JP2004289570A - Image processing method and image processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a picture quality by combining and applying a plurality of processing even when a plurality of trouble such that "dots stand out", "the base is unnecessarily colored", the occurrence of sight through back and "lightness or contrast is lacked" are mixed within image data. <P>SOLUTION: In processing of dot removal 12, base color removal 13, sight through back removal 14 and contrast correction 15, at least the contrast correction processing 15 is finally performed, and the dot removal processing 12 is first performed. Thus, the color difference caused by the dots, the base color or sight through back is prevented from being expanded and the contrast correction processing can be performed in the state of removing such trouble beforehand, thereby improving the picture quality without incurring the side effect of mutual processing as little as possible. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image processing method and apparatus for performing processing for improving halftone dots, background colors, show-through, and insufficient contrast on input image data, and outputting the processed data.
[0002]
[Prior art]
Various inconveniences may occur in image data obtained by reading a magazine or printed matter with a scanner or the like. Typical examples of defects include "dots are conspicuous", "unnecessary color is applied to the background", "show-through occurs", "brightness and contrast are insufficient", and the like. For these defects, image quality can be improved by performing image processing such as "dot removal", "background color removal", "show-through removal", and "contrast correction". Proposed.
[0003]
Examples of the four processes of halftone dot removal, background color removal, show-through removal, and contrast correction can be specifically described as the following processes.
[0004]
As the halftone dot removing process, a process of “analyzing image data to detect a halftone dot region, and performing a smoothing process on the detected halftone dot region” can be considered. FIG. 8 shows an example of a flowchart of the halftone dot removal processing.
[0005]
First, brightness data is calculated for the input image data (# 20). Then, an isolated point detection filter is applied to the obtained brightness data (# 22), and it is determined whether the target pixel is an isolated point. As the isolated point detection filter, for example, a filter indicated by reference numeral 22 in FIG. 9 is exemplified. That is, when the pixel value of the focused pixel is higher or lower than the pixel value of any of the surrounding pixels 22 and 23 in the partial region 20 of the image, the focused pixel is determined to be an isolated point. You.
[0006]
When the isolated point detection processing is completed, the number of isolated points is counted next in a certain area including the target pixel (# 24). If the number of isolated points is equal to or greater than a certain value, the pixel of interest is determined to be a halftone dot region, and a smoothing process is performed (# 25). The smoothing process is performed by applying, for example, a smoothing filter 25 as shown in FIG. 10 to remove halftone dots.
[0007]
As the background color removal processing, "analyze image data to detect color bias (which color component of RGB is excessive), and subtract the excess from the RGB color component of each pixel." Can be considered. FIG. 11 shows an example of a flowchart of the base color removal processing.
[0008]
First, for the input image data, the number of components having the maximum value among the RGB color components of each pixel is counted for all the pixels (# 30). Then, the occupancy is calculated for each of the RGB color components by dividing the counted value by the total number of pixels (# 32). (CMY is similarly calculated by taking the complement of the RGB pixel value (# 33).)
[0009]
Next, the excess amount of the RGB color components of each pixel is calculated for the image data, and the sum is added for all the elements. Then, the average excess amount is calculated for each of the RGB color components by dividing the total excess amount by the total number of pixels. (CMY is similarly calculated by taking the complement of the RGB pixel value (# 35).)
[0010]
Then, a histogram of the excess amount is created for a color component for which both the occupancy and the average excess amount are equal to or larger than the threshold, and the peak value of the histogram is set as the color deletion amount for each color component (# 37) (see FIG. 12). ). Finally, the background color is removed by subtracting the color removal amount from the corresponding color components of all pixels (# 38).
[0011]
As the show-through removal processing, it is conceivable that “the show-through correction amount (RGB color component correction amount) is calculated for each pixel by analyzing the image data and the show-through removal processing is performed based on the correction amount”. . FIG. 13 shows an example of a flowchart of the show-through removal processing.
[0012]
First, brightness data of all pixels is calculated for the input image data (# 40). Then, a correction amount M is calculated for each pixel based on the calculated brightness data (# 42). Here, a linear expression such as M = L / 3 (L: lightness value of the pixel of interest) is used such that the correction amount increases as the lightness increases.
