JP2003234912A - Image processing method, image processing apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus capable of surely determining that each of pixels in a target region, such as a character image is chromatic or achromatic, by correcting the influence of reading errors or the like. <P>SOLUTION: The apparatus determines that a pixel determined belonging to at least either the high-density portion of a target pixel region, having stable color information, or the low-density portion of the region is chromatic or achromatic. Since the color information of a target pixel processed is represented by color information of either a first color or a second color, by recognizing that the first and second colors are chromatic or achromatic, except the intermediate density portion where color shift may occur on account of reading errors due to mechanical vibration, it can be surely determined that the target pixel is chromatic or achromatic. In this way, it is surely determined that the two colors of the target pixel region, i.e., the first and second colors are chromatic or achromatic, and an output image can be enhanced in reproducibility. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method for determining input image data input by an image input device or the like as a character area and determining whether a character in the character area is chromatic or achromatic. And an image processing apparatus and an image forming apparatus. In this specification, the approximate color group means a group of a certain color and a color having a lightness, saturation and hue close to that color.

[0002]

2. Description of the Related Art An image input device for reading an image formed on an original document stores color components related to tristimulus values red, green and blue from an original image in a stored charge coupled device (charge c).
Oupled device: Abbreviated as CCD) A color image component obtained by a solid-state image sensor such as an image sensor is supplied as an analog signal to the image processing apparatus as input image data representing a document image.

The conventional image processing apparatus is configured to enhance the reproducibility of the original image by switching the processing for improving the image quality based on the color information of the pixels belonging to the character area included in the input image data. Has become. When it is determined that the character area is a black character area, the achromatic color correction processing is performed so that the color components of cyan, magenta, and yellow are completely removed and represented by black. Also, when it is determined that the color character area includes chromatic color characters, on the contrary, instead of being expressed in black, cyan,
A chromatic color correction process is performed using magenta and yellow so as to represent the image area. In this way, the image processing apparatus corrects the input image data with achromatic color or chromatic color, and supplies the corrected image data as output image data to the image forming apparatus.

The image forming apparatus provided with the output image data forms a clear output image based on the image data corrected by the image processing apparatus. Therefore, in order to form a clear output image on the image forming apparatus, the image processing apparatus needs to determine whether each pixel of the image represented by the input image data is chromatic or achromatic.

In the image input device used conventionally, noise which does not exist in the original image may occur in the input image data. Further, when a plurality of color components are used as input values, the image represented by the input image data may have color component misalignment with respect to the original image. In this way, the original image and the image represented by the input image data are not always equal. In order to obtain input image data representing the same image as the original image, it is necessary to use an extremely accurate image input device, which is unrealistic.

When the image represented by the input image data is not equal to the original image and the chromatic or achromatic color correction is performed by the image processing apparatus as described above, the image represented by the corrected image data becomes , The reproducibility of the original image is reduced. For example, when the image processing apparatus erroneously determines a color shift that occurs in the peripheral portion of the black character area as a chromatic color, the originally black character portion is chromatically corrected as a colored portion by cyan, magenta, and yellow. Further, when the highlighting process is performed to improve the readability of the characters, the hue due to the color shift is further emphasized, and an image different from the original image of the original image may be formed.

Conventionally, in order to determine the chromatic / achromatic color of the target pixel in the input image data, the density of the color component of each pixel in a predetermined range including the target pixel is checked to determine the chromatic / achromatic color of the target pixel. There is an image forming apparatus. For example, JP-A-5-16
The image processing apparatus of the related art disclosed in Japanese Patent No. 7842 determines whether the predetermined area is a black character area or a color character area by obtaining the sum of the density differences for each pixel in the predetermined area.

Further, in another conventional image processing apparatus disclosed in Japanese Patent Laid-Open No. 5-56287, whether the target pixel is a chromatic color by using the maximum density difference among cyan, magenta and yellow in the target pixel. It is determined whether or not it is an achromatic color, and the pixel group determined as a chromatic color pixel is further 3 ×.
It is expanded by 3 pixels and then contracted by 5 × 5 pixels. As a result, due to the color shift, the pixel of interest erroneously determined as a chromatic color is corrected to an achromatic pixel.

[0009]

[Patent Document 1] Japanese Patent Application Laid-Open No. 5-16784
The image processing apparatus of the prior art disclosed in Japanese Patent Laid-Open No. 2 discloses a sum average value of density differences between color components of pixels belonging to a predetermined area including a target pixel, and thresholds the sum average value. By doing so, it is determined whether the pixel of interest is a chromatic color or an achromatic color.

When color misregistration occurs in the image represented by the input image data due to an image reading error or the like, particularly in the peripheral pixels of the black character pixels, pseudo color pixels which do not originally exist in the original document due to the reading error occur. , The density difference between the color components of each pixel increases, and black characters may be erroneously determined as color pixels. That is, when a color shift occurs in the input image data due to a reading error or the like, there is a possibility that the pixel of interest may be erroneously determined as a chromatic color pixel even if it is originally achromatic.

Another prior art image processing apparatus disclosed in Japanese Patent Laid-Open No. 5-56287 calculates a maximum density difference between color components of a pixel of interest, and based on the maximum density difference, the pixel of interest is detected. Achromatic and achromatic are judged. By expanding or contracting each pixel of interest that has been determined to be chromatic in a predetermined image area, pixels that have been erroneously determined to be chromatic due to noise and color shift errors during image reading are removed. However, since the chromatic / achromatic color is determined by the target pixel alone, the target pixel cannot be sufficiently recognized as an achromatic pixel. For example,
When a pixel originally representing a black thin line has a color shift, the thin line may be corrected to have the same color as the background color by being expanded and reduced. Therefore, the other conventional image processing apparatuses also cannot correct the color-shifted pseudo color pixels, which causes a problem that the reproducibility of the output image with respect to the original image is deteriorated.

Therefore, an object of the present invention is to correct the influence of a reading error or the like, and to have a chromatic achromatic image of each pixel of a target area having pixels of an approximate color group which is a set of two approximate colors such as a character image. It is an object of the present invention to provide an image processing device capable of accurately determining.

[0013]

According to the present invention, a target pixel area having pixels of an approximate color group, which is a group of two approximate colors, from an image in which colors of a plurality of pixels are represented by a plurality of color components. And a second step of extracting a high-density portion having a high density of color components in the target pixel area and a low-density portion having a low density of color components in the target pixel area; Based on the color information of the determination pixel belonging to at least one of the portion and the low-density portion,
And a third step of determining whether the target pixel to be processed included in the target pixel area is a chromatic color or an achromatic color.

According to the present invention, in the third step, it is determined whether the color of the target pixel to be processed is a chromatic color or an achromatic color. The target pixel area is a character area that is composed of pixels of an approximate color group that is a group of two similar colors, and is composed of pixels that represent a background portion and a character portion, for example.
By determining the chromatic / achromatic color of each target pixel to be processed in the target pixel area, it is possible to determine whether the target pixel area is chromatic or achromatic.

The target pixel area has pixels of an approximate color group, which is a group of two approximate colors. The plurality of pixels forming the target pixel area are divided into pixels having high density and low density of color components. A pixel represented by the input image data may have a pseudo-color pixel portion which is originally achromatic but is input as a chromatic color due to a reading error of the image input device due to noise and mechanical vibration. Further, due to the above-mentioned reading error, pixels of intermediate density color of high density color and low density color may be formed at the edge portion (intermediate density portion) of the target pixel area.

According to the present invention, at least one of the high-density portion of the target pixel area and the low-density portion of the target pixel area, the color information of which is stable, is excluded, except for the intermediate density portion of the target pixel area caused by the reading error. It is possible to determine whether the high-density color and the low-density color of the target pixel area are chromatic or achromatic by determining the chromatic / achromatic color of the determination pixel that belongs to. Originally, the color information of the target pixel to be processed is represented by the color information of either the high-density color or the low-density color, so it is necessary to recognize the chromatic achromaticity of the high-density color and the low-density color with stable color information. This makes it possible to accurately determine whether the target pixel to be processed is originally a chromatic color or an achromatic color.

Further, according to the present invention, a target area for extracting a target pixel area having pixels of an approximate color group, which is a set of two approximate colors, from an image in which colors of a plurality of pixels are represented by a plurality of color components. An extraction unit, a determination pixel portion extraction unit that extracts a determination pixel portion including at least one of a high-density portion having a high color component density and a low-density portion having a low color component density in the target pixel region; And a chromatic / achromatic determination unit that determines whether the target pixel to be processed included in the target pixel region is a chromatic color or an achromatic color based on color information of the determination pixel belonging to the determination pixel portion. Is an image processing device.

According to the present invention, the chromatic / achromatic determination unit determines whether the target pixel to be processed is a chromatic color or an achromatic color. The target pixel area has pixels of an approximate color group, which is a group of two approximate colors. The plurality of pixels forming the target pixel area are divided into pixels having high density and low density of color components. If a reading error occurs in the image input device,
In the input image data, a pixel portion represented by the intermediate density between the high density color and the low density color is formed in the pseudo color pixel area or the intermediate density area of the target pixel area.

The determination pixel portion extraction unit extracts the determination pixel portion including at least one of the high density portion and the low density portion, excluding the intermediate density portion of the target pixel area. Since the intermediate density portion is an unstable portion where the color of the pixel is not stable, the chromatic / achromatic determination of the determination pixel included in the determination pixel portion formed by the stable color pixels excluding the intermediate density portion is determined. By doing so, it is possible to accurately determine whether the high-density color and the low-density color are chromatic colors or achromatic colors. Originally, the color information of the target pixel to be processed is represented by the color information of either the high-density color or the low-density color, and therefore it is determined whether the high-density color and the low-density color are chromatic or achromatic. By doing so, it is possible to accurately determine whether the target pixel to be processed is originally a chromatic color or an achromatic color.

Further, the present invention further includes an edge determining unit which determines whether or not the target pixel to be processed belonging to the target pixel area is an edge, and the chromatic / achromatic determining unit determines that the target pixel to be processed is a chromatic color. A first determining unit that determines whether the target pixel is a target pixel to be processed, a second determining unit that determines whether the determination pixel is a chromatic color or an achromatic color, and first and second It is characterized by further comprising a third determination unit that determines again whether the target pixel to be processed is a chromatic color or an achromatic color based on the determination result of the two determination units.

According to the present invention, the chromatic / achromatic determination unit has the first
The determination unit determines whether the target pixel to be processed is a chromatic color or an achromatic color by the target pixel to be processed alone, and the second determination unit determines whether the determination pixel belonging to the determination pixel portion is a chromatic color or not. It is determined whether or not it is colored, and based on the determination results of the first determination unit and the second determination unit, the third determination unit
It is determined again whether the target pixel to be processed is a chromatic color or an achromatic color. As described above, the chromatic / achromatic color of the processing target pixel can be accurately determined by determining the chromatic / achromatic color of the processing target pixel based on the determination results of the determination pixel and the processing target pixel. it can.

Since the edge determining unit can determine whether the target pixel to be processed is an edge, it is possible to determine whether the target pixel to be processed is a pixel belonging to a character portion or a background portion. You can

Further, according to the present invention, the determination pixel portion extraction unit is
A sub-target pixel portion including a target pixel in the area belonging to the target pixel area and a plurality of pixels around the target pixel in the area is set, and based on color information of each pixel belonging to the sub-target pixel portion, within the area A sub-target pixel portion setting unit that sets color information of the target pixel is provided, and the determination pixel is extracted based on the color information of the target pixel in each area set by the sub-target pixel portion setting unit. And

According to the invention, the sub target pixel portion setting unit sets the color information of the target pixel in the area based on the color information of each pixel belonging to the sub target pixel portion, and the sub target pixel portion setting unit sets the color information. Based on the set color information of the target pixel in the area, the target pixel in the area belonging to the determination pixel portion is extracted as the determination pixel.

When a deviation occurs in each color component due to a reading error, one or a plurality of color components of the original color component are input to the pixel around the pixel of interest while being shifted. For example, if the target pixel, which originally has cyan, magenta, and yellow color components and has a color shift of cyan to the target pixel represented by black, has the color components of magenta and yellow, and the target pixel is adjacent to the target pixel. The pixel to be converted contains a cyan color component.

