JPH09186901A - Color image processor and output original discrimination device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain optimum color correction by discriminating whether or not an object original is an original (generation original) outputted from an electrophotographic color copying machine with high accuracy and selecting a color correction means accordingly when the generation original is discriminated. SOLUTION: An original discrimination circuit 5 discriminates whether or not an original is a generation original at preliminary scanning. When the original is discriminated as the generation original, a coefficient for the generation original is selected from a color correction coefficient storage section 6 at main scanning and set to a color correction circuit 3 to apply optimum color correction processing to the original.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention highly accurately determines whether or not an input original is a generation original output by an electrophotographic color copying machine, and optimally corrects the color of the generation original. The present invention relates to a color image processing device and an output document determining device that perform the above.

[0002]

2. Description of the Related Art Generally, in a color copying machine, color correction is performed on an RGB signal obtained by a color scanner in order to faithfully reproduce the color of a document. By the way, as a color reading spectral characteristic of a color scanner, only an approximate color matching function can be obtained. As a result, for a certain color of different color materials, for example, a certain color of printing ink and printing paper, a difference occurs in an RGB signal obtained by a color scanner even if the color looks the same when viewed by a human. For this reason, since color correction is generally designed according to the printed document,
Roughly speaking, colors of other originals made of color materials other than the print original do not match.

To address such a problem, the applicant of the present invention has previously proposed an image processing apparatus which automatically guarantees color reproduction for both print originals and photographic paper originals (JP-A-6-197218).
Reference). That is, the type of the original is determined during the prescan, and the color correction coefficient group is selected based on the determination result during the main scan to perform the optimum color correction on the original.

By the way, one of the documents input to the color copying machine is a document output by the color copying machine, that is, a so-called generation document. The above-mentioned problem also occurs in color reproduction of this generation document. That is, the color reproduction of the generation original is not guaranteed by the only color correction unit designed for printing.

As a solution to this, a color image recording apparatus that determines whether or not the read original is output by the own color copying machine that is about to output and automatically switches the color correction (Japanese Patent Laid-Open No. 5-27)
See 6369). The point of judgment in this device is to always have the first means for marking a machine-specific mark on a document and judging it with a dedicated sensor, or the line-line dither pattern that is currently the mainstream in color copying machines. The point is to have a second means for detecting it.

In the case of classifying by color material, it is more advantageous for the user not only to use the color copying machine of the own machine but also to make the documents output by the electrophotographic method into one category.
That is, the color of any manuscript is matched without the user being particularly aware of it.

[0007]

Therefore, in the case of determining a general document output by an electrophotographic color copying machine, the first means described above is "a bar code mark or a predetermined character or pattern. It may be arbitrary "(statement number 0020 of the above publication),
Although it is possible to recognize the originals output by its own machine, including the originals output by other companies is less common. That is, at present, many color copying machine manufacturers do not have an agreement to print a predetermined barcode, for example.

Further, the second means is less general in view of the fact that the density of the printer will further increase and the multi-value of one dot will increase in the future. Moreover, the current 4
Drum-type electrophotographic color copiers often do not use line-type dither.

The present invention has been made in view of the above circumstances, and an object of the present invention is whether or not a target original is an original output by an electrophotographic color copying machine (hereinafter referred to as a generation original). It is an object of the present invention to provide a color image processing apparatus and an output original document determining apparatus that select color correction means according to the determination with high accuracy and a generation original document when it is determined to be a generation original document.

[0010]

In order to achieve the above object, the invention according to claim 1 provides a color correction means for digitally reading an original and performing color correction on at least two or more color materials. In a provided color image processing device, means for determining whether or not the read original is an output image by a color copying machine, and output by the color copying machine when it is determined that the read original is an output image by the color copying machine. It is characterized in that a color correction means for performing color correction on the color material used in the image is provided.

