pixel determined as the background / printing paper region, it can be determined as the background pixel.

  As shown in FIG. 5 (b), the density distribution in the photographic paper photographic area usually has a smooth density change, and the maximum density difference and the total density busyness are both small and slightly larger than the background area. Therefore, the distribution as shown in FIG. 6 is taken. Therefore, when the maximum density difference is larger than the background / printing paper determination threshold (Th1) for the pixels determined as the background / printing paper region, it is possible to determine that the pixel is the printing paper region.

  As shown in FIG. 5C, the density distribution in the halftone dot region varies depending on the halftone dot. However, since the total density busyness varies depending on the number of halftone dots, the maximum density difference. The ratio of the total density busyness with respect to increases. For this reason, the distribution shown in FIG. 6 is taken. Therefore, when the total density busyness is larger than the product (L2) of the maximum density difference and the character / halftone determination threshold, it can be determined that the pixel is a halftone pixel.

  As shown in FIG. 5 (d), the density distribution of the character area has a large maximum density difference, and the total density complexity increases accordingly. However, since the density change is smaller than that of the halftone area, the density distribution is smaller than that of the halftone area. The total density complexity decreases. In particular, since the ratio of the total density busyness with respect to the maximum density difference becomes small, the distribution as shown in FIG. 6 is taken. Therefore, when the total density busyness is smaller than the product (L2) of the maximum density difference and the character / halftone determination threshold in the pixel determined as the character / halftone area, it is determined that the pixel is a character pixel. Is possible.

  Next, the processing content in the ACS discrimination | determination part 54 is demonstrated. FIG. 7 is a block diagram illustrating the configuration of the ACS determination unit 54. The ACS determination unit 54 includes a chromatic / achromatic pixel determination unit 541, a chromatic pixel histogram creation unit 542, a histogram analysis unit 543, and a data conversion unit 544.

  The chromatic / achromatic pixel determination unit 541 determines whether each pixel is a chromatic pixel or an achromatic pixel based on the RGB signal input from the document type determination unit 53. FIG. 8 is a block diagram illustrating the configuration of the chromatic / achromatic pixel determination unit 541. In the chromatic / achromatic pixel determination unit 541, first, the target pixel average value calculation units 5411 to 5413 calculate an average value of an n × m pixel block (for example, a 3 × 3 pixel block) centered on the target pixel. Calculated for each input signal. Next, the maximum density difference value calculation unit 5414 calculates the maximum value and the minimum value of the average value of each signal, and calculates the difference between the calculated maximum value and the minimum value. The calculated difference value becomes the maximum density difference value in the target pixel.

  Next, the target pixel determination unit 5415 compares the magnitude relationship between the maximum density difference value and the chromatic pixel determination threshold set by the chromatic pixel determination threshold setting unit 5416. When the maximum density difference difference value is larger than the chromatic pixel determination threshold, the target pixel is determined as a chromatic pixel, and when the maximum density difference value is smaller than the chromatic pixel determination threshold, the target pixel is determined as an achromatic pixel.

  Returning to the block diagram of FIG. When the chromatic / achromatic pixel determination unit 541 determines that the pixel is a chromatic pixel, the chromatic pixel histogram creation unit 542 creates a histogram. Note that no histogram is created for data determined to be achromatic pixels. The histogram analysis unit 543 analyzes the histogram created by the chromatic pixel histogram creation unit 542 and determines whether or not the document is to be color copied. The analysis method will be described in detail later. If the histogram analysis unit 543 determines that color copying should not be performed, the data conversion unit 544 performs data conversion that is optimal for monochrome copying of chromatic pixels. For example, a process of replacing a pixel determined to be a chromatic pixel with an achromatic pixel is performed.

  FIG. 9 is a flowchart for explaining a processing procedure in the ACS discriminating unit 54. The chromatic / achromatic pixel determination unit 541 of the ACS determination unit 54 performs chromatic / achromatic pixel determination based on the RGB signals input from the document type determination unit 53 (step S31). For the determination, an n × m pixel block centered on the target pixel is used.