[0013]
Next, the maximum value of the RGB components of the pixel of interest is set to V (# 43), and when V + M> 255, the amount exceeding 255 is deleted from all the RGB color components (# 45). That is, the correction amount M is corrected to M− (V + M−255) = 255−V. Then, using the corrected amount of correction, R ′ = R + 255-V, G ′ = G + 255-V, B ′ = B + 255-V (RGB: value before correction, R′G′B ′: value after correction) ) And the respective conversion processes. FIG. 14 shows the effect of this processing. As can be seen from FIG. 14, the pixels having relatively high lightness and the same hue / saturation are corrected so that the lightness components also match. The show-through area and its surrounding area generally have such a tendency (high brightness and the same hue / saturation), so show-through is removed.
[0014]
On the other hand, when V + M ≦ 255, R ′ = R + M, G ′ = G + M, and B ′ = B + M (# 46). That is, only the process of increasing the brightness is performed on the low brightness region in the image.
[0015]
As the contrast correction processing, "applying an S-shaped tone curve to image data to enhance contrast" can be considered. FIG. 15 shows an example of a tone curve to be applied.
[0016]
However, in the image processing combining the above-described processes, it has been found that the image quality of the obtained image differs depending on the processing order of the two processes, and the image quality may not always be proper.
[0017]
That is, when a plurality of the above-described defects (dots, background color, show-through, lack of contrast) occur in the acquired image in combination, for example, an image in which halftone dots occur and the contrast is insufficient is obtained. On the other hand, it has been found that the effect of the correction changes depending on the order of performing the “halftone dot removal” and the “contrast correction”. As described above, when performing a plurality of image processes on image data in which a plurality of defects are mixed, the effect may not be sufficiently obtained or may have an adverse effect depending on the order of the processes.
[0018]
As described above, in the case where a plurality of digital image processes are performed in combination, the techniques of Patent Literatures 1 to 5 are disclosed in order to solve the problem that the processed images differ depending on the order.
[0019]
However, each of the above techniques specifies a specific image processing, and adjusts and changes the processing order in the specified image processing. That is, if the combination of the processes performed in the digital image processing is different, the processing order is usually different.
[0020]
[Patent Document 1]
JP 2001-320581 A [Patent Document 2]
JP 2001-216509 A [Patent Document 3]
JP 2001177773 [Patent Document 4]
JP-A-11-345321 [Patent Document 5]
JP-A-10-285362
[Problems to be solved by the invention]
The problem to be solved by the present invention is to solve the above-mentioned problems, and “dots are conspicuous”, “unnecessary color is applied to the background”, “show-through occurs”, “brightness and contrast” Even if a plurality of defects such as "sufficiency" exist in the image data, the image quality can be improved by combining and applying a plurality of processes.
[0022]
[Means for Solving the Problems]
The present invention provides the following image processing method to solve the above technical problem.
[0023]
According to the first aspect of the present invention, image processing is performed on an acquired image by combining a plurality of halftone dot removal processes and at least one of background color removal, show-through removal, and contrast correction processes. An image processing method is provided, wherein the halftone removal processing is controlled to be performed first as a processing order of the plurality of processings.
[0024]
According to the second aspect of the present invention, image processing is performed on an acquired image by combining a plurality of combinations of a contrast correction process and one or more processes of background color removal, show-through removal, and halftone dot removal. An image processing method is provided, wherein control is performed such that a contrast correction process is performed last as a processing order of the plurality of processes.
[0025]
According to the third aspect of the present invention, a dot removal processing unit that performs a dot removal process on an acquired image, a background color removal processing unit that performs a background color removal process, and a show-through that performs a show-through removal process A correction processing unit including a removal processing unit and a contrast correction processing unit that performs contrast correction processing; and a processing selection unit that selects one or more processes from among the processing units of the correction processing unit and executes the processing. , When the plurality of processes including the halftone dot removal processing unit are selected by the process selection unit, the halftone dot removal processing unit is executed prior to the execution of the process by the other processing units. An image processing apparatus characterized by executing a process according to (1).
[0026]
According to a fourth aspect of the present invention, in the third aspect, when a process including a contrast correction processing unit is selected by the selection processing unit, the processing is performed by the contrast correction processing unit after execution of the processing by another processing unit. Provided is an image processing device that performs a process.
[0027]
According to a fifth aspect of the present invention, in the third and fourth aspects, the selection processing unit includes a selection unit for requesting a user to input selection information on which processing unit to perform processing. An image processing apparatus is provided.