Since the color information of the pixel of interest in the area is set based on the color information of each pixel belonging to the sub-target pixel portion,
Even if the pixel of interest in the area has a color shift,
It is possible to reduce the influence of the deviation of the color component of the determination pixel from the color information of the pixels around the target pixel in the area. As a result, the original color information of the pixel of interest in the area corresponding to the original image can be estimated. With this, it is possible to determine whether or not the pixel of interest in the region where the original color information is estimated belongs to the determination pixel portion, and it is possible to more accurately extract the determination pixel that belongs to the target pixel region. .

Further, according to the present invention, the determination pixel portion extraction unit is
The maximum and minimum densities of the average densities of the color components and the difference between the maximum and minimum densities are multiplied by a predetermined value to obtain a value. When the high density part is extracted by using the value obtained by multiplying the maximum density of the values and the difference between the maximum density and the minimum density by a predetermined value, and the low density part is extracted, the minimum density of the average value of the density of the above color components The low density portion is extracted using a value obtained by multiplying the difference between the highest density and the lowest density by a predetermined value.

According to the present invention, the determination pixel part extraction unit obtains the maximum density and the minimum density of the average values of the color components, and determines the maximum density and the maximum density and the minimum density of the average values of the color components. The high density part is multiplied by a predetermined value and the lowest density of the average value of the color components, and the difference between the highest density and the lowest density is multiplied by a predetermined value. Extract low-density areas. As a result, it is possible to set the determination pixel portion having a further limited range by using the high-density portion having a higher density and the low-density portion having a lower density. Higher high-density portions are likely to include high-density color pixels in the target pixel area, and lower low-density portions are likely to include low-density color pixels in the target pixel area. Therefore, by determining the chromatic / achromatic color of the determination pixels belonging to the determination pixel portion whose range is further limited, it is possible to determine whether the high-density color and the low-density color of the target pixel area are chromatic colors or more accurately. Can be determined. This makes it possible to more accurately determine whether the target pixel to be processed is a chromatic color or an achromatic color.

Further, according to the present invention, the determination pixel portion extraction unit is
While extracting at least one of the high-density portion and the low-density portion, the determination pixel portion including at least one of the high-saturation portion with high saturation and the low-saturation portion with low saturation in the target pixel area is extracted. It is characterized by doing.

According to the present invention, the determination pixel portion extraction unit extracts the determination pixel portion including at least one of the high saturation portion and the low saturation portion in the target pixel area. As a result, when the difference in density is not clear, it is not clear that the high-density color and the low-density color of the target pixel area are distinct.
For example, even when the first color is yellow and the second color is white, the target pixel area can be easily converted into pixels of two colors due to the difference in saturation of the color components of the target pixel area. Can be divided into

By excluding the intermediate saturation part between the high saturation part and the low saturation part, pixels of high saturation color stably belong to the high saturation part, and stable low saturation part belongs to the low saturation part. Chromatic pixels belong. Therefore, the chromatic / achromatic color of the high-saturation color can be determined by determining the chromatic / achromatic color of the determination pixel belonging to the high-saturation portion, and the chromatic / achromatic color of the determination pixel belonging to the low-saturation portion can be determined. Thus, it is possible to determine the chromatic / achromatic color of the low saturation color.

As described above, the chromatic / achromatic color of the target pixel to be processed can be determined more accurately by dividing the target pixel region into two approximate pixel groups based on the saturation difference in addition to the density difference.

Further, according to the present invention, the chromatic / achromatic judgment unit determines whether or not a color component shift occurs in the pixel of interest to be processed based on the judgment results of the first judgment unit and the third judgment unit. It is characterized by having a color misregistration determination unit for determining.

According to the present invention, the color shift determining section
Since it is possible to determine whether or not the color component shift has occurred, it is possible to detect the color shift portion in which the color component shift of the target pixel region has occurred, based on the determination result.

Further, according to the present invention, it is determined whether the target pixel to be processed is a chromatic color character, an achromatic color character, or a color shift character based on the judgment results of the edge judgment section and the chromatic / achromatic judgment section. In addition, if the number of processing target pixel of interest that is a color-shifted character and the number of processing target pixels of interest that are determined to be a color-shifted character is greater than or equal to a predetermined threshold value, a color-shifted character is used. And a notification unit that notifies that a certain pixel to be processed exists.

According to the present invention, the color character determination unit
By obtaining the processing target pixel of interest that is the color misaligned character and notifying that the processing target pixel of interest that is the color misaligned character exists, the accuracy of the image input device regarding the color misregistration can be evaluated.

The present invention is also an image forming apparatus including the image processing apparatus.

According to the present invention, the image forming apparatus is provided with the above-mentioned image processing apparatus, so that an error at the time of reading the original input image is corrected so that each pixel has a chromatic color. An achromatic color can be accurately determined, and an output image with high reproducibility can be obtained.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Image input devices such as digital scanners and digital still cameras for reading original images are
Monochrome or color information of the image, tristimulus value red,
It is converted into color components relating to green and blue, and such data is given to the image processing apparatus as input image data representing a document image.

The image processing apparatus according to the embodiment of the present invention is
Each area of the character area, halftone dot area, and photographic area included in the input image data is identified by a local unit based on the color information, and the image quality improvement processing is switched according to the characteristics of each area, so that the original image It is designed to enhance reproducibility.

The image processing apparatus complements the detection result of the edge portion showing a sharp density change in the input image data with the three stimulus values of red, green, and blue, and complements them by 3
The character area is extracted based on the color information represented by the color components of cyan, magenta, and yellow, which are stimulus values, and it is determined whether the character area is color or monochrome. Then, a correction process such as an emphasis process is performed on the determined character region to correct the image data with high reproducibility of the character region at the time of output.

The image processing apparatus uses cyan Cin and magenta M, which are tristimulus values obtained by complementing the input image data represented by the color components of the tristimulus values of red, green and blue.
in and yellow Yin, then the image represented by the input image data is separated into predetermined small areas, and it is determined whether the image represented by the small areas is a character area, a halftone dot area, or a photographic area. If the small area is a character area, the color of the character image is determined.

FIG. 1 is a block diagram showing the configuration of the color determination section 100. The color determination unit 100 determines that a processing target pixel of interest (hereinafter simply referred to as pixel of interest 1)
04)), a target area extraction unit 101 that extracts a mask 105 that is a target pixel area including a target pixel area, and a determination pixel portion extraction unit that extracts a determination pixel for determining whether the target pixel 104 is a chromatic color or an achromatic color. A chromatic / achromatic determination unit 103 that determines whether the pixel of interest 104 is a chromatic color or an achromatic color using the color information of the pixel 102 and the pixel of interest 104 and the determination pixel.
It is configured to include and. The target pixel region has a first color and a first color composed of a color similar in brightness, saturation, and hue to the first color.
The pixels of the approximate color group and the first approximate color group are different from each other in the second approximate color group consisting of a second color having different lightness, saturation and hue and a color having similar lightness, saturation and hue to the second color. It is configured to include pixels. The first approximate color group and the second approximate color group are collections of colors that have different color components and are distinguishable from each other. For example, the target pixel area is a character area, and is composed of pixels of the first approximate color group forming the character portion and pixels of the second approximate color group forming the background portion.

The target area extraction unit 101 divides the character area and extracts the mask 105 which becomes the target pixel area. The mask 105 is composed of M × N pixels and includes a target pixel 104. For example, the mask 105 has the pixel 1 of interest.
It is composed of 7 × 7 pixels centered on 04.

The target area extraction unit 101 includes an image storage device such as a hard disk device for storing one original image, and preferably includes a plurality of line memories 115 for storing the size of the original main scanning direction. By using the line memory 115, the processing speed can be improved and the processing can be performed in real time without increasing the capacity of the memory as compared with the hard disk. Also, the cost can be reduced.

FIG. 2 is a schematic diagram showing the structure of the line memory 115. The line memory 115 is a first-in-first-out memory (First In First Out: abbreviated as FIFO) and outputs input data in the order in which they are input. For example, a line memory 115 can be provided for each color component of 6 line memories, that is, 3 × 6, and a mask 105 formed by a 7 × 7 pixel region can be formed around the target pixel 104.

The size of the mask 105 described above is merely an example of the present invention and does not necessarily limit the size of the mask 105. For example, a mask of any size can be formed by increasing the number of line memories and by using a storage device such as a hard disk.

As shown in FIG. 1, the determination pixel portion extraction unit 1
02 includes a maximum / minimum calculation unit 107, a color component average value calculation unit 106, a high-density portion detection unit 108, and a low-density portion detection unit 109. The color component average value calculation unit 106 receives the pixel information in the mask 105 from the target area extraction unit 101. The color component average value calculation unit 106 calculates the density average value of each pixel in the mask and gives the calculation result to the maximum / minimum calculation unit 107. Maximum / minimum calculation unit 107
Determines the maximum value and the minimum value of the average density value in the mask, and sets a high density portion having a high density and a low density portion having a low density with respect to the pixels in the mask. Also, the maximum / minimum calculation unit 107
Gives the calculation result to the high-density portion detection unit 108 and the low-density portion detection unit 109.

The high-density portion detection unit 108 receives the calculation result of the maximum / minimum calculation unit 107, and detects, in other words, extracts a high-density determination pixel belonging to the high-density portion from each pixel in the mask.

The low-density portion detection unit 109 receives the calculation result of the maximum / minimum calculation unit 107, and detects, or extracts, the low-density determination pixels belonging to the low-density portion from each pixel in the mask.

The chromatic / achromatic judgment section 103 is a pixel color judgment section 113 of interest which is a first judgment section, a high density / low density partial color judgment section 112 which is a second judgment section, and a third judgment section. The overall determination unit 114 and the color shift determination unit 115 are included. The high-density / low-density color determination unit 112 is composed of a determination pixel color determination unit 110 and a counting unit 111, and the color of each determination pixel belonging to the high-density portion and the low-density portion is chromatic or achromatic. Determine if there is.

The judgment pixel color judgment unit 110 receives the information of the judgment pixels belonging to the high density portion and the low density portion from the high density portion detection unit 108 and the low density portion detection unit 109, and each judgment pixel has a chromatic color. Or the achromatic color is determined, and the determination result is given to the counting unit 111. The counting unit 111
By counting the determination pixels determined by the color determination processing unit 110 as chromatic colors and comparing them with a predetermined threshold value,
It is determined whether the high-density portion and the low-density portion are chromatic or achromatic.

The pixel-of-interest color determination section 113 determines the pixel-of-interest 10
Based on the color information of 4 itself, it is determined whether the color of the pixel of interest 104 is a chromatic color or an achromatic color. The total color determination unit 114 receives the determination results of the high-density / low-density partial color determination unit 112 and the target pixel color determination unit 113, and determines whether the target pixel 104 is a chromatic color or an achromatic color based on each determination result. To judge. The color misregistration determination unit 115 receives the determination results of the comprehensive determination unit 114 and the pixel-of-interest color determination unit 113, and determines whether the pixel of interest 104 has a color misregistration based on each determination result. In this way, the chromatic / achromatic determination unit 103 determines whether the pixel of interest 104 is a chromatic color or an achromatic color, determines whether there is a color shift, and outputs the determination result.

FIG. 3 is a flowchart showing the pixel color determination operation according to the embodiment of the present invention. Step a0
If it is determined that the image represented by the input image data includes a character area, the process proceeds to step a1 to determine whether each pixel belonging to the character area has a chromatic color or an achromatic color. The color determination operation of is started. The color of a pixel is, for example, a color component of input image data, a color component in which red R, green G, and blue B are complemented, and cyan C.
It is determined by the density values of in, magenta Min, and yellow Yin.

At step a1, the target area extraction unit 101
Thus, a mask 105 that includes a pixel centered on the target pixel 104 and divides the character region is formed. If the coordinates of the pixel of interest 104 in the character region are (i, j), the cyan density of the pixel of interest 104 is Cin, the magenta density is Min, and the density of yellow Yin, the input signal value at this pixel of interest 104 is ( Cin (i,
j), Min (i, j), Yin (i, j)). When the mask 105 is formed with 7 × 7 pixels as described above, the mask 10 including the pixel P (m, n)
5 is given by the following equation.

