JP2003230006A - Image processing method, image processing apparatus, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing method, an image processing apparatus, and an image forming device capable of suppressing a gap caused at adjacent parts of different image areas adjacent to each other in the case of image forming while suppressing an amount of calculation. <P>SOLUTION: A character area discrimination section 10 and a dot area discrimination section 11 discriminate to which of a plurality of image areas each pixel of a received image belongs (discrimination step), a replacement means 14 replaces an adjacent part of different image areas adjacent to each other on the basis of each discrimination result with an intermediate area (replacement step) to correct the discrimination result by each of the discrimination sections 10, 11. In a correction step by a black production under color elimination section 18, a spatial filter processing section 19, and a gradation reproduction processing section 21, the image in the intermediate area is corrected at an intermediated correction level so as to become an image with an intermediate characteristic of each image area adjacent to the intermediate area. Thus, the gap caused at the adjacent part can be suppressed while suppressing the amount of calculation. <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 improving the reproducibility of an original image at the time of image formation and removing a boundary between image areas, for example, a boundary between a character area and a halftone dot area. The present invention relates to an image processing device and an image forming device.

[0002]

2. Description of the Related Art A conventional image forming apparatus extracts various image areas such as a character area, a halftone dot area, and a photograph area from an input image in which a plurality of image areas coexist, and reproduces an original at the time of image formation. In order to improve the property, various image areas are subjected to suitable image processing. For example, an image corresponding to a character area is required to have a high resolution, and therefore, in the spatial filter process, an edge enhancement filter is used to enhance the reproducibility of characters during image formation, and in the halftone process, 1 × 1. Is processed using a small dither matrix of. Since an image corresponding to a halftone dot area is required to have high gradation, it is processed using a smoothing filter for suppressing the generation of moire in the spatial filter processing, and 3 × 3 in the halftone processing. It is processed using a large dither matrix.

Specifically, in the mixed image processing apparatus disclosed in Japanese Patent No. 3188804, a document image including a plurality of image areas is determined as an image area for each predetermined block including a plurality of pixels, and a character area and a halftone dot are displayed. The image is classified into a dot area, a photograph area, and an intermediate area. The middle region is
The image area does not belong to any of the character area, the halftone dot area, and the photograph area. The sorted intermediate area is further classified in one of the row direction and the column direction of the document image based on the image classification of neighboring blocks. For example, if both sides of the middle area are character areas, the middle area is classified as a character area, and if both sides of the middle area are halftone areas, the middle area is classified as a halftone area and When one of both sides is a character area and the other is a halftone area, the intermediate area is classified into a character / halftone area. The intermediate area classified into the character area is subjected to halftone processing using a 1 × 1 dither matrix, and the intermediate area classified into the halftone dot area is subjected to halftone processing using a 3 × 3 dither matrix. The intermediate area classified into the character / dot area is a dither matrix intermediate between the dither matrix used for the dot area and the dither matrix used for the character area, for example, 3 ×.
Halftone processing is performed using a dither matrix of 1. By performing halftone processing using various dither matrices on the intermediate area classified in this way, the character portion isolated in the intermediate area and the halftone dot portion isolated in the intermediate area are corrected, and The affinity of the boundary between the area and the halftone dot area is achieved.

[0004]

[Patent Document 1] Japanese Patent No. 3188804
In the mixed image processing device shown in No. 6, since the image area is determined for each predetermined block in order to suppress the gap between the character area and the halftone dot area, the intermediate area is further classified. There is a problem that the processing becomes complicated and the calculation amount increases. Further, since the intermediate area is classified based on the image classification of the neighboring blocks in only one of the row direction and the column direction of the original image, accuracy is not accurate as a method of extracting various image areas without erroneous determination. Low. In particular, in a document image in which a character area and a halftone area are mixed, both a halftone dot portion and a character portion are included in one block, so that the number of blocks classified as an intermediate area increases. As a result, the intermediate area cannot be accurately classified with only the information on one of the column direction and the row direction, so that the gap generated between the character area and the halftone area cannot be suppressed.
Two or more intermediate areas are arranged in the row and column directions of the original image.
In the case where blocks and three blocks are lined up consecutively, not only information on image regions on both sides of the intermediate region but also information on image regions two blocks and three blocks ahead are considered in the classification process for the intermediate region of interest. Therefore, the classification process for the intermediate region becomes more complicated, and the amount of calculation increases accordingly.

In order to improve the reproducibility of an original at the time of image formation, with respect to an intermediate area classified into various image areas,
Although halftone processing is performed using the dither matrix, in black generation undercolor removal processing and spatial filter processing other than halftone processing, settings are made so that processing is performed on the intermediate area based on the classification results of the intermediate area. Since this is not done, there is a problem that the gap at the boundary between the character area and the halftone dot area will not disappear.

An object of the present invention is to provide an image processing method, an image processing apparatus, and an image provided with the image processing method, which can suppress a gap generated between adjacent portions where different image areas are adjacent to each other during image formation while suppressing the calculation amount. A forming device is provided.

[0007]

According to the present invention, different image areas are adjacent to each other based on a determination step of determining which of a plurality of image areas each pixel of an input image belongs to, and a determination result of the determination step. The replacement step of replacing the adjacent portion with the intermediate area portion and the correction step of correcting the image of each image area and the intermediate area portion according to the characteristics of each image area and the intermediate area portion. So that the image has intermediate characteristics of each adjacent image area,
An image processing method, comprising: a correction step of correcting an image of an intermediate area portion.

According to the present invention, based on the result of the determination in the determination step of determining which of the plurality of image areas each pixel of the input image belongs to, the adjacent portions where different image areas are adjacent are the intermediate area portions. Is replaced in the replacement step.
A new image area is created between different image areas by replacing the adjacent area where different image areas are adjacent to each other with the intermediate area. Each image area determined in the determination step and the image of the newly created intermediate area portion are corrected in the correction step according to the characteristics of each image area and the intermediate area portion. The adjacent portion is replaced with the intermediate area portion, the determination result in the determination step is corrected, and only the correction step is performed according to the characteristics of each image area and the intermediate area portion, so that complicated processing is not required. , The calculation amount can be suppressed as much as possible. When the newly created image of the intermediate area portion is corrected so as to have an intermediate characteristic between adjacent image areas with the intermediate area portion interposed therebetween, the feature amounts of the pixels may be significantly different. It is possible to suppress the gap generated in the adjacent portion due to the cause.

According to the present invention, in the correction step, correction processing is performed on each image area in the same processing mode with different correction levels, and two images adjacent to each other with the intermediate area portion interposed therebetween are provided for the intermediate area portion. It is characterized in that the correction processing of the same processing mode as the correction processing applied to each image area is performed at an intermediate correction level between the correction level applied to one image area of the area and the correction level applied to the other image area.

According to the present invention, in the correction step, the correction processing of the same processing form with different correction levels is applied to each image area. With respect to the intermediate region portion, each of the two image regions adjacent to each other with the intermediate region portion interposed therebetween is set at a correction level intermediate between the correction level applied to one image region and the correction level applied to the other image region. A correction process having the same processing form as the correction process applied to the region is performed in the correction step. By setting the correction level for the intermediate area portion to the intermediate correction level as described above and performing the correction, it is possible to suppress the gap existing in the adjacent portion where different image areas are adjacent.

Further, in the present invention, in the replacement step, two adjacent
When one of the two image areas is a character area and the other of two adjacent image areas is a halftone dot area, the edge area portion adjacent to the halftone dot character area is replaced with the intermediate area portion. To do.

According to the present invention, in the replacement step, when one of the two adjacent image areas is a character area and the other of the two adjacent image areas is a halftone dot area, the character area of the halftone dot area is selected. The adjacent edge area portion is replaced with the intermediate area portion. By replacing the edge area portion with the intermediate area portion, the intermediate area portion plays the role of the character portion in the character area, and the character area is expanded. The extended portion of the character area, that is, the intermediate area portion, is subjected to correction processing at a correction level closer to that of the character than the correction level for the halftone dot area. It is possible to prevent the color from fading.

According to the present invention, in the replacing step, when the character area is a black character area, the edge area portion adjacent to the black character area of the halftone dot area is replaced with the black character corresponding intermediate area portion, and the character area is a color character area. In the case of, the edge area portion adjacent to the color character area of the halftone dot area is replaced with the color character corresponding intermediate area portion.

According to the present invention, in the replacing step, when the character area is a black character area, the edge area portion adjacent to the black character area in the halftone dot area is replaced with the black character corresponding intermediate area portion, and the character area is changed. In the case of the color character area, the edge area portion adjacent to the color character area of the halftone dot area is replaced with the color character corresponding intermediate area portion. Suppressing a gap generated between adjacent areas where the character area and the halftone dot area are adjacent to each other by performing a correction process by substituting predetermined intermediate area parts according to various image areas of the black character area and the color character area. You can

For example, when the character area is a black character area, the black generation amount for the black character area is considerably larger than that for the halftone dot area. Therefore, the black generation amount for the black character corresponding intermediate area portion is larger than that for the halftone dot area. By setting so that it is possible to suppress the gap in the adjacent portion where the black character area and the halftone dot area are adjacent to each other. When the character area is a color character area, the black generation amount for the color character area is the same as the amount for the halftone dot area, so the black generation amount for the color character corresponding intermediate area portion is the same as the amount for the halftone dot area. By setting, it is possible to suppress the gap between the adjacent portions where the color character area and the halftone dot area are adjacent to each other.

Further, in the present invention, in the replacing step, the number of pixels belonging to each image area in the local pixel block and a threshold value preset for each image area are determined based on the judgment result in the judging step. By comparing, it is determined whether or not the local pixel blocks are configured with the same image area. If it is determined that the local pixel blocks are configured with the same image area, the image area to which each pixel in the local pixel block belongs is unified. To do
It is characterized in that the determination result in the determination step is corrected.

According to the present invention, in the replacement step, the number of pixels belonging to each image area in the local pixel block including a plurality of pixels and the number of pixels set in advance in each image area are set based on the determination result in the determination step. The threshold value is compared to determine whether or not the local pixel blocks are formed of the same image area. When it is determined that the local pixel blocks are composed of the same image area in the replacement step, the determination result in the determination step is corrected so as to unify the image areas to which the pixels in the local pixel block belong. Since it is determined whether the local pixel block is composed of the same image region or two or more types of image regions in consideration of all the information about each pixel in the local pixel block, it is assumed that Even if other image areas are mixed due to erroneous determination, the determination result in the determination step can be corrected with high accuracy. By unifying the image area to which each pixel in the local pixel block belongs, it is possible to prevent a plurality of pixels belonging to another image area different from the desired image area from being isolated and contained in the local pixel block. You can

Further, the present invention is characterized in that each threshold value can be set and changed based on a command indicating which one of the image regions is to have the highest reproducibility. .

According to the present invention, it is possible to change the setting of each threshold value based on a command indicating which one of the image regions should have the highest reproducibility.
By setting each threshold value in the replacement step to a value according to each command, it is possible to improve the detection accuracy of pixels that are isolated and included in the local pixel block, and to accurately correct the determination result in the determination step. You can

According to the present invention, a judging means for judging to which of a plurality of image regions each pixel of the input image belongs,
Based on the determination result by the determination means, a replacement means for replacing an adjacent portion where different image areas are adjacent to the intermediate area portion, and an image of each image area and the intermediate area portion according to the characteristics of each image area and the intermediate area portion. A correction means for correcting the image of the intermediate area portion so that an image having intermediate characteristics of adjacent image areas sandwiching the intermediate area portion is formed. Image processing apparatus.

