JP3636802B2 - Output document determination apparatus and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an output document determination device that determines with high accuracy whether or not an input document is a generation document output by an electrophotographic color copying machine, and performs an optimum color correction on the generation document. Regarding the method .
[0002]
[Prior art]
Usually, in a color copying machine, color correction is performed for the purpose of faithfully reproducing the color of an original with respect to RGB signals obtained by a color scanner. By the way, only an approximate color matching function can be obtained as a color reading spectral characteristic in a color scanner. As a result, even for colors that are different from each other, such as printing ink and photographic paper, that appear to be equal to each other, a difference occurs in the RGB signals obtained by the color scanner. For this reason, since color correction is generally designed in accordance with a printed document, generally speaking, the colors of other documents made of color materials other than the printed document do not match.
[0003]
In order to deal with such problems, the present applicant has previously proposed an image processing apparatus that automatically guarantees color reproduction for both printed and photographic paper originals (see Japanese Patent Laid-Open No. Hei 6-197218). That is, the type of document is determined at the time of pre-scanning, and a color correction coefficient group is selected based on the determination result at the time of main scanning, and color correction optimal for the document is performed.
[0004]
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 the color reproduction of this generation document. That is, the color reproduction of the generation document cannot be guaranteed with the only color correction means designed for printing.
[0005]
As a solution to this problem, there is a color image recording apparatus that determines whether or not a read original is output by the color copying machine that is about to output and automatically switches color correction ( (See JP-A-5-276369). The point of determination in this apparatus is that it always has a first means for marking a machine-specific mark on a document and determining it with a dedicated sensor, or a line-type dither pattern that is currently mainstream in color copiers. It is the point which has the 2nd means which pays attention to and detects it.
[0006]
When classified according to color materials, it is more advantageous for the user not only to use his own color copying machine but also to set the originals output by the electrophotographic method as one category. That is, the color of any manuscript is matched without the user being particularly conscious.
[0007]
[Problems to be solved by the invention]
Therefore, when judging general documents output by an electrophotographic color copying machine, the first means described above may be “anything such as a bar code mark or a predetermined character or pattern”. (Sentence No. 0020 in the above publication), it is possible to recognize the original output document, but it is less general when including other company output originals. That is, at present, there are no agreements that many color copying machine manufacturers print a predetermined barcode, for example.
[0008]
Also, the second means is less general in consideration of the future increase in printer density and the progress of multi-valued one dot. Moreover, current 4-drum type electrophotographic color copying machines often do not use a line-type dither.
[0009]
The present invention has been made in consideration of the above circumstances,
An object of the present invention is to determine with high accuracy whether a target document is a document output by an electrophotographic color copier (hereinafter referred to as a generation document). It is an object of the present invention to provide an output document determination apparatus and method in which correction means is selected and optimal color correction is performed.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, means for reading an original as image signals of r, g, and b, and first means for performing pattern matching between the r signal of the target pixel and the white pixel pattern. A second means for performing pattern matching between the g signal of the target pixel and the white pixel pattern; a third means for performing pattern matching between the b signal of the target pixel and the isolated region pattern surrounded by a white background; Means for determining the pixel of interest as a tracking pattern pixel when matching is performed by all of the first, second, and third means; and based on the determined number of tracking pattern pixels, the original is an output image from a color copying machine. It is characterized by having means for determining that there is.
[0011]
According to the second aspect of the present invention, an original is read as r, g, and b image signals, pattern matching between the r signal of the target pixel and the white pixel pattern is performed, and pattern matching between the g signal of the target pixel and the white pixel pattern is performed. Pattern matching is performed between the b signal of the target pixel and the isolated region pattern surrounded by a white background. When matching is performed with all patterns, the target pixel is determined as the tracking pattern pixel, and the determined number of tracking pattern pixels Based on the above, it is determined that the original is an output image by a color copying machine .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
In the present invention, a pre-scan is used to detect a tracking pattern unique to the color copier output image. This is to prevent abuse of copying of banknotes and securities. That is, measures are taken so that some pattern is printed when banknotes or securities are copied. Such a tracking pattern is detected with high accuracy by local image processing using the fact that it is isolated on the white ground and printed in yellow.
[0013]
(Generation manuscript judgment)
FIG. 2 shows the configuration of the generation document determination 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, 8 is a pattern matching circuit (PM1 to PM3), 9 is a comprehensive determination circuit, 10 is a counter, and 11 is a comparator. .
[0014]
In order to determine whether or not the document is a generation document, in the present invention, attention is paid to the trace pattern that is always printed on the color copier output image, and the trace pattern is detected using pattern matching. In general, a tracking pattern is printed with yellow toner in a size of about 2 pixels × 2 pixels or 1 pixel × 3 pixels in a 400 dpi printer. Accordingly, the tracking pattern can be detected by performing pattern matching as shown in FIG. 4B described later on the b signal which is a complementary color of yellow.