[0056]

[Equation 1]

At this time, each pixel in the mask is given an individual identification number K for each pixel. For example, when the mask 105 has 7 × 7 pixels, identification numbers 1 to 49 are assigned to each pixel. When such a mask 105 is extracted, the process proceeds to step a2.

In step a2, the color component average value calculation unit 1
From 06, the average value of the density values of the color components in the mask 105 is calculated. Next, the maximum / minimum calculation unit 107
The maximum and minimum densities of the average density values of the color components in the mask 105 are detected. The maximum density of the average value of the color components in the mask 105 centered on the pixel of interest 104 is Top
If (i, j) and the lowest density is Bot (i, j), then each density value Top (i, j), Bot (i, j) is
It is given by the following formula.

[0059]

[Equation 2]

Maximum density of the average value of color components Top (i,
j) and the lowest density Bot (i, j) of the average value of the color components
Is detected, the process proceeds to step a3.

In step a3, the maximum / minimum calculation unit 107
Thus, among the pixels in the mask, a high-density portion (Ha (i, j)) formed by a high-density pixel and a low-density portion (La by a low-density pixel)
(I, j)) is determined. FIG. 4 is a schematic diagram showing the distribution of the average density values of the color components of the pixels in the mask. High concentration part (Ha (i, j)) and low concentration part (La (i, j)
The pixel belonging to j)) is the average value (C +) of the color components of each pixel.
Using M + Y) / 3, it is determined, for example, by the following equation.

[0062]

[Equation 3]

Here, the coefficient TH is preset with an arbitrary real number of 0≤TH≤1. High concentration part (Ha (i, j))
Is the maximum density of the average value of the color components in the mask Top (i,
It is a portion extending from j) to a region where the density is low by a predetermined range. For example, the predetermined range is the maximum density T of the average value of the color components.
op (i, j) and the minimum density Bot of the average value of the color components
Difference from (i, j) (TOP (i, j) -Bot (i,
j)) is the density range obtained by multiplying the coefficient TH. Similarly, the low-density portion (La (i, j)) is a portion extending from the lowest density Bot (i, j) of the average value of the color components in the mask to a region having a high density by a predetermined range. For example, the predetermined range is the difference (TO between the maximum density TOP (i, j) of the average value of the color components and the minimum density Bot (i, j) of the average value of the color components.
It is a density range obtained by multiplying P (i, j) -Bot (i, j)) by the coefficient TH.

Each density portion (Ha (i, j))
When (La (i, j)) is detected, the process proceeds to step a4. In step a4, first, the pixel having the identification number K set in step a1 is selected, the selected pixel is set as the target pixel in the area, and the process proceeds to step a5.

In step a5, first, the color component average value calculation unit 106 causes the average density value In of the target pixel in the region to be In.
(M, n) is calculated. Mask Mask _i, the coordinates of the area of interest pixel belonging to the _{j (m, n) ∈Mask i} , when the _j, average density value of the region within the pixel of interest In (m, n) is
It is expressed by the following formula.

[0066]

[Equation 4]

When the density average value of the target pixel in the area is calculated, the high-density portion detection unit 108 determines whether or not the target pixel in the area belongs to the high-density portion. That is, it is determined whether or not the density average value of the target pixel in the region belongs to the high density portion. The density average value In (m, n) of the pixels belonging to the high density portion satisfies the following expression.

[0068]

[Equation 5]

If the selected target pixel in the area belongs to the high density portion, the target pixel in the area becomes the high density determination pixel, and the process proceeds to step a6. If not, the process proceeds to step a8. In step a6, the determination pixel color determination unit 110 determines whether the high density determination pixel is a chromatic color or an achromatic color. When the high-density determination pixel having the coordinates (m, n) is chromatic, the condition of the following equation is satisfied.

[0070]

[Equation 6]

That is, the difference between the highest density color component and the lowest density color component of the judgment pixel is the color judgment threshold value THc.
If it is larger than color, it is determined that the determination pixel is a chromatic color. Also, the color determination threshold value THcolor
May be preset as shown in FIG. 3, and the color determination threshold value T may be set in accordance with the density value of the determination pixel.
You may set Hcolor.

For example, as an example of setting the color determination threshold THcolor according to the density value, when the density values of cyan, magenta and yellow are low, that is, on the highlight side, the maximum density difference between the color components is low. Therefore, a low value is set as the color determination threshold value. When the density values of cyan, magenta, and yellow are high, the maximum density difference between the color components becomes high, so a high value is set as the color determination threshold value. For example, the color determination threshold THcol
or is set according to the following equation, and the color determination threshold value differs depending on the size of the minimum density value min (C, M, Y) of the color components of the determination pixel.

[0073]

[Equation 7]

However, THintensity1 <TH
intensity2 <THintensity3.

As described above, one of a plurality of color judgment threshold values may be selected according to the density of the target pixel in the area,
It is also possible to set different thresholds for the case of belonging to the high density portion and the case of belonging to the low density portion.

At step a6, as described above, the determination pixel color determination section 110 determines whether or not the color of the high density determination pixel is chromatic, and if determined to be chromatic, the process proceeds to step a7. If not, the process proceeds to step a8. In step a7, the counting unit 111 integrates and counts one high-density determination pixel,
Go to 8. In step a6, the chromatic / achromatic color of the target pixel in the region is determined based on the maximum density difference among cyan, magenta, and yellow. However, the color determination may be performed by another method.

In step a8, the color component average value calculation unit 1
Using the density average value of the target pixel in the area calculated in 06, the low-density portion detection unit 109 determines whether the target pixel in the area belongs to the low-density portion. The density average value In (m, n) of the pixels belonging to the low density portion satisfies the following expression.

[0078]

[Equation 8]

If the selected target pixel in the area belongs to the low density portion, the target pixel in the area becomes the low density determination pixel, and the process proceeds to step a9. If not, the process proceeds to step a11. In step a9, the threshold value is processed by the determination pixel color determination unit 110 by the preset fixed threshold value shown in FIG. 3 as in step a6 or the threshold value switched according to the density value of the determination pixel. By doing so, it is determined whether the low-density determination pixel is a chromatic color or an achromatic color. Specifically, it is determined whether or not the pixel determined to be the low density determination pixel in step a8 satisfies the above-mentioned formula 6. At this time, the color determination threshold value TH
A different value from that used in step a6 is used for color2. If it is determined that the color is chromatic, the process proceeds to step a10, and if not, the process proceeds to step a11. In step a9, the chromatic / achromatic color of the target pixel in the area is determined based on the maximum density difference among cyan, magenta, and yellow, but the color determination may be performed by another method. In step a10, the counting unit 111 integrates and counts one low-density determination pixel, and then proceeds to step a11.

At step a11, the determining pixel color determining section 110 determines whether or not the identification number K set for the selected target pixel in the region is the maximum, and if it is determined to be the maximum, the step is determined. If it is determined that it is not, the process proceeds to step a12. Step a12
Is a new identification number K + obtained by adding 1 to the identification number K
The pixel marked with 1 is set as the target pixel in the area, and step a5
And repeat steps a5 to a11.

In step a11, the determination pixel color determination unit 110 determines that the identification number K set for the selected target pixel in the area is the maximum, that is, all pixels in the mask are determined. Then, the process proceeds to step a13. At step a13, the counting unit 1
11, it is determined whether the colors of the determination pixels belonging to the high density portion and the low density portion are chromatic or achromatic.
The counting unit 111 belongs to the high-density portion, and the number CH: count of pixels determined to be chromatic indicates a predetermined threshold value TH.
If it is larger than color_num_high, it is determined that the high-density portion is chromatic, and if the condition that satisfies the following expression is satisfied, it is determined that the high-density portion is chromatic.

[0082]

[Equation 9]

However, the threshold value THcolor_n in the above equation
um_high is an arbitrary integer.

Further, the number CL: count of pixels which belong to the low density portion and are determined to be chromatic is a predetermined threshold value THco.
If it is larger than lor_num_low, it is determined that the low-density portion is chromatic, and if the condition satisfies the following equation, it is determined that the low-density portion is chromatic.

[0085]

[Equation 10] However, the threshold value THcolor_num_low in the above equation
Is an arbitrary integer.

When the chromatic / achromatic determination of the high density portion and the low density portion is completed in step a13, step a14
Proceed to. In step a14, first, the pixel-of-interest color determination unit 1
13, it is determined whether the pixel of interest 104 is a chromatic color or an achromatic color by the pixel of interest to be processed alone. The determination is chromatic if the maximum density difference between the three color components of the pixel of interest 104 is larger than a predetermined threshold THcolor, and chromatic if the following condition is satisfied. .

[0087]

[Equation 11] However, the threshold value THcolor3 in the above equation is an arbitrary positive real number.

Next, the chromatic / achromatic determination result of the target pixel obtained by the target pixel color determining section 113 and the chromatic / achromatic determination result of the high density portion and the low density portion determined by the counting section 111. Based on the
However, it is determined whether the target pixel 104 is chromatic or achromatic.

The overall judgment unit 114 judges the final color of the pixel of interest based on the judgment table showing the judgment rules set in advance. Table 1 shows an example of the determination rule. In Table 1, assuming that the chromatic / achromatic determination result of the high density portion is CH, the chromatic / achromatic determination result of the low density portion is CL, and the chromatic / achromatic determination result of the pixel of interest is CC, each determination result The final chromatic / achromatic color of the pixel of interest is shown in accordance with the combination. In case of chromatic, it is set to True, and in case of achromatic,
Shown as False.

[0090]

[Table 1]

In Table 1, it is determined that the high density portion is chromatic (CH
→ True) and it is determined that the low density area is achromatic (CL → F
and the target pixel alone is determined to be achromatic (CC →
False), the color determination result on the high-density side is prioritized, and the final color of the pixel of interest is determined to be chromatic.

In this way, in step a14, when the comprehensive determination section 114 finally determines whether the color of the pixel of interest is chromatic or achromatic, the process proceeds to step a15.
In step a15, it is determined whether or not the chromatic / achromatic color has been determined for all the pixels belonging to the character area. If there is a pixel for which the chromatic / achromatic color has not been determined, the chromatic / achromatic color is determined. As the target pixel of interest,
The process proceeds to step a1 again, and steps a1 to a1 are repeated until chromatic / achromatic is determined for all pixels in the character area.
Repeat 5 At this time, the color determination process is performed on all the pixels in the character area while sliding the mask on a pixel-by-pixel basis. Further, by performing the color determination of the pixel of interest by the pixels in the mask, it is possible to perform the color determination with high accuracy. When it is determined that all the pixels belonging to the character area are chromatic or achromatic, the process proceeds to step a16, and the pixel color determination operation ends.

In the present embodiment, the comprehensive judgment section 11 is further added.
After the chromatic / achromatic color is determined by 4, the color misregistration determination unit 1
15 determines whether or not each pixel of interest 104 has a color shift. The color misregistration determination unit 115 first determines whether the pixel of interest 104 is chromatic or achromatic by itself. This determination is performed using, for example, the maximum difference between the color components, and if the color is chromatic, the following expression is satisfied.

[0094]

[Equation 12]

Here, THcolor_r is a predetermined threshold value. However, the above-described determination method performed by the color shift determination unit 115 is an example, and the color shift determination unit 11
5 does not particularly limit the color determination method performed by the pixel alone. The color misregistration determination unit 115 may obtain the color determination result for each pixel based on the determination result of the pixel-of-interest color determination unit 113.

When the color shift occurs, the pixel is originally achromatic, but the color shift of the color component occurs, so that it may be determined that the pixel unit is chromatic. Table 2 shows the judgment result obtained by the comprehensive judgment unit 114 as CM (i, j).
Is a table showing conditions under which color misregistration occurs when CR (i, j) is the result obtained based on the color determination method performed by the target pixel alone.