According to the present invention, based on the determination result by the determination means for determining which of the plurality of image areas each pixel of the input image belongs to, the adjacent portions where different image areas are adjacent are the intermediate area portions. Is replaced by the replacement means. A new image area is created between different image areas by replacing the adjacent area where different image areas are adjacent to each other with the intermediate area. Each image area included in the input image and the newly created image of the intermediate area portion are corrected by the correction unit according to the characteristics of each image area and the intermediate area portion. The adjacent portion is replaced with the intermediate area portion, the determination result by the determination means is corrected, and the correction means is only corrected according to the characteristics of each image area and the intermediate area portion, so that complicated processing is not required. , The calculation amount can be suppressed as much as possible. When the newly created image of the intermediate area portion is corrected so as to have an intermediate characteristic between adjacent image areas with the intermediate area portion interposed therebetween, the feature amounts of the pixels may be significantly different. It is possible to suppress the gap generated in the adjacent portion due to the cause.

Further, according to the present invention, the correction means performs correction processing on each image area in the same processing mode with different correction levels, and two images adjacent to the intermediate area portion with the intermediate area portion interposed therebetween. It is characterized in that the correction processing of the same processing mode as the correction processing applied to each image area is performed at an intermediate correction level between the correction level applied to one image area of the area and the correction level applied to the other image area.

According to the present invention, each image area is subjected to the correction processing of the same processing form with different correction levels by the correction means. With respect to the intermediate region portion, each of the two image regions adjacent to each other with the intermediate region portion interposed therebetween is set at a correction level intermediate between the correction level applied to one image region and the correction level applied to the other image region. The correction means performs the same correction processing as the correction processing applied to the area. By setting the correction level for the intermediate area portion to the intermediate correction level as described above and performing the correction, it is possible to suppress the gap existing in the adjacent portion where different image areas are adjacent.

Further, according to the present invention, the replacing means, when one of the two adjacent image areas is a character area and the other of the two adjacent image areas is a halftone dot area, is adjacent to the halftone dot character area. It is characterized in that the edge area portion to be replaced is replaced with the intermediate area portion.

According to the present invention, when one of the two adjacent image areas is a character area and the other of the two adjacent image areas is a halftone dot area, an edge area adjacent to the halftone dot character area. The part is replaced by the replacement means in the intermediate region part. By replacing the edge area portion with the intermediate area portion, the intermediate area portion plays the role of the character portion in the character area, and the character area is expanded.
The expanded part of the character area, that is, the intermediate area,
Since the correction processing is performed at a correction level closer to that of the character than the correction level for the halftone dot area, it is possible to prevent the end of the character from being missing or the color of the end of the character from becoming lighter during image formation.

According to the present invention, when the character area is a black character area, the replacing means replaces the edge area portion adjacent to the black character area of the halftone dot area with the black character corresponding intermediate area portion,
When the character area is a color character area, the edge area portion adjacent to the color character area of the halftone dot area is replaced with the color character corresponding intermediate area portion.

According to the present invention, when the character area is a black character area, the edge area portion adjacent to the black character area of the halftone dot area is replaced with the black character corresponding intermediate area portion by the replacing means, and the character area is colored. In the case of the character area, the edge area portion adjacent to the color character area of the halftone dot area is replaced by the color character corresponding intermediate area portion by the replacement means. According to various image areas of black character area and color character area,
By substituting each of the predetermined intermediate area portions and performing the correction processing on each of the intermediate area portions, it is possible to suppress the gap generated in the adjacent portion where the character area and the halftone dot area are adjacent to each other.

For example, when the character area is a black character area, the black generation amount for the black character area is considerably larger than that for the halftone dot area. Therefore, the black generation amount for the black character corresponding intermediate area portion is larger than that for the halftone dot area. By setting so that it is possible to suppress the gap in the adjacent portion where the black character area and the halftone dot area are adjacent to each other. When the character area is a color character area, the black generation amount for the color character area is the same as the amount for the halftone dot area, so the black generation amount for the color character corresponding intermediate area portion is the same as the amount for the halftone dot area. By setting, it is possible to suppress the gap between the adjacent portions where the color character area and the halftone dot area are adjacent to each other.

Further, according to the present invention, the replacing means sets the number of pixels belonging to each image area in the local pixel block and a threshold value preset for each image area based on the result of the judgment by the judging means. By comparing, it is determined whether or not the local pixel blocks are configured with the same image area. If it is determined that the local pixel blocks are configured with the same image area, the image area to which each pixel in the local pixel block belongs is unified. As described above, the determination result by the determination means is corrected.

According to the present invention, the number of pixels belonging to each image area in the local pixel block including a plurality of pixels and the threshold value set in advance for each image area based on the judgment result by the judging means. Are compared, and whether or not the local pixel blocks are formed in the same image area is determined by the replacement means. When the replacement unit determines that the local pixel blocks are formed of the same image area, the replacement unit determines the result of the determination by the determination unit so as to unify the image areas to which the pixels in the local pixel block belong. Will be corrected. Since it is determined whether the local pixel block is composed of the same image region or two or more types of image regions in consideration of all the information about each pixel in the local pixel block, it is assumed that Even if other image areas are mixed due to erroneous determination, the determination result by the determination unit can be corrected with high accuracy. By unifying the image area to which each pixel in the local pixel block belongs, it is possible to prevent a plurality of pixels belonging to another image area different from the desired image area from being isolated and contained in the local pixel block. You can

Further, the present invention is characterized in that the setting of each threshold value can be changed based on a command indicating which one of the image areas is to be the most reproducible. .

According to the present invention, it is possible to change the setting of each threshold value based on a command indicating which one of the image regions is to have the highest reproducibility.
By setting each threshold value used by the replacement means to a value according to each command, the detection accuracy of the pixels isolated in the local pixel block is improved, and the judgment result by the judgment means is accurately corrected. can do.

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

According to the present invention, a plurality of image regions can be accurately extracted from the input image by correcting the determination result by the determination means so that the local pixel block is composed of the same image region. It is possible to replace an adjacent portion where different image areas are adjacent with an intermediate area portion and perform a correction process according to the intermediate area portion. Since the correction process is performed according to the image of each image region and the intermediate region, it is possible to form an image in which the reproducibility of the image of the input image is improved at the time of image formation.

[0035]

1 is a block diagram showing the configuration of an image forming apparatus 1 according to an 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, an image processing device 3, and an image output device 4. It is configured to include.

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 a sensor using D). The image input device 2 irradiates the original with white light by the light source, and divides the color of reflected light from the original, that is, the wavelength and intensity, into a plurality of pixels arranged in the main scanning direction and the sub-scanning direction by the CCD sensor. Then, the image of the original is read and the original image data representing the image of the original by the color and intensity of each pixel is supplied to the image processing device 3 by an electric signal.

Original image data is represented by numerical values corresponding to the densities of three color components, red, green and blue,
The red signal R, the green signal G, and the blue signal B are given to the image processing device 3 by the image input device 2. The red traffic light R is
It is an electric signal that represents the reflectance of red light from the document in analog for each pixel. The green signal G is an electric signal that represents the reflectance of green light from the document in analog for each pixel. Green light B
Is an electric signal that represents the reflectance of blue light from the original in analog for each pixel.

The image processing apparatus 3 can extract a plurality of image areas from the input image based on the supplied original image data and improve the reproducibility of the original image at the time of image output with respect to the image areas. Is a device for performing image processing. The image processing includes area separation processing for extracting a plurality of image areas from the input image and color correction processing for correcting the color component of each pixel included in the input image. The image processing device 3 includes an analog / digital conversion unit (hereinafter referred to as 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 179, and a black generation undercolor. It includes a removing unit 18, a spatial filter processing unit 19, an output gradation correction unit 20, and a gradation reproduction processing (halftone generation) unit 21.

The A / D converter 5 converts the given analog signal into a digital signal. The A / D converter 5 converts the red signal R, the green signal G, and the blue signal B, which are analog signals and is given by the image input device 2, into digital reflectances of red light, green light, and blue light for each pixel. Are converted into digital signals. The A / D conversion unit 5 supplies the red signal R, the green signal G, and the blue signal B converted into digital signals to the shading correction unit 6.

The shading correction section 6 removes the distortion component contained in the data represented by the red signal R, the green signal G and the blue signal B from the A / D conversion section 5. The shading correction unit 6 generates various signals in the illumination system, the imaging optical system, and the imaging system (image receiving system) of the image input device 2 with respect to the red signal R, the green signal G, and the blue signal B from the A / D conversion unit 5. Processing for removing the distortion component of, and the processed red signal R, green signal G, and blue signal B are given 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 signal R, the green signal G, and the blue signal B from the shading correction unit 6 so as to adjust the color balance of each reflectance value based on the reflectance values, and also corrects each color component. The light reflectance value is converted into a signal indicating the density value of red light, the density value of green light, and the density value of blue light. After that, the input gradation correction unit 7 further represents 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 the three color components that are complementary colors to these. A signal, and thus a cyan signal C that digitally represents the cyan density of each pixel,
A magenta signal M that digitally represents the magenta density of each pixel and a yellow signal Y that digitally represents the yellow density of each pixel are converted.

The input tone correction section 7 supplies a cyan signal C, a magenta signal M and a yellow signal Y representing the pixel values of the pixels of the input image to the area separation processing section 8 and the color correction section 17. The cyan signal C, the magenta signal M, and the yellow signal Y are digital signals representing the image of the document. In the present embodiment, the pixel value of a pixel represents a density value.

The area separation processing unit 8 determines which of the plurality of image areas each pixel of the input image belongs to, and performs the area separation processing for extracting the plurality of image areas from the input image. In the present embodiment, the plurality of image areas are a character area representing a character, a halftone area representing an image with halftone dots, and a photograph area representing a photograph. The area separation processing unit 8 outputs an area identification signal indicating which area each pixel of the input image belongs to, based on the area separation processing result, to the black generation undercolor removal unit 18, the spatial filter processing unit 19, and the gradation. It is given to the reproduction processing unit 21.

The area separation processing section 8 comprises a judging means 9 and a replacing means 14. The determination unit 9 is a unit that determines which of a plurality of image regions each pixel that is the input image belongs to, and includes a character region determination unit 10 and a halftone dot region determination unit 11.

The character area determination unit 10 determines whether or not each pixel of the input image belongs to the character area, and also determines whether or not each pixel of the input image is represented by an achromatic color.
Based on the determination result by the character region determination unit 10, a black character region including pixels represented by achromatic color and a color character region including pixels represented by chromatic color are extracted from the input image.

The character area determination unit 10 includes a character edge determination unit 12 and a chromatic / achromatic determination unit 13. The character edge determination unit 12 determines, based on the cyan signal C, the magenta signal M, and the yellow signal Y from the input tone correction unit 7, whether or not each pixel of the input image is an edge pixel belonging to the character region. To do. In other words, the character edge determination unit 12 determines whether or not each pixel of the input image is included in the character portion in the character area. The character edge determination unit 12
A character area signal representing the determination result for each pixel of the input image is given to the replacing means 14.

The chromatic / achromatic judging section 13 is an input gradation correcting section 7.
Based on the cyan signal C, the magenta signal M, and the yellow signal Y from, it is determined whether or not each pixel of the input image is a pixel representing an achromatic color. The chromatic / achromatic determination unit 13 supplies the chromatic / achromatic signal representing the determination result to the black generation / undercolor removal unit 18, the spatial filter processing unit 19, and the gradation reproduction processing unit 21.

