JP2004312118A - Color image processing method, color image processing apparatus, program, and recording medium - Google Patents

Abstract

A color image processing method capable of correcting a wide show-through that cannot be corrected by a conventional show-through correction method using local two-coloring is provided.
According to this color image processing method, a digital color original image obtained by inputting an original color-printed on paper is cut out by a local window function used for local processing for specifying show-through components. Assuming that the image range is A, a show-through component inside A is detected using information obtained from the local window function B set around A, and show-through and spread-through are selectively reduced. When the correction is made by using the local window function B set around A, information on the background color of the print content on the front surface of the document or information on the print content on the back surface of the document is used to show through components inside A. Is detected and selectively corrected. Alternatively, an appropriate image division process may be performed as preprocessing, and the above show-through correction process may be selectively performed only on a highly uniform area.
[Selection diagram] FIG.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a color image processing method, a color image processing device, a program, and a recording medium, and more particularly, to a technique for reducing show-through and spread-out in digital color image processing.
[0002]
[Prior art]
With the spread of image input devices such as scanners, digital cameras, digital copiers, and the like, it has become common for document images on paper media such as books, magazines, catalogs, advertisements, and newspapers to be color-inputted.
When inputting using these image input devices, when printing is performed on both sides of thin paper having high transmittance, the image on the back side is transparent, and “show-through” occurs, which is input in the image on the front side. Would.
Further, in the case of a color document, the background color is not uniform, and a pattern, a pattern, and a photograph are often mixed.
[0003]
For this reason, the problem of removing “show-through” from an input image has been regarded as important for improving image quality but difficult to handle.
Techniques related to show-through correction are roughly classified into mechanical methods and image processing methods.
The mechanical method is to reduce the reflectivity of the pressure plate to reduce the show-through component from the image on one side.However, since it cannot be applied directly to digital data, it is a problem today when the digital data environment is widespread. is there.
[0004]
As a method for detecting and reducing a show-through component from a single-sided image by image processing without using a mechanical device such as a pressure plate, there is an “image data processing device” in Patent Document 1. The method disclosed in Japanese Patent Application Laid-Open No. H11-157421 aims to handle not only a normal image but also an image with much dirt by determining a noise removal threshold from the distribution of the luminance histogram of the document.
[0005]
However, since the histogram of the entire image is required in advance and only the threshold value for removing noise is adaptively changed, for example, for show-through generated in the halftone area, removal of each halftone is performed. Or the show-through remains.
[0006]
Also, in the techniques of Patent Document 2, Patent Document 3, and Patent Document 4, similarly to Patent Document 1, the image density distribution is adaptively changed by the value of an evaluation function that prepares the image density histogram in advance. And has the same problems as Patent Document 1.
[0007]
In the techniques of Patent Documents 5 and 6, only one image is input, and image processing for show-through correction is performed without using a histogram for the entire image.
The technique of Patent Document 5 mainly separates show-through and foreground images based on edge information extracted from an input image, and selectively corrects a show-through area.
In other words, a run is formed by pixels having no edges around a pixel having show-through (hereinafter, target pixel), and the show-through is corrected by replacing the target pixel with an image feature amount inside the run.
[0008]
However, this technique cannot correct show-throughs larger than the run, but as an extreme example, a wide show-through such as painting the back side of a document is possible, and the uniform area of the front print content is also considered. The size of the run is limited because the size of the run is not guaranteed to exceed the show-through.
[0009]
In the technique of Patent Document 6, a read image is divided into partial areas, and show-through is detected and corrected for each area. In calculating the show-through detection threshold value, the threshold value of the attention area is calculated by a weighted average of the provisional threshold value of the attention area and the application threshold value of a plurality of neighboring partial areas. The information about the separation boundary in the binarization for specifying the show-through and the paper color is provided from outside the processing area, and the show-through having a size exceeding the processing area cannot be corrected.
[0010]
[Patent Document 1]
JP-A-7-30757 [Patent Document 2]
Japanese Patent Application Laid-Open No. 10-65521 [Patent Document 3]
JP 10-257325 A [Patent Document 4]
JP-A-11-187266 [Patent Document 5]
JP 2001-169080 A [Patent Document 6]
JP-A-2002-314790
[Problems to be solved by the invention]
As described above, with the conventional show-through correction method, show-through having a size exceeding the local window for show-through detection cannot be corrected.