According to the second aspect of the invention, in the output document determining apparatus which digitally reads the document and determines whether the document is an output image from a color copying machine, the output document determining device corresponds to a tracing pattern from the document. It is characterized by comprising means for detecting pixels and means for judging whether or not the original is an output image by a color copying machine based on the frequency of the detected pixels.

According to a third aspect of the present invention, the tracking pattern pixel is an isolated area surrounded by a white background.

The invention according to claim 4 is characterized in that the tracking pattern pixel is an isolated region of a specific color.

According to a fifth aspect of the present invention, the tracking pattern pixel is a yellow isolated region.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be specifically described below with reference to the drawings. In the present invention, a tracking pattern peculiar to a color copier output image is detected using prescan. This is to prevent abuse of copying of bills and securities. That is, measures are taken so that some pattern is printed when a bill or securities is copied. Such tracking patterns are detected with high accuracy by local image processing, utilizing the fact that they are isolated on a white background and that they are printed in yellow.

(Generation Original Judgment) FIG. 2 shows the configuration of the generation original judgment unit of the present invention. In the figure, 1 is a color scanner, 6 is an MTF correction unit, 7 is a binarization processing unit, and 8 is a pattern matching circuit (PM1 to PM1).
PM3), 9 are comprehensive judgment circuits, 10 is a counter, and 11 is a comparator.

In order to determine whether the document is a generation original or not, in the present invention, attention is paid to the trace pattern that is always printed on the output image of the color copying machine, and the trace pattern is detected by using pattern matching. In general, the tracking pattern is 2 pixels x 400 dpi in a 400 dpi printer.
The size of about 2 pixels or 1 pixel × 3 pixels is printed with yellow toner. Therefore, a tracking pattern can be detected by performing pattern matching as shown in FIG. 4B, which will be described later, on the b signal that is the complementary color of yellow.

However, the following problems occur. (1) The printed document is formed of many halftone dots. In the pattern of FIG. 4B, halftone dots are erroneously detected as a tracking pattern, and as a result, the print document is erroneously determined as a generation document.

Therefore, in the apparatus of the present invention, as a countermeasure against halftone dots, it is decided to detect an isolated dot on a wide white background as a tracking pattern. In a general printed document, dots are densely packed to some extent even in the highlight part.

(2) Even if the tracking pattern is limited to isolated dots on a white background as described above, dust (noise) is often placed on the original. Since it is noise, such dust is unlikely to be yellow, and most of it is achromatic. Therefore, the tracking pattern is limited to the yellow region using three signals.

The respective parts of the device of the present invention will be described in detail below. A color scanner 1 having a photoelectric conversion element such as a CCD camera, reading an original, obtaining three-color separation signals (analog) of red, green, and blue, and performing A / D conversion on these three signals; , Rgb digital signals (8 bits each). The resolution of the scanner is 400 dpi. Here, the output signal value is 255 for paper white and 0 for black.

MTF correction unit 6: As a pre-processing of the subsequent binarization processing, an MTF correction filter is applied to each rgb signal. FIG. 3 shows an example of coefficients of the MTF correction filter.

Binarization processing unit 7: Performs binarization processing on the signal after MTF correction. When the pixel level of interest is X, if (X <th) → black pixel (●) else → white pixel (◯) pattern matching circuit 8; PM1 FIG. 4A shows patterns for r and g signals. As a result, cyan and magenta, which are complementary colors of r and g, do not exist near the target pixel, in other words, the yellow area is detected.

PM2 FIG. 4B shows a b signal pattern. As described above, since the tracking pattern has a size of 3 pixels × 3 pixels or less at 400 dpi at most, a pattern as shown in FIG. 4B was prepared. However, since this pattern alone matches the halftone dot of yellow, it is necessary to prepare a PM3 for determining whether or not it is an area surrounded by a white background, which will be described next.

PM3 is a b signal pattern for determining whether or not the pixel of interest is surrounded by a white background and is a truly isolated region. Although the halftone dots in the print are highlight areas, there is no way for them to match the pattern as shown in FIG. That is, the halftone dots are a little more dense.