The halftone dot judging section 11 has a cyan signal C, a magenta signal M and a yellow signal Y from the input gradation correcting section 7.
Based on the above, it is determined whether or not each pixel of the input image belongs to the halftone dot area. A halftone dot area is extracted from the input image based on the determination result by the halftone dot determination unit 11.

The halftone dot area is based on the draft of the IEICE Technical Committee (9
0-06-04) can be used to extract from the input image. An arbitrary pixel included in the input image is set as a target pixel, and m × n centering on the target pixel
The following determination process is performed on the block including the number of pixels. The determination result represents the determination result of the pixel of interest by the halftone dot determination unit 11. m and n are natural numbers and may be the same as or different from each other. In the present embodiment, the pixel of interest is a pixel set according to a predetermined order for each pixel of the input image.

First, the average value Dave of the pixel values of the 9 pixels in the center of the block, in other words, the pixel value of each of the 3 × 3 pixels centering on the pixel of interest, is obtained, and the average value Dave is used. The pixel value of each pixel in the block is 2
Valued. Further, with respect to each pixel in the block including m × n pixels, the maximum value Dmax and the minimum value Dmin of the pixel value are obtained based on the pixel value of each pixel before being binarized.

Next, in the halftone dot area, the fluctuation of the image signal in the small area is large, in other words, in the small area, the fluctuation of the pixel value of each pixel continuously arranged in the predetermined scanning direction is large. It is determined whether or not each pixel of the input image belongs to the halftone dot area by utilizing the feature that the density of the halftone dot portion is higher than that of the background portion. Based on the binarized pixel value of each pixel in the block, the number of change points from 0 to 1 and the number of change points from 1 to 0 are respectively counted in the main scanning direction, and the sum of each change point is the main scanning direction. It is calculated as the number of change points Kh in the direction.

Similarly, based on the binarized pixel value of each pixel in the block, 0 to 1 in the sub-scanning direction.
And the number of change points from 1 to 0 are respectively counted, and the sum of the number of change points is the number of change points Kv in the sub-scanning direction.
Is required as. Number of change points in the main scanning direction Kh
Is compared with a predetermined threshold Th, and the number of change points Kv in the sub-scanning direction is compared with a predetermined threshold Tv. Further, in order to prevent erroneous determination of the background, a value obtained by subtracting the average value Dave from the maximum value Dmax is compared with a predetermined threshold value B1, and a value obtained by subtracting the minimum value Dmin from the average value Dave is calculated in advance. Defined threshold B2
And are compared.

Whether or not the pixel of interest belongs to the halftone dot area is determined based on the following conditions. Dmax-Dave> B1 and Dave-Dmin> B2 and Kh> Th and Kv> Tv ... Other than the conditions on the halftone dot region ... Non-halftone dot region

Maximum value Dmax as in the conditional expression shown above
The condition that the value obtained by subtracting the average value Dave from is larger than the threshold value B1 and the average value Dave is the minimum value Dm.
The condition that the value obtained by subtracting in is larger than the threshold value B2, the condition that the number of change points Kh in the main scanning direction is larger than the threshold value Th, and the number of change points Kv in the sub-scanning direction are the threshold values. When all of the conditions of being larger than Tv are satisfied, the pixel of interest is determined to be a pixel belonging to the halftone dot area. The halftone dot determination unit 11 sets each pixel of the input image as a target pixel in a predetermined order, and performs determination processing on all the pixels of the input image. The halftone dot decision section 11 gives the halftone dot area signal representing the decision result to the replacing means 14. The area identification signal includes a character area signal, a halftone dot area signal, and a chromatic / achromatic signal.

In the present embodiment, the pixels which do not belong to any of the image areas of the character area and the halftone dot area are pixels which belong to the photograph area, and are not pixels which belong to the character area in the character area determination unit 10. The pixels determined to belong to the photographic region are determined to belong to the photographic region.

The replacing means 14 is a means for replacing an adjacent portion where different image areas are adjacent to each other with an intermediate area portion on the basis of the result of the determination by the determining means 9, and includes an isolated area portion determining portion 15 and an intermediate area portion determining portion. 16 are included. In the present embodiment, different image regions indicate a character region and a halftone dot region, and the adjacent portion includes pixels belonging to the halftone dot region adjacent to pixels belonging to the character region and is adjacent to the halftone dot character region. The margin area part to be shown is shown.

The isolated area portion determination section 15 of the replacing means 14
Compares the number of pixels belonging to each image region in a local pixel block including a plurality of pixels with a threshold value set in advance for each image region, based on the determination result by the determination unit 9. It is determined whether or not the pixel block is composed of the same image area. When it is determined that the local pixel block is composed of the same image region, the isolated region portion determination unit 15 determines the determination result by the determination unit 9 so as to unify the image regions to which the pixels in the local pixel block belong. To correct.

The isolated area portion determination section 15 produces a black area undercolor removal section 18 and a spatial filter processing section 19 for the character area signal, the halftone dot area signal and the chromatic / achromatic signal representing the corrected determination result.
And the tone reproduction processing unit 21.

Intermediate region part determination unit 16 of the replacement unit 14
Performs processing on information contained in the character area signal, the halftone dot area signal, and the chromatic / achromatic signal from the determination unit 9 which is not corrected by the isolated area portion determination unit 15.

When one of the two adjacent image areas is a character area and the other of the two adjacent image areas is a halftone dot area, the intermediate area part determination unit 16 is adjacent to the halftone dot character area. The edge area portion is replaced with the intermediate area portion.
Further, when the character area is the black character area, the intermediate area part determination unit 16 replaces the edge area part adjacent to the black character area of the halftone dot area with the intermediate area part corresponding to the black character area, and the character area is the color character area. In this case, the edge area portion adjacent to the color character area of the halftone dot area is replaced with the color character corresponding intermediate area portion. The intermediate area portion includes a black character corresponding intermediate area portion and a color character corresponding intermediate area portion.

The intermediate area portion determination unit 16 corrects the determination result by the determination means 9 for the pixels included in the edge area portion replaced with the black character intermediate area portion, and the black character corresponding intermediate area representing the corrected determination result. The signal is given to the black generation undercolor removal unit 18, the spatial filter processing unit 19, and the gradation reproduction processing unit 21.

The intermediate area portion determination section 16 corrects the determination result of the determination means 9 for the pixels included in the edge area portion replaced with the color character intermediate area portion, and corresponds to the color character representing the corrected determination result. The intermediate region signal is given to the black generation and undercolor removal unit 18, the spatial filter processing unit 19, and the gradation reproduction processing unit 21. The black character corresponding intermediate area signal and the color character corresponding intermediate area signal are included in the area identification signal.

The color correction unit 17 removes unnecessary absorption components contained in cyan, magenta, and yellow used as color materials from cyan, magenta, and cyan so that the color reproducibility of the original image can be improved during image formation. Correction processing for removing color turbidity is performed based on the spectral characteristics of each yellow color material. The color correction unit 18 supplies a cyan signal C, a magenta signal M, and a yellow signal Y representing the corrected density values of cyan, magenta, and yellow to the black generation undercolor removal unit 18.

The black generation undercolor removal unit 18 includes a color correction unit 17
Cyan signal C, magenta signal M, and yellow signal Y from the above, and the corrected character area signal, halftone dot area signal, chromatic achromatic signal, intermediate area signal for black characters, and intermediate area for color characters from the area separation processing unit 8. Area signals and are given. The spatial filter processing unit 19 includes a cyan signal C, a magenta signal M, and a yellow signal Y from the black generation and undercolor removal unit 18.
And the corrected character area signal, halftone dot area signal, chromatic achromatic signal, black character corresponding intermediate area signal, and color character corresponding intermediate area signal from the area separation processing unit 8. The gradation reproduction processing unit 21 includes a cyan signal C, a magenta signal M and a yellow signal Y from the output gradation correction unit 20, a corrected character area signal and a halftone dot area signal from the area separation processing unit 8,
A chromatic achromatic signal, a black character corresponding intermediate area signal, and a color character corresponding intermediate area signal are provided.

The black generation undercolor removal unit 18, the spatial filter processing unit 19, and the gradation reproduction processing unit 21 are adapted to the respective image areas and the intermediate areas according to the characteristics of the respective image areas and the intermediate area portions based on the given signals. It is a correction means for correcting the image of the area portion. In the black generation undercolor removal unit 18, the spatial filter processing unit 19, and the gradation reproduction processing unit 21, the image of the intermediate area portion becomes an image having intermediate characteristics of adjacent image areas with the intermediate area portion interposed therebetween. To correct.

The black generation undercolor removal unit 18, the spatial filter processing unit 19 and the gradation reproduction processing unit 21 perform the correction processing of the same processing form with different correction levels for each image area. The black generation undercolor removal unit 18 performs black generation processing and undercolor removal processing with different correction levels on each image area. The spatial filter processing unit 19, for each image region,
Spatial filter processing with different correction levels is performed. The gradation reproduction processing unit 21 performs processing with different correction levels on each image area so that the gradation of the image can be reproduced at the time of image formation.

The black generation undercolor removal unit 18, the spatial filter processing unit 19, and the tone reproduction processing unit 21 are arranged in one of two image regions adjacent to each other with the intermediate region portion sandwiched therebetween. With the correction level intermediate between the correction level to be applied and the correction level to be applied to the other image area, the correction processing of the same processing form as the correction processing to be applied to each image area is performed.

The black generation / undercolor removal unit 18 performs black generation processing and undercolor removal (Under Color Removal) for each pixel based on the density values of cyan, magenta, and yellow of each pixel.
rRemoval: Abbreviated as UCR) processing is performed.

The black generation process is a process for generating a black density value of each pixel based on each density value of cyan, magenta and yellow of each pixel. The undercolor removal processing is processing for newly obtaining the density values of cyan, magenta, and yellow of each pixel by subtracting the generated density value of black from the density values of cyan, magenta, and yellow of each pixel.

As an example of black generation processing, there is a method using skeleton black. In this method, the minimum density value among the density values of cyan, magenta, and yellow of the pixel that is the target of the black generation processing is used as the input value. The minimum density value is substituted into the function for obtaining the black density value, and the obtained output value is set as the black density value for the target pixel.

For example, the function y representing the input / output characteristic of the skeleton curve for obtaining the black density value is represented by y = f (x), and the cyan density value based on the cyan signal C is C1 for the density value of each pixel. The density value of magenta based on the magenta signal M is represented by M1, and the density value of yellow based on the yellow signal Y is represented by Y1. Regarding the density value of each pixel newly generated, for example, the cyan density value is C2.
The density value of magenta that is newly generated is represented by M2, the density value of yellow is newly represented by Y2, and the density value of black that is newly generated is represented by K. Undercolor removal rate is α (0 <α
When expressed by <1), the black generation processing and the undercolor removal processing are
It is expressed by the following formula. K = f {min (C1, M1, Y1)} C2 = C1-αK M2 = M1-αK Y2 = Y1-αK

Black generation undercolor removal unit 1 by color correction unit 17
The signals of the three colors of the cyan signal C, the magenta signal M, and the yellow signal Y given to 8 are processed by the black generation lower color removal unit 18 and the cyan signal C, the magenta signal M,
The signals are converted into four color signals of yellow signal Y and black signal K. The color correction unit 17 supplies the spatial filter processing unit 19 with a cyan signal C, a magenta signal M, a yellow signal Y, and a black signal K representing the density value of each pixel.