[0015]
However, the following problems arise.
(1) A printed document is formed from a large number of halftone dots. In the pattern of FIG. 4B, halftone dots are erroneously detected as tracking patterns, and as a result, the printed document is erroneously determined as a generation document.
[0016]
Therefore, in the apparatus of the present invention, as a countermeasure against halftone dots, a large white isolated dot is detected as a tracking pattern. In a general printed document, dots are concentrated to some extent even in a highlight portion.
[0017]
(2) Even if the tracking pattern is limited to isolated dots on the white ground as described above, dust (noise) often appears on the original. Because of the noise, there is little possibility that such dust is yellow, and many are achromatic colors. Therefore, the tracking pattern is limited to the yellow area using three signals.
[0018]
Below, each part of the apparatus of this invention is explained in full detail.
Color scanner 1;
It has a photoelectric conversion element such as a CCD camera, reads a document, obtains three color separation signals (analog) of red, green, and blue, performs A / D conversion on these three signals, and performs rgb digital A signal (8 bits each) is output. The resolution of the scanner is 400 dpi. Here, the output signal value is 255 for paper white and 0 for black.
[0019]
MTF correction unit 6;
As a pre-process for the binarization process at the subsequent stage, an MTF correction filter is applied to each rgb signal. FIG. 3 shows an example of the coefficients of the MTF correction filter.
[0020]
Binarization processing unit 7;
Binarization processing is performed on the signal after MTF correction. Let the pixel level of interest be X,
if (X <th) → black pixel (●)
else → White pixel (○)
Pattern matching circuit 8;
PM1
FIG. 4A shows r and g signal patterns. As a result, the cyan and magenta colors that are complementary colors of r and g do not exist in the vicinity of the target pixel, in other words, the yellow region is detected.
[0021]
PM2
FIG. 4B shows a b signal pattern. As described above, since the tracking pattern is 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 yellow dot dots, it is necessary to prepare PM3 for determining whether or not the area is surrounded by a white background, which will be described next.
[0022]
PM3
This is a b signal pattern for determining whether or not the pixel of interest is a truly isolated region surrounded by a white background. A halftone dot for printing is a highlight area, but there is no way to match a pattern as shown in FIG. In other words, halftone dots are a little denser.
[0023]
For brevity of explanation, the b signal is used. However, when the region surrounded by a white background is detected more accurately, binarization is performed for min (r, g, b) after MTF correction. This pattern matching may be performed on those that have been performed.
[0024]
Comprehensive judgment circuit 9;
When the outputs from the four pattern matching circuits 8 are all on, i.e., all match, the target pixel is determined as the tracking pattern pixel.
[0025]
Counter 10;
The number of pixels of the tracking pattern described above is counted over the entire surface of the document.
[0026]
Comparator 11;
The tracking pattern pixel count value (V) described above is compared with a predetermined threshold value (THgen), and if V> THgen, a signal indicating that the document is a generation document is output.
[0027]
In order to simplify the description, the rgb signal is used as a signal used for generation document determination. However, in order to improve accuracy, generation color correction is performed on the rgb signal to obtain a cmy signal. It is also effective to make the same determination using the cmy signal. FIG. 5 shows another configuration of the generation document determination unit of the present invention provided with a color correction circuit. In addition, an actual scanner may contain noise, and it is also effective to apply a smoothing filter to the signal from the scanner to remove noise.
[0028]
(Image playback device using generation manuscript judgment)
Here, a description will be given of an apparatus (color image processing apparatus) that reproduces an image using the above-described generation document determination unit of FIG. FIG. 1 shows a configuration of an image reproducing apparatus according to 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 a document determination circuit, and 6 is a color correction coefficient storage unit.
[0029]
Hereinafter, in order to simplify the explanation, the color correction means to be prepared has two types, one for halftone photographs (printing) and one for generation documents. Of course, using the technique described in the above-mentioned Japanese Patent Application Laid-Open No. Hei 6-197218, further preparation for silver salt photography (printing paper) or a mixture thereof can be applied to a wide range of documents. It is effective in ensuring the fidelity of
[0030]
Each part which comprises an apparatus is demonstrated.
The color scanner 1 is as described above.
Log conversion circuit 2;
The output signal of the color scanner 1 is a substantially linear signal with reflectivity. This is converted into an advantageous density signal (RGB signal) by color correction processing. Thereby, the linearity of the color correction conversion is further guaranteed, in other words, the color correction circuit can be simplified.
[0031]
Color correction circuit 3;
Here, it is assumed that color correction is performed using the following linear linear expression. That is, R, G, and B are signals (8 bits each) after log conversion, Y, M, and C are printer drive signals, and a0 to a3, b0 to b3, and c0 to c3 are color correction coefficient groups. The color correction circuit is represented by the equation (1).