Further, in the method of simply enlarging the local window, there is a problem that the reproducibility of the print content on the front surface of the document is reduced because the resolution of the effective output image is reduced.
[0012]
The present invention has been made in view of the above-described circumstances, and is a color image capable of correcting a wide show-through, which cannot be corrected by a show-through correction method using a conventional local two-color image. It is an object of the present invention to provide a processing method, a color image processing apparatus, a program for executing the color image processing method, and a computer-readable recording medium storing the program.
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, claim 1 of the present invention is used for local processing for specifying a show-through component on a digital color original image obtained by inputting an original color-printed on paper. Assuming that the image range cut out by the local window function is A, a show-through component inside A is detected using information obtained from the local window function B set around A, and show-through or lay-through is detected. In the color image processing method of selectively reducing and correcting the inside, the show-through inside A is performed by using information about the background color of the print content on the front surface of the original obtained from the local window function B set around A. It is characterized in that components are detected and selectively corrected.
[0014]
According to a second aspect of the present invention, there is provided the color image processing method according to the first aspect, wherein information on a print content on the back surface of the original obtained from the local window function B set around the A is used. It is characterized in that an internal show-through component is detected and selectively corrected.
[0015]
According to a third aspect of the present invention, in the color image processing method according to the first or second aspect, information on a background color of a print content on a front surface of the document obtained from a plurality of local window functions set around the A is provided. Is used to detect the show-through component inside A and selectively correct it.
[0016]
According to a fourth aspect of the present invention, an appropriate image division process is performed as preprocessing, and the color image processing method according to any one of the first to fourth aspects is selectively performed only on a highly uniform region. It is characterized by.
[0017]
A fifth aspect of the present invention is a program for causing a computer to execute the color image processing method according to any one of the first to fourth aspects.
According to a sixth aspect of the present invention, there is provided a color image processing apparatus having the program according to the fifth aspect.
According to a seventh aspect of the present invention, there is provided a computer-readable recording medium storing the program according to the sixth aspect.
[0018]
With the above configuration, it is possible to correct a wide show-through that could not be corrected by the conventional show-through correction method using local two-coloring.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a color image processing apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram illustrating a hardware configuration of a color image processing apparatus according to an embodiment of the present invention. Referring to FIG. 1, a color image processing apparatus according to the present embodiment includes an image input device 1 such as a scanner or a digital camera for inputting a color image, and a RAM (Random) for storing the input color image and various data in a processing process. Access Memory) 6, a display device 2 such as a CRT or a liquid crystal display for presenting the progress and results of the process to the user, a keyboard 3 for the user to input parameters necessary for the process as needed, a series of (described later) A ROM (Read Only Memory) 7 for storing a program for executing processing, a CPU 5 for executing a series of processing by executing a program stored in the ROM 7, and a read-through removal image generated as a result of the series of processing is read from the RAM 6. It consists of an image printing device (printer) 4 for outputting, The components are connected by a data bus.
[0020]
Intermediate data (reduced color images, color conversion images, edge strength images, binary edge images, background color images, binary edge difference images, show-through removal images, etc.) created during the execution of the processing described below are created and corrected. Is performed and stored in the RAM 6.
[0021]
FIG. 2 is a flowchart illustrating a color image processing procedure according to the present embodiment.
First, a document is read by the image input device 1 and A / D converted, and then image data is output as image signals of three colors of R (red), G (green), and B (blue) for each read pixel. I do. Further, processing such as shading correction and gamma correction is performed on the image signal (step S1).
[0022]
Preprocessing is performed on the input image data so as to perform smoothing, color space conversion, and the like so that color feature amounts can be easily extracted in a subsequent stage (step S2). This processing may be omitted depending on the type of the input image.
For smoothing, for example, the average of the pixel values within the smoothing reference range may be used, or appropriate thinning may be performed. This color space conversion refers to conversion from an RGB color space to a Lab color space or the like.
[0023]
The show-through correction processing is performed on the preprocessed image data, and general image processing such as isolation point removal, color correction, and moiré reduction is performed on the resulting image data (step S3).
In the show-through correction processing, the correction method is not particularly limited as long as it satisfies the following criteria.
-Use only the image scanned from one side of the document printed on both sides.
-Selectively correct a part of the input image where show-through has occurred.
[0024]
The image data processed by the image processing is subjected to a color separation filter and a color correction for removing a turbid component of the ink, and the result is subjected to black generation and under color removal, and γ-converted according to the characteristics of the output device. The image data is post-processed so as to reproduce the halftone of the image by dithering or error diffusion (step S4).