Although the b signal is used for the sake of simplicity, in the case of detecting a region surrounded by a white background more accurately, the min (r, g, b) after MTF correction is used. The pattern matching may be performed on the binarized one.

Comprehensive determination circuit 9: When all the outputs from the four pattern matching circuits 8 are on, that is, when all of them match, the pixel of interest is determined as a tracking pattern pixel.

Counter 10: Counts the number of pixels of the above-mentioned tracking pattern over the entire surface of the original.

Comparator 11; compares the count value (V) of the tracking pattern pixels described above with a predetermined threshold value (THgen), and outputs V
If> THgen, a signal indicating that the document is a generation document is output.

Although the rgb signal is used as the signal used for the determination of the generation original in order to simplify the explanation, in order to further improve the accuracy, the generation color correction is performed on the rgb signal to obtain the cmy signal. It is also effective to make a similar determination with this cmy signal. FIG. 5 shows another configuration of the generation original determination unit of the present invention, which is provided with a color correction circuit. In addition, since an actual scanner may contain noise, it is effective to apply a smoothing filter to the signal from the scanner to remove noise.

(Image Reproducing Apparatus Using Generation Original Judgment) Here, an apparatus (color image processing apparatus) for reproducing an image using the generation original judging section of FIG. 2 will be described. FIG. 1 shows the configuration of the image reproducing apparatus of the present invention. In the figure, 1 is a color scanner, 2 is a Log conversion circuit, 3 is a color correction circuit, 4 is a color printer, 5 is an original determination circuit, and 6 is a color correction coefficient storage unit.

Hereinafter, for the sake of simplicity, it is assumed that there are two types of color correction means to be prepared, one for halftone photographs (printing) and the other for generation documents. Of course, using the technique described in Japanese Patent Application Laid-Open No. 6-197218, it is necessary to prepare silver halide photograph (photographic paper) or a mixture thereof for the color of a wide range of originals. It is effective in guaranteeing the fidelity of.

The components constituting the apparatus will be described. The color scanner 1 is as described above. The output signal of the Log conversion circuit 2; the color scanner 1 is a substantially linear reflectance signal. With this color correction processing,
Convert to an advantageous density signal (RGB signal). Thereby, the linearity of the color correction conversion is further ensured, in other words, the color correction circuit can be simplified.

Color correction circuit 3; here, color correction is performed by the following linear linear expression. That is, R, G, B
Is a signal after Log conversion (8 bits each), and Y, M, C
Is a printer drive signal, and a0 to a3, b0 to b3, c
When the color correction coefficient group is 0 to c3, the color correction circuit is represented by Expression (1).

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 (1).

Color printer 4; here is a printer for forming an image with three colors of cyan, magenta and yellow, which receives drive signals (C, M, Y) and forms an image. When the printer reproduces four colors with black added, for example, a black signal is created with min (C, M, Y), and a drive signal is created by so-called UCR processing that subtracts the black signal from C, M, and Y. Just print out.

Original document determination circuit 5: The generation original document determination section shown in FIG. 2 is used here. Accordingly, the determination is made by discriminating between the generation document (electrophotographic printer document) and the other, that is, the print document, and outputting the result. The document determination circuit 5 operates during prescan.

Next, the method of setting the color correction coefficient group to be prepared is basically determined by the procedure described in Japanese Patent Laid-Open No. 6-197218. The gazette includes a halftone dot photo,
A setting method for a silver halide photograph is described. Here, a method for setting a color correction coefficient for a generation original will be particularly described.

(A) Printer approximation formula (L
*, A *, b * -C, M, Y). That is, C
MY signals are selected at appropriate intervals, and a color patch group as shown in FIG. 6 is created using an electrophotographic printer (printer unit of a color copying machine). Here, it is assumed that the color printer inputs 8-bit signals for each of the three colors cyan, magenta, and yellow. The mixed color patch is measured with an appropriate measuring instrument (L
*, A *, b *). Equation (2) is obtained using the least squares method for these data groups.