[0032]
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)
[0033]
Color printer 4;
Here, it is a printer that creates an image with three colors of cyan, magenta, and yellow, and receives a drive signal (C, M, Y) and creates an image. When the printer reproduces four colors with black added, for example, a black signal is created by min (C, M, Y), and a drive signal is created by so-called UCR processing by subtracting the amount from C, M, Y, Just print out.
[0034]
Document determination circuit 5;
Here, the generation document determination unit shown in FIG. 2 is used. Therefore, the determination identifies a generation original (electrophotographic printer original) and the other, that is, a print original, and outputs the result. The document determination circuit 5 operates during pre-scanning.
[0035]
Next, the setting method of the color correction coefficient group to be prepared is basically determined according to the procedure described in Japanese Patent Laid-Open No. 6-197218. This publication describes a setting method for halftone dot photography and silver salt photography. Here, a method for setting a color correction coefficient for a generation document will be described.
[0036]
(A) Obtain a printer approximate expression (L *, a *, b * -C, M, Y) as follows. That is, the CMY signals are selected at appropriate intervals, and a color patch group as shown in FIG. 6 is created using an electrophotographic printer (a 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 of cyan, magenta, and yellow. Measure the mixed color patch with an appropriate meter (L *, a *, b *). Equation (2) is obtained by using the least square method for these data groups.
[0037]
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)
[0038]
(B) Further, a color patch group as shown in FIG. 6 is input from a color scanner (data is averaged when several types of electrophotographic printers are used at this time), and each patch after log conversion is input. R, G, B signals are obtained. On the other hand, these color patches are measured with a colorimeter, and the L *, a *, and b * values of each patch are obtained.
[0039]
(C) As described above, the data group (R, G, BC, M, Y) can be obtained via the above equation (2). For this data group, a color correction coefficient group (a0 to a3, b0 to b3, c0 to c3) that matches the generation original color with the printed color by using the least square method for the above equation (1). )
[0040]
The color correction coefficient for the generation document determined in this way is set in the color correction coefficient storage unit 6 constituted by ROM or RAM. The document determination circuit 5 operates during pre-scanning to determine whether the document is a generation document. When it is determined that the document is a generation document, a signal for selecting a generation document coefficient in the color correction coefficient storage unit 6 is output. Then, during the main scan, the selected generation document coefficient is read out and set in the color correction circuit 3, and color correction processing is performed according to Equation (1) using the color correction coefficient suitable for the generation document.
[0041]
【The invention's effect】
As described above, according to the present invention , when a document is a document (generation document) output from a color copying machine having an electrophotographic printer, a color correction coefficient for the document is selected. Since color correction processing is performed, faithful color reproduction is achieved. In addition, in the conventional apparatus, the color is guaranteed only for the own machine. However, according to the apparatus of the present invention, it is possible to guarantee faithful color reproduction even for a document printed by a color copier of another company. it can.
[0042]
According to the present invention , it is possible to recognize not only the own machine but also a general generation original having a tracking pattern as a generation original.
[0043]
According to the present invention , since information of an isolated region is used, recognition accuracy is improved. That is, it is possible to reduce erroneous determinations on halftone originals.
[0044]
According to the present invention , since information that is close to yellow is used, the recognition accuracy is improved. That is, misjudgments can be reduced with respect to dust (noise).
[0045]
According to the present invention , since yellow information is used, recognition accuracy is further improved.
[Brief description of the drawings]
FIG. 1 shows a configuration of an image reproduction 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.
FIGS. 4A to 4C show generation document determination patterns. FIG.
FIG. 5 shows another configuration of the generation document determination unit.
FIG. 6 shows an example of a color patch.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Color scanner 2 Log conversion circuit 3 Color correction circuit 4 Color printer 5 Original determination circuit 6 Color correction coefficient storage part

Claims (2)

A means for reading an original as image signals of r, g, b, a first means for performing pattern matching between the r signal of the target pixel and the white pixel pattern, and pattern matching between the g signal of the target pixel and the white pixel pattern. When matching is performed by the second means to be performed, the third means for performing pattern matching between the b signal of the target pixel and the isolated region pattern surrounded by the white background, and all of the first, second, and third means An output document comprising: means for determining the pixel of interest as a tracking pattern pixel; and means for determining that the document is an output image from a color copying machine based on the determined number of tracking pattern pixels Judgment device. The original is read as r, g, b image signals, pattern matching between the r signal of the target pixel and the white pixel pattern is performed, pattern matching between the g signal of the target pixel and the white pixel pattern is performed, and the b signal of the target pixel Is matched with the isolated region pattern surrounded by a white background, and when all the patterns are matched, the target pixel is determined as a tracking pattern pixel, and the original is color copied based on the determined number of tracking pattern pixels An output document determination method, wherein the output document is determined to be an output image by a machine.

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