JPH06205204A - Picture processing unit - Google Patents

Abstract

PURPOSE:To obtain the picture processing unit in which a photograph in an area is reproduced with excellent color reproducibility by discriminating automatically whether the area is a color area or a monochromatic area and whether the area is a silver salt picture or a dot picture and selecting suitable processing to the photograph such as color correction. CONSTITUTION:An original discrimination circuit 5 discriminates a kind of an original (color/monochromatic, dot/sliver salt) as to an area designated for a photograph prior to preliminary scanning. Then a required color correction coefficient group is read among color correction coefficient groups prepared in advance in a color correction coefficient group storage section 6, that is, the color correction coefficient group for a dot photograph, the color correction coefficient group for a silver salt photograph and the color correction coefficient group for a silver salt/dot photograph and set to a color correction circuit 3 and the color correction processing is executed by using the color correction coefficient group suitable for an input original. Since the proper color correction coefficient group is set to each kind of originals in this way, most proper color reproduction is attained for a silver salt photograph original, a dot photograph original, and monochromatic original.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus which performs optimum color correction according to the type of original.

[0002]

2. Description of the Related Art With the progress of digital image processing technology, full-color digital copying machines for reproducing color images with high image quality have been commercialized. In such a digital copying machine, "area processing" is one of the additional functions. This function is to "designate an area" of a specific area of a document before copying and perform "area editing" to perform a target process.

The editing menu includes, for example, "magnification" for enlarging / reducing an image, "move" for moving and copying an image, "color selection" for copying a designated area in full color or monochrome, and original document. There is a "photo mode" where you can specify the type and copy. Of these, in the "photograph mode", the process for a photograph (for example, color correction) is performed on the target area.

There are two types of photographs, namely photographs of silver salt and halftone photographs of printing and newspapers. Generally, when an operator operates the above-mentioned digital copying machine, a manuscript is used. It is very troublesome to determine which picture the picture inside is.

[0005]

By the way, even if a silver halide photograph and a halftone dot photograph appearing to have the same color in the original, if the original is read by a general color scanner and input,
The signal values are different, that is, the scanner does not read the same color. This is a phenomenon mainly caused by the difference in the dyes of silver salt photographs and halftone photographs.

Therefore, when the same processing, for example, color correction, is performed on a silver halide photograph and a halftone photograph, satisfactory photographic color reproduction cannot be expected from any photographic original. A general color correction coefficient for a copying machine is calculated based on information obtained by reading a color patch output by the color printer of the copying machine itself with a color scanner. For this reason, the dyes of the silver salt photographic original and the color printer are greatly different from each other, resulting in a problem that the color reproduction of the silver salt photographic is deteriorated.

If the copy original is a monochrome original,
Although it is limited to the case where the recording system has black, it is also possible to reproduce a monochrome original with a single black color, for example. As described above, reproducing black monochromatic color has an advantage that gray balance is easier to take and ink is saved as compared with a case where a monochrome original is reproduced with three colors of cyan, magenta, and yellow. The present invention has been made in consideration of the above points, and an object of the present invention is to determine whether the area is color or monochrome, and whether the area of the original is specified when the photograph mode processing is performed in the area designated by the area. An image that automatically determines the type, especially whether the pattern is a silver salt photograph or a halftone photograph, and switches the processing such as color correction suitable for each at the time of main scanning to reproduce the photograph in the area with good color reproducibility It is to provide a processing device.

[0008]

In order to achieve the above object, according to the invention of claim 1, the original is read as R, G, B digital signals, and a group of color correction coefficients determined in advance by a predetermined method. For each pixel,
In an image processing apparatus for converting G and B signals into recording signals, means for designating a picture area in the original document, means for detecting a predetermined characteristic amount from the designated picture area, and the picture pattern according to the characteristic quantity. It is characterized by comprising means for determining the color and type of the area and means for selecting the color correction coefficient group based on the determination result.