[0097]

[Table 2]

As shown in Table 2, when the result obtained by the comprehensive judgment unit 114 is an achromatic color and the obtained result is a chromatic color based on the color judgment method performed by the pixel of interest pixel alone, Color shift occurs. The color misregistration determination unit 115 is shown in Table 2
The color misregistration is determined based on the table shown in (1) and the information indicating the color misregistration is transmitted to the color correction unit or the black generation undercolor removal unit in the subsequent stage. For example, in black material generation processing such as UCR,
Pixels that have been determined to have color misalignment are subjected to processing equivalent to that of the black pixel area, or the cyan, magenta, and yellow of the input signals are balanced, and are corrected as achromatic colors to correct the output image. The reproducibility can be improved.

FIG. 5 is a schematic diagram showing the density distribution of each color component of each pixel in the black character area. FIG. 6 is a schematic diagram showing the density distribution of each color component of each pixel in the color character area. When color misregistration occurs in an image having a black character area as shown in FIG. 5, a pixel serving as a boundary portion 121 between a character and a background in an image represented by input image data is a high density pixel portion 120a. It has an intermediate density with the low-density pixel portion 120b and becomes a chromatic color due to color shift. The boundary portion 121 between the character and the background is similar to the boundary portion 121 between the character and the background in the case of the color image shown in FIG.

In the character area, the normal character portion becomes the high density portion 120a. Therefore, as shown in FIG. 5, in the case of black characters, in the high density portion 120a, cyan,
The densities of magenta and yellow are almost constant. Further, as shown in FIG. 6, in the case of a color character, even in the high density portion 120a, a density difference occurs in the color components of cyan, magenta and yellow. The same is true when the background is chromatic and achromatic.

According to the present invention, the high-density portion 120a and the low-density portion 12 where the difference between the black character and the color character is clear.
By determining the chromatic / achromatic state of the character and the background in the portion 0b, in other words, the portion where the color information is stable except for the intermediate density portion of the target pixel area caused by the reading error of the image input device due to mechanical vibration. By determining the chromatic / achromatic color of the character and the background with the pixel of, the influence of the reading error can be removed, the reproducibility of the output image with respect to the original image can be improved, and a high-quality image can be obtained. For example, the target pixel to be processed corresponding to the black portion of the original image is corrected for the reading error and is accurately determined to be black instead of chromatic color, whereby the reproducibility with respect to the original image can be improved. Further, since the input image data can be corrected by the pixel reading error, an image input device having high reading accuracy is not required, and even if the input image data is input from the image input device having low reading accuracy, a simple configuration is possible. The original image can be reproduced with high accuracy.

Further, based on the results of the pixel-of-interest color judging section 113 which is the first judging section of the chromatic / achromatic judging section and the high density / low density partial color judging section 112 which is the second judging section, the third judging section By determining whether the target pixel to be processed is a chromatic color or an achromatic color, the comprehensive determination unit 114 can more accurately determine the chromatic / achromatic color of the target pixel to be processed. Thereby, the reproducibility of the output image with respect to the input image can be further improved, and a high quality output image can be obtained.

FIG. 7 is a block diagram showing the configuration of the image forming apparatus 1 including the image processing apparatus 3 according to the embodiment of the present invention. The image forming apparatus 1 is an apparatus for forming an image on a recording material including a recording sheet made of paper and a material other than paper, and includes an image input device 2 and an image processing device 3.
And an image output device 4.

The image input device 2 is a device for reading an image formed on a document, and is a solid-state image pickup device, for example, a charge coupled device (abbreviated as CC).
It is configured to include a scanner unit including an image sensor using D). The image input device 2 irradiates the original with white light from the light source, and reflects the color of reflected light from the original, that is, the wavelength and the intensity, into a plurality of pixels arranged in the main scanning direction and the sub-scanning direction by the CCD image sensor. The original image is read by being divided and detected, and original image data representing the original image by the color and intensity of each pixel is supplied to the image processing apparatus 3 by an electric signal.

The original image data is represented by numerical values corresponding to the densities of red, green and blue which are three color components, and is supplied to the image processing device 3 as red R ', green G'and blue B'signals. The red R ′ signal is an electric signal that represents the reflectance of red color light from the document in analog for each pixel. Green G'signal is
It is an electric signal that represents the reflectance of green light from the original in analog for each pixel. The blue B ′ signal is an electric signal that represents the reflectance of blue light from the document in analog for each pixel.

The image processing device 3 is a device for performing image processing for correcting given image data so that the reproducibility of a document image can be improved at the time of image output. The image processing device 3 includes an analog / digital conversion unit (hereinafter referred to as an A / D conversion unit) 5, a shading correction unit 6, an input gradation correction unit 7, a region separation processing unit 8, a color correction unit 9, and a black generation undercolor. Removal unit 10, spatial filter processing unit 11,
The output gradation correction unit 12 and the gradation reproduction processing unit 13 are included.

The A / D converter 5 converts the applied analog signal into a digital signal. The A / D conversion unit 5 converts the red R ′ signal, the green G ′ signal, and the blue B ′ signal, which are analog signals, into digital signals that digitally represent the reflectance of red light, green light, and blue light for each pixel. It is converted into a certain red R signal, green G signal and blue B signal, respectively. The A / D conversion unit 5 supplies the red R signal, the green G signal, and the blue B signal to the shading correction unit 6.

The shading correction section 6 removes the distortion component contained in the data represented by the red R signal, green G signal and blue B signal. The shading correction unit 6 removes various distortion components generated in the illumination system, the imaging optical system, and the imaging system (image receiving system) of the image input device 2 from the red R signal, the green G signal, and the blue B signal. Processed red R signal, green G
The signal and the blue B signal are supplied to the input gradation correction unit 7.

The input tone correction section 7 adjusts the color balance of the data represented by the given signal, and at the same time, converts it into a signal of data which is easy to handle when performing image processing. The input tone correction unit 7 corrects the red R signal, the green G signal, and the blue B signal from the shading correction unit 6 so as to adjust the color balance on the basis of the reflectance values, and also corrects each color component. The reflectance value of the light is converted into a signal representing the density value of each color component of red, green and blue. After that,
The input tone correction unit 7 outputs a signal representing the color of each pixel represented by the density values of red, green, and blue by the density values of cyan, magenta, and yellow, which are complementary colors thereof, and thus the cyan density of each pixel. Is converted into a cyan Cin signal that represents digitally, a magenta Min signal that digitally represents the magenta density of each pixel, and a yellow Yin signal that digitally represents the yellow density of each pixel, and this is supplied to the area separation processing unit 8. Cyan Cin signal, Magenta Min
The signal and the yellow Yin signal are digital signals representing a document image. Hereinafter, the cyan Cin signal may be referred to as a “Cin signal”, the magenta Min signal may be referred to as a “Min signal”, and the yellow Yin signal may be referred to as a “Yin signal”.

The area separation processing section 8 extracts the correction target image area including the correction target image portion to be corrected from the entire original image represented by the given image data.
The area separation processing unit 8 separates each pixel of the original image represented by the original image data as a constituent element of a plurality of image areas based on the Cin signal, the Min signal, and the Yin signal from the input gradation correction unit 7. Thus, the correction target image area is extracted. In the present embodiment, the image area is a character area representing a character, a halftone area representing an image with halftone dots, and a photograph area representing a photograph. The area image processing unit 8 gives the Cin signal, the Min signal, and the Yin signal from the input gradation correction unit 7 to the color correction unit 9 as they are, and determines which image area each pixel belongs to based on the area separation result. The area identification signal is applied to the color correction unit 9, the black generation undercolor removal unit 10, the spatial filter processing unit 11, and the gradation reproduction processing unit 13.

The color correction unit 9 performs a process for removing color turbidity based on the spectral characteristics of each of the cyan, magenta, and yellow color materials containing unnecessary absorption components so that the reproducibility of the original image at the time of image output can be improved. To do. The color correction unit 9
The C ″ signal, the M ″ signal, and the Y ″ signal representing the corrected color component are supplied to the black generation undercolor removal unit 10.

The black generation undercolor removal unit 10 performs a black generation process for generating black and a black generation process for the cyan, magenta, and yellow color components on the basis of the density values of the given cyan, magenta, and yellow color components. Undercolor removal (UnderColor R) that subtracts the obtained black color component and obtains the density values of the new cyan, magenta, and yellow color components
emoval: Abbreviated as UCR) processing. The signals of the three colors, that is, the cyan C ″ signal, the magenta M ″ signal, and the yellow Y ″ signal, which represent the color components corrected by the color correction unit 9, are processed by the black generation lower color removal unit 10 to obtain a cyan C signal and a magenta M signal. Signal, a yellow Y signal, and a black K signal are converted into four color signals: a cyan C signal is a “C signal”, a magenta M signal is a “M signal”, a yellow Y signal is a “Y signal”, and a black K signal. The signal may be referred to as a “K signal”. As an example of the black generation processing, a black generation method using skeleton black can be mentioned. In this method, the function representing the input / output characteristics of the skeleton curve is represented by y = f (x), the input value is represented by the color components represented by the C ″ signal, the M ″ signal and the Y ″ signal, and the C ″ signal, When the undercolor removal rate of the density values of the color components represented by the M "signal and the Y" signal is α (0 <α <1), the colors of cyan, magenta, yellow, and black after the black generation process and the undercolor removal process are performed. The component is calculated by the following equation (1). The black generation / undercolor removal unit 10 supplies the spatial filter processing unit 11 with the C signal, M signal, Y signal, and K signal after black generation and undercolor removal. K = f {min (C ", M", Y ")} C = C" -αK M = M "-αK (1) Y = Y" -αK

The spatial filter processing section 11 corrects the spatial frequency characteristic of each image area on the image data based on the area identification signal to prevent blurring and graininess deterioration of the output image. Perform spatial filtering using. The output gradation correction unit 12 performs a process of converting a given signal into a signal representing a characteristic value of the image output device 4 when outputting an image.

The gradation reproduction processing section 13 performs gradation reproduction processing for outputting an image based on the given signal.

For example, the image data of the character area extracted by the area separation processing unit 8 is subjected to a high-frequency emphasis amount by the spatial filter processing by the spatial filter processing unit 11 so as to improve the reproducibility of characters at the time of image output. Be made bigger. After that, the image data in the character area is binarized or multivalued in the gradation reproduction processing unit 13 by a high-resolution screen suitable for reproducing frequencies in a high range.

The image data of the halftone dot area extracted by the area separation processing unit 8 is processed by the spatial filter processing unit 11 using a low pass filter for removing the input halftone dot component. Further, the image data of the halftone dot area is converted into a halftone dot area ratio, which is a characteristic value of the image output device 4, in the output gradation correction unit 12, and then in the gradation reproduction processing unit 13. Finally, the image is separated into pixels and processed so that each gradation can be reproduced.

The image data of the photographic area extracted by the area separation processing section 8 is binarized or multivalued by the screen in which the gradation reproducibility is emphasized in the gradation reproduction processing section 13. The image data processed by the gradation reproduction processing unit 13 is temporarily stored in the storage unit, read from the storage unit at a predetermined timing, and given to the image output device 4. The above processing is performed by a CPU (Centra, not shown).
l Processing Unit).

The image output device 4 is a device for forming an image on a recording material on the basis of the image data image-processed by the image processing device 3. Examples of the image output device 4 include, but are not particularly limited to, a color printer using an electrophotographic method and an inkjet method.

FIG. 8 is a block diagram showing the structure of the area separation processing section 8. The area separation processing unit 8 includes the area determination unit 20.
And a character area determination unit 21. Based on the cyan Cin signal, the magenta Min signal, and the yellow Yin signal representing the original image data from the input gradation correction unit 7, the area determination unit 20 determines that each pixel of the original image represented by the original image data is a character area or a halftone dot. It is determined which image area of the area and the photograph area it belongs to. In addition, the area determination unit 20
Separates the original image into image areas, that is, gives identification data indicating to which image area each pixel belongs,
An area identification signal representing this identification data is given to the color correction section 9, the black generation undercolor removal section 10, the spatial filter processing section 11, the gradation reproduction processing section 13, and the character area determination section 21. The area identification signal includes a character area identification signal indicating that the area-determined pixel belongs to the character area, a halftone area identification signal indicating that the area-determined pixel belongs to the halftone area, and the area-determined pixel Is a signal including a photograph area identification signal indicating that the symbol belongs to the photograph area.