[0028]
In each of the above-described configurations, any processing may be performed as the halftone dot removal processing as long as the processing makes the color of the halftone area uniform by the smoothing processing. In the background color removal processing and show-through removal processing, any processing may be performed as long as the processing can remove or reduce the background color and show-through. Further, in the contrast correction processing, any processing may be performed as long as the processing increases the lightness difference between the dark area and the bright area of the image, that is, enhances the contrast of the image.
[0029]
According to each configuration of the present invention, it is possible to improve image quality without causing side effects of mutual processing as much as possible.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an image processing system according to an embodiment of the present invention will be described with reference to the drawings.
[0031]
FIG. 1 is a block diagram showing a configuration of an image processing system according to an embodiment of the present invention. The image processing system 1 sends image data read by an image input device 2 typified by a scanner or the like as an acquired image to an image processing device 3 typified by a computer or the like. After being subjected to appropriate processing, it is stored in an image storage device 4 typified by a hard disk or the like. Alternatively, after appropriate processing is performed on the image data, the image data is sent to an image output device 5 such as a printer and output.
[0032]
FIG. 2 is a diagram showing the data flow in the block configuration diagram of the image processing system of FIG. 1 in more detail. The image processing apparatus 3 includes a correction selection processing unit 10, a reception unit 11, a halftone dot removal processing unit 12, a base color removal processing unit 13, a show-through removal processing unit 14, and a contrast correction processing unit 15. These are the functions of the image processing program installed in the image processing apparatus 3 which is a computer, and are realized by installing a program that exerts the function in the image processing apparatus.
[0033]
The correction processing selection unit 10 performs a halftone removal processing unit 12, a background color removal processing unit 13, a show-through removal, in order to perform only an image correction process that is predetermined or selected by a user of the image processing system. The processing section 14 sends selection information to the processing section 14 and the contrast correction processing section 15 to control the execution of the processing.
[0034]
The receiving unit 11 receives image data transmitted from the image input device 2. The receiving unit 11 transmits the image data input from the image input device 2 to the dot removal processing unit 12 inside the image processing device 3.
[0035]
The halftone removal processing unit 12 performs halftone removal processing on the image data based on the selection information input from the correction processing selection unit 10 when performing the process. The processed image data is sent to the background color removal processing unit 13.
[0036]
The background color removal processing unit 13 performs a background color removal process on the image data based on the selection information input from the correction process selection unit 10 when performing the process. The processed image data is sent to the show-through removal processing unit 14.
[0037]
The show-through removal processing unit 215 performs show-through removal processing on the image data based on the selection information input from the correction processing selection unit 10 when performing the processing. The processed image data is sent to the contrast correction processing unit 15.
[0038]
The contrast correction processing unit 15 performs contrast correction processing on the image data based on the selection information input from the correction processing selection unit 10 when performing the processing. The processed image data is sent to the image storage device 4 or the image output device 5. The image storage device 4 stores the received image data. The image output device 5 outputs the received image data.
[0039]
FIG. 3 is a flowchart of image correction performed by the image correction processing device. First, it is determined whether or not to perform the dot removal processing on the input image data based on the presence or absence of the selection information from the correction processing unit 10 (# 10). It is assumed that the user can freely select which correction process is to be performed, for example.
[0040]
The user can determine which of the processes is to be applied, for example, by using a correction process selection screen 20 as shown in FIG. Specifically, among the check boxes 21 to 24 corresponding to the respective correction processes displayed on the screen, a process in which the user optionally checks one or more check boxes is selected. FIG. 4 shows a state where the dot processing and the show-through removal processing are selected to be performed.
[0041]
When the dot removal processing is performed, the processing is performed on the image data by the dot removal processing unit 12 as described above (# 11). When the dot removal processing is not performed, the image data is passed through as it is.
[0042]
Next, it is determined whether or not to perform the background color removal processing on the image data on which the halftone dot removal processing has been performed (or the passed-through image data) based on the presence or absence of the selection information from the correction processing unit 10 (# 12). When performing the processing, the processing is performed on the image data by the base color removal processing unit 13 (# 13). If the background color removal processing is not performed, the image data is passed through as it is.
[0043]
Next, it is determined whether or not to perform show-through removal processing on the image data that has been subjected to the background color removal processing (or the image data that has been passed through) based on the presence or absence of the selection information from the correction processing unit 10 (# 14). When performing the process, the show-through removal processing unit 14 performs the process on the image data (# 15). If the show-through removal processing is not performed, the image data is passed through as it is.