According to the second aspect of the invention, the manuscripts are R, G,
It is read out as a digital signal of B, and a group of color correction coefficients determined in advance by a predetermined method is used for each pixel.
In the image processing apparatus for converting the R, G, B signals into recording signals, means for designating a picture area in the document, and means for detecting a predetermined feature amount from the designated picture area,
A means for judging whether the picture area is color or monochrome, a picture of a silver salt photograph or a picture of a halftone dot photograph based on the characteristic amount; and the color correction coefficient based on the judgment result. And a means for selecting a group.

According to a third aspect of the present invention, the means for determining whether the pattern area is color or monochrome is
A feature is that a pixel in which the absolute value of the difference between R, G, and B values is smaller than a predetermined value is detected as a monochrome pixel, and determination is performed based on the histogram of the pixel.

According to a fourth aspect of the present invention, the means for determining whether the picture area is a picture of a silver halide photograph or a picture of a halftone dot photograph detects a pixel pattern corresponding to the center of the halftone dot dot. It is characterized in that the determination is made based on the histogram of the pixel.

[0012]

The document determination circuit determines the type of document (monochrome / color, halftone dot photograph / silver salt photograph) in the area designated area from the green signal during the prescan. The color correction coefficient storage unit stores a color correction coefficient group for each type of document. At the time of the main scan, a color correction coefficient group is selected from the color correction coefficient storage unit based on the determination result of the original determination circuit, set in the color correction circuit, and the optimum color correction processing is performed on the original. In another embodiment, the degree of smoothing processing and edge enhancement processing is controlled based on the determination result of the original determination circuit.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. In FIG. 1, reference numeral 1 is a color scanner that reads a color original document and outputs color separation signals of three colors r, g, and b. Reference numeral 2 is a log conversion that performs density conversion of digital signals of r, g, and b and outputs them. Circuit 3 is R after log conversion,
A color correction circuit for generating Y, M, and C printer drive signals from G and B density data, 4 is a color printer, and 5 is
An original determination circuit 6 that determines the original type using g (green) data during prescanning, and 6 is a color correction coefficient storage unit that stores a group of color correction coefficients corresponding to the original type.

According to the present invention, the color correction processing is performed based on the result of the determination of the original at the time of prescanning. First, the document determination circuit 5 will be described. Before performing pre-scan, the operator uses a device called a digitizer to specify the type of the document (color / monochrome, halftone dot) for the area designated as a "photograph" (for example, a rectangle and a polygon can be designated). / Silver salt)
Optimal processing is performed on the document based on the determination result. As for the prescan area, all of the designated area may be searched, but if the prescan is stopped in a part of the search in order to shorten the time, the speed can be increased.

FIG. 2 is a block diagram of the document determination circuit 5. In FIG. 2, in the monochrome pixel detection unit 21,
The color of the original is judged. That is, using the input signals r, g, and b, as shown in the following equation (1), a pixel whose absolute value of r, g, and b value is smaller than a predetermined value th1 is detected as a monochrome pixel, and Is counted by the counter 22, and the count value M (histogram) is compared with a predetermined threshold value THa by the comparator 23 to determine whether the target document is monochrome or color.

Max (| r−g |, | g−b |, | b−r |) <th1. ． ． ． Expression (1) The peak pixel detection unit 24 determines the type of document, that is, whether it is a halftone dot. As this method, the paper “Image area separation method for mixed image of characters / pictures (dots, photographs)” previously proposed by the present applicant (The Institute of Electronics, Information and Communication Engineers, Vol.
J75-DI1 No. 1 pp39-47, January 1992), the technique of dot area detection by "peak pixel" detection is used.

That is, the peak pixel is detected by calculation. Specifically, in a 3 × 3 block, the density level L of the central pixel is higher or lower than that of all the surrounding pixels, and the density of the diagonal pixel existing diagonally across L and the central pixel. Levels a and b are 4 pairs,
When | 2 × L−a−b |> TH (fixed threshold),
The central pixel is the peak pixel.

In the peak pixel detecting section 24 of this embodiment, the peak pixel is detected by the pre-scan, the counter 25 counts it, and the count value P (histogram) is compared with a predetermined threshold value THb. , It is determined whether the target document is a halftone dot or a silver salt. The g (green) signal is used as the input signal for the determination.