The spatial filter processing section 19 outputs the original image data based on the cyan signal C, the magenta signal M, the yellow signal Y and the black signal K from the black generation / undercolor removal section 18 from the area separation processing section 8. Based on the region identification signal,
Spatial filter processing by a predetermined filter is performed. The spatial filter process includes a sharp enhancement process for increasing the enhancement amount of the high frequency component and a low pass filter process for removing a noise component included in the pixel value of the pixel for each image region.

The spatial filter processing by the spatial filter processing section 19 corrects the spatial frequency characteristic of each image area, and prevents blurring and graininess deterioration of the image at the time of image formation. The spatial filter processing section 19 supplies the output gradation correction section 20 with the cyan signal C, the magenta signal M, the yellow signal Y, and the black signal K after the spatial filter processing.

Further, the tone reproduction processing section 21 is similar to the processing by the spatial filter processing section 19 in that the spatial filter processing section 1
The original image data based on the cyan signal C, the magenta signal M, the yellow signal Y, and the black signal K from 9 are subjected to predetermined processing based on the area identification signal from the area separation processing unit 8.

For example, with respect to the character area extracted by the area separation processing unit 8, the spatial filter processing unit 19 is arranged so that the reproducibility of black characters and color characters is improved during image formation.
Then, the amount of high frequency enhancement is increased by the sharpening process. After that, the gradation reproduction processing unit 21 selects either the binarization processing or the multi-value conversion processing on the high resolution screen suitable for the reproduction of the high frequency for the character area.

The halftone dot area extracted by the area separation processing unit 8 is subjected to a low-pass filter process for removing the input halftone dot component in the spatial filter processing unit 19. The output gradation correction unit 20 converts an applied signal representing the density value of each pixel into a halftone dot area ratio, which is a characteristic value of the image output device 4, for the output gradation. Correction processing is performed. Then, the gradation reproduction processing unit 21 divides the image into pixels and performs a halftone generation processing for processing so that each gradation can be finally reproduced at the time of image formation.

With respect to the photographic area extracted by the area separation processing unit 8, the gradation reproduction processing unit 21 performs either one of binarization processing and multi-value conversion processing on the screen with an emphasis on gradation reproducibility. Is given.

The original image data which has been subjected to the above-described respective processes, in other words, the information contained in the cyan signal C, the magenta signal M, the yellow signal Y and the black signal K after being processed by the gradation reproduction processing section 21 is temporarily stored. The image output device 4 is stored in the image output device 4 and is read out from the storage device at a predetermined timing.
Given to.

The image output device 4 is a device for forming an image on a recording material based on the document image data which has been subjected to various kinds of image processing by the image processing device 3. Examples of the image output device 4 include, but are not particularly limited to, a color image output device using an electrophotographic method and an inkjet method. The image output device may be an image display device such as a liquid crystal display.

In the present embodiment, each processing in the image forming apparatus 1 is controlled by a control means (not shown) such as a central processing unit (abbreviated as CPU).

FIG. 2 is a block diagram showing the configuration of the character edge determination unit 12. The character edge determination unit 12 determines, for each pixel of the input image, for each color of cyan, magenta, and yellow, whether each pixel is an edge pixel in the character region. An edge pixel is a pixel whose pixel value shows a sharp change that is significantly different from the pixel value of an adjacent pixel, for example, the density value. The character edge determination unit 12
The edge detection unit 30 and the logical sum determination unit 31 are included.

The edge detection section 30 performs edge determination processing for determining whether or not the pixel of interest is an edge pixel based on the cyan signal C, the magenta signal M and the yellow signal Y from the input gradation correction section 7. . The edge determination unit 30 sets each pixel of the input image as a pixel of interest in a predetermined order, and performs determination processing on all pixels of the input image.

In the present embodiment, the character edge determination unit 12
Has three edge determination units 30 because it performs edge determination processing for each color of cyan, magenta, and yellow for the pixel of interest. The edge determination process performed for each color of cyan, magenta, and yellow is different only in color, and since the procedure of the process is the same, the same description will be omitted and the same reference numerals will be given to the same configurations. .

The edge judging section 30 is composed of a line memory 32 and a density difference judging section 33. The line memory 32 holds information on three pixels lined up continuously in a predetermined scanning direction based on the cyan signal C, the magenta signal M, and the yellow signal Y from the input gradation correction unit 7. The information about the pixel includes information on the density value of the pixel.
The edge determination unit 30 has two line memories 32. Information based on 6 pixels by the two line memories 32, and 3 based on the signal from the input gradation correction unit 7
The information regarding the number of pixels is provided to the density difference determination unit 33, so that the edge determination process is performed for each local pixel block including 3 × 3 pixels centered on the target pixel.

The one line memory 32 of the two line memories supplies the information about the three held pixels to the density difference determination section 33, and the other line memory 3
Information on 3 pixels from 2 is newly held. Two
The other line memory 32 of the book line memory 32 gives the held information about the three pixels to the one line memory 32 and the density difference determination unit 33, and also receives the signal from the input tone correction unit 7. Based on the above, information on three pixels is newly held.

With respect to the local pixel block including 3 × 3 pixels, the density difference determining unit 33 determines the density value of the target pixel and the remaining pixels, in other words, the eight pixels except the target pixel in the local pixel block. The density difference, which is the difference between the density values of adjacent pixels, is obtained. For example, the density difference determination unit 33 subtracts the density value of one adjacent pixel from the density value of the pixel of interest, and obtains the absolute value of the subtracted value as the density difference. Concentration difference determination unit 3
3 similarly obtains the density differences for the remaining 7 adjacent pixels.

The density difference determining unit 33 compares each density difference obtained for the pixel of interest and the eight adjacent pixels with a predetermined threshold value. If any one of the density differences is greater than the threshold value, it is determined that the pixel of interest is an edge pixel, and if all the density differences are less than or equal to the threshold value, it is determined that the pixel of interest is not an edge pixel. . The density difference determination unit 33 outputs the signal indicating the determination result to the logical sum determination unit 31.
Give to.

In the present embodiment, as the threshold value in the density difference determination unit 33, the threshold value THc is used for cyan, the threshold value THm is used for magenta, and the threshold value THy is used for yellow. cyan,
The threshold values for each color of magenta and yellow may be set to different values, or may be set to the same value.

The logical sum judging section 31 calculates a logical sum based on the information contained in the given signals. Logical sum determination unit 3
In FIG. 1, a determination result of determining whether each pixel of the input image is an edge pixel is given for each color of cyan, magenta, and yellow. The logical sum determination unit 31 has the characteristic of the character region that the density difference between the target pixel and the adjacent pixel is large and the gradation property, so that the density difference between two pixels adjacent to each other in the photo region is The determination processing is performed in consideration of the characteristic of the photo area that the size is smaller than that of the text area.

When it is determined that the target pixel is an edge pixel for any one of the colors cyan, magenta, and yellow, the logical sum determination unit 31 is the edge pixel belonging to the character area. Is determined.
When it is determined that the pixel of interest is not an edge pixel for all colors of cyan, magenta, and yellow, the logical sum determination unit 31 determines that the pixel of interest belongs to the photographic area. The logical sum determination unit 31 gives a signal representing the determination result to the black generation undercolor removal unit 18, the spatial filter processing unit 19, and the gradation reproduction processing unit 21 as a character region signal.

FIG. 3 is a block diagram showing the configuration of the chromatic / achromatic determination unit 13. The chromatic / achromatic determination unit 13 includes a maximum value calculation unit 35, a minimum value calculation unit 36, a difference unit 37, and a comparator 3.
8 is included. Based on the cyan signal C, the magenta signal M, and the yellow signal Y from the input gradation correction unit 7, the chromatic / achromatic determination unit 13 determines whether each pixel of the input image is a pixel representing an achromatic color. judge. In other words, the chromatic / achromatic determination unit 13 determines, for each pixel in the input image, whether the set target pixel is a pixel representing an achromatic color. The chromatic / achromatic determination unit 13 sets each pixel of the input image as a pixel of interest in a predetermined order, and performs determination processing on all the pixels of the input image.

The maximum value calculating section 35
Of the density values of cyan, magenta, and yellow, the maximum density value of the color is calculated, and a signal representing the calculation result is given to the differentiator 37. The minimum value calculation unit 36
With respect to the pixel of interest, the density value of the minimum color is calculated from among the density values of each color of cyan, magenta, and yellow, and a signal representing the calculation result is given to the differentiator 37.

The differencer 37 subtracts the minimum density value from the maximum density value of the pixel of interest based on the calculation results of the maximum value calculation section 35 and the minimum value calculation section 36.
The difference value is calculated, and the signal representing the difference value is calculated by the comparator 38.
Give to.

The comparator 38 uses the cyan pixel at the pixel of interest,
Considering the characteristic that the pixel of interest is represented by an achromatic color when the difference in density value between magenta and yellow is small, and the pixel of interest is represented by a chromatic color when the difference in density value is large, Perform judgment processing. Comparator 38
Is a pixel represented by an achromatic color when the difference value is less than or equal to the threshold value TH by comparing the difference value with a predetermined threshold value TH based on the calculation result of the differencer 37. If it is determined that the difference is larger than the threshold value TH, it is determined that the pixel of interest is a pixel represented by a chromatic color. The comparator 38 uses the signal representing the determination result as a chromatic / achromatic signal to generate the black generation undercolor removal unit 18 and the spatial filter processing unit 19.
And the tone reproduction processing unit 21.

FIG. 4 is a diagram showing an example of a local pixel block. FIG. 4 (1) shows an image area in the case where an isolated character area portion 40 exists in a halftone dot area, and FIG. )
Indicates the corrected halftone dot area. FIG. 5 is a diagram showing an example of a local pixel block, FIG. 5 (1) shows an image area in the case where an isolated halftone dot area portion 41 exists in a character area, and FIG. 5 (2) shows The corrected character area is shown. The isolated area portion determination unit 15 determines the number of pixels belonging to each image area in a local pixel block including a plurality of pixels and a threshold value set in advance for each image area based on the determination result of the determination unit 9. Are compared to determine whether the local pixel blocks are formed of the same image area. When it is determined that the local pixel block is composed of the same image region, the isolated region portion determination unit 15 determines the determination result by the determination unit 9 so as to unify the image regions to which the pixels in the local pixel block belong. To correct.

The determination result by the determination means 9 is given to a memory block of 50 rows and 50 columns which holds information about, for example, 50 × 50 pixels, before the processing by the isolated area portion determination section 15. Information on one pixel is held in one memory. The memory block of 50 rows and 50 columns holds information about each pixel of the input image for every 50 × 50 pixels. The isolated area part determination unit 15 performs a correction process on a local pixel block of 50 rows and 50 columns including 50 × 50 pixels based on a memory block.

The isolated area portion determination unit 15 determines the number Ns of pixels belonging to the halftone dot area based on the determination result of the determination unit 9 for the local pixel block including 50 × 50 pixels.
cr, the number Ned of pixels belonging to the character area, the number Ned_k of pixels belonging to the black character area, and the number Ned_c of pixels belonging to the color character area are counted. Isolated area portion determination unit 15
Compares each pixel number Nscr, Ned with a preset threshold value.