  The chromatic / achromatic pixel determination unit 541 determines whether or not the pixel of interest is a chromatic pixel (step S32). If it is determined that the pixel is a chromatic pixel (S32: YES), the determination to that effect is made. The result is notified to the chromatic pixel histogram creation unit 542. If it is determined that the pixel of interest is an achromatic pixel (S32: NO), the histogram is not created, so the process returns to step S31 to perform chromatic / achromatic determination with the next pixel as the pixel of interest. .

  When the determination result that the target pixel is a chromatic pixel is received, the chromatic / achromatic pixel histogram creation unit 542 creates a histogram (step S33). Then, it is determined whether or not the processing for all the pixels has been completed (step S34). If it is determined that the processing has not been completed (S34: NO), the processing is returned to step S31.

  When it is determined that the processing for all the pixels has been completed (S34: YES), the histogram analysis unit 543 performs a histogram analysis process described later based on the document type determination signal input from the document type determination unit 53 (Step S34). In step S35, it is determined whether or not the document is for color copying based on the analysis result (step S36). If it is determined that the document is not for color copying (S36: NO), chromatic pixels are converted into data that is optimal for monochrome copying (step S37). On the other hand, if it is determined that the document is for color copying (S36: YES), the processing according to this flowchart is terminated without performing data conversion.

Note that the ACS discriminating unit 54 discriminates whether the document is a color document or a monochrome document based on the RGB signal. However, the CMY 1976 L ^* a ^* b ^* CMY signal or the RGB signal obtained by inverting the RGB signal is used ^. The signal may be converted into a signal (CIE: Commission International de l'Eclairage: L ^* : brightness, a ^* , b ^* : chromaticity).

  Next, processing contents in the histogram analysis unit 543 will be described. 10 to 12 are histograms showing the density distribution of the document image. The histogram in FIG. 10 shows the density distribution of a document partially discolored due to dirt, blots, or the like. Since the partially discolored original exists in a part of the original with the same color system, one peak having a narrow density area width is formed on the high density area side in all signals.

  The histogram in FIG. 11 shows the density distribution of a colored document, a document whose color has changed as a whole, and the like. As shown in FIG. 11, although the frequency of the chromatic pixels is large, the chromatic pixel histogram has a high density and the same color for each signal as in the partially discolored document. Narrow peaks are formed. In other words, in a partially discolored document, a colored document, and an entirely discolored document, the peak frequency depends on the total number of chromatic pixels in the document, so the determination is based on the peak density position and density width frequency. can do.

  The histogram in FIG. 12 shows a general color document density distribution. In a general color original, the peak width increases as the number of colors increases, and a peak is formed in which the frequency increases as the color area in the original increases.

  FIG. 13 is a flowchart for explaining the procedure of the histogram analysis process. The histogram analysis unit 543 first determines whether or not the document type is a photographic paper photograph based on the document type determination signal input from the document type determination unit 53 (step S41). If it is determined that the document type is a photographic paper photograph (S41: YES), the density threshold is set low and the achromatic determination frequency threshold is set high (step S42). This setting makes it easy to select a color copying mode.

  If it is determined that the read original is not a photographic paper photograph (S41: NO), it is determined whether or not the original type is a printed photograph (step S43). If it is determined that the document type is a printed photograph (S43: YES), the density threshold is set high and the achromatic determination frequency threshold is set low (step S44). This setting makes it easy to select the monochrome copying mode. If it is determined that the photograph is not a printed photograph (S43: NO), the density threshold value and the achromatic determination frequency threshold value are not changed, and thus the processing according to this flowchart ends.

  After setting the threshold value in step S42 or step S44, the density value having the highest frequency is detected from the histogram created in the chromatic pixel histogram creation unit 542, and the detected density value is set to the maximum frequency density. A value is set (step S45). Next, a comparison is made between the maximum power density value and a density threshold value that is a density threshold value for which monochrome copying is desired, and it is determined whether or not the maximum power density value is larger than the density threshold value (step S46).