As described above, the present invention selects the color correction coefficient group based on the determination result of the original at the time of prescanning and performs the color correction processing suitable for the original. In order to simplify the description, the color correction circuit 3 is assumed to perform color correction using a linear linear equation.

In other words, this color correction method uses R, G, B
Be the signals after log conversion (8 bits each), and Y, M, C
As a printer drive signal (8 bits each), a0 to a3,
When b0 to b3 and c0 to c3 are a color correction coefficient group, the color correction coefficient group is represented by Expression (2).

C = a0 + a1 * R + a2 * G + a3 * B M = b0 + b1 * R + b2 * G + b3 * B Y = c0 + c1 * R + c2 * G + c3 * B. ． ． Formula (2) The present embodiment is not limited to the above-described color correction method, and may be, for example, a non-linear quadratic color correction method considering a quadratic term such as R squared or G × B, or By using the result of the non-linear quadratic approximation formula, C
A memory interpolation method for performing color correction by setting MY values and interpolating the values (for example, Japanese Patent Publication No. 58-16180).
(See Japanese Patent Publication) and the like. Also,
When applied to four colors (C, M, Y, K), the so-called UCR-processed C ′ of the equation (3) after the color correction of the equation (2),
The M ', Y', K signals may be obtained.

K = min (C, M, Y) C ′ = C−K M ′ = M−K Y ′ = Y−K. ． ． ． Formula (3) A group of color correction coefficients for silver salt photography (a0 to a3, b0 to b3, c0 to c3), which will be described later, based on the determination result (silver salt photography / halftone dot photography) of the original determination circuit 5 described above. Alternatively, a group of color correction coefficients for halftone pictures (a0 to a3, b0 to b3, c0
~ C3) is selected. Further, since the document determination processing is not performed outside the designated area, a group of color correction coefficients (a0 to a3, b0 to b3, c0 for silver salt / halftone dot photography).
Color correction is performed using c3).

If the result of the determination by the document determination circuit 5 is monochrome, the color correction circuit 3 is instructed to select, for example, the following color correction coefficient during the main scan. That is, a0 = 0, a1 = 0, a2 = 1, a3 = 0 b0 = 0, b1 = 0, b2 = 1, b3 = 0 c0 = 0, c1 = 0, c2 = 1, c3 = 0 The color correction coefficient storage unit 6 stores a color correction coefficient group prepared in advance, that is, a color correction coefficient group for halftone dot photographs, a color correction coefficient group for silver halide photographs, and a color correction coefficient group for silver salt / halftone dots photographs. The setting method will be described.

(B) To set this color correction coefficient group,
A printer approximation formula (L *, a *, b * -C, M, Y) is created. That is, the C, M and Y signals are selected at appropriate sampling intervals, and the color mixture patch is output by the color printer 4. Then, this mixed color patch is measured with an appropriate colorimeter. Here, the measured colorimetric values are represented by L *, a *, and b *. As a result, the following data group is obtained.

C, M, Y−L *, a *, b * 0 0 0 88.5, −2.5, 0.8 0 0.88. ． ． ． ． ． ． ． ． ． ． ． ． ． ． 0 0 16. ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． ． 255, 255, 255. ． ． ． ． ． ． ． ． ． ． ． ． ． ． Based on the above data group, for example, the coefficients (α0 to α9, β0 to β9, γ0 to γ9) of an approximate expression such as the following expression are determined by the least squares method.

C = α0 + α1L * + α2a * + α3b * + α4L * L * + α5a * a * + α6 b * b * + α7L * a * + α8a * b * + α9b * L * M = β0 + β1L * + β2a * + β3b * + β4L * L * + β5a * a * + β6 b * b * + β7L * a * + β8a * b * + β9b * L * Y = γ0 + γ1L * + γ2a * + γ3b * + γ4L * L * + γ5a * a * + γ6b * b * + γ7L * a * + γ8a * b * + γ9b * L *. ． ． Formula (4).

(B) Subsequently, a color patch (for example, about 512 colors) composed of a silver halide photograph is input from the color scanner 1 to obtain R, G, B signals of each patch after log conversion. In practice, a plurality of pixels near the center of each patch are averaged (smoothed) for the purpose of reducing noise. On the other hand, a color patch consisting of a silver salt photograph was measured by the above-mentioned colorimeter (L
*, A *, b *). As a result, (R,
The relationship between (G, B) and (L *, a *, b *) is obtained.