In the present embodiment, the character area includes the black character area and the color character area, and the pixels belonging to the black character area are determined by the character area determination unit 10 to belong to the character area and are represented by achromatic color. It is a pixel determined to be. Pixels belonging to the color character area are determined by the character area determination unit 10
Is a pixel that is determined to belong to the character area and is represented by a chromatic color. The number of pixels Ned belonging to the character area is represented by a value obtained by adding the number of pixels Ned_k belonging to the black character area and the number of pixels Ned_c belonging to the color character area.

The number of pixels Nscr belonging to the halftone dot area is larger than the preset threshold value THs1 and the number of pixels Ned belonging to the character area is the preset threshold value Ts.
When it is smaller than He1, as shown in FIG. 4 (1), a plurality of pixels erroneously determined by the determination means 9 to belong to the character area within the local pixel block that should originally be determined to be the halftone dot area. There is an isolated character area portion 40 including

The isolated character area portion 40 is a pixel judged by the judging means 9 as belonging to the character area, and includes at least one pixel. The preset threshold THs1 has a value sufficiently larger than the preset threshold THe1.

The isolated area portion determination unit 15 determines that the number of pixels Nscr belonging to the halftone dot area is a preset threshold value THs.
Number of pixels larger than 1 and belonging to the character area Ned
However, if the condition is smaller than the threshold value THe1 set in advance, it is determined that the local pixel blocks are formed of the same image area, that is, a halftone dot area. The conditional expression for forming the local pixel block in the halftone dot area is expressed as follows. Nscr> THs1 and Ned <THe1

As described above, the isolated area portion determination unit 15 sets the image area to which each pixel in the local pixel block belongs to the halftone dot area based on the comparison result between the number of pixels belonging to each pixel area and the threshold value. In order to unify, the isolated character area portion 40
The decision result of the decision means 9 for the pixel included in is corrected. When the determination result by the determination means 9 is corrected for the pixels included in the isolated character area portion 40 in the halftone dot area,
As shown in FIG. 4B, the image area to which each pixel in the local pixel block belongs is unified into a halftone dot area.

The number Ned of pixels belonging to the character area is larger than the preset threshold THe2, and the number Nscr of pixels belonging to the halftone dot area is the preset threshold T.
If it is smaller than Hs2, as shown in FIG. 5 (1), a plurality of pixels erroneously determined by the determination means 9 to belong to the halftone dot region within the local pixel block that should originally be determined to be the character region. There is an isolated halftone dot area portion 41 including.

The isolated halftone dot area portion 41 is a pixel judged by the judging means 9 to belong to the halftone dot area, and includes at least one pixel. The preset threshold value THe2 has a value sufficiently larger than the preset threshold value THs2.

The isolated area portion determination unit 15 determines that the number of pixels Ned belonging to the character area is a preset threshold value THe2.
Number of pixels belonging to the halftone dot region and larger than Nscr
However, if the condition is smaller than a preset threshold value THs2, it is determined that the local pixel blocks are formed of the same image area, that is, a character area. Further, the isolated area portion determination unit 15 compares the number of pixels Ned_k belonging to the black character area and the number of pixels Ned_c belonging to the color character area for the local pixel block. When the number of pixels belonging to the black character area is larger than the number of pixels belonging to the color character area, the isolated area part determination unit 15 determines that the local pixel block is composed of the black character area, and determines the pixels belonging to the black character area. If the number is less than or equal to the number of pixels belonging to the color character area, it is determined that the local pixel block is composed of the color character area.

The conditional expression for forming the local pixel block in the black character area is expressed as follows. Ned_k> Ned_c and Ned> THe2 and Nscr <THs2

The conditional expression for forming the local pixel block in the color character area is expressed as follows. Ned_k ≦ Ned_c and Ned> THe2 and Nscr <THs2

The isolated area part determination unit 15 determines the image area to which each pixel in the local pixel block belongs as a black character area and a color based on the comparison result between the number of pixels belonging to each pixel area and the threshold value as described above. The determination result of the determination unit 9 for the pixels included in the isolated halftone dot area portion 41 is corrected so as to be unified in any of the character areas. When the determination result by the determination unit 9 is corrected for the pixels included in the isolated halftone dot area portion 41 in the halftone dot area, the image area to which each pixel in the local pixel block belongs is changed as shown in FIG. 5B. , The black character area and the color character area are unified.

Since it is determined whether the local pixel block is composed of the same image area or two or more types of image areas in consideration of all the information about each pixel in the local pixel block, the same image area is temporarily assumed. Even if another image region is mixed in the region due to an erroneous determination, the determination result by the determination unit 9 can be corrected with high accuracy.

By unifying the image areas to which each pixel in the local pixel block belongs, a plurality of pixels belonging to another image area different from the desired image area can be isolated and included in the local pixel block. Can be prevented.

After the determination result by the determination means 9 is corrected by the isolated area portion determination section 15, the adjacent area where different image areas are adjacent is replaced by the intermediate area portion determination section 16, so that the local pixel block. It is possible to prevent the pixels included in the inside from being replaced by the intermediate area portion. This makes it possible to suppress the conventionally existing gap in the edge area portion adjacent to the character area in the halftone dot area.

The thresholds THs1, THe1, THs2, and THe2 in the isolated area portion determination unit 15 are set based on a command indicating which one of the image areas should have the highest reproducibility. Be changed. For example, the threshold value group A (THs1_m
s, THE1_ms, THs2_ms, THE2_m
s) and a threshold group B (THs1_m, for character mode)
(THe1_m, THs2_m, THe2_m) are held in the memory, and the threshold value corresponding to each command is prepared in advance. The character / print photo mode is a command for maximizing the reproducibility of the halftone dot area during image formation. The character mode is a command for maximizing the reproducibility of the character area during image formation. Each threshold value group A and B is a set including a plurality of preset threshold values.

The isolated area portion determination section 15 determines one of the threshold group A for the character / print photograph mode and the threshold group B for the character mode in accordance with a command during image formation. A value group is selected, and each threshold value of the selected threshold value group is used as a threshold value in the isolated region part determination unit 15.

The threshold value THs1_ms of the threshold value group A and the threshold value THs1_m of the threshold value group B correspond to the threshold value THs1 in the isolated area portion determination section 15, and when the character / print photo mode is selected, for example, The threshold value THs1_ms of the threshold value group A is used as the threshold value THs1 in the isolated region part determination unit 15.

The threshold value THe1_ms of the threshold value group A and the threshold value THe1_m of the threshold value group B correspond to the threshold value THe1 in the isolated area portion determining section 15, and, for example, when the character / print photo mode is selected, The threshold value THe1_ms of the threshold value group A is used as the threshold value THe1 in the isolated region part determination unit 15.

The threshold value THs2_ms of the threshold value group A and the threshold value THs2_m of the threshold value group B correspond to the threshold value THs2 in the isolated area portion determining section 15, and, for example, when the character / print photo mode is selected, The threshold value THs2_ms of the threshold value group A is used as the threshold value THs2 in the isolated region part determination unit 15.

The threshold value THe2_ms of the threshold value group A and the threshold value THe2_m of the threshold value group B correspond to the threshold value THe2 in the isolated area portion determining section 15, and, for example, when the character / print photo mode is selected, The threshold value THe2_ms of the threshold value group A is used as the threshold value THe2 in the isolated region part determination unit 15.

In the character / print photo mode, the threshold value THs of the threshold value group A is set so that the reproducibility of the halftone dot area becomes high.
1_ms is set to a value smaller than the threshold value THs1_m of the threshold value group B, and the threshold value THe of the threshold value group A is set.
1_ms is set to a value larger than THe1_m of the threshold value group B. Accordingly, the detection accuracy of the isolated character area portion 40 in the halftone dot area can be made higher than the detection accuracy of the isolated character area portion 40 in the halftone dot area in the character mode, and the correction processing in the isolated area portion determination unit 15 can be performed. The accuracy of can be further increased.

In the character mode, the threshold value THe2_m of the threshold value group B is set to increase the reproducibility of the character area.
It is set to a value smaller than the threshold value THe2_ms of the threshold value group A, and the threshold value THs2_m of the threshold value group B is
It is set to a value larger than the threshold value THs2_ms of the threshold value group A. As a result, the detection accuracy of the isolated halftone dot area portion 41 in the character area can be made higher than the detection accuracy of the isolated halftone dot area portion 41 in the character area in the character / print photograph mode. It is possible to further improve the accuracy of the correction processing in.

As an example of the setting of the command at the time of image formation described above, the command is selected by the operator operating the operation panel provided in the image forming apparatus 1. The operation panel includes, for example, a liquid crystal display which is a display device, various command setting buttons, and a ten-key pad. Instead of using the operation panel, the document may be pre-scanned in advance, the type of the image formed on the document may be automatically determined, and the command may be set based on the determination result.

FIG. 6 is a diagram showing an example of a block of 5 rows and 5 columns in which the edge area portion adjacent to the black character area of the halftone dot area is replaced with the black character corresponding intermediate area portion. Figure 7
It is a figure which shows an example of the block of 5 row 5 columns by which the edge area part adjacent to the color character area of a halftone dot area was replaced by the color character corresponding intermediate area part. The intermediate area portion determination unit 16 did not perform the correction processing by the isolated area portion determination unit 5.
A correction process is performed on a local pixel block of 50 rows and 50 columns including 0 × 50 pixels.

For the local pixel block of 50 rows and 50 columns, the intermediate area portion determination section 16 intermediates adjacent portions in which different image areas are adjacent based on the determination result of the determination means 9 for each block of 5 rows and 5 columns. Perform processing to replace the area. The block of 5 rows and 5 columns is an image region including 25 pixels including the target pixel.

In the determination processing by the intermediate area portion determination unit 16, for the local pixel block of 50 rows and 50 columns, for example, the pixel of 1st row and 1st column is first set as the pixel of interest, and the block of 5th row and 5th column is set. , Applied to that block. Next, the row is not changed, and the pixel in the first row and the second column, which is shifted by one column in the predetermined scanning direction, is set as the target pixel, and a new pixel is added.
A block in row and column 5 is set, and the intermediate region part determination unit 16 performs the determination process on the block.

In the same procedure, with respect to the first row, the pixels from the third column to the final column, that is, the 50th column are sequentially set as the target pixel, and the 5th row and 5th column centering on each target pixel are set. The determination processing by the intermediate area portion determination unit 16 is performed on each block. When the determination process for the block of 5th row and 5th column centered on the pixel of the 1st row and 50th column is completed,
With respect to each pixel on the second row which is shifted by one row in the row direction, a procedure similar to the procedure for setting the pixel of interest for each pixel on the first row and the block of 5th row and 5th column is executed. In this way, the processing similar to the setting procedure of the pixel of interest and the block of 5th row and 5th column regarding each pixel of the 1st row is executed in the third row and thereafter, and the intermediate area portion for the local pixel block of 50th row and 50th column is executed. The determination processing by the determination unit 16 is performed.

In the present embodiment, regarding the local pixel block of 50 rows and 50 columns, for example, when the pixel of the 1st row and 1st column is set as the pixel of interest and the block of 5 rows and 5 columns is set,
In the block of 5 rows and 5 columns, not only the pixels inside the local pixel block but also the pixels outside the local pixel block exist. In this way, when the pixels in the 5 × 5 block correspond to the pixels outside the local pixel, the pixels in the 5 × 5 block corresponding to the pixels outside the local pixel block are 5 rows and 5 columns. Are treated formally as the pixels for forming the block, and are not subject to the determination processing by the intermediate area portion determination unit 16.