[0044]
Finally, it is determined whether or not to perform contrast correction processing on the image data (or through image data) on which show-through removal processing has been performed, based on the presence or absence of the selection information from the correction processing unit 10 (# 16). ). When performing the processing, the processing is executed on the image data by the contrast correction processing unit 15 (# 17). If the contrast correction processing is not performed, the image data is passed through as it is.
[0045]
As described above, in the correction processing on the image data, the processing is performed such that the halftone dot removal processing is performed first and the contrast correction processing is performed last. The reason why the processing is performed in the above order is to improve the image quality without causing the side effects of the mutual processing as much as possible.
[0046]
Regarding the relationship between the halftone dot removal processing and the background color removal processing, for example, when a catalog material or the like having a light background color of an image is read by a scanner, the background may be a halftone dot. In this case, the background color is not uniform, and various colors are often mixed. If the background color removal processing is first performed on such image data, the correct background color cannot be determined, and a part of the background color remains. Therefore, by performing the halftone dot removal processing first, the background color is made uniform, and the background color of the background can be effectively removed.
[0047]
Regarding the relationship between the halftone dot removal processing and the show-through removal processing, when show-through occurs in a halftone dot area, the show-through area and its surrounding area often have various colors intermingled. If the show-through removal processing is first performed on such image data, the correction amount greatly differs for each pixel, and as a result, the image quality deteriorates. For this reason, by performing the halftone dot removal processing first, the color of the show-through area and its surrounding area is made uniform, and the show-through area can be effectively removed.
[0048]
In the relationship between the halftone dot removal processing and the contrast correction processing, if halftone dots and contrast correction processing are applied to an image in which halftone dots and insufficient contrast are mixed, the effect differs depending on the order. As shown in FIG. 5, when the contrast correction processing is performed first, the halftone dots are emphasized (see FIG. 5D), and the smoothing effect in the subsequent halftone dot removal processing may not be sufficient. For this reason, by performing the halftone dot removal processing first, it is possible to reduce the problem of emphasizing halftone dots by contrast correction.
[0049]
In the relationship between the contrast correction processing and the background color removal processing, for example, if the background color removal processing and the contrast correction processing are performed on an image in which the background is colored and the contrast is insufficient, the order is determined according to the order. Different effects. As shown in FIG. 6, when there is a difference in the brightness of the background color, if the contrast correction process is performed first, the color difference between the bright background color and the dark background color is enlarged, and the effect of the subsequent background color removal process is improved. There is a case where the background color of the dark area does not sufficiently appear and remains. Therefore, by performing the background color removal processing first, it is possible to reduce the problem of enhancing the background color by contrast correction.
[0050]
In the relationship between the contrast correction processing and the show-through removal processing, if show-through removal processing and contrast correction processing are performed on an image in which show-through has occurred and the contrast is insufficient, the effect will depend on the order. Are different. As shown in FIG. 7, since there is a difference in brightness between the show-through area and the surrounding area, if the contrast correction processing is performed first, the color difference between the show-through area and the surrounding area is enlarged, and the subsequent show-through removal processing is performed. The effect may not be sufficient, and show-through may remain. Therefore, by performing the show-through removal processing first, it is possible to reduce the problem of enhancing show-through due to contrast correction.
[0051]
That is, by performing the dot removal processing first, the disadvantage that the dots are emphasized by the contrast correction is reduced. Further, since the color of the halftone dot area is made uniform, the effect of the background color removal processing and the show-through removal processing is enhanced.
[0052]
Further, by finishing the contrast correction processing, the contrast correction processing can be performed in a state where the halftone dots, the background color, and the show-through have been removed in advance. That is, it is possible to reduce the phenomenon that the contrast correction process deteriorates a defect such as a halftone dot, a background color, or show-through.
[0053]
As a modification of the above-described embodiment, the show-through removal processing detects a show-through area and a background area as described in Japanese Patent Application Laid-Open No. 2001-169080 and sets the color of the show-through area to the background. Processing such as replacement with the color of the area may be performed. In this case, in order to remove show-through, it is necessary to divide each area such as show-through area / background area / background area. In the area division processing, areas of similar brightness / saturation / hue are generally connected to each other, and for this purpose, it is desirable that the color of each area be uniform. For this reason, by pre-equalizing the colors in the halftone area by the halftone removal processing, the area division processing can be performed effectively, and as a result, the performance of the show-through removal processing is improved. That is, as described above, it is desirable to perform the processing in the order of removing show-through before removing halftone dots.