(C) In the same manner as in (a) above, a color patch of a halftone picture is input and the relationship between (R, G, B) and (L *, a *, b *) of the patch is obtained. .

From the results of the above (a), (b) and (c), the color correction coefficient group (a0 to a3, b0 to b) of the equation (2) is obtained.
3, c0 to c3) are determined. That is, a group of color correction coefficients for silver salt photography (a0 to a3, b0 to b3, c0 to c
3); (R, G, B) and (L *, a *, obtained in (b))
By using the relationship of b *) and the equation (4),
A data group of (R, G, B) and (C, M, Y) can be obtained. For this data group, using the least squares method,
A group of color correction coefficients for silver salt photographs (a0 to a3, b0 to b) so that the original color of the silver salt photograph matches the color printed.
3, c0 to c3) are determined.

Color correction coefficient group (a0 to a3,
b0 to b3, c0 to c3); (R), (R, G,
B) and (L *, a *, b *), and by using equation (4), (R, G, B) and (C, M, Y)
Get the data group of. For this data group, a color correction coefficient group (a0 to a3, b0
b3, c0 to c3) are determined.

A group of color correction coefficients for silver salt / halftone dot photography (a0-a0)
a3, b0 to b3, c0 to c3); the data groups of (R, G, B) and (C, M, Y) obtained in (b) and (c) are set to an appropriate ratio (here, 1 [512 [Patch]: 1 [512 patch]), and the least squares method is applied to this data group for the silver salt / halftone dot color correction coefficient group (a0 to a).
3, b0 to b3, c0 to c3) are determined.

The color correction coefficient group for the halftone dot photograph, the color correction coefficient group for the silver salt photograph, and the color correction coefficient group for the silver salt / halftone dot photograph thus determined are respectively ROM or RAM.
It is written in the color correction coefficient storage unit 6 configured by.

Then, the document determination circuit 5 detects monochrome pixels at the time of prescanning and calculates the count value (M). This value M is compared with a predetermined threshold THa, and M> TH
If a, it is determined to be monochrome, otherwise it is determined to be color. When it is determined to be monochrome, a signal for selecting a color correction coefficient is given to the color correction circuit 3 based on the above determination signal at the time of main scanning, and as described above, the coefficients a2 and b2 of the equation (2) are given. , C2 are set to "1".

At the same time, the peak pixel is detected and the count value (P) thereof is calculated. This value P is compared with a predetermined threshold value THb, and if P> THa, a signal for selecting a color correction coefficient group (a0 to a3, b0 to b3, c0 to c3) for halftone dot photography is output, and Otherwise, it outputs a signal for selecting a color correction coefficient group (a0 to a3, b0 to b3, c0 to c3) for silver salt photography.

Then, during the main scan, the color correction coefficient group is read out from the color correction coefficient storage unit 6 based on the previous selection signal and set in the color correction circuit 3, and the color correction coefficient group suitable for the input document is read. Is used to perform color correction processing in accordance with equation (2).

FIG. 3 is a block diagram of another embodiment of the present invention. In the figure, 1 is a color scanner that reads a color original and outputs color separation signals of three colors r, g, and b. 2 is a log conversion circuit that density-converts and outputs the digital signals of r, g, and b. 3 is R after log conversion,
A color correction circuit for generating Y, M, and C printer drive signals from the G and B density data (this color correction circuit uses color correction coefficients set in advance by a predetermined method, for example, according to equation (2)). (Color correction processing is performed), 4 is a color printer, 5 is a document determination circuit that determines the type of document using g (green) data during prescan, and 6 is
A filter coefficient storage unit that stores a filter coefficient group corresponding to the type of document, 7 is a smoothing processing unit, and 8 is an edge enhancement unit.

In this embodiment, the filter coefficient is switched based on the judgment result of the manuscript judgment circuit 5. That is, in a color copying machine, a filter process is performed to improve image quality, but a halftone dot photograph and a silver salt photograph differ from each other in a filter process required in terms of preventing moire peculiar to a halftone dot. Therefore, in this embodiment, adaptive filter processing is performed based on the document determination result in the prescan. Further, outside the designated area, since the original document determination processing is not performed, through processing is performed.