Regarding the block of 5 rows and 5 columns shown in FIG. 6, for example, one of the column directions is set to the main scanning direction H and one of the row directions is set to the sub scanning direction V. An address indicating where each pixel is in the block is set to each pixel of the block of 5 rows and 5 columns. The address of each pixel in the block of 5 rows and 5 columns is represented in the form of coordinates. 1 row 1
The address of the pixel in the column is represented by (0, 0), and the addresses of the pixels in the first row and second column to the first row and fifth column arranged in the main scanning direction H are (1, 0), (2, 0), (3,0),
Represented by (4,0) respectively, when the number of columns changes, the number on the left side in parentheses changes. The addresses of the pixels from the first row and first column to the second row and first column to the fifth row and first column arranged in the sub-scanning direction V are (0, 1), (0, 2),
Represented by (0,3) and (0,4) respectively, when the number of lines changes, the numerical value on the right side in parentheses changes.

With respect to the block of 5 rows and 5 columns, the intermediate area portion determination section 16 determines that the pixel of interest at the address (2, 2) is a pixel belonging to the character area and is adjacent to the pixel of interest in the predetermined scanning direction. If the pixel belongs to a halftone dot area different from the character area, the intermediate area part determination unit 16 replaces two pixels in the predetermined scanning direction from the pixel of interest with a pixel included in the intermediate area part.

For example, in the main scanning direction H, when the pixel of interest at the address (2,2) is a pixel belonging to the character area, the pixel of address (1,2) adjacent to the pixel of interest is a pixel belonging to the halftone dot area. In some cases, the pixel at the address (1, 2) and the pixel at the address (0, 2) are replaced with the pixel included in the intermediate area portion, and the pixel at the address (3, 2) is a pixel belonging to the halftone dot area. In this case, the pixel at the address (3, 2) and the pixel at the address (4, 2) are replaced with the pixel included in the intermediate area portion.

Similarly, in the sub-scanning direction V, when the pixel of interest at address (2,2) belongs to the character area, the pixel of address (2,1) adjacent to the pixel of interest belongs to the halftone dot area. If pixel, address (2,1)
When the pixel at the address (2, 0) is replaced with the pixel included in the intermediate area and the pixel at the address (2, 3) adjacent in the main scanning direction H is a pixel belonging to the halftone dot area, The pixel at the address (2,3) and the pixel at the address (2,4) are replaced with the pixel included in the intermediate area portion.

In the present embodiment, the processing by the intermediate area portion determination unit 16 is performed only when the pixels adjacent to the pixels belonging to the character area are the pixels belonging to the halftone dot area and the pixels included in the intermediate area portion. In other cases, for example, when the pixel adjacent to the pixel belonging to the character area is the pixel belonging to the character area and the pixel belonging to the photographic area, it is not performed.

As described above, the pixels in the local pixel block of 50 rows and 50 columns are subjected to the processing by the intermediate area determination unit 16 so that the edge area portion adjacent to the character area of the halftone dot area is , The intermediate area portion is replaced.

Regarding the block of 5 rows and 5 columns shown in FIG.
The pixel of interest at the address (2, 2) is a pixel belonging to the black character area. When the pixel of interest at the address (2, 2) is a pixel belonging to the black character region and the pixel adjacent to the pixel of interest in the predetermined scanning direction is a pixel belonging to the halftone dot region, Area portion determination unit 16
Replaces two pixels in the predetermined scanning direction from the pixel of interest with pixels included in the black character corresponding intermediate area portion.

For the pixel of interest at address (2,2),
The pixel at the address (1, 2) adjacent in the main scanning direction H is
Since it is a pixel belonging to the halftone dot area, the intermediate area portion determination unit 16 replaces the pixel at the address (1, 2) with the pixel included in the black character corresponding intermediate area portion. Then, the intermediate area portion determination unit 16 further replaces the pixel at the address (0, 2) with the pixel included in the black character corresponding intermediate area portion. The black character corresponding intermediate area portion is included in the intermediate area portion.

Regarding the block of 5 rows and 5 columns shown in FIG.
Since the pixels at the addresses (2,1), (2,3), (3,2) adjacent to the pixel of interest at the address (2,2) belong to the black character area, like the pixel of interest, The processing by the area portion determination unit 16 is not performed.

In the present embodiment, the processing by the intermediate area portion determination unit 16 is performed only when the pixels adjacent to the pixels belonging to the black character area are the pixels belonging to the halftone dot area and the pixels included in the black character corresponding intermediate area portion. Otherwise, in other words, when the pixel adjacent to the pixel belonging to the black character area is the pixel belonging to the black character area, the pixel belonging to the color character area, and the pixel belonging to the photographic area. Is not applied.

In this way, each pixel in the local pixel block of 50 rows and 50 columns is subjected to the processing by the intermediate area portion determination section 16, so that the edge area portion adjacent to the black character area of the halftone dot area is processed. Is replaced with the intermediate area portion corresponding to the black character area.

Regarding the 5 × 5 block shown in FIG.
The pixel of interest at the address (2, 2) is a pixel belonging to the color character area. When the pixel of interest at the address (2, 2) is a pixel belonging to the color character region and the pixel adjacent to the pixel of interest in the predetermined scanning direction is a pixel belonging to the halftone dot region, Intermediate region part determination unit 16
Replaces the two pixels in the predetermined scanning direction from the pixel of interest with the pixels included in the color-character corresponding intermediate region portion.

For the pixel of interest at address (2,2),
The pixel at the address (1, 2) adjacent in the main scanning direction H is
Since it is a pixel belonging to the halftone dot area, the intermediate area part determination unit 16 replaces the pixel at the address (1, 2) with the pixel included in the color character corresponding intermediate area part. Further, the intermediate area portion determination unit 16 replaces the pixel at the address (0, 2) with the pixel included in the color character corresponding intermediate area portion. The color character corresponding intermediate area portion is included in the intermediate area portion.

Regarding the block of 5 rows and 5 columns shown in FIG. 7,
Since the pixels at the addresses (2,1), (2,3), (3,2) adjacent to the pixel of interest at the address (2,2) belong to the color character area, like the pixel of interest, The processing by the intermediate area part determination unit 16 is not performed.

In the present embodiment, the processing by the intermediate area portion determination unit 16 is such that the pixels adjacent to the pixels belonging to the color character area are the pixels belonging to the halftone dot area and the pixels included in the color character corresponding intermediate area portion. In other cases, the pixels adjacent to the pixels belonging to the character area are pixels belonging to the black character area, the pixels belonging to the color character area, and the pixels belonging to the photo area. In case it is not applied.

As described above, the pixels in the local pixel block of 50 rows and 50 columns are subjected to the processing by the intermediate area portion determination unit 16, so that the edge area portion adjacent to the color character area of the halftone dot area is processed. Is replaced with the intermediate area portion corresponding to the color character area.

FIG. 8 is a graph showing the correction level applied to each image area in the black generation and undercolor removal unit 18. The black generation undercolor removal unit 18 receives the cyan signal C from the color correction unit 17,
The magenta signal M, the yellow signal Y, and the black signal K, and the corrected halftone dot area signal, the character area signal, the chromatic achromatic signal, the black character corresponding intermediate area signal, and the color character corresponding intermediate area signal from the area separation processing unit 8. Based on the above, the correction processing is performed at the optimum correction level for each image area according to each image area.

The black generation / undercolor removal unit 18 sets the density value of black generated by the black generation processing to the minimum density value min (C, C, among the cyan, magenta and yellow colors of each pixel of each image area). M, Y). Regarding the black character area, the relationship between the density value of the generated black and the minimum density value min (C, M, Y) is represented by the solid line 45 shown in FIG. The density value of generated black and the minimum density value min for the black character corresponding intermediate area portion
The relationship with (C, M, Y) is represented by the broken line 46 shown in FIG. FIG. 8 shows the relationship between the density value of the generated black and the minimum density value min (C, M, Y) for the halftone dot area, the photograph area, the color character area, and the color character corresponding intermediate area portion. It is represented by a one-dot chain line 47.

As shown in FIG. 8, the black density value in the black character area is larger than the black density values in the black character corresponding intermediate area portion, the halftone dot area, the photograph area, the color character area and the color character corresponding intermediate area portion. Is set. As a result, the black generation amount in the black character area becomes larger than the black generation amount in the black character corresponding intermediate area portion, the halftone dot area, the photograph area, the color character area and the color character corresponding intermediate area portion.

As shown in FIG. 8, the black density value in the black character corresponding intermediate area portion is smaller than the black density value in the black character area, and the halftone dot area, the photograph area, the color character area and the color character corresponding intermediate area portion Is set to be larger than the black density value in. As a result, the black generation amount in the black character corresponding intermediate area portion is smaller than the black generation amount in the black character area and larger than the black generation amount in the halftone dot area, the photograph area, the color character area and the color character corresponding intermediate area portion.

As described above, the black character corresponding intermediate area portion is set to a correction level intermediate between the black character area and the halftone dot area. For example, in a document image in which halftone dots and black characters coexist, even if the pixels belonging to the image area that should originally be determined to be the black character area are included in the black character corresponding intermediate area portion, the black generation undercolor of the black character corresponding intermediate area portion is generated. The correction level in the removal unit 18 is set to be higher than the correction level in the black generation undercolor removal unit 18 in the halftone dot area. As a result, the black character corresponding intermediate region portion plays the role of a character expansion region that can be regarded as a character region, and therefore, compared to the case where the pixels belonging to the image region that should be determined to be the black character region are included in the halftone dot region. The black ink amount can be further increased.

Further, the edge area portion adjacent to the black character area of the halftone dot area is replaced with the black character corresponding intermediate area portion, and the correction level in the black generation undercolor removal unit 18 of the black character corresponding intermediate area portion is set to the black character area and the halftone dot area. By setting the correction level in the middle of the area, it is possible to suppress the conventionally existing gap in the edge area portion adjacent to the black character area in the halftone dot area.

The black density value in the color-character corresponding intermediate area portion is also set to be an intermediate value between the black density value in the black character area and the black density value in the halftone dot area. In order to further enhance the effect of the present invention, as shown in FIG. 8, the density value of black in the color character corresponding intermediate area portion is the same as the density value of black in the halftone dot area, the photograph area and the color character area. Is set as follows.
As a result, the black generation amount in the color character corresponding intermediate region portion becomes smaller than the black generation amount in the black character region and the black character corresponding intermediate region portion.

As described above, the color character corresponding intermediate area portion is set to the same correction level as that of the halftone dot area, the photograph area and the color character area, so that the black amount in the color character corresponding intermediate area portion is suppressed and the halftone dot area is reduced. It is possible to suppress the conventionally existing gap in the edge area portion adjacent to the color character area of the area, and to suppress the newly generated gap by replacing the edge area portion with the color character corresponding intermediate area portion. .

By performing the correction processing in the black generation undercolor removal unit 18 as described above, the edge area portion adjacent to the black character area of the halftone dot area and the edge area portion adjacent to the color character area of the halftone dot area are obtained. It is possible to suppress the gap that occurs in the black character area, and since the black amount increases in the black character area, it is possible to form a black character with an improved image quality during image formation.

FIG. 9 is a diagram showing an example of a filter in the spatial filter processing section 19, FIG. 9 (1) shows a halftone dot area filter 50, and FIG. 9 (2) shows a photograph area filter. 9 (3) shows a character area filter 52, and FIG. 9 (4) shows a character corresponding intermediate area filter 53. The spatial filter processing unit 19 receives the cyan signal C, the magenta signal M, the yellow signal Y, and the black signal K from the black generation and undercolor removal unit 18, and the corrected halftone dot area signal and character area from the area separation processing unit 8. Based on the signal, the chromatic / achromatic signal, the black character corresponding intermediate area signal, and the color character corresponding intermediate area signal, correction processing is performed at an optimum correction level for each image area according to each image area.

