JP3496911B2 - Document judgment device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document determination method for determining with high accuracy whether an input document is a generation document output by an electrophotographic color copying machine. Equipment related. 2. Description of the Related Art Normally, 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 RGB signals 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 print original,
Roughly speaking, the colors of other documents made of color materials other than the printed document do not match. [0003] One of the originals input to the color copier includes an original output by the color copier, a grandchild copy or a generation (hereinafter referred to as a generation original). The above-described problem also occurs in color reproduction of this generation original. That is, the color reproduction of the generation original is not guaranteed by the only color correction unit designed for printing. [0004] In response to such a problem, the present applicant has previously positively detected a tracking pattern struck on a generation original, and if it is determined that the original is a generation original, performs color correction in accordance therewith. By doing so, a color image processing device and an output document discriminating device that automatically guarantee color reproduction for both print documents and generation documents have been proposed. In the apparatus described in Japanese Patent Application Laid-Open No. Hei 7-336541, a chase pattern hit on a generation document is positively detected, and if it is determined that the document is a generation document, a gamma correction corresponding thereto is performed. By doing so, an output image having linear gradation characteristics is obtained. [0006] By the way, in the above proposed device, when a yellow tracking pattern is detected,
Binarization is performed with a fixed threshold. Some of the images output by the color copier use so-called recycled paper. In this case, the background level is also high. Therefore, if the threshold value is adjusted to a paper with a low ground level, the tracking pattern cannot be detected properly. There is a problem to say. On the other hand, in the tracking pattern detection method described in the above-mentioned publication, the original is not influenced by the ground level of the original as described above, but there is a high possibility that other originals are erroneously determined to be generation originals. . Specifically, the pattern detection described in the above-mentioned publication uses a 3 × 3 mask, and when the density of the target pixel i satisfies the following logical expression and the pixel is yellow, the pattern is detected as an identification pattern. To detect. Dot detection signal = (i <a) ∩ (i <b)
{(I <c)} (i <d) {(i <e)} (i <f)}
(I <g) ∩ (i <h). In such a detection method, since the pattern limitation is small, a tracking pattern can be detected when the ground level is high. However, a dot document or an ink jet document, that is, a picture document expressing a medium tone with small dots. Alternatively, the possibility of erroneously detecting noise is high. The present invention has been made in consideration of the above circumstances, and an object of the present invention is to determine with high precision whether or not a target document is a document output by an electrophotographic color copying machine. An object of the present invention is to provide a document determination device. In order to achieve the above object, according to the first aspect of the present invention, an original is composed of r, g, and b digital images.
A document reading device for reading out a pixel signal corresponding to a tracking pattern, and a device for determining whether the document is an output image of a color copying machine based on the detection result. Means for detecting a pixel corresponding to the tracking pattern, means for binarizing the r signal
And a pattern of the binarized signal and a white pixel pattern
First means for matching and binarizing the g signal
Means and a pattern of the binarized signal and a white pixel pattern.
A second means for performing the tone matching, and for the b signal
Means for locally obtaining an average value, and b
Means for binarizing the signal, and the binarized signal and the tracking signal;
Third means for performing pattern matching with the turn,
Matching by all of the first, second and third means
Means for determining the pixel of interest as a tracking pattern.
It is characterized by being constituted . 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 adaptively binarize a tracking pattern peculiar to an image output from a color copier of a document without being affected by the level of a background, and thereafter, a shape peculiar to the tracking pattern is formed. By actively utilizing and detecting, the generation original is determined with high accuracy. <Generation Document Judgment Apparatus> FIG. 1 shows a configuration of a generation document judgment apparatus of the present invention. In order to determine whether or not the document is a generation document, the apparatus according to the present embodiment focuses on the tracking pattern always printed on the output image of the color copying machine, and detects the tracking pattern using pattern matching. Generally, the tracking pattern is printed with a yellow toner in a specific shape (for example, about 1 pixel × 3 pixels) in a 400 dpi printer. Therefore, conventionally, a method of detecting this tracking pattern by several methods has been adopted. As one of the methods, there is a method proposed by the present applicant as described above, but after binarization with a fixed threshold value,
As described above, since the pattern matching is performed, there is a problem that a tracking pattern hit on a slightly colored generation original such as recycled paper cannot be detected as intended. [0015] As another method, there is a method disclosed in the above-mentioned gazette. However, a halftone printing or a dither-output ink jet document locally has information similar to the above-mentioned tracking pattern at a considerable frequency. Therefore, they may be mistaken for generation manuscripts. Further, there is a high possibility that the yellow spike noise is erroneously detected as a tracking pattern, and as a result, there is a problem that the determination of the document is erroneously performed. In view of the above, the apparatus according to the present invention proposes a generation document judging apparatus provided with a tracking pattern detecting means for solving the above-mentioned problem. Hereinafter, each part of the apparatus of the present invention will be described in detail. The color scanner 1 has a photoelectric conversion element such as a CCD camera, reads an original, obtains color separation signals (analog) of three colors of red, green, and blue, and A / D converts these three signals. And rgb
(8 bits each) are output. The resolution of the scanner is 400 dpi. Log conversion unit 2 The signal from the scanner is a signal having a substantially linear reflectance, and is converted into a signal having a linear density. Therefore, Lo
The output signal after the g conversion is 0 for paper white and 255 for black. MTF correction unit 3: As a pre-process of the subsequent binarization process, an MTF correction filter is applied to each of the rg signals. FIG. 2 shows an example of the coefficients of the MTF correction filter. Binarization processing section 4 (for r and g); The binarization processing section 4 performs binarization with a fixed threshold. Here, in the present invention, a threshold value is set in consideration of recycled paper (that is, such that the ground of the recycled paper is determined to be white). Average value calculation (+ addition processing) section 5: In order to set a threshold value for binarization independent of the ground level, first, an average value around the target pixel is obtained. Here, for example, an average value in 1 × 5 pixels as shown in FIG. 3 is obtained.