Driving is performed in accordance with the image data output from the post-processing unit, and an image is output to the image printing device 4 (step S5).
[0025]
The present invention performs show-through correction by utilizing the fact that the correlation is low when the print content on the front side of the document and the print content on the back side of the document are locally viewed.
For example, considering the change in image from position a to position b on the document, if the print content on the back of the document is uniform, the print content on the back of the document estimated at position a (corresponding to the show-through component) ) Is expected to be close to the estimated value of the print content on the back of the document at the position b. This tendency is the same even when the print content on the front surface of the document changes in the range from position a to position b.
[0026]
Next, when the internal region of the local window function formed from the position a and the position b is two-colored, the show-through component of the internal region of the local window function and the background color of the print content on the front surface of the document are estimated. think of. It is considered that, of the two colors obtained at this time, the brighter one corresponds to the original background color of the print content on the front side of the document, and the darker one corresponds to the background color of the print content on the front side of the document plus the show-through component.
Therefore, as the difference between the two, an estimated value of the print content on the back of the document can be obtained.
[0027]
In this case, by adding a value obtained by multiplying the estimated value related to the original background color of the print content of the front surface of the document at the position a by a predetermined ratio to the local window function at the position b, the print content of the front surface of the document at the position b is obtained. The estimation accuracy of the original background color can be improved.
[0028]
Similarly, an estimated value of the print content on the back of the document can be used. In this case, it is necessary to simultaneously use the original background color of the print content on the front surface of the document, the estimated value of the print content on the back surface of the document, and the above-described relationship regarding the detected show-through.
[0029]
If there are a plurality of processed areas around the position a where the show-through correction processing is currently performed, a weighted average of the estimated values related to the background color of the print content on the front surface of the original obtained from those areas is used. , The estimation accuracy can be improved. Further, as described above, the same processing can be performed on the estimated value of the print content on the back of the document.
[0030]
FIG. 3 is a flowchart for explaining show-through detection and correction processing in the present embodiment.
First, since a color image input from the image input device 1 is mainly considered as show-through reduction processing, pre-processing is performed on digital data after performing processing such as scanner gamma correction on read image data. The applied image data is input (step S11).
[0031]
Next, “contents printed on the front side of the document” such as characters and photographs are extracted from the input image data, and are protected by excluding them from the target of correction processing in the subsequent stage (step S12). As a feature of the content printed on the front side, for example, a character or the like has a strong edge strength. Therefore, whether or not the front side printing is performed may be determined by threshold processing for the edge strength. If the characteristics of the image input device (scanner) are known, foreground pixels are determined and protected by performing threshold processing on the pixel value itself or the luminance value based on the information.
This processing may be omitted depending on the type of the input image.
[0032]
Next, based on these information, the input image data is divided to extract a highly uniform area (step S13). In order to keep the reproducibility of the content printed on the front surface high, show-through correction processing may be performed only on a highly uniform area.
[0033]
The divided region is further divided into regions cut out by a plurality of local window functions (for example, N) (step S14). This i-th local window function is called a local window function i, and i = 1 at first.
[0034]
The internal region of the local window function i is binarized (step S15). This color clustering for binarization usually requires an iterative calculation. Here, a fast color thresholding algorithm “SC Pei and C” based on the quaternion representation of an image and the principle of moment preservation is used. M. Cheng, "Color image processing by using binary quaternion-moment-preserving thresh- ing technology", "Computing with IEEE Trans. Processing, IEEE Trans. To improve efficiency.
The two colors obtained at this time are called representative colors of the local window function i, and the brighter representative color is L (i) and the darker representative color is D (i).
[0035]
If the show-through correction processing has already been performed by the surrounding local window function j (j <i) at the time of the two-color processing, the original background color of the print content on the front surface of the original document obtained therefrom corresponds to the original background color. L (j) is multiplied by a predetermined ratio α, a value selected from L calculated by a plurality of surrounding local window functions, or those L are synthesized by a synthesis formula such as a weighted average. After adding the value to the local window function i, a two-color processing is performed.
[0036]
Estimated value B of the print content on the back of the document defined as the difference between L (i) and D (i)
B = | L (i) -D (i) |, (| a | represents the absolute value of the value a.)
Is calculated and stored for use when processing the subsequent local window function i (step S16).
Here, in the area around the local window function i, the show-through may be corrected using the estimated value B only when the estimated value B is nearly uniform.