The spatial filter processing section 19 applies a low-pass filter process for removing the input halftone dot component to the halftone dot region by using the halftone dot region filter 50 shown in FIG. 9 (1). The spatial filter processing unit 19 performs a certain smoothing process on the high frequency components using the filter 51 for the photo regions shown in FIG. , To some extent sharpening treatment. The spatial filter processing unit 19 uses the character area filter 52 shown in FIG. 9C for the black character area and the color character area so as to improve the reproducibility of the black character and the color character during image formation. Emphasize processing.

By thus performing the predetermined spatial filter processing on the character area, the halftone dot area and the photographic area, a high resolution can be obtained in the character area and a high gradation can be obtained in the halftone dot area and the photographic area. And the reproducibility in the character area can be improved during image formation, and moire in the halftone dot area can be suppressed.

The spatial filter processing section 19 adjusts the black character-corresponding intermediate area portion and the color character-corresponding intermediate area portion so that the correction level is intermediate between the correction level in the character area and the correction level in the halftone dot area. Spatial filter processing is performed using the character corresponding intermediate area part filter 53 shown in 9 (4).

For example, in an image in which halftone dots and black characters coexist, even if the pixels that should originally be determined to belong to the black character area are included in the black character corresponding intermediate area portion, the black character corresponding intermediate area portion is included in the halftone dot. Since the spatial frequency emphasis amount is large compared to the above, the black character corresponding intermediate region portion functions as a character expansion region, and the reproducibility of characters can be further improved during image formation.

The correction level for the black character corresponding intermediate area portion is set to the intermediate correction level between the black character area and the halftone dot area as described above. Therefore, by replacing the edge area portion adjacent to the black character area of the halftone dot area with the black character corresponding intermediate area portion, it is possible to suppress the conventionally existing gap in the adjacent portion between the black character area and the halftone dot area.

The correction level for the color character corresponding intermediate area portion is set to the intermediate correction level between the color character area and the halftone dot area as described above. Therefore, by replacing the edge area portion adjacent to the color character area of the halftone dot area with the color character corresponding intermediate area portion, it is possible to suppress the gap that has conventionally existed in the adjacent portion between the color character area and the halftone dot area. it can.

Similarly to the black generation processing and the undercolor removal processing in the black generation / undercolor removal section 18, the spatial filter processing in the above-described spatial filter processing section 19 also accurately extracts each image area and the intermediate area corresponding to the black character. Since a predetermined process is performed on the color and character intermediate region,
An image with improved reproducibility can be formed during image formation.

FIG. 10 is a diagram showing an example of the dither matrix in the tone reproduction processing section 21, which is shown in FIG.
Indicates a 1 × 1 dither matrix 54, and is shown in FIG.
Indicates a 2 × 2 dither matrix 55, and is shown in FIG.
Indicates a 4 × 4 dither matrix 56. The gradation reproduction processing unit 21 receives the cyan signal C, the magenta signal M, the yellow signal Y, and the black signal K from the output gradation correction unit 20, and the corrected halftone dot area signal and character area from the area separation processing unit 8. Based on the signal, the chromatic / achromatic signal, the black character corresponding intermediate area signal, and the color character corresponding intermediate area signal, correction processing is performed at an optimum correction level for each image area according to each image area.

The tone reproduction processing section 21 applies dither processing to each image area by using a dither matrix having a predetermined size. The dither process uses a dither matrix having a predetermined size so that the gradation of the image in each image region can be accurately reproduced at the time of image formation, and for each region corresponding to the size of the dither matrix in each image region, This is a process of comparing the pixel value of each pixel in each image region with the value of the dither matrix corresponding to each pixel to perform binarization.

The gradation reproduction processing section 21 binarizes the pixel value of each pixel for each black pixel area and color character area using the 1 × 1 dither matrix 54 shown in FIG. 10A. . The gradation reproduction processing unit 21 compares the pixel value of each pixel with the value of the 1 × 1 dither matrix 54,
For example, when the pixel value is equal to or larger than the value of the 1 × 1 dither matrix 54, the pixel value is replaced with 1 and the pixel value is
If the value is smaller than the value of the 1 × 1 dither matrix 54, the pixel value is replaced with 0.

By performing the dither processing on the black character area and the color character area as described above, the high frequency of the black character area and the color character area can be reproduced, and an image with improved character resolution at the time of image formation can be obtained. Can be formed.

The gradation reproduction processing section 21 uses the 4 × 4 dither matrix 56 shown in FIG. 10 (3) for the halftone dot area and the photographic area to determine the pixel value of each pixel for each 4 × 4 area. Binarize. By performing the dither processing on the halftone dot area and the photographic area as described above, the gradation of the halftone dot area and the photographic area can be reproduced, and at the time of image formation, the print photograph and the floor of the photograph included in the original image can be reproduced. The tonality can be maintained.

The gradation reproduction processing section 21 performs the processing shown in FIG. 10 for the black character corresponding intermediate area portion and the color character corresponding intermediate area portion.
Using the 2 × 2 dither matrix 55 shown in (2), the pixel value of each pixel is binarized for every 2 × 2 regions. The dither processing in the black character corresponding intermediate area portion and the color character corresponding intermediate area portion is set so as to be an intermediate correction level between the correction level in the black character area and the color character area and the correction level in the halftone dot area.

For example, in an image in which halftone dots and black characters are mixed, even if the pixels that should originally be determined to belong to the black character area are included in the black character corresponding intermediate area portion, in the dither processing in the black character corresponding intermediate area portion, A 2 × 2 dither matrix 55 having a size smaller than the halftone dot area is used. As a result, the intermediate area corresponding to black characters is
It plays the role of a character expansion area and can further improve the resolution of characters during image formation.

The size of the dither matrix in the black character corresponding intermediate area portion is set to an intermediate size between the character area and the halftone dot area. Therefore, the edge area portion adjacent to the black character area of the halftone dot area is set to the black character corresponding intermediate area. By substituting the portions, it is possible to suppress the gap that has existed in the past between the black character area and the halftone dot area. The dither processing in the color character corresponding intermediate area portion has the same effect as the dither processing in the black character corresponding intermediate area.

The dither processing in the tone reproduction processing section 21 described above is also accurately extracted in the same manner as the black generation processing and the undercolor removal processing in the black generation / undercolor removal section 18, and the spatial filter processing in the spatial filter processing section 19. Predetermined processing is performed on each of the image areas, the intermediate area portion corresponding to black characters, and the intermediate area portion corresponding to color characters, so that an image with improved reproducibility can be formed at the time of image formation.

FIG. 11 is a flow chart showing the processing procedure of the isolated area portion determination step included in the replacement step in the embodiment of the present invention. FIG. 12 is a flowchart showing a processing procedure of the intermediate region part determination step included in the replacement step in the embodiment of the present invention. According to the image processing method of the present invention, an intermediate area portion is replaced by replacing an adjacent area where different image areas are adjacent to each other with an intermediate area portion so that an image having intermediate characteristics of adjacent image areas sandwiching the intermediate area is formed. This is a method of suppressing the gap generated in the adjacent portion by correcting the image of.

The image processing method of the present invention includes a determining step, a replacing step and a correcting step. In the determining step, it is determined to which of the plurality of image regions each pixel of the input image belongs. In the replacing step, the adjacent area where different image areas are adjacent to each other is replaced with the intermediate area based on the result of the judgment in the judging step. The replacement step includes an isolated area portion determination step and an intermediate area portion determination step.

In the isolated area portion determination step, the number of pixels belonging to each image area in the local pixel block including a plurality of pixels and the threshold value set in advance for each image area are determined based on the determination result in the determination step. Are compared with each other, and it is determined whether or not the local pixel blocks are formed in the same image area. In the isolated region part determination step, the local pixel block is
When it is determined that they are composed of the same image area, the determination result in the determination step is corrected so that the image area to which each pixel in the local pixel block belongs is unified. In the isolated region part determination step, for the local pixel block, step s1, step s2, step s3, step s4, step s5, step s6, step s in FIG.
7 and each processing in step s8 is performed.

In step s0 of FIG. 11, it is determined in the determination step which of the plurality of image regions each pixel of the input image belongs to, and the process proceeds to step s1.

At step s1, for each pixel of the input image, a local pixel block of 50 rows and 50 columns including a plurality of pixels is extracted, and the process proceeds to step s2.

At step s2, the number of pixels Nscr belonging to the halftone dot area, the number of pixels Ned_k belonging to the black character area and the number Ne of pixels belonging to the color character area in the local pixel block.
Each d_c is counted, and the process proceeds to step s3.

In step s3, the condition that the number of pixels Nscr belonging to the halftone dot area is larger than a preset threshold value THs1 and the number of pixels Ned belonging to the character area Ned
However, it is determined whether or not both satisfy the condition of being smaller than a preset threshold value THe1. The pixel number Ned belonging to the character area is a value obtained by adding the pixel number Ned_k belonging to the black character area and the pixel number Ned_c belonging to the color character area.

In step s3, when both of the above two conditions are satisfied, it is determined that the local pixel block is composed of a halftone dot area, and the process proceeds to step s4. Go to s5.

In step s4, with respect to the local pixel block determined to be composed of the halftone dot area, the judgment result in the judgment step is made so that the image area to which each pixel in the local pixel block belongs is unified to the halftone dot area. Is corrected and the process proceeds to step s17.

In step s5, the condition that the number of pixels Nscr belonging to the halftone dot area is smaller than a preset threshold value THs2, and the number of pixels Ned belonging to the character area Ned
, Both of which satisfy the condition of being larger than a preset threshold value THe2.

In step s5, if both of the above two conditions are satisfied, it is determined that the local pixel block is composed of a character area, and the process proceeds to step s6. 1 to the intermediate area portion determination step shown in FIG.

At step s6, the number of pixels Ned_k belonging to the black character area is equal to the number of pixels Ned_k belonging to the color character area.
It is determined whether or not it is larger than c. In step s6, if the number Ned_k of pixels belonging to the black character area is larger than the number Ned_c of pixels belonging to the color character area, it is determined that the local pixel block is composed of the black character area, and the process proceeds to step s7. Number of pixels belonging to black character area Ned_
If k is equal to or less than the number of pixels Ned_c belonging to the color character area, it is determined that the local pixel block is composed of the color character area, and the process proceeds to step s8.

In step s7, with respect to the local pixel block determined to be composed of the black character area, the determination result in the determination step is corrected so that the image area to which each pixel in the local pixel block belongs is unified to the black character area. Then, the process proceeds to step s17.

In step s8, with respect to the local pixel block determined to be composed of the color character area, the determination result in the determination process is performed so that the image area to which each pixel in the local pixel block belongs is unified to the color character area. Is corrected and the process proceeds to step s17.

The threshold values THs1, THe1, THs2, and THe2 in the isolated area portion determination step are changed based on a command indicating which one of the image areas should have the highest reproducibility. To be done. For example, the threshold value group A (THs1_m
s, THE1_ms, THs2_ms, THE2_m
s) and a threshold group B (THs1_m, for character mode)
(THe1_m, THs2_m, THe2_m) are stored in the memory, and the threshold value corresponding to each command is prepared in advance.