  When it is determined that the maximum power density threshold is greater than the density threshold (S46: YES), the total value of the density range area (maximum density area) set in advance around the maximum power density value is calculated (step S46). S47). As the value of the density range, for example, about ± 8 is preferable with the maximum frequency density value as the center.

  Next, a comparison is made between the total density value of the maximum density area calculated in step S47 and a preset achromatic determination frequency threshold value, and whether or not the total density value of the maximum density area is larger than the achromatic determination frequency threshold value. Judgment is made (step S48). Here, the achromatic determination frequency threshold is a value set as a ratio to the total number of pixels determined to be chromatic pixels, and for example, a value such as the total number of chromatic pixels × 90% is appropriate.

  When it is determined that the total density value of the maximum density area is larger than the achromatic determination frequency threshold (S48: YES), the read document is determined as a document to be monochrome copied (step S49). On the other hand, when it is determined in step S46 that the maximum power density value is equal to or lower than the density threshold value (S46: NO), or in step S48, it is determined that the total power value of the maximum density area is equal to or lower than the achromatic determination power threshold value. (S48: NO), the read original is determined as an original to be color copied (step S50).

  By performing such processing, the chromatic / achromatic color of the document is determined, and based on the result, input tone correction, color correction, and black generation and under color removal processing are respectively performed by the input tone correction unit 55, This is performed by the color correction unit 57 and the black generation and under color removal unit 58. For example, when it is determined that the input image is a color original, the color image processing described with reference to FIG. 2 is performed. If it is determined that the input image is a monochrome document, the RGB signal is converted into a K signal in the input tone correction process, and the color correction process and the black generation and under color removal process are omitted. In the spatial filter processing, output tone correction processing, and tone reproduction processing, the same processing is performed for both color copying and monochrome copying.

  Note that each of the above-described threshold values can be arbitrarily adjusted so that more appropriate processing can be performed on the document data. A plurality of values predicted for each threshold value may be stored in advance in a storage unit such as a ROM, and appropriate values may be selected by a switch or the like provided in the operation unit 9 as necessary.

Embodiment 2. FIG.
In the present embodiment, the determination of the region attribute indicating whether the pixel belongs to a plurality of regions including a character region or a halftone dot region, and the chromatic / achromatic determination whether the pixel is chromatic or achromatic. A configuration for determining the document type in combination will be described. The configuration of the image processing apparatus is the same as that of the first embodiment, but includes a document type determination unit 53A instead of the document type determination unit 53, and an ACS determination unit 54A instead of the ACS determination unit 54.

  FIG. 14 is a block diagram illustrating the configuration of the document type determination unit 53A. The document type determination unit 53A includes the signal conversion unit 5300, the minimum density value calculation unit 5301, the maximum density value calculation unit 5302, the maximum density difference calculation unit 5303, the total density busyness calculation unit 5304, the determination area setting unit 5305, and the maximum. Density difference threshold setting unit 5306, total density busyness threshold setting unit 5307, character / halftone determination unit 5310, character / halftone determination threshold setting unit 5311, character pixel counting unit 5312, halftone pixel counting unit 5313, background / printing In addition to the paper determination unit 5320, the background / photographic paper determination threshold setting unit 5321, the background pixel counting unit 5322, the photographic paper pixel counting unit 5323, and the document determination unit 5330, the chromatic / achromatic determination of the pixel of interest is performed. An achromatic pixel determination unit 531 is provided.

  FIG. 15 is a block diagram illustrating the internal configuration of the chromatic / achromatic pixel determination unit 531. The chromatic / achromatic pixel determination unit 531 is for determining whether each pixel is a chromatic pixel or an achromatic pixel with respect to the input RGB signal. 5311 to 5313, a maximum density difference value calculation unit 5314, a target pixel determination unit 5315, and a chromatic pixel determination threshold setting unit 5316.

  First, in an n × m block (for example, 3 × 3) centering on a target pixel (a hatched pixel in FIG. 15), the target pixel average value calculation units 5311 to 5313 calculate an average value for each input signal. Perform the calculation.