Then, the average value is used as a threshold for binarization. Or
In order to output the tracking pattern shape more clearly, a predetermined value may be added to this average value to obtain a threshold for binarization. Binarization processing section 4 (for b): Binarization is performed using the threshold value calculated by the average value calculation section 5 described above. Here, in the present invention, a threshold value is set in consideration of recycled paper (that is, such that the ground of the recycled paper is determined to be white). Pattern matching circuit 6: PM1 (pattern for r and g signals) FIG. 4A shows a pattern for r and g signals. As a result, cyan and magenta colors, which are complementary colors of r and g, do not exist near the target pixel, in other words, the yellow area is detected. PM2 (pattern for b signal) FIG. 4B shows a pattern for b signal. Here, a typical pattern of a 400 dpi printer is 1 pixel × 3 pixels.
A pattern for detecting a pixel tracking pattern was prepared. Generally, halftone dots for printing are circular or square,
You won't hit the pattern you prepared. Comprehensive judging section 7: When all the outputs from the three pattern matching circuits are on, that is, when all of the outputs match, the target pixel is judged as a tracking pattern pixel. A counter 8 counts the number of pixels of the above-mentioned tracking pattern in a predetermined area (for example, the entire surface of the document). Comparator 9: Compares the count value (V) of the tracking pattern pixels described above with a predetermined threshold (THgen) to determine whether or not the document is a generation document. If V> THgen, a signal indicating that the document is a generation document is output. FIG. 5 shows another configuration of the generation original discriminating apparatus of the present invention provided with a color correction circuit. The details of the color correction processing will be described later. The reason for providing the color correction circuit is as follows. When a tracking pattern hit with a single yellow color is viewed with an RGB signal, ideal color separation cannot be performed, and a yellow component also responds to the RG signal. That is, the signal level is not 0. Also, B
There is a possibility that the signal slightly deviates from the ideal, and the shape is slightly distorted from the original tracking pattern shape (1 × 3 pixels). Therefore, C, which is obtained by subjecting the R, G, B signals to color correction processing,
A tracking pattern is detected from the M and Y signals. As will be described later, a color correction coefficient is
There are two types, one for printed originals and one for generations, but if you set a color correction coefficient for generation during pre-scanning for document recognition, the tracking pattern will be closer to ideal, so it will be advantageous for detection and improve judgment performance. I do. <Image Reproducing Apparatus Using Generation Document Determining Apparatus> Here, an apparatus (color image processing apparatus) for reproducing an image using the above-described generation document determining apparatus shown in FIG. 1 will be described. FIG. 6 shows the configuration of the image reproducing apparatus of the present invention. In the figure, 21 is a color scanner, 2
2 is a Log conversion circuit, 23 is a color correction circuit, 24 is a color printer, 25 is a document determination circuit, and 26 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. Needless to say, using the technology described in JP-A-6-197218, for example, further preparing for silver halide photographs (photographic paper) or for mixing them, etc. It is effective in guaranteeing fidelity. Each part of the apparatus will be described. The color scanner 21 is as described above. Log conversion circuit 22; The output signal of the color scanner 21 is a signal having a substantially linear reflectance. This is converted into an advantageous density signal (R
(GB 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 23: Here, it is assumed that color correction is performed by the following linear linear equation. That is, the signals after the R, G, and B log conversion (each 8
Bit), Y, M, and C are printer drive signals, and a
Assuming that 0 to a3, b0 to b3, and c0 to c3 are color correction coefficient groups, the present 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. . . Equation (1) In this apparatus, a color correction coefficient group for a print document and a color correction coefficient group for a generation document are prepared. Here, the color printer 24 is a printer that creates an image in three colors of cyan, magenta, and yellow, and receives drive signals (C, M, Y) to create an image. When the printer reproduces four colors by adding black, for example, min (C, M, Y)
, A drive signal is created by so-called UCR processing of subtracting the black signal from C, M, and Y, and printed out. Document determination circuit 25; Here, the generation document determination device shown in FIG. 1 is used. Therefore, the determination is made by discriminating between the generation document (electrophotographic printer document) and the other, that is, the printed document, and outputting the result. The document determination circuit 25 operates at the time of prescan. At the time of pre-scanning, it is not necessary to scan the entire original, and only a part of the original, for example, the periphery of the original having a high possibility of a white background may be used. Further, the color correction coefficient may be switched during the reproduction of the image without performing the prescan. That is, a printing color correction coefficient is set as an initial value, a document is determined at any position during scanning, and if it is determined that the document is a generation document, the color correction coefficient is switched to a generation document after that. . Next, the method of setting the prepared color correction coefficient group is basically determined by the procedure described in the above-mentioned Japanese Patent Application Laid-Open No. Hei 6-197218. The gazette includes a halftone photo,