The area determination unit 20 supplies the original image data including at least the image data of the character area and the character area identification signal to the character area determination unit 21. In addition, the area determination unit 20
Is a color correction unit 9, a black generation undercolor removal unit 10, a spatial filter processing unit 11 for the halftone dot area identification signal and the photograph area identification signal.
And to the gradation reproduction processing unit 13. Character area determination unit 2
In the area 1, the area determination unit 20 extracts a character portion based on the document image data and the character area identification signal.

The original image is separated and extracted by the area determining unit 20 into image data of a character area, a halftone dot area and a photographic area using the following method. Area determination unit 20
Is a region including a natural number of pixels in the main scanning direction and the sub-scanning direction, that is, M × N pixels, centering on a processing target pixel (hereinafter simply referred to as a target pixel) that is an arbitrary pixel of the original image data. Is taken, and to which region the pixel of interest belongs is determined based on the data of the pixels in this block. M and N are natural numbers and may be the same or different from each other.

The determination result is used as a region identification signal of the pixel of interest. In the pixels included in the block,
The value of a signal that is the density of a pixel (hereinafter, "signal level"
The maximum value and the minimum value are obtained, and the maximum value is set as the maximum pixel signal level Dmax, and the minimum value is set as the minimum pixel signal level Dmin. Among the pixels included in the block, the average value Dave of the signal levels of nine pixels including the pixel of interest and eight pixels around the pixel of interest is calculated. Using this average value Dave as a threshold value, the image of the block is binarized by replacing the signal level of each pixel with 0 (less than the threshold value) and 1 (above the threshold value).

After such binarization processing, first, the pixel of interest
Is a pixel belonging to the halftone dot area. network
In the point area, the background has a plurality of density values that differ greatly from the background.
The dots (dots) of
An image with a high signal level is formed and
The signal level of each pixel in the main scanning direction and the sub scanning direction
, There is a large change between adjacent pixels, and main scanning
Between adjacent pixels in the vertical and sub-scanning directions.
There are many changes in the issue level. The area determination unit 20
The pixel of interest of the block that satisfies the condition
It is determined that the pixel is a pixel that does. Display the pixels that represent halftone dots and the background
The maximum pixel signal level is
The difference between the maximum Dmax and the average value Dave is the threshold value B₁When
The average value Dave and the minimum pixel signal level Dmi are compared.
The difference from n is the threshold value B₂Compared to. In the main scanning direction
, The signal level of each binarized pixel is from 0 to 1
And the number of points K changing from 1 to 0_HIs required
Change points K_HIs the threshold T_HCompared to. In the sub-scanning direction
, The signal level of each binarized pixel is from 0 to 1
And the number of points K changing from 1 to 0_VIs required
Change points K_VIs the threshold T _VCompared to. Maximum pixel signal
The difference between the level Dmax and the average value Dave, and the average value Da
The difference between ve and the minimum pixel signal level Dmin, and the number of change points
K_HAnd the number of changes K_VCompare and with the threshold and compare
The image area to which the pixel of interest belongs is determined using the condition. Dmax-Dave> B₁And Dave-Dmin> B₂ And K_H> T_HAnd K_V> T_V  ... halftone dot area Other than the above conditions ... Non-dot area

The conditions for determining whether or not the pixel of interest is a pixel belonging to the halftone dot area are that the difference between the maximum pixel signal level Dmax and the average value Dave is larger than the threshold value B ₁ . Average value Dave and minimum pixel signal level Dm
The condition that the difference from in is larger than the threshold value B ₂ , the condition that the number of changing points K _{H in the} main scanning direction is larger than the threshold value T _H, and the number of changing points K _{V in the} sub scanning direction are: There is a condition that it is larger than the threshold value T _V, and when all of these conditions are satisfied, it is determined that the pixel of interest belongs to the halftone dot area. If any of these conditions is not satisfied, the pixel of interest is determined to be a pixel belonging to the non-halftone dot region that is the character region and the photograph region.

When it is determined that the pixel of interest belongs to the non-halftone dot area, it is determined whether the pixel of interest belongs to the character area or the photograph area. In the character area, the difference between the maximum pixel signal level Dmax and the minimum pixel signal level Dmin is large, and the signal level of the pixels belonging to the character area is considered to be high as a whole. Therefore, the target pixel belongs using the following conditions. Determine the image area. Dmax> P _A or Dmin <P _B or the difference between Dmax and Dmin Dsub> P _C ... Other than the conditions on the character area ... Photo area

The maximum pixel signal level Dma is a condition for determining whether or not the pixel of interest is a pixel belonging to the character area.
The condition that x is larger than the threshold P _A , the condition that the minimum pixel signal level Dmin is smaller than the threshold P _B , and the difference Dsub between the maximum pixel signal level Dmax and the minimum pixel signal level Dmin are , And the condition that it is larger than the threshold value P _C , and if at least one of these conditions is satisfied, the pixel of interest is determined to be a pixel belonging to the character area. When all of these conditions are not satisfied, that is, when all of them are equal to or less than the threshold value, the pixel of interest is determined to be a pixel belonging to the photograph area. After the region determination of a certain pixel of interest is completed, another pixel is set as a new pixel of interest, and M
A block including × N pixels is taken and the above-mentioned image area is determined. Such area determination is applied to all the pixels of the original image to the pixel of interest, and area determination is performed.

The area determination unit 20 gives a character area identification signal indicating which pixel of the original image the pixel determined to belong to the character area to the character area determination unit 21 and belongs to the halftone dot and photograph area. A halftone dot and a photograph area identification signal indicating which pixel of the original image the pixel determined to be are given to the color correction unit 9.

The character area determination unit 21 is means for extracting a character portion from the character area based on the character area identification signal, and includes an edge determination unit 22, a color determination unit 23, and a color character determination unit 24. Composed. The edge determination unit 22 is
A means for detecting a pixel corresponding to an edge portion showing a sharp change in signal level between adjacent pixels, that is, a sharp change in density, which is based on a character area identification signal from the area determination unit 20 It is determined whether or not the pixel to which the pixel belongs belongs to the edge portion, and an edge determination signal representing the determination result is given to the color character determination unit 24. This edge portion serves as a boundary between the character portion and the background portion. By the edge determination unit,
By determining the character portion and the background portion, it is possible to more accurately determine whether the color of the character portion and the background portion of the image is chromatic or achromatic.

The color judging section 23 is means for judging whether the pixel is a pixel representing a chromatic color or a pixel representing an achromatic color, and has a structure as shown in FIG. Color determination unit 2
3 determines whether or not the pixel belonging to the character area is a pixel representing a chromatic color based on the character area identification signal from the area determining unit 20, and outputs a chromatic determination signal representing the result of the determination. It is given to the color character determination unit 24. Based on the determination results of the edge determination unit 22 and the color determination unit 23, the color character determination unit 24 determines whether the pixel belonging to the character region is a chromatic character portion, an achromatic character portion, or a color shift. Is a means for determining whether or not it is a character portion that has occurred.

In the color character determining section 24, it is determined that the pixel is a color character portion and a black character portion based on the following conditions. (Edge) and (chromatic color) → colored character part (edge) and (achromatic color) → black character part (edge) and (color shift) → color shift character

In the color / character determination unit 24, when the edge determination unit 22 determines that the pixel of interest is an edge portion, and when the color determination unit 23 determines that the pixel of interest represents a chromatic color, the pixel of interest is When it is determined that the pixel of interest is a color character portion, the edge determination unit 22 determines that the target pixel is an edge portion, and the color determination unit 23 determines that the target pixel is an achromatic color pixel, the target pixel is a black character. It is determined to be a portion, and the color character determination signal which is the determination result is given to the color correction unit 9.

Further, the color character judging section 24, based on the judgment results of the edge judging section 22 and the color judging section 23,
It is determined whether the target pixel to be processed is a color character, a black character, or a color-shifted character, the number of target pixels to be processed that are determined to be color-shifted characters is calculated, and the calculation result is given to the notification unit 60.

When the number of target pixels to be processed which are color-shifted characters is equal to or larger than a predetermined threshold value, the notification means 60 notifies that the target pixel to be processed which is a color-shifted character exists. When the color misregistration pixel number counted by the color / character determination unit 24 is count_error, the color misregistration pixel number is given by the following equation.

[0134]

[Equation 13]

Therefore, when the number of color-shifted pixels is larger than the predetermined threshold value THerror, that is, when the following equation is satisfied, count_error> THe
It is possible to determine that a color shift has occurred, and the notification means 60 provides information indicating that a color shift has occurred.
Informs the user. This can be used as an index that allows the user to be warned or repaired by assuming that some trouble is expected in the image input device that causes color misregistration. The threshold value THerro
r can be set in advance by measuring the performance of the image input device. Alternatively, the number of pixels detected as a black character is c
It is also possible to detect a trouble of the image input device by thresholding the ratio of pixel deviation to the number of black character pixels as the number of out_bktxt. That is, the threshold value of the rate of pixel blurring THerror_rati
It is also possible to detect a trouble in the image input device by determining whether or not the value exceeds o. For example, when the following expression is satisfied, it may be determined that a trouble has occurred in the image input device.

[0136]

[Equation 14]

The notification means 60 may be, for example, an operation panel composed of a display section composed of a liquid crystal display and setting buttons, and may also be an LED (Light Emitti).
ngDiode: light emitting diode) or the like, and an alarm lamp configured to display color misregistration information may be displayed. The notification means may be any means that notifies the user, and may be, for example, a buzzer.

FIG. 9 is a block diagram showing the configuration of the edge determination section 22 included in the area separation processing section 8. Figure 10
FIG. 1 is a diagram showing a filter for edge detection, and FIG.
0 (1) shows the Sobel filter 40 in the main scanning direction, and FIG. 10 (2) shows the Sobel filter 4 in the sub-scanning direction.
1 is shown. The edge determination unit 22 includes a main scanning Sobel filter unit 30, a sub-scanning Sobel filter unit 31, each color absolute value calculation unit 32, each color adder 33, each color comparator 34, an adder 35, and a comparator 36. To be done. The edge determination unit 22 uses a filter for detecting edges,
It is determined whether or not the pixel is an edge portion that is a character portion. Whether or not the pixel is an edge portion is determined for each of the cyan, magenta, and yellow color components. Main scanning Sobel filter unit 30, sub-scanning Sobel filter unit 3
1. The processing of each color absolute value calculation unit 32, each color adder 33, and each color comparator 34 is the same for the cyan, magenta, and yellow color components, so a specific description will be given only for the cyan color component. To do. The same means is used for magenta and yellow.

A mask having a certain number of pixels in the main scanning direction and the sub-scanning direction with the pixel of interest as the pixel of interest, for example, a 7 × 7 mask, is read out from a line memory (not shown), and further 7 A 3 × 3 mask centered on the pixel of interest is extracted from the × 7 mask. The mask represents a local area including a plurality of pixels, and is, for example, 3 × 3.
The mask represents a local region in which pixels are arranged in 3 rows and 3 columns.

In the main scanning Sobel filter section 30,
When the cyan Cin signal is given, the Sobel filter 40 in the main scanning direction for obtaining the difference value in the main scanning direction of the target pixel is convoluted with the 3 × 3 mask. Specifically, the convolution processing is performed by the value of the pixel in the first row and the first column of the 3 × 3 mask and the pixel 4 in the first row and the first column of the main scanning Sobel filter 40.
The value of 2a is integrated. Similarly, the value of the pixel in the first row and the second column and the value of the pixel 43a in the first row and the second column of the Sobel filter 40 in the main scanning direction are integrated. Further, the values of the other pixels of the 3 × 3 mask and the values of the corresponding pixels of the main scanning Sobel filter 40 are integrated, and the sum of the values obtained by the integration is calculated to obtain a difference value. In the sub-scanning Sobel filter unit 31, when the cyan Cin signal is supplied, the sub-scanning direction Sobel filter 41 for obtaining the difference value of the pixel of interest in the sub-scanning direction is convoluted into the 3 × 3 mask. Similar to the process of the main scanning Sobel filter unit 30, the sub scanning Sobel filter unit 31 integrates the pixel value of the 3 × 3 mask and the corresponding pixel value of the Sobel filter 41 in the sub scanning direction. By obtaining the sum of the obtained values, the difference value of the target pixel in each scanning direction is obtained.