  Next, the maximum value and the minimum value of each signal calculated by the maximum density difference value calculation unit 5314 are calculated, and the difference value between the maximum value and the minimum value is calculated as the maximum density difference value in the target pixel. Then, the pixel-of-interest determination unit 5315 compares the calculated maximum density difference value with a chromatic pixel determination threshold value (for example, 20) set in advance in the chromatic pixel determination threshold value setting unit 5316 to obtain the maximum density difference value. Is larger than the chromatic pixel determination threshold, it is determined that the target pixel is a chromatic pixel, and if the maximum density difference value is smaller than the chromatic pixel determination threshold, it is determined that the target pixel is an achromatic pixel.

  At this time, based on the determination result of the character / halftone dot determination unit 5310, the value of the chromatic pixel determination threshold set in the chromatic pixel determination threshold setting unit 5316 is changed. For example, when it is determined that the target pixel is a character, the chromatic pixel determination threshold is set to a small value. This is often the case for characters that have a small difference (maximum density difference value) from an achromatic color such as brown, so that it is easier to determine that the color is chromatic compared to the area such as the background. This is because the determination accuracy of color characters can be improved.

  On the other hand, when it is determined that the target pixel is a halftone dot, the chromatic pixel determination threshold is set to a large value. This is to prevent erroneous determination that the pixel of interest is a chromatic color (color) when gray is represented by CMY mixed color halftone dots (in the case of composite gray).

  FIG. 16 is a flowchart showing a procedure of processing executed by the document type determination unit 53A. The document type determination unit 53A performs region determination for an n × m block (for example, 7 × 7 block) including the target pixel (S51 to S63) in the same manner as the procedure described in the flowchart of FIG. Determine the attribute. Thus, it is determined whether the target pixel belongs to the background area (S58), the photographic paper area (S59), the character area (S62), or the halftone dot area (S63).

  Next, a chromatic / achromatic pixel determination process is executed for the target pixel (S64). Details of the chromatic / achromatic pixel determination process will be described later. Here, a chromatic pixel determination threshold is set based on the attribute of the target pixel determined by the processes of steps S51 to S63.

  Next, it is determined whether or not all the pixels have been processed (step S65). If it is determined that the processing has not ended (S65: NO), the process returns to step S51. If it is determined that all the pixels have been processed (S65: YES), document discrimination is determined based on the count results in steps S58 and S59 and steps S62 and S63 (step S66). A threshold value is set for each of the background area, the photographic paper area, the halftone dot area, and the photographic paper area, and the document type can be determined by comparing the threshold value with the count result of each area.

  Note that pixel attribute determination is not limited to the above method, and a method described below can also be used. The following determination is performed in a block of M × N pixels (for example, 7 × 7 pixels) centered on the pixel of interest, and this is used as a region identification signal of the pixel of interest.

  An average value Dave of the signal level is obtained for the pixels in the block, and each pixel in the block is binarized using the average value. Further, the maximum pixel signal level Dmax and the minimum pixel signal level Dmin are also obtained at the same time.

  In the character area, it is considered that the difference between the maximum pixel signal level Dmax and the minimum pixel signal level Dmin is large and the density is high. Therefore, when Dsub> PC or Dmin <PB is satisfied, the character area is determined.

  In the halftone dot region, the halftone dot region is identified by utilizing the fact that the fluctuation of the image signal in the small region is large and the density is higher than the background. For the binarized data, the number of change points from 0 to 1 in the main scanning direction and the sub-scanning direction is obtained, respectively, and the change points from 1 to 0 are obtained as KH and KV, respectively, and compared with the threshold values TH and TV. If both values exceed the threshold value, a halftone dot region is set. Further, in order to prevent erroneous determination with the background, the previously obtained Dmax, Dmin, and Dave are compared with the threshold values B1 and B2, and Dmax-Dave> B1, Dave-Dmin> B2, KH> TH, and KV> TV. In this case, it is determined as a halftone dot region.