The halftone dot photograph is filtered for the halftone dot photograph. That is, on the basis of the determination result of the document determination circuit 5, the filter coefficient group for halftone dot photography is read from the filter coefficient storage unit 6 and the smoothing unit 7 is executed during the main scan.
Is set in the edge enhancement unit 8, the smoothing unit 7 performs strong smoothing processing, and the edge enhancement unit 8 performs weak edge enhancement processing or through processing (in the example of FIG. 4, coefficient values other than 32 at the center are set to 0). And)). The strong smoothing process is performed to remove moire.

FIG. 4 shows specific filter coefficients for performing the strong smoothing process and the weak edge emphasizing process. In the present embodiment, the case where two filters are arranged in series has been described in order to explain the effect of filtering, but it is also possible to configure with one convoluted filter.

As for the filtering process for the silver salt photograph, the smoothing unit 7 performs a weak smoothing process, and the edge enhancing unit 8 performs a strong edge enhancing process. The weak smoothing process is for noise removal, and the strong edge enhancement process is for enhancing the contour. FIG. 5 shows specific filter coefficients for performing weak smoothing processing and strong edge enhancement processing.

[0041]

As described above, according to the first and second aspects of the present invention, the optimum color correction coefficient group is set for each type of original, so that silver halide photograph originals and halftone dot photographs are set. Optimal color reproduction is possible for originals and even for monochrome originals.

According to the third aspect of the present invention, it is automatically determined whether the original document to be copied is a monochrome original document or a color original document, and an optimum color correction coefficient group is selected based on the determination result. Therefore, optimal color reproduction is possible.

According to the fourth aspect of the present invention, it is automatically determined whether the original to be copied is a halftone dot original or a silver halide photographic original, and the optimum color correction coefficient is determined based on the result of the determination. Since a group is selected, optimal color reproduction is possible.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block configuration diagram of a document determination circuit.

FIG. 3 is a block diagram of another embodiment of the present invention.

FIG. 4 shows filter coefficients for performing strong smoothing processing and weak edge enhancement processing.

FIG. 5 shows filter coefficients for performing weak smoothing processing and strong edge enhancement processing.

[Explanation of symbols]

 1 Color Scanner 2 Log Conversion Circuit 3 Color Correction Circuit 4 Color Printer 5 Original Discrimination Circuit 6 Color Correction Coefficient Storage Section 7 Smoothing Section 8 Edge Enhancement Section

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04N 1/46 9068-5C

Claims (4)

[Claims] 1. An original document is read out as R, G, B digital signals, and the R, G, B signals are converted into recording signals for each pixel by using a color correction coefficient group determined in advance by a predetermined method. In the image processing apparatus for conversion, means for designating a picture area in the original document, means for detecting a predetermined characteristic amount from the designated picture area, and determining the color and type of the picture area based on the characteristic quantity. An image processing apparatus comprising: means and means for selecting the color correction coefficient group based on the determination result. 2. An original is read out as R, G, B digital signals, and the R, G, B signals are converted into recording signals for each pixel by using a color correction coefficient group determined in advance by a predetermined method. In the image processing apparatus for conversion, means for designating a picture area in the original, means for detecting a predetermined characteristic amount from the designated picture area, and whether the picture area is color or monochrome depending on the characteristic quantity. Or a pattern of a silver halide photograph or a pattern of a halftone photograph, and a means for selecting the color correction coefficient group based on the determination result. Image processing device. 3. The means for determining whether the pattern area is color or monochrome detects a pixel whose absolute value of the difference between R, G and B values is smaller than a predetermined value as a monochrome pixel,
The image processing apparatus according to claim 2, wherein the determination is performed based on a histogram of the pixels. 4. The means for determining whether the picture area is a picture of a silver halide photograph or a picture of a halftone dot photograph detects a pixel pattern corresponding to the center of the halftone dot dot, and a histogram of the pixel is obtained. The determination is based on
The image processing device described.