A setting method for a silver halide photograph is described. Here, an example of a method for setting a color correction coefficient for a generation original will be described. (A) A printer approximation formula (L
*, A *, b * -C, M, Y). That is, C
The MY signal is selected at appropriate intervals, and a color patch group as shown in FIG. 7 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 using a suitable measuring instrument (L
*, A *, b *). Equation (2) is obtained by 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 * + β8
a * b * + β9b * L * Y = γ0 + γ1L * + γ2a * + γ3b * + γ4L * L
* + Γ5a * a * + γ6b * b * + γ7L * a * + γ8
a * b * + γ9b * L *. . . (B) Further, a group of color patches as shown in FIG. 7 is input from a color scanner (the data is averaged when patches are created using several types of electrophotographic printers). , R, G, B of each patch after Log conversion
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) As described above, a 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 coefficients for the generation original determined in this way are set in the color correction coefficient storage section 26 constituted by a ROM or a RAM. At the time of pre-scanning, the document determination circuit 25 operates to determine whether the document is a generation document. If it is determined that the document is a generation document, the color correction coefficient storage unit 26
The signal for selecting the coefficient for the generation document in the above is output. Then, at the time of the main scan, the selected generation document coefficient is read out and set in the color correction circuit 23, and the color correction process is performed according to equation (1) using a color correction coefficient suitable for the generation document. In the above-described embodiment, an example is shown in which the color correction coefficient is switched by using the generation original discriminating apparatus. However, the present invention is not limited to this. For example, Japanese Patent Laid-Open No. 7-
It is also possible to apply to the image processing apparatus described in JP-A-336541 and change the gradation correction means according to the document. As described above, according to the present invention, it is possible to accurately determine whether or not a document is a document (generation document) output by a color copying machine having an electrophotographic printer. Can be determined. In particular, even when a tracking pattern is hit on a high-level paper such as recycled paper, the pattern can be stably detected, that is, it can be determined that the document is a generation original. is there. In addition, since the pattern to be detected is accurately limited by the pattern matching, a printed document or an ink jet output document which has been relatively erroneously determined in the past is hardly erroneously determined to be a generation document.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a configuration of a generation original discriminating apparatus of the present invention. FIG. 2 shows an example of coefficients of an MTF correction filter. FIG. 3 shows an example of a reference pixel when calculating an average value around a target pixel. FIGS. 4A and 4B show patterns for generation original determination. FIG. 5 shows another configuration of the generation original discriminating apparatus. FIG. 6 shows a configuration of an image reproducing apparatus according to the present invention. FIG. 7 shows an example of a color patch. [Description of Signs] 1 Color scanner 2 Log conversion unit 3 MTF correction unit 4 Binarization processing unit 5 Average value calculation unit 6 Pattern matching circuit 7 Overall judgment unit 8 Counter 9 Comparator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/40 G03G 15/01 H04N 1/60

Claims (1)

(57) Claims: 1. A means for reading a document as r, g, b digital signals and detecting a pixel corresponding to a tracking pattern, and based on the detection result, Means for determining whether or not the document is an output image from a color copying machine, wherein the means for detecting a pixel corresponding to the tracking pattern includes means for binarizing an r signal; , The binarized signal and the white image
First means for performing pattern matching with an elementary pattern
Means for binarizing the g signal, and the binarized signal and a white image
Second means for performing pattern matching with an elementary pattern
Means for locally obtaining an average value for the b signal;
Means for binarizing the b signal based on the value;
Pattern matching between the detected signal and the tracking pattern
The third means and the first, second, and third means have matched.
Original determination apparatus characterized by being configured the pixel of interest comes from, means for determining a tracking pattern.