  The pixel of interest is classified using the above two determination results. That is, when it is determined that the image is a halftone dot region in the halftone dot determination, it is determined that the target pixel belongs to the halftone dot region regardless of the character determination determination result. Further, when it is determined that it is not a halftone dot region in the halftone dot determination and is determined as a character region in the character determination, it is determined that the target pixel belongs to the character region. Further, when it is determined that the pixel is not a halftone dot region in the halftone dot determination and is not a character region in the character determination, it is determined that the target pixel belongs to another region. By classifying the target pixel in this way and counting the pixels in the same manner as described above, the document type can be determined.

  It is not always necessary to determine the document type, and only chromatic / achromatic determination may be performed.

  Next, chromatic / achromatic pixel determination processing will be described. FIG. 17 is a flowchart for explaining the procedure of the chromatic / achromatic pixel determination process. The chromatic / achromatic pixel determination unit 531 first determines whether or not the target pixel belongs to the character region (step S71). If it is determined that the pixel of interest belongs to the character area (S71: YES), the chromatic pixel determination threshold is set to a small value (step S72), and the processing according to this flowchart ends.

  When it is determined that the target pixel does not belong to the character area (S71: NO), the chromatic / achromatic pixel determination unit 531 determines whether the target pixel belongs to the halftone dot area (step S73). If it is determined that the pixel of interest belongs to the halftone dot region (S73: YES), the chromatic pixel determination threshold is set to a large value (step S74), the processing according to this flowchart is terminated, and the pixel of interest enters the dot region. When it is determined that it does not belong (S73: NO), the chromatic pixel determination threshold value is set to a default value (step S75), and the processing according to this flowchart is terminated.

  Next, the ACS determination unit 54A will be described. FIG. 18 is a block diagram illustrating the configuration of the ACS determination unit 54A. The ACS determination unit 54A includes a chromatic pixel histogram creation unit 542, a histogram analysis unit 543, and a data conversion unit 544. The processing content in each processing unit is the same as that mounted in the ACS determination unit 54 described in the first embodiment, and the chromatic pixel histogram creation unit 542 is the chromatic / achromatic pixel determination unit described above. A histogram is created only for data determined to be chromatic pixels by 531. The histogram analysis unit 543 determines whether the document is to be color-copied or not by analyzing the shape of the histogram using the histogram created by the chromatic pixel histogram creation unit 542. When the histogram analysis unit 543 determines that color copying should not be performed, the data conversion unit 544 performs processing for converting chromatic pixels into data optimal for monochrome copying. For example, a process of replacing a pixel determined to be a chromatic pixel with an achromatic pixel (white pixel) is performed.

  FIG. 19 is a flowchart illustrating a procedure of processing executed by the ACS determination unit 54A. First, the chromatic pixel histogram creation unit 542 creates a histogram only for data determined as chromatic pixels by the chromatic / achromatic pixel determination unit 531 (step S81). Next, it is determined whether or not the processing of all pixels has been completed (step S82). If there is a pixel for which processing has not ended (S82: NO), the ACS determination unit 54A returns the processing to step S81.

  If it is determined that all the pixels have been processed (S82: YES), a histogram analysis process (to be described later) is performed (step S83), and it is determined from the histogram shape whether the document is to be color copied.

  Based on the analysis result in step S83, it is determined whether or not the document is for color copying (step S84). If it is determined that the document is not for color copying (S84: NO), the chromatic pixels are converted into data that is optimal for monochrome copying (step S85). On the other hand, if it is determined that the document is for color copying (S84: YES), the processing according to this flowchart is terminated without performing data conversion.

  FIG. 20 is a flowchart for explaining the processing procedure of the histogram analysis processing. First, a density value having the largest power value is detected in the chromatic pixel histogram (step S91), and the density value is set as the maximum power density value. Next, a comparison is made between the maximum power density value and a density threshold value (for example, 150) which is a density threshold value for which monochrome copying is desired, and it is determined whether or not the maximum power density value is larger than the density threshold value (step S92). ).