[0054]
In the above-described embodiment, the processing is performed in the order of removal of background color and removal of show-through. This is because the show-through that occurs on a colored background is more effective if the background color is removed first and then another processing (all white or skipping white) is performed as a show-through for a white background area. Is high.
[0055]
However, the order of these two processes is not particularly limited. Furthermore, two processes may be combined into one. For example, since both the background color and show-through often occur in relatively bright areas, forcibly whitening pixels with high lightness and low saturation, or emphasizing contrast to brighten out bright areas, Under color and show-through can be removed at the same time.
[0056]
In the above-described embodiment, a process is selected from among four processes. However, in practice, image processing may be additionally performed. Here, for example, a process for improving image quality such as an edge enhancement process is desirably applied after performing a contrast correction process, that is, after removing a defect of an image.
[0057]
As described above, according to the embodiment, even when a plurality of defects are mixed in an image, a plurality of processes are performed in an optimal order without the user being particularly aware of the order of the processes. It can be applied.
[0058]
The present invention is not limited to the above embodiment, but can be implemented in various other modes.
[0059]
In the above-described embodiment, the user selects an arbitrary process. However, the present invention is not limited to this, and all processes may be performed collectively. In this case, the user can perform all the processing on the image data by clicking a button such as “automatic image correction”. In addition, not all the processes but two or three processes may be collectively processed.
[0060]
In the above-described embodiment, each process has been described with specific examples. However, the method of each processing is not limited to this. For example, as the dot removal processing, it is possible to simply perform smoothing processing on the entire image without performing dot detection. Also in this case, as described above, it is desirable to perform the dot removal processing first.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an image processing system according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a data flow in the image processing system of FIG. 1 in more detail.
FIG. 3 is a flowchart of image correction performed by the image correction processing device.
FIG. 4 is a screen display example of a correction processing selection screen when a user sets processing to be applied;
FIG. 5 is a diagram for explaining a difference in effect depending on a processing order of a contrast correction process and a tug-point removal process.
FIG. 6 is a diagram for explaining a difference in effect depending on a processing order of a contrast correction process and a background color removal process.
FIG. 7 is a diagram illustrating a difference in effect depending on the processing order of the contrast correction processing and the show-through removal processing.
FIG. 8 is a flowchart showing a flow of a conventional halftone dot removing process.
FIG. 9 is a diagram illustrating an isolated point detection filter used in the dot removal processing.
FIG. 10 is a diagram illustrating a smoothing filter used in the dot removal processing.
FIG. 11 is a flowchart showing the flow of a conventional undercolor removal process.
FIG. 12 is a diagram illustrating an effect of a background color removal process.
FIG. 13 is a flowchart showing the flow of a conventional undercolor removal process.
FIG. 14 is a diagram illustrating the effect of show-through removal processing.
FIG. 15 is a diagram illustrating a tone curve used in the contrast correction processing.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 image processing system 2 image input device 3 image processing device 4 image storage device 5 image output device 10 correction selection processing unit 11 reception unit 12 halftone dot removal processing unit 13 background color removal processing unit 14 show-through removal processing unit 15 contrast correction processing Department

Claims (5)

An image processing method for performing a combination of a plurality of halftone dot removal processes and one or more processes of each of a background color removal process, a show-through removal process, and a contrast correction process on an acquired image. An image processing method characterized by performing control such that halftone removal processing is performed first as a processing order. An image processing method for performing a plurality of combinations of a contrast correction process and at least one of a background color removal process, a show-through removal process, and a halftone dot removal process on an acquired image. An image processing method, characterized in that control is performed such that contrast correction processing is performed last as a processing order. Performs a dot removal processing unit that performs a dot removal process on the acquired image, a background color removal processing unit that performs a background color removal process, a show-through removal processing unit that performs a show-through removal process, and performs a contrast correction process. Correction processing means comprising a contrast correction processing unit;
A process selecting unit that selects one or more processes from among the respective processing units of the correction processing unit and executes the process.
When a plurality of processes including the halftone dot removal processing unit are selected by the process selection unit, the process is executed by the halftone dot removal processing unit prior to execution of the process by another processing unit. Processing equipment. The method according to claim 3, wherein when a process including a contrast correction processing unit is selected by the selection processing unit, a process by the contrast correction processing unit is executed after execution of a process by another processing unit. Image processing device. The image processing apparatus according to claim 3, wherein the selection processing unit includes a selection unit that requests a user to input selection information indicating which processing unit performs processing.

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