Sobel filters 40, 41 in each scanning direction
However, the result of convolution with the 3 × 3 mask is given to each color absolute value calculation unit 32. In each color absolute value calculation unit 32, the absolute value of the result obtained by convoluting the Sobel filters 40 and 41 in each scanning direction into the 3 × 3 mask is obtained by each color absolute value calculation unit 32 and given to each color adder 33. To be In each color adder 33, the Sobel filters 40, 41 in each scanning direction are used.
Is added to the 3 × 3 mask to obtain an added value, which is obtained by each color adder 33, and the added value is given to each color comparator 34. The process of obtaining the absolute value of the result obtained by convolving the Sobel filters 40 and 41 in each scanning direction with the 3 × 3 mask is a process that considers that negative coefficients are present in each Sobel filter 40 and 41 in the scanning direction. The process for obtaining the added value is a process for considering the results in both the main scanning direction and the sub scanning direction.

Each color comparator 34 compares the added value with a predetermined threshold value edgeTH, and if the added value is greater than or equal to the threshold value, gives a signal representing "1" to the adder 35, If it is smaller than the threshold value, a signal representing “0” is given to the adder 35.

The adder 35 adds the values of the signals representing the comparison results for the respective color components of cyan, magenta, and yellow from the color comparators 34, and gives the signals representing the addition results to the comparator 36. The comparator 36, based on the addition result from the adder 35, sets a threshold value a that determines a predetermined addition value.
Compared with ddTH, an edge determination signal representing “1” is given to the color character determination unit 24 if the pixel of interest is an edge portion, and an edge determination signal representing “0” is provided if the pixel of interest is not an edge portion. It is given to the color character determination unit 24. For example, if it is determined by the color comparators 34 that the pixel of interest is the edge portion only when all the color components of cyan, magenta, and yellow are determined to be the edge portion, the threshold value addTH is set to "3". If only one color component is determined to be the edge portion, and if the pixel of interest is determined to be the edge portion, the threshold value addTH is set to “1”.

FIG. 11 is a block diagram showing the configuration of the color determining section 200 according to another embodiment of the present invention. The color determination unit 200 shown in FIG. 11 is different from the color determination unit 100 shown in FIG. 1 in the configuration of the determination pixel portion extraction unit 202, and since the other configurations are the same, the description thereof will be omitted and the same reference numerals will be given. .

The determination pixel part extraction unit 202 includes a sub-target pixel including the in-region target pixel 116 belonging to the mask 105 extracted by the target region extraction unit 101 and a plurality of pixels around the in-region target pixel 116. The sub-mask 120 that is a portion is set, and the determination pixels that belong to the determination pixel portion are extracted based on the color information of each pixel that belongs to the sub-mask 120.

FIG. 12 is a schematic diagram showing a part of the character area 121. The target area extraction unit 101 extracts a mask 105 that is a processing target area centered on the processing target pixel of interest 104. Further, the determination pixel portion extraction unit 202
Thus, the sub-mask 120, which is the sub-target pixel portion formed in the region of the mask 105, is set with the pixel of interest 116 in the region of the mask 105 as the center. For example, the mask 105 is formed by 7 × 7 pixels, and the submask 120 is formed by 3 × 3 pixels.

The determination pixel portion extraction unit 202 includes a color component average value calculation unit 106, a maximum / minimum calculation unit 107, a sub-mask maximum / minimum value calculation unit 205, a high density portion detection unit 206, and a low density portion detection unit 207. Have.

The color component average value calculator 106 receives the pixel information in the mask 105 from the target area extractor 101. The color component average calculation unit 106, for each pixel in the mask,
The respective density average values are calculated, and the calculation result is given to the maximum / minimum calculation unit 107. The maximum / minimum calculation unit 107 obtains the maximum and minimum values of the average density value in the mask and sets a high density portion having a high density and a low density portion having a low density with respect to the pixels in the mask.

The maximum / minimum value calculation unit 205 in the submask is
The sub-mask 120 centering on the target pixel in the area is set. In addition, the maximum / minimum value calculation unit 205 in the submask is
The sub-target pixel portion setting unit detects a pixel having the maximum or minimum density average value for each color component among the pixels belonging to the sub-mask 120 and sets it as color information of the in-region attention pixel 116. To the high-density portion detection unit 206 and the low-density portion detection unit 207.

The high-density portion detection unit 206 receives the information indicating the high-density portion and the maximum density value for each color component of the sub-mask centering on the target pixel 116 in each area from the maximum / minimum value calculation unit 205 in the sub-mask. The information shown is received, it is determined whether or not the pixel of interest 116 in each region belongs to the high density portion, and the determination result is given to the chromatic / achromatic determination unit 103.

The low-density portion detection unit 207 receives the information indicating the low-density portion and the minimum density value for each color component of the sub-mask centering on the pixel of interest 116 in each area from the intra-sub-mask maximum / minimum value calculation unit 205. The information shown is received, it is determined whether or not the target pixel 116 in each region belongs to the low density portion, and the determination result is given to the chromatic / achromatic determination unit 103. The color determination unit 200 includes a chromatic / achromatic determination unit 103 similar to that in FIG. 1, and includes a target area extraction unit 101 and a determination pixel portion extraction unit 2
02 to be processed based on the calculation result
Determines whether is chromatic or achromatic.

FIG. 13 is a flowchart showing a part of the pixel color judgment operation according to another embodiment of the present invention.
4 and 15 are flowcharts partially showing the color determination operation not shown in FIG. The flowcharts shown in FIGS. 13, 14 and 15 are performed by the color determination unit 200 shown in FIG. 11, and operations similar to those of the flowchart of FIG. 3 are performed. Therefore, operations similar to those in the flowchart shown in FIG. 3 will be described briefly or omitted.

When it is determined in step b0 that the image represented by the input image data includes a character area, the process proceeds to step b1 and each pixel belonging to the character area is chromatic or achromatic. The pixel color determination operation for determining whether or not is started.

In step b1, the target pixel extraction unit 101 determines the target pixel 10 as in step a1.
A mask 105 that includes a pixel centered at 4 and divides a character region is formed. When the mask 105 is formed, the process proceeds to step b2. In step b2, the color component average value calculation unit 106 calculates the average value of the density values of the color components in the mask 105. Next, the maximum / minimum calculation unit 107
Detects the maximum density and the minimum density of the average value of the density values of the color components in the mask 105.

Mask 105 centered on pixel of interest 104
If the maximum density of the average values of the color components inside is Top (i, j) and the minimum density is Bot (i, j), the density value To is
p (i, j) and Bot (i, j) are given by the following equations.

[0156]

[Equation 15]

Maximum density of average values of color components Top (i,
j) and the lowest density Bot (i, j) of the average value of the color components
Is detected, the process proceeds to step b3.

At step b3, the maximum / minimum value calculation unit 10
7, the high-density portion (Ha (i, j)) formed by the high-density pixel and the low-density portion (La by the low-density pixel among the pixels in the mask)
(I, j)) is determined. High concentration part (Ha (i,
j)) and the low-density portion (La (i, j)) are determined, for example, by the following equations.

[0159]

[Equation 16]

Here, the coefficient TH is preset with an arbitrary real number satisfying 0 ≦ TH ≦ 1. High concentration part (Ha (i, j))
Is the maximum density of the average value of the color components in the mask Top (i,
It is a portion extending from j) to a region where the density is low by a predetermined range. For example, the predetermined range is the maximum density T of the average value of the color components.
op (i, j) and the minimum density Bot of the average value of the color components
Difference from (i, j) (TOP (i, j) -Bot (i,
j)) is the density range obtained by multiplying the coefficient TH. Similarly, the low-density portion (La (i, j)) is a portion that extends from the lowest density Bot (i, j) of the average value of the color components to a region having a high density by a predetermined range.

Each density portion (Ha (i, j))
When (La (i, j)) is detected, the process proceeds to step b4. In step b4, first, the pixel having the identification number K of 1 is selected, the selected pixel is set as the in-region target pixel 116, and the process proceeds to step b5.

In step b5, first, the maximum-minimum-value calculating unit 205 in the submask detects the maximum density value for each color component in each pixel in the submask. The maximum value of the cyan density of the pixel in the sub mask 120 is C
max (m, n), and the maximum value of magenta density is Mma
x (m, n), and the maximum value of yellow density is Ymax
If (m, n), the maximum density value for each color component is calculated by the following equation.

[0163]

[Equation 17]

Similarly, the minimum cyan density of pixels in the submask 120 is Cmin (m, n), the maximum magenta density is Mmin (m, n), and the maximum yellow density is Ymin (m, n). n), the minimum density value for each color component is obtained by the following equation.

[0165]

[Equation 18]

When each density average value is calculated based on the maximum density value and the minimum density value for each color component in the sub-mask centering on the pixel of interest 116 in the area, the high density portion detection unit 2
Based on 06, it is determined whether the in-region pixel of interest 116 belongs to the high-density portion. If the in-region pixel of interest 116 belongs to the high density portion, the condition of the following equation is satisfied.

[0167]

[Formula 19]

When the selected in-region pixel of interest 116 belongs to the high density portion, the in-region pixel of interest becomes a high density determination pixel, and the process proceeds to step b6 shown in FIG. 14, otherwise, to step b9. move on.

At step b6, the maximum density for each color component in the sub-mask determined to belong to the high density portion obtained at step b5 is calculated, and the process proceeds to step b7. In step b7, the determination pixel color determination unit 110 obtains the density difference of the maximum densities between the color components based on the maximum densities of the color components calculated in step b6, and the threshold TH
If it is compared with color11 and is larger than the threshold value, the pixel of interest 11 in the region located at the center of the submask
It is determined that 6 is chromatic. Specifically, the determination pixel color determination unit 110 performs color determination processing using the following formula.
If it is determined that the determination pixel is chromatic, the process proceeds to step b8, and if not, the process proceeds to step b9.

[0170]

[Equation 20]

At step b8, the counting section 111 integrates and counts one high-density determination pixel, and then at step b8.
Proceed to 9.

In step b9, as in step b5, the low-density portion detection unit 207 is used by using the minimum density average value obtained by the in-submask maximum / minimum value calculation unit 205.
However, it is determined whether or not the in-region attention pixel 116 belongs to the low-density portion. When the in-region pixel of interest 116 belongs to the low-density portion, the condition of the following equation is satisfied.

[0173]

[Equation 21]

If the selected in-region pixel of interest 116 belongs to the low density portion, the in-region pixel of interest 116 becomes the low density determination pixel, and the process proceeds to step b10 shown in FIG.
If not, the process proceeds to step b13.

At step b10, the minimum density for each color component in the sub-mask determined to belong to the low density portion obtained at step b9 is calculated, and the process proceeds to step b11.
In step b11, the density difference of the minimum density between the color components is obtained by the determination pixel color determination unit 110 based on the minimum density of each color component calculated in step b10 and compared with the threshold THcolor12. When it is larger than the threshold value, it is determined that the in-region attention pixel 116 located at the center of the submask is chromatic. Specifically, the determination pixel color determination unit 110 performs color determination processing using the following formula. If it is determined that the determination pixel is chromatic, the process proceeds to step b12, and if not, the process proceeds to step b13.

[0176]

[Equation 22]

At step b12, the counting section 111 integrates and counts one low-density determination pixel, and then proceeds to step b13.

Steps b13 to b18 correspond to the above steps a11 to a16, respectively.
Similar operations are performed.

According to the present embodiment, in the submask including the target pixel in the area, the color determination is performed by using the maximum density value for each color component and the maximum density difference between the color components at the minimum density value. I do. As a result, pixel color determination can be performed based on a pixel with a higher density on the high density side and a pixel with a lower density on the low density side. Therefore, even if a color shift occurs in the pseudo color area around the achromatic area due to the accuracy of the image input device, particularly in an achromatic one line, each pixel is more accurately determined as an achromatic color. be able to.