  When it is determined that the maximum power density threshold is larger than the density threshold (S92: YES), the total numerical value of the area having the preset density width (maximum density area) around the maximum power density value is calculated (step) S93). As the value of the density range, for example, about ± 8 is preferable with the maximum frequency density value as the center.

  Next, the total density value of the maximum density area calculated in step S93 is compared with the preset achromatic determination frequency threshold value, and it is determined whether or not the total density value of the maximum density area is larger than the achromatic determination frequency threshold value. Judgment is made (step S94). Here, the achromatic determination frequency threshold is a value set as a ratio to the total number of pixels determined to be chromatic pixels, and for example, a value such as the total number of chromatic pixels × 90% is appropriate.

  When it is determined that the total density value of the maximum density area is larger than the achromatic determination frequency threshold (S94: YES), the read document is determined as a document to be monochrome copied (step S95). On the other hand, when it is determined in step S92 that the maximum power density value is equal to or lower than the density threshold (S92: NO), or in step S94, it is determined that the total power value of the maximum density area is equal to or lower than the achromatic determination power threshold. (S94: NO), the read original is determined as an original to be color-copied (step S96).

  Note that each of the above-described threshold values can be arbitrarily adjusted so that more appropriate processing can be performed on the document data. Further, a plurality of values predicted for each threshold value may be stored in advance in a storage unit such as a ROM, and appropriate values may be selected as necessary.

  Through the processing operation described above, the chromatic / achromatic color of the document is determined, and input tone correction, color correction, and black generation and under color removal processing are switched based on the result. For example, when it is determined that the input image is a color original, the color image processing described with reference to FIG. 2 is performed. If it is determined that the input image is a monochrome document, the RGB signal is converted into a K signal in the input tone correction process, and the color correction process and the black generation and under color removal process are omitted. In the spatial filter processing, output tone correction processing, and tone reproduction processing, the same processing is performed for both color copying and monochrome copying.

  In the above, only a chromatic pixel is extracted to create a histogram, and the shape of the histogram is analyzed to determine whether the document is to be color-copied. For example, Japanese Patent Laid-Open No. 4-282968 discloses. The method described can also be applied. In this method, it is determined whether each pixel is a color pixel or a monochrome pixel, and when the presence of a predetermined number or more of continuous color pixels in the given pixel order is detected, this continuous color pixel is color-coded. If a predetermined number or more of color blocks exist in one line, the line is counted as a color line. If a predetermined number of color lines are present in the document, it is determined as a color image. Otherwise, it is determined as a monochrome image. In the above method, when determining whether each pixel is a color pixel or a monochrome pixel, pixel attribute identification (determination of whether it belongs to a plurality of areas including characters and halftone dots) Color pixels and monochrome pixels may be determined based on the identification result.

  In addition to the above-described method, the chromatic / achromatic determination method includes (1) a method of determining the difference between the maximum value and the minimum value of the RGB signal with a predetermined threshold, and (2) the RGB signal. It is also possible to use a known method such as a method of obtaining an absolute value of a difference between each color component and comparing it with a threshold value.

Embodiment 3 FIG.
In the first embodiment, each processing is realized by hardware. However, the image processing according to the present invention may be realized by software processing.

  FIG. 21 is a block diagram illustrating the internal configuration of an image processing apparatus in which the computer program of the present invention is installed. In the figure, reference numeral 100 denotes an image processing apparatus according to the present embodiment, specifically a personal computer, a workstation, or the like. The image processing apparatus 100 includes a CPU 101, and hardware such as a ROM 103, a RAM 104, a hard disk 105, an external storage unit 106, an input unit 107, a display unit 108, and a communication port 109 is connected to the CPU 101 via a bus 102. Yes. The CPU 101 controls the above-described hardware units according to a control program stored in advance in the ROM 103.

  The RAM 104 is a volatile memory that temporarily stores various data generated during execution of the control program described above or the computer program according to the present invention. The hard disk 105 is a storage unit having a magnetic recording medium, and stores the computer program of the present invention, image data to be processed, and the like. The external storage unit 106 includes a reading device for reading the program code from the recording medium M on which the program code (execution format program, intermediate code program, source program) of the computer program of the present invention is recorded. As the recording medium M, an FD (Flexible Disk), a CD-ROM, or the like can be used. The program code read by the external storage unit 106 is stored in the hard disk 105. The CPU 101 loads the program code stored in the hard disk 105 onto the RAM 104 and executes it, thereby realizing the image processing method according to the present invention as described in the first and second embodiments.