[0037]
The internal area of the local window function i is replaced with L (i) corresponding to the original background color of the print content on the front surface of the document (step S18), i is advanced by one (step S19), and all the local window functions i are replaced. Until the processing is performed (until i becomes N), the process returns to step S15 and is repeated (step S20).
[0038]
FIG. 4 shows an example of an input image having show-through and a show-through correction result of the input image. FIG. 4A shows an input image in which the blue image area 10 on the back is input as the show-through to the characters “GABA” and “NH3” on the front print. FIG. 4B shows an image after the show-through correction of the present invention has been performed. The print content of the front surface such as characters is preserved, and the show-through component is selectively corrected.
[0039]
FIG. 5 is a diagram for explaining processing of the show-through correction method according to the present invention. The information on the background color of the print content on the front surface of the document estimated by the local window function 1 indicated by the frame 11 is also used when processing the adjacent local window function 2 indicated by the frame 12. The information on the background color of the print content on the front surface of the document calculated in the process of the local window function 2 is also used in the process of the local window function 3 indicated by the frame 13. Since the distribution is similar to the distribution of the pixel values in the internal region of the local window function 1, the influence of the show-through component and the printed content of the front surface on the local window function 3 in estimating the background color is small.
[0040]
In the above-described embodiment, the recording medium of the program is the ROM 7, but other recording media, for example, a semiconductor medium (for example, a non-volatile memory card), an optical medium (for example, DVD-ROM, MO, MD) , CD-R, etc.), and a recording medium in any form such as a magnetic medium (for example, a magnetic tape, a flexible disk, etc.).
Alternatively, a program stored in a storage device may be directly supplied from a server computer via a communication network such as a network. In this case, the storage device of the server computer is also included in the recording medium of the present invention.
[0041]
When the program is recorded on the recording medium as described above, the recording medium is mounted on a medium driving device, the recorded program is installed in a storage device (not shown), and the installed program is executed by the CPU 5. .
As described above, the program itself read from the recording medium storing the program realizes the functions of the above-described embodiment, and the program and the recording medium storing the program also constitute the present invention. .
[0042]
Further, not only the functions of the above-described embodiment are realized by executing the program, but also the processing of the above-described embodiment is performed in cooperation with an operating system or another application program based on an instruction of the program. The case where the function is realized is also included.
[0043]
It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various changes and modifications can be made without departing from the gist of the present invention.
[0044]
【The invention's effect】
As described above, according to the present invention, it is possible to correct a wide show-through that could not be corrected by the conventional show-through correction method using local two-coloring.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a hardware configuration of a color image processing apparatus according to the present invention.
FIG. 2 is a flowchart illustrating a color image processing procedure according to the embodiment.
FIG. 3 is a flowchart for explaining show-through detection and correction processing in the embodiment.
FIG. 4 is an example of an input image having show-through and an image of a show-through correction result of the input image.
FIG. 5 is a diagram for explaining processing of a show-through correction method according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image input device, 2 ... Display device, 3 ... Keyboard, 4 ... Image printing device, 5 ... CPU, 6 ... RAM, 7 ... ROM, 10 ... Blue image area, 11, 12, 13 ... Local window function Frame to do.

Claims (7)

Assuming that an image range cut out by a local window function used for local processing for specifying a show-through component with respect to a digital color original image obtained by inputting an original color-printed on a paper is represented by A In a color image processing method for detecting a show-through component inside A using information obtained from a local window function B set around and selectively reducing and correcting show-through or lay-off, Using the information on the background color of the print content on the front surface of the document obtained from the local window function B set around A, detecting a show-through component inside A and selectively correcting it. Processing method. 2. The color image processing method according to claim 1, wherein a show-through component inside A is detected and selected by using information about print contents on the back of the document obtained from a local window function B set around A. A color image processing method, comprising: 3. The color image processing method according to claim 1, wherein information on the background color of the print content on the front surface of the original obtained from a plurality of local window functions set around the A is used. A color image processing method comprising detecting a component and selectively correcting the component. 5. A color image processing method according to claim 1, wherein an appropriate image division processing is performed as preprocessing, and the color image processing method according to claim 1 is selectively performed only on a region having high uniformity. A program for causing a computer to execute the color image processing method according to claim 1. A color image processing apparatus equipped with the program according to claim 5. A computer-readable recording medium on which the program according to claim 6 is recorded.

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