Since the color information of the target pixel in the area is set based on the color information of each pixel belonging to the sub mask,
Even if the pixel of interest in the area has a color shift,
It is possible to correct the deviation of the color component of the determination pixel from the color information of the pixels around the target pixel in the area. by this,
The original color information of the determination pixels corresponding to the original image can be determined more accurately. In this way, the original color information can be estimated to determine whether or not the pixel of interest in the region belongs to the determination pixel portion, and the influence of the color component shift can be corrected to determine whether or not the pixel belongs to the target pixel region. The use pixel can be extracted more accurately.

FIG. 16 is a block diagram showing the configuration of the color determination unit 300 of the image processing apparatus according to still another embodiment of the present invention. The color determination unit 300 shown in FIG. 16 has a configuration similar to that of the color determination unit 200 shown in FIG. 11, and the description of the same configuration will be omitted and the same reference numerals will be given.

In order to improve the accuracy of the color judgment processing, the color judgment section 300 makes color judgment based on the pixels belonging to the high-saturation portion and the low-saturation portion, as well as the pixels belonging to the high-saturation portion and the low-saturation portion. I do. The color determination unit 300 includes a determination pixel portion extraction unit 302, and the determination pixel portion extraction unit 302 includes the color component average value calculation unit 106, the maximum / minimum calculation unit 107, the sub-mask maximum / minimum value calculation unit 205, and In addition to the density portion detection unit 206 and the low density portion detection unit 207,
It has a color coordinate conversion unit 305, a high saturation part detection unit 306, and a low saturation part detection unit 307.

The color coordinate conversion unit 305 converts the image data given in cyan, magenta and yellow into image data represented by the L ^* a ^* b ^* color system in order to obtain the saturation information. The image data is CIE19 that uses a uniform color space.
76L ^* a ^* b ^* color system (Commission Internatinale de
l'Eclairage: International Certification Board: Abbreviation CIE. ). Hereinafter, the CIE1976L ^* a ^* b ^* color system is referred to as “L ^* a ^* ” ^.
b ^* color system.

L ^* is a color component representing lightness. a ^* and b ^* are color components that can be used to express hue and saturation, and hue is tan ⁻¹ (b ^* / a ^* )
It is obtained using the formula represented by. Since the color components of the L ^* a ^* b ^* color system can be represented by the linear sum of the color components of cyan, magenta and yellow, the CMY color system represented by the color components of cyan, magenta and yellow is Using a simple 3-by-3 matrix, L ^* a ^*
b ^* Converted to color system. Therefore, from the color system represented by the color components of cyan, magenta, and yellow, L
The conversion formula to the ^* a ^* b ^* color system can be expressed as follows.

[0185]

[Equation 23]

The value Satur representing the saturation is expressed by the following equation.

[Equation 24]

The high-saturation part detection unit 306 detects the pixel having the highest saturation in the plurality of pixels in the mask and calculates the maximum saturation value Tops (i, j). The maximum saturation value Tops (i, j) is calculated in the same manner as when the high density and low density values are detected, and is obtained by the following formula.

[0188]

[Equation 25]

The high-saturation part detection unit 306 extracts pixels in the mask belonging to the high-saturation part (HS (i, j)),
Pixels belonging to the high saturation portion satisfy the following conditions.

[0190]

[Equation 26]

The low-saturation part detection unit 307 detects the pixel with the lowest saturation in the plurality of pixels in the mask and calculates the minimum saturation value Bots (i, j). The minimum saturation value Bots (i, j) is calculated in the same manner as when the high and low density values are detected, and is obtained by the following formula.

[0192]

[Equation 27]

The low-saturation part detection unit 307 extracts the pixels in the mask belonging to the low-saturation part (Ls (i, j)),
The pixels belonging to the low saturation portion satisfy the following conditions.

[0194]

[Equation 28]

The threshold value THs in the above equation is 0 ≦ THs ≦ 1.
Is preset with an arbitrary real number that satisfies

The high-saturation portion detection unit 306 and the low-saturation portion detection unit 307 give the calculation result to the chromatic / achromatic determination unit 103. The chromatic / achromatic determination unit 103 further includes a determination pixel color determination unit 310 and a counting unit 311 that counts pixels belonging to a high saturation portion and a low saturation portion.

The judgment pixel color judgment unit 310 judges whether the judgment pixels belonging to the high-saturation portion and the low-saturation portion are chromatic colors or achromatic colors (details will be described later), and the judgment result is counted. It is given to the part 311. Counting unit 311
Is the number of pixels belonging to the high-saturation portion or the low-saturation portion and determined to be chromatic color SH: count, SL: cou
nt is counted, and the number of counted pixels is a predetermined threshold value THsatur_num_high, THsatur_
It is determined whether or not num_low is exceeded. That is, it is determined whether or not the following expression is satisfied.

[0198]

[Equation 29]

In this case, the color determination processing for determining whether the pixels belonging to the high saturation portion and the low saturation portion are chromatic colors is cyan,
By using the color component information of magenta and yellow, FIG.
Further, the method described with reference to FIG. 15 may be performed, or the color determination processing of chromatic color or achromatic color may be performed by comparing the saturation value with a predetermined threshold value.

The overall judgment unit 114 judges the final color of the pixel of interest based on the judgment table showing the judgment rules. Table 3 shows an example of the determination rule. In Table 3, the chromatic / achromatic determination result of the high density portion is CH, the chromatic / achromatic determination result of the low density portion is CL, and the two chromatic / achromatic determination results are collectively referred to as CI. The chromatic / achromatic judgment result is C
Let C be the high-saturation low-saturation determination result of the high-saturation part be SH, and the high-saturation low-saturation determination result of the low-saturation part be SL, the final chromatic achromatic color of the pixel of interest depending on the combination of the respective determination results. Is shown. For chromatic and high saturation,
True and False for achromatic and low saturation
Shown as e.

[0201]

[Table 3]

Although it is possible to make a determination using a table of five parameters of CH, CL, SH, SL, and CC, the determination process becomes complicated, and therefore the chromaticity in the high-density and low-density portions is chromatic. After the achromatic determination, the chromatic / achromatic determination based on the color of the pixel is performed when it is determined to be the achromatic region.

FIG. 17 is a flow chart showing a part of the pixel color judgment operation of still another embodiment of the present invention, and FIG. 18 is a flow chart showing step c5 of FIG. 17 in detail. The flowcharts shown in FIGS. 17 and 18 are performed by the color determination unit 300 shown in FIG. 16, and an operation similar to that of the flowchart of FIG. 13 is performed. Therefore, operations similar to those in the flowchart shown in FIG. 13 will be described briefly or omitted.

The color judgment operation shown in FIG. 17 is performed in step c0.
If it is determined that the image represented by the input image data includes a character area, the process proceeds to step c1 to determine whether each pixel belonging to the character area is chromatic or achromatic. The color determination operation of is started.

The operation of steps c1 to c3 is shown in FIG.
The steps are the same as steps b1 to b3 shown in FIG. 5, and in step c3, the high density portion and the low density portion are determined. Next, it progresses to step c4 and step c5.
Steps c4 and c5 can be processed independently, and either step c4 or step c5 may be performed in parallel, or either step may be performed first. Step c4 is a counting process of color pixels in the high density portion and the low density portion,
The processes of steps b4 to b13 shown in FIG. 13 are sequentially performed. Step c5 is a color pixel counting process in the high saturation portion and the low saturation portion, and steps d1 to d14 described later are performed.

When the counting processing of the high-density portion and the low-density portion in step c4 and the counting processing of the high-saturation portion and the low-saturation portion in step c5 are thus completed, the process proceeds to step c6. In step c6, the counting unit 111 determines whether the colors of the determination pixels belonging to the determination pixels belonging to the high density portion, the low density portion, the high saturation portion and the low saturation portion are chromatic or achromatic. Go to step c7. Steps c7 to c9 correspond to steps b16 to b18 shown in FIG. 13, respectively, and the same processing as steps b16 to b18 is performed.

The high saturation part shown in step c5 of FIG.
As shown in FIG. 18, the color pixel count processing in the low saturation portion includes steps d1 to d14. First, in step d1, the color pixel counting process in the high saturation portion and the low saturation portion is started. In step d2, the color coordinate conversion unit 305 performs color coordinate conversion. Accordingly, the color information indicating the color of the pixel is L ^* a ^* b
^* Converted to the color system, and if converted, proceed to step d3. In step d3, the identification number L that is set first is 1
Pixel is selected, the selected pixel is set as the target pixel in the area, and the process proceeds to step d4.

At step d4, the high saturation part detection unit 30
6 and the low-saturation part detection unit 307, among the pixels belonging to the mask 105 including the target pixel to be processed in the center,
The maximum saturation value that maximizes the two chromaticities a ^* and b ^* and the minimum saturation value that minimizes the two chromaticities a ^* and b ^* are detected. As a result, the maximum saturation value and the minimum saturation value are calculated, and the high saturation portion and the low saturation portion are detected.

Next, the high saturation part detection unit 306 detects the maximum saturation value having the maximum saturation among the pixels belonging to the mask 105, and determines whether or not the mask 105 belongs to the high saturation part. Then, if it is determined that it belongs to the high saturation part,
When it is determined that the procedure is not right, the procedure proceeds to Step d8.

At step d5, the maximum density for each color component in the sub-mask determined to belong to the high saturation portion is calculated, and the process proceeds to step d6. In step d6, the color difference determination unit 310 determines the density difference of the maximum densities between the color components based on the maximum densities of the color components calculated in step d5, and compares the density difference with the threshold THcolor21.
If it is larger than the threshold value, it is determined that the pixel of interest in the region located at the center of the submask is chromatic. If it is determined that the determination pixel is chromatic, step d
7. If not, proceed to step d8. At step d7, the counting unit 111 integrates and counts one pixel for high saturation determination, and then proceeds to step d8.

At step d8, the low saturation part detection unit 30
7 detects the minimum saturation value having the minimum saturation among the pixels belonging to the mask 105, determines whether the mask 105 belongs to the low saturation portion, and belongs to the low saturation portion. If it is determined, the process proceeds to step d9, and if not, the process proceeds to step d12.

At step d9, the minimum density for each color component within the sub-mask determined to belong to the low saturation portion is calculated, and the routine proceeds to step d10. In step d10, the color difference determination unit 310 determines the density difference of the minimum density between the color components based on the minimum density of each color component calculated in step d9, compares the density difference with the threshold THcolor22, and determines the threshold. When it is larger than the value, it is determined that the target pixel in the region located at the center of the submask is chromatic.
If it is determined that the determination pixel is chromatic, the process proceeds to step d11, and if not, the process proceeds to step d12. In step d11, the counting unit 111 integrates and counts one low-saturation determination pixel, and the process proceeds to step d12.

At step d12, the judgment pixel color judgment section 310 judges whether or not the identification number L set for the pixel of interest in the selected region is the maximum, and if it is judged as the maximum, the step is judged. If not, the process proceeds to step d13. Step d13
Is a new identification number L + obtained by adding 1 to the identification number L +.
The pixel marked with 1 is set as the pixel of interest in the area, and step d4
And the steps d4 to d12 are repeated. Step d
12, the determination pixel color determination unit 310
If it is determined that the identification number L set for the pixel of interest in the selected region is the maximum, that is, if the determination is made for all the pixels in the mask, the process proceeds to step d14,
At step d14, the process proceeds to step c6 shown in FIG.

According to still another embodiment of the present invention as described above, the determination pixel portion extraction unit extracts the determination pixel portion including the high saturation portion and the low saturation portion in the target pixel area. As a result, when the difference in density between the first and second colors in the target pixel region is not clear, for example, even when the first color is yellow and the second color is white, The first color and the second color can be determined based on the difference in saturation.

As described above, in addition to the density difference, the color difference of the first color and the color difference of the second color are used to determine the chromatic achromaticity of the first color and the second color more accurately. Therefore, it is possible to accurately determine whether the target pixel to be processed, which is either the first color or the second color, is chromatic or achromatic.