  The input unit 107 functions as an interface for acquiring image data from the outside. For example, a color scanner device or the like is connected to the input unit 107. The display unit 108 functions as an interface for displaying image data to be processed, image data during image processing, image data after image processing, and the like. The display unit 108 may be configured to display image data by connecting an external display device such as a liquid crystal display device, or the display unit 108 may include a display device and display image data. The communication port 109 is an interface for connecting the printer 200 to the outside. When the image data subjected to image processing is printed by the printer 200, the image processing apparatus 100 generates print data that can be decoded by the printer 200 based on the image data, and transmits the generated print data to the printer 200. .

  In the present embodiment, the CPU 101 performs various calculations. However, a dedicated chip for performing calculations related to image processing may be separately provided and calculations may be performed according to instructions from the CPU 101.

  In addition to the above-described FD and CD-ROM, the recording medium M for recording the above-described program code includes optical disks such as MO, MD, and DVD, magnetic recording media such as a hard disk, IC card, memory card, and optical card. It is also possible to use a semiconductor memory such as a card-type recording medium such as a mask ROM, an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory), or a flash ROM. In addition, since the system configuration allows connection to a communication network including the Internet, the program code described above may be downloaded from the communication network. When the program code is downloaded from the communication network in this way, the download program may be stored in the main device in advance or installed from another recording medium.

  The present invention can also be realized in the form of a computer data signal embedded in a carrier wave in which the program code is embodied by electronic transmission.

  In addition, the computer program of the present invention may be provided as a single application program or utility program, or may be incorporated into another application program or utility program and provided as a partial function of the program. May be. For example, as one form, a form provided by being incorporated in a printer driver is conceivable. In this case, the ACS is discriminated for the image data obtained by reading the document image, the image processing according to the discrimination result is performed, and the image is translated into the printer language and transmitted to the target printer apparatus. .

Embodiment 4 FIG.
In the present embodiment, a mode in which the image processing apparatus of the present invention is applied to an image reading apparatus will be described. FIG. 22 is a block diagram illustrating a configuration of an image processing unit of the image reading apparatus according to the present embodiment. The image processing unit includes an AD conversion unit 51, a shading correction unit 52, a document type determination unit 53, and an ACS determination unit 54. The processing contents of each processing unit are the same as those described in the first embodiment. The image data, the document type determination signal, and the ACS determination signal subjected to the above processes are input to a computer or a printer. The above processing is controlled by a CPU (not shown). The image processing unit may include the input tone correction unit 55 and the region separation processing unit 56 described in the first embodiment.

It is a block diagram explaining the internal structure of the image processing apparatus which concerns on this invention. It is a block diagram explaining the structure of an image process part. 3 is a block diagram illustrating a configuration of a document type determination unit. FIG. 6 is a flowchart illustrating a procedure of processing executed by a document type determination unit. It is a schematic diagram which shows an example of pixel density distribution in each area | region. It is a schematic diagram which shows the distribution by the maximum density difference of each area | region and total density busyness. It is a block diagram explaining the structure of an ACS discrimination | determination part. It is a block diagram explaining the structure of a chromatic / achromatic pixel determination part. It is a flowchart explaining the procedure of the process in an ACS discrimination | determination part. 6 is a histogram showing a density distribution of a document image. 6 is a histogram showing a density distribution of a document image. 6 is a histogram showing a density distribution of a document image. It is a flowchart explaining the procedure of a histogram analysis process. 3 is a block diagram illustrating a configuration of a document type determination unit. FIG. It is a block diagram explaining the internal structure of a chromatic / achromatic pixel determination part. 6 is a flowchart illustrating a procedure of processing executed by a document type determination unit. It is a flowchart explaining the procedure of a chromatic / achromatic pixel determination process. It is a block diagram explaining the structure of an ACS determination part. It is a flowchart explaining the procedure of the process which an ACS determination part performs. It is a flowchart explaining the process sequence of a histogram analysis process. It is a block diagram explaining the internal structure of the image processing apparatus in which the computer program of this invention was installed. FIG. 3 is a block diagram illustrating a configuration of an image processing unit of the image reading apparatus according to the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control part 3 Image input part 5 Image processing part 7 Image output part 9 Operation part 53 Document type determination part 54 ACS discrimination | determination part 541 Chromatic / achromatic pixel determination part 542 Chromatic pixel histogram creation part 543 Histogram analysis part 544 Data conversion Part