C = α0 + α1L * + α2a * + α3b * + α4L * L * + α5a * a * + α6b * b * + α7L * a * + α8a * b * + α9b * L * M = β0 + β1L * + β2a * + β3b * + β4L * L * + β5a * a * + β6b * 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 (2).

(B) Further, a color patch group as shown in FIG. 6 is inputted from a color scanner (data is averaged when patches are created using several kinds of electrophotographic printers at this time), and after Log conversion. R, G, B of each patch
Get the signal. On the other hand, these color patches are measured by a colorimeter to obtain L *, a *, b * values of each patch.

(C) By the above, the data group of (R, G, BC, M, Y) can be obtained through the above equation (2). Using this data group, a color correction coefficient group (a0 to a3,
b0 to b3, c0 to c3) are obtained.

The color correction coefficient for the generation original determined in this way is set in the color correction coefficient storage unit 6 composed of a ROM or a RAM. During the prescan, the document determination circuit 5 operates to determine whether or not the document is a generation document. When it is determined that the original document is a generation original document, a signal for selecting the generation original document coefficient in the color correction coefficient storage unit 6 is output. Then, at the time of main scanning, the selected generation original coefficient is read and set in the color correction circuit 3, and the color correction coefficient suitable for the generation original is used.
Color correction processing is performed according to the equation (1).

[0044]

As described above, according to the first aspect of the invention, when the original is an original output by a color copying machine having an electrophotographic printer (generation original), the original is generated. Since the color correction coefficient is selected and the color correction processing is performed, faithful color reproduction is performed. Further, in the conventional apparatus, the color is guaranteed only for the self-apparatus, but according to the apparatus of the present invention, faithful color reproduction can be assured even for an original printed by a color copying machine of another company. it can.

According to the second aspect of the present invention, not only the apparatus itself but also a general generation original having a tracking pattern can be recognized as a generation original.

According to the third aspect of the invention, since the information of the isolated area is used, the accuracy of recognition is improved.
That is, it is possible to reduce erroneous determinations for halftone dot originals.

According to the fourth aspect of the invention, since the information that the color is close to yellow is used, the recognition accuracy is improved. That is, it is possible to reduce erroneous determination with respect to dust (noise).

According to the invention described in claim 5, since the yellow information is used, the recognition accuracy is further improved.

[Brief description of the drawings]

FIG. 1 shows a configuration of an image reproducing apparatus of the present invention.

FIG. 2 shows a configuration of a generation document determination unit of the present invention.

FIG. 3 shows an example of coefficients of an MTF correction filter.

4A to 4C show patterns for generation document determination.

FIG. 5 shows another configuration of a generation document determination unit.

FIG. 6 shows an example of a color patch.

[Explanation of symbols]

 1 Color Scanner 2 Log Conversion Circuit 3 Color Correction Circuit 4 Color Printer 5 Original Judgment Circuit 6 Color Correction Coefficient Storage

Claims (5)

[Claims] 1. A color image processing apparatus comprising a color correction means for digitally reading an original and performing color correction on at least two or more color materials, wherein the read original is an output image from a color copying machine. And a color correction means for performing color correction on the color material used in the output image from the color copying machine when it is determined to be the output image from the color copying machine. A color image processing device characterized by the above. 2. A means for detecting a pixel corresponding to a tracking pattern from the original in an output original determination device for digitally reading the original and determining whether the original is an output image from a color copying machine. An output original document determining device comprising means for determining whether or not the original document is an output image from a color copying machine based on the detected pixel frequency. 3. The output document determining apparatus according to claim 2, wherein the tracking pattern pixel is an isolated area surrounded by a white background. 4. The output document determining apparatus according to claim 2, wherein the tracking pattern pixel is an isolated area of a specific color. 5. The output document determining apparatus according to claim 2, wherein the tracking pattern pixel is a yellow isolated area.