The above configuration is merely an example of the invention, and the configuration can be changed within the scope of the invention. For example, it is assumed that the determination pixels belonging to both the high-brightness portion and the low-brightness portion and both the high-saturation portion and the low-saturation portion are detected, but the determination pixel belonging to at least one of the high-brightness portion and the low-brightness portion is determined. By doing so, it is possible to more accurately determine the chromatic / achromatic color of the target pixel to be processed, excluding the pixel of the intermediate color. In addition, the target pixel area does not necessarily include the character portion, and is roughly 2
It may be a surface area composed of color pixels and a pattern area.

The image read by the image input means need not be a document but may be a three-dimensional object read by a CCD sensor. Further, the image output means does not have to form an image on a document, and may be a display means such as a display.

[0218]

As described above, according to the present invention, in a target pixel area having pixels of an approximate color group, which is a group of two approximate colors, a high density portion having a high density and a low density portion having a low density are obtained. After extracting and, it is determined whether the target pixel to be processed is a chromatic color or an achromatic color, based on the color information of the determination pixels belonging to the high density portion or the low density portion. By excluding the intermediate area between the high density area and the low density area, it is possible to accurately determine whether the target pixel to be processed is originally chromatic or achromatic.

As described above, since the image processing apparatus can determine the color of the pixel of interest to be processed, the influence of the reading error is removed, the reproducibility of the output image with respect to the original image is improved, and a high quality image is obtained. Obtainable. For example, the target pixel to be processed corresponding to the black portion of the original image is corrected for the reading error and is accurately determined to be black instead of chromatic color, whereby the reproducibility with respect to the original image can be improved. Further, since input image data having a pixel reading error can be corrected and output, an image input device having high reading accuracy is not required, and the input image data is input from the image input device having low reading accuracy. Also, the original image can be accurately reproduced with a simple configuration.

Further, according to the present invention, the determination pixel portion is
The chromatic / achromatic determination unit extracts the determination pixel portion including at least one of the high-density portion and the low-density portion in the target pixel region, and the processing target pixel is determined based on the color information of the determination pixel. It is determined whether the color is chromatic or achromatic. The image processing apparatus can accurately determine whether the original color of the processing target pixel of interest is originally chromatic or achromatic even when the image represented by the processing target pixel of interest is different from the original image.

As a result, the image represented by the input image data can be corrected to the original color information of the original image and output, the reproducibility of the output image with respect to the original image can be improved, and a high-quality image can be obtained. be able to. For example, even if a pixel representing a black character is erroneously input as a chromatic color pixel due to an error, the color of the pixel can be determined to be black instead of the chromatic color, so that the image can be reproduced more clearly. it can. Further, since the pixel reading error of the image input device can be corrected, an image input device with high reading accuracy is not required, and the original image can be accurately reproduced with a simple configuration.

Further, according to the present invention, based on the results of the first determination unit and the second determination unit of the chromatic / achromatic determination unit, the third determination unit determines whether the pixel of interest to be processed is a chromatic color or an achromatic color. It is possible to more accurately determine the chromatic / achromatic color of the target pixel to be processed by determining whether or not As a result, the reproducibility of the output image with respect to the original image can be improved, and a high quality output image can be obtained. Further, by determining the character portion and the background portion by the edge determination unit, it is possible to determine whether the color of the character portion and the background portion of the image is chromatic or achromatic.

Further, according to the present invention, the color information of the target pixel in the area is set based on the color information of each pixel belonging to the sub target pixel portion. The original color information of the determination pixel can be estimated by extracting the determination pixel based on the color information set for the target pixel in the area. For example, for a thin line image represented by a plurality of color components, even if a thin line with a shifted color component is input to a pixel adjacent to the pixel of interest, the pixel with a shifted color component will become the sub-target pixel portion. By belonging, the original color information of the target pixel can be estimated. With this, the chromatic / achromatic determination unit can determine whether the pixel of interest representing the thin line is chromatic or achromatic. This makes it possible to realize an image processing device with higher reproducibility.

Further, according to the present invention, it is possible to set a judgment pixel portion having a more limited range by using a high density portion having a higher density and a low density portion having a lower density. This makes it possible to more accurately determine whether the target pixel to be processed is a chromatic color or an achromatic color.
Pseudo color area due to the accuracy of the image input device such as physical displacement of the line sensor and vibration during reading,
Particularly in an image in which a plurality of achromatic thin lines are formed, output image data representing the achromatic thin lines can be accurately output even when the color components are misaligned.

Further, according to the present invention, it is possible to more accurately determine whether the target pixel to be processed is chromatic or achromatic by extracting the determination pixel based on the saturation difference in addition to the density difference. Can be determined.

Further, according to the present invention, since the color misregistration determining section can detect the color misregistration part, the color misregistration part is optimized by adjusting the color balance and the black material generation rate. Processing is possible,
The reproducibility of the output image can be improved. For example, in the case where one of the first approximate color group and the second approximate color group, which are distinguished into two of the target pixel areas, is an achromatic color, the color balance of each color component of the pixels belonging to the color shift portion is set. In the same manner, it is possible to perform achromatic correction processing.

Further, according to the present invention, the color-character determining unit obtains the pixel of interest to be processed which is a color-shifted character, and the notifying means reports that the pixel of interest to be processed which is a color-shifted character exists. , It is possible to evaluate the accuracy of color shift of the image input device. Further, by mounting the image processing apparatus including the color character determination unit and the notification means on the image forming apparatus, the color misregistration character information notified by the notification means can be used as one of the maintenance information of the image forming apparatus. .

Further, according to the present invention, the image forming apparatus is provided with the above-mentioned image processing apparatus, so that an error at the time of reading the original input image is corrected, and each pixel has a chromatic color. It is possible to accurately determine whether the color is achromatic or not, and obtain an output image with high reproducibility.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a configuration of a color determination unit 100.

FIG. 2 is a schematic diagram showing a configuration of a line memory 115.

FIG. 3 is a flowchart showing a pixel color determination operation according to the embodiment of the present invention.

FIG. 4 is a schematic diagram showing a high density portion and a low density portion in a mask.

FIG. 5 is a schematic diagram showing a density distribution for each color component of each pixel in a black character area when color misregistration occurs.

FIG. 6 is a schematic diagram showing a density distribution for each color component of each pixel in a color character area.

FIG. 7 is a block diagram showing a configuration of an image forming apparatus 1 including an image processing apparatus 3 according to an embodiment of the present invention.

FIG. 8 is a block diagram showing a configuration of a region separation processing unit 8.

FIG. 9 is an edge determination unit 22 included in the area separation processing unit 8.
3 is a block diagram showing the configuration of FIG.

FIG. 10 is a diagram showing a filter for detecting an edge portion, and FIG. 10 (1) shows a Sobel filter 4 in the main scanning direction.
0, and FIG. 10B shows the Sobel filter 41 in the sub-scanning direction.

FIG. 11 is a block diagram showing a configuration of a color determination unit 200 according to another embodiment of the present invention.

FIG. 12 is a diagram showing a relationship between a mask 105 which is a processing target region and a sub mask 120 which is a sub target pixel portion.

FIG. 13 is a flowchart showing a part of a pixel color determination operation according to another embodiment of the present invention.

FIG. 14 is a flowchart partially showing the color determination operation of FIG.

FIG. 15 is a flowchart partially showing the color determination operation of FIG.

FIG. 16 is a color determination unit 3 according to still another embodiment of the present invention.
It is a block diagram which shows the structure of 00.

FIG. 17 is a flowchart showing a part of a pixel color determination operation according to still another embodiment of the present invention.

FIG. 18 is a flowchart showing in detail step c5 of FIG.

[Explanation of symbols]

100 color judgment section 101 target area extraction unit 102 determination pixel portion extraction unit 103 Chromatic achromatic judgment section 104 target pixel to be processed 105 mask 106 Color Component Average Value Calculation Unit 107 maximum / minimum calculation unit 108 High-density area detector 109 Low-density portion detection unit 110 determination pixel color determination unit 111 counting section 112 High-density / low-density partial color judgment part 113 Target pixel color determination unit 114 Comprehensive judgment section 115 Color misregistration determination unit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/48 H04N 1/40 FF term (reference) 5B057 AA11 BA02 BA30 CA01 CA08 CA12 CA16 CB01 CB08 CB12 CB16 CC03 CE17 CE18 DA08 DA17 DB02 DB06 DB09 DC16 DC25 DC36 5C077 LL19 MP08 PP27 PP28 PP32.

Claims (9)

[Claims] 1. A first step of extracting, from an image in which colors of a plurality of pixels are represented by a plurality of color components, a target pixel region having pixels of an approximate color group, which is a group of two approximate colors, A second step of extracting a high-density portion where the color component density is high in the target pixel area and a low-density portion where the color component density is low in the target pixel area; and at least the high-density portion and the low-density portion And a third step of determining whether the target pixel to be processed included in the target pixel region is a chromatic color or an achromatic color based on color information of the determination pixel belonging to either one of them. Image processing method. 2. A target area extraction unit that extracts a target pixel area having pixels of an approximate color group, which is a group of two approximate colors, from an image in which colors of a plurality of pixels are represented by a plurality of color components. A determination pixel portion extraction unit that extracts a determination pixel portion that includes at least one of a high-density portion with high color component density and a low-density portion with low color component density in the target pixel area; A chromatic / achromatic determination unit that determines whether the target pixel to be processed included in the target pixel region is a chromatic color or an achromatic color based on the color information of the determination pixel belonging to the portion. Image processing device. 3. A chromatic / achromatic determination unit further includes an edge determining unit that determines whether or not the target pixel to be processed belonging to the target pixel region is an edge, and the chromatic / achromatic determining unit determines whether the target pixel to be processed is a chromatic color or not. A first determination unit that determines whether or not the target pixel to be processed is chromatic, a second determination unit that determines whether the determination pixel is chromatic or achromatic, and first and second determination units 3. The image processing apparatus according to claim 2, further comprising a third determination unit that determines again whether the target pixel to be processed is a chromatic color or an achromatic color based on the determination result in 3. 4. The determination pixel portion extracting unit sets a sub-target pixel portion including a target pixel in the area belonging to the target pixel area and a plurality of pixels around the target pixel in the area, and the sub-target pixel portion is set. The sub-target pixel portion setting unit that sets the color information of the target pixel in the area based on the color information of each pixel belonging to the sub-target pixel portion setting unit sets the color information of the target pixel in each area set by the sub-target pixel portion setting unit. The image processing apparatus according to claim 2, wherein the determination pixel is extracted based on the determination. 5. The determination pixel portion extraction unit obtains a value obtained by multiplying the maximum density and the minimum density of the average values of the color components and a difference between the maximum density and the minimum density by a predetermined value to obtain a high density. When extracting a part, the high density part is extracted using the value obtained by multiplying the difference between the maximum density and the maximum density and the minimum density of the average value of the density of the color components by a predetermined value, and the low density part is extracted. In this case, the low density portion is extracted by using a value obtained by multiplying the difference between the minimum density, the maximum density and the minimum density of the average value of the density of the color components by a predetermined value. The image processing device according to any one of claims. 6. The determination pixel portion extraction unit extracts at least one of a high-density portion and a low-density portion, and a high-saturation portion having a high saturation and a low-saturation portion having a low saturation in the target pixel area. The image processing apparatus according to claim 2, wherein a determination pixel portion including at least one of the above is extracted. 7. The chromatic / achromatic determination unit determines whether or not a color component shift has occurred in a pixel of interest to be processed, based on the determination results of the first determination unit and the third determination unit. The image processing apparatus according to claim 3, further comprising a color shift determination unit. 8. Based on the determination results of the edge determination unit and the chromatic / achromatic determination unit, it is determined whether the target pixel to be processed is a chromatic color character, an achromatic color character, or a color shift character, A color character determination unit that determines the number of target pixels to be processed that are determined to be color-shifted characters, and a processing target that is a color-shifted character when the number of target pixels to be processed that are color-shifted characters is equal to or greater than a predetermined threshold value. The image processing apparatus according to claim 3, further comprising a notification unit that notifies that the target pixel exists. 9. An image forming apparatus comprising the image processing apparatus according to claim 2.