Claims (5)

In an image processing method for determining whether or not the document is a document including a chromatic color based on image data obtained by reading the document, and performing image processing on the image data according to the determined result,
Determining whether the pixel of interest among the pixels included in the image data belongs to a character region, a halftone dot region, or a third region other than the character region and the halftone dot region;
If the determined area is a character area, the determination criterion for determining whether or not the pixel of interest is a chromatic color is determined to be a chromatic color rather than a predetermined determination criterion used when it is determined to be the third region. Set the criteria to make it easier
When the determined region is a halftone dot region, the determination criterion for determining whether or not the pixel of interest is a chromatic color is more achromatic than the predetermined criterion used when it is determined as the third region. Set the criteria to make it easier to judge,
A process of determining whether the target pixel is a chromatic color using the predetermined determination criterion or the set determination criterion is executed for each pixel included in the image data,
An image processing method, comprising: setting a determination criterion for determining whether or not the document is a document including a chromatic color based on a total number determined to be chromatic color pixels. In an image processing apparatus that determines whether or not the document is a document including a chromatic color based on image data obtained by reading the document, and performs image processing on the image data according to the determined result.
Means for determining whether the pixel of interest among the pixels included in the image data belongs to a character region, a halftone dot region, or a third region other than the character region and the halftone dot region;
If the determined area is a character area, the determination criterion for determining whether or not the pixel of interest is a chromatic color is determined to be a chromatic color rather than a predetermined determination criterion used when it is determined to be the third region. Means for setting a determination criterion that makes it easy to be performed;
When the determined region is a halftone dot region, the determination criterion for determining whether or not the pixel of interest is a chromatic color is more achromatic than the predetermined criterion used when it is determined as the third region. Means for setting a determination criterion that facilitates determination;
Means for executing, for each pixel included in the image data, processing for determining whether or not the target pixel is a chromatic color using the predetermined determination criterion or the set determination criterion;
An image processing apparatus comprising: means for setting a determination criterion for determining whether or not the document is a document including a chromatic color based on the total number determined to be chromatic color pixels. An image forming apparatus comprising: the image processing apparatus according to claim 2 ; and a unit that forms an image on a sheet based on image data subjected to image processing by the image processing apparatus. In a computer program for causing a computer to determine whether or not the document is a document including a chromatic color based on image data obtained by reading the document and performing image processing on the image data according to the determination result ,
On the computer,
Determining whether the pixel of interest among the pixels included in the image data belongs to a character region, a halftone dot region, or a third region other than the character region and the halftone dot region;
If the determined area is a character area, the determination criterion for determining whether or not the pixel of interest is a chromatic color is determined to be a chromatic color rather than a predetermined determination criterion used when it is determined to be the third region. Set the criteria to make it easier
When the determined region is a halftone dot region, the determination criterion for determining whether or not the pixel of interest is a chromatic color is more achromatic than the predetermined criterion used when it is determined as the third region. Set the criteria to make it easier to judge,
A process of determining whether the target pixel is a chromatic color using the predetermined determination criterion or the set determination criterion is executed for each pixel included in the image data,
A computer program for executing a process for setting a criterion for determining whether or not the document is a document including a chromatic color based on the total number of pixels determined to be chromatic colors. A computer-readable recording medium on which the computer program according to claim 4 is recorded.

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