In the isolated area portion determination step, one of the threshold value group A for the character / print photograph mode and the threshold value group B for the character mode is selected according to a command during image formation. A group is selected, and each threshold value of the selected threshold value group is used as a threshold value in the isolated region part determination unit 15. By thus preparing the threshold value corresponding to each command and setting the threshold value in the isolated region portion determination step according to the command, the accuracy of the correction in the isolated region portion determination step can be improved. .

In the intermediate area portion determination step, when one of the two adjacent image areas is a character area and the other of the two adjacent image areas is a halftone dot area, the edge of the halftone dot area adjacent to the character area is determined. The area portion is replaced with the intermediate area. In the intermediate area portion determination step, when the character area is a black character area, the edge area portion adjacent to the black character area of the halftone dot area is replaced with the black character corresponding intermediate area portion, and the character area is a color character area. , The edge area portion adjacent to the color character area of the halftone dot area is replaced with the color character corresponding intermediate area portion.

In the intermediate area portion determining step, steps s9, s10, s11, step s12, step s13, and step s of FIG. 12 are applied to the local pixel blocks which are not corrected in the isolated area portion determining step.
14, each processing in step s15 and step s16 is performed.

In step s9, a block of 5 rows and 5 columns centering on the pixel of interest is extracted from the local pixel block that has not been corrected in the isolated region portion determination step, and the process proceeds to step s10. With respect to the local pixel block that has not been corrected in the isolated region portion determination step, the target pixel is set according to a predetermined order.

At step s10, it is judged whether or not the pixel of interest belongs to the black character area based on the judgment result in the judgment step. In step s10, if it is determined that the target pixel belongs to the black character area, the process proceeds to step s11, and if it is determined that the target pixel does not belong to the black character region, the process proceeds to step s13.

In step s11, it is determined whether or not the pixel adjacent to the pixel of interest belongs to the halftone dot area. If it is determined in step s11 that the pixel adjacent to the target pixel belongs to the halftone dot area, the process proceeds to step s12. If it is determined that the pixel adjacent to the target pixel does not belong to the halftone dot area, step s16. Proceed to.

In step s12, the pixel determined to belong to the halftone dot area in step s11 and the pixel adjacent to the pixel of interest sandwiching the pixel are replaced with the pixels included in the black character corresponding intermediate area portion. The determination result in the determination step is corrected, and the process proceeds to step s16.

At step s13, it is judged whether or not the pixel of interest belongs to the color character area based on the judgment result in the judgment step. In step s13, if it is determined that the target pixel belongs to the color character area, the process proceeds to step s14, and if it is determined that the target pixel does not belong to the color character region, the process proceeds to step s16.

In step s14, it is determined whether or not the pixel adjacent to the pixel of interest belongs to the halftone dot area. If it is determined in step s14 that the pixel adjacent to the target pixel belongs to the halftone dot area, the process proceeds to step s15, and if it is determined that the pixel adjacent to the target pixel does not belong to the halftone dot area, step s16. Proceed to.

In step s15, the pixel determined to belong to the halftone dot area in step s14 and the pixel adjacent to the pixel of interest sandwiching the pixel are replaced with the pixels included in the color character corresponding intermediate area portion. The determination result in the determination step is corrected, and the process proceeds to step s16.

In step s16, it is determined whether or not the intermediate region portion determination process has been completed for the local pixel block of 50 rows and 50 columns. In the intermediate region partial determination step, with respect to the local pixel block of 50 rows and 50 columns, all the pixels in the local pixel block are set as the target pixel,
The processing is performed on the blocks of 5 rows and 5 columns. If it is determined in step s16 that the intermediate region partial determination step has been completed for the local pixel block, the connector proceeds to step s17 shown in FIG. If it is determined that the processing has not ended, the process proceeds to step s9.

In step s17, it is determined whether or not the replacement process has been completed for the entire input image. When it is determined in step s17 that the process in the replacement step has been completed for the entire input image, the process proceeds to step s18, all the processing steps in the replacement process are completed, and the process in the replacement step is completed for the entire input image. If it is determined that it has not been performed, the process proceeds to step s1.

In the replacement step, when one of the two adjacent image areas is a character area and the other of the two adjacent image areas is a halftone dot area, the edge area portion adjacent to the halftone dot character area is By being replaced with the intermediate area portion, the intermediate area portion functions as a character expansion area that can be regarded as a character area. The extended portion of the character area, that is, the intermediate area portion, is subjected to correction processing at a correction level closer to that of the character than the correction level for the halftone dot area. It is possible to prevent the color from fading.

In the replacing step, a predetermined intermediate area portion is replaced according to various image areas of the black character area and the color character area, and a correction process is performed, thereby adjoining the character area and the halftone dot area. It is possible to suppress the gap that occurs in the.

After the processing in the replacement step is completed, the processing in the correction step is performed based on the judgment result in the judgment step and the judgment result in the corrected judgment step in the replacement step.

In the correction step, the images of the image areas and the intermediate area are corrected according to the characteristics of the image areas and the intermediate area. In the correction step, the image of the intermediate area portion is corrected so as to be an image having an intermediate characteristic between the character area and the halftone dot area which are adjacent to each other with the intermediate area portion interposed therebetween.

In the correction step, the black generation processing and the undercolor removal processing in the black generation / undercolor removal section 18 and the spatial filter processing in the spatial filter processing section 19 are performed on each image area and the intermediate area portion as described above. The dither processing is performed in the gradation reproduction processing unit 21.

In the correction step, the character area, the halftone dot area, and the photograph area extracted from the input image are subjected to the correction processing of the same processing form having different correction levels, and the intermediate area portion is subjected to the intermediate area portion. With the correction level intermediate between the correction level applied to the character area and the correction level applied to the halftone dot area, the correction processing of the same processing form as the correction processing applied to each image area is performed.

The above-described embodiment is merely an example of the present invention, and the configuration can be changed within the scope of the present invention. For example, the edge pixel detection processing in the edge detection unit 30 is not limited to the above processing, and may be processing using a filter for edge pixel detection such as a Sobel filter. The block including a plurality of pixels in the isolated area portion determination unit 15 and the intermediate area portion determination unit 16 is not limited to the size described above, and may be set to have a size suitable for the system used.

According to the embodiment of the present invention, the determination means 9 determines which of the plurality of image areas each pixel of the input image belongs to, and based on the determination result, the character area of the halftone dot area. The edge area portion adjacent to is replaced with the intermediate area portion by the replacement means 14. In this way, a new image area is created between different image areas. Each of the image areas determined by the determination means and the image of the newly created intermediate area portion are generated in accordance with the characteristics of each image area and the intermediate area portion, the black generation undercolor removal unit 18, the spatial filter processing unit 19, and It is corrected by the gradation reproduction processing unit 21.

As described above, the adjacent portion is replaced with the intermediate area portion, the determination result of the determining means 9 is corrected, and the black generation undercolor removal portion 18, the spatial filter processing portion 19 and By the gradation reproduction processing unit 21,
Since only the intermediate area is corrected, the complicated processing is not required and the calculation amount can be suppressed as much as possible.
Furthermore, a black generation undercolor removal unit 18 and a spatial filter processing unit 19
Since the correction level of the intermediate area portion in the gradation reproduction processing unit 21 is set to the intermediate correction level between the character area and the halftone dot area, the image of the intermediate area portion is such that the characters adjacent to each other with the intermediate area portion sandwiched therebetween. It is corrected to have an intermediate property between the area and the halftone dot area. With this, it is possible to suppress the gap generated in the adjacent portion due to the feature amount of the pixel being significantly different.

[0205]

According to the present invention, each pixel of the input image is
Based on the result of the determination in the determination step of determining which one of the plurality of image areas it belongs to, the adjacent portion where different image areas are adjacent is replaced with the intermediate area portion in the replacement step. A new image area is created between different image areas by replacing the adjacent area where different image areas are adjacent to each other with the intermediate area. Each image area determined in the determination step and the image of the newly created intermediate area portion are corrected in the correction step according to the characteristics of each image area and the intermediate area portion. The adjacent portion is replaced with the intermediate area portion, the determination result in the determination step is corrected, and only the correction step is performed according to the characteristics of each image area and the intermediate area portion, so that complicated processing is not required. ,
The calculation amount can be suppressed as much as possible. The newly created image of the intermediate region portion is corrected in the correction process so that the image having the intermediate characteristics of the image regions adjacent to each other with the intermediate region portion interposed therebetween is corrected, and the feature amount of the pixel is reduced. Due to the significant difference, it is possible to suppress the gap conventionally existing in the adjacent portion.

Further, according to the present invention, in the correction step, the correction processing of the same processing form with different correction levels is performed on each image area. With respect to the intermediate region portion, each of the two image regions adjacent to each other with the intermediate region portion interposed therebetween is set at a correction level intermediate between the correction level applied to one image region and the correction level applied to the other image region. A correction process having the same processing form as the correction process applied to the region is performed in the correction step. By setting the correction level for the intermediate area portion to the intermediate correction level as described above and performing the correction, it is possible to suppress the gap that was conventionally present in the adjacent portion where different image areas are adjacent.

Further, according to the present invention, in the replacing step, when one of the two adjacent image areas is a character area and the other of the two adjacent image areas is a halftone dot area, the character area of the halftone dot area is The edge area portion adjacent to is replaced with the intermediate area portion. By replacing the edge area portion with the intermediate area portion, the intermediate area portion functions as a character expansion area that can be regarded as a character area. The extended portion of the character area, that is, the intermediate area portion, is subjected to correction processing at a correction level closer to that of the character than the correction level for the halftone dot area. It is possible to prevent the color from fading.

Further, according to the present invention, in the replacing step, when the character area is a black character area, the edge area portion adjacent to the black character area of the halftone dot area is replaced with the black character corresponding intermediate area portion, Is a color character area,
The edge area portion adjacent to the color character area of the halftone dot area is replaced with the color character corresponding intermediate area portion. Depending on the various image areas of the black character area and the color character area, by replacing each with a predetermined intermediate area portion and performing correction processing,
It is possible to suppress the gap that has been conventionally present in the adjacent portion where the character area and the halftone dot area are adjacent to each other.

For example, when the character area is a black character area, the black generation amount for the black character area is considerably larger than that for the halftone dot area. Therefore, the black generation amount for the black character corresponding intermediate area portion is larger than that for the halftone dot area. By setting so that it is possible to suppress the gap in the adjacent portion where the black character area and the halftone dot area are adjacent to each other. When the character area is a color character area, the black generation amount for the color character area is the same as the amount for the halftone dot area, so the black generation amount for the color character corresponding intermediate area portion is the same as the amount for the halftone dot area. By setting the gap, it is possible to suppress the gap that has been conventionally present in the adjacent portion where the color character region and the halftone dot region are adjacent to each other.

Further, according to the present invention, in the replacement step, the number of pixels belonging to each image area in the local pixel block including a plurality of pixels and the preset number for each image area are set in advance based on the determination result in the determination step. Is compared with a threshold value to determine whether or not the local pixel blocks are formed in the same image area. When it is determined that the local pixel blocks are composed of the same image area in the replacement step, the determination result in the determination step is corrected so as to unify the image areas to which the pixels in the local pixel block belong. By unifying the image area to which each pixel in the local pixel block belongs, it is possible to prevent a plurality of pixels belonging to another image area different from the desired image area from being isolated and contained in the local pixel block. You can Since it is determined whether the local pixel block is composed of the same image region or two or more types of image regions in consideration of all the information about each pixel in the local pixel block, it is assumed that Even if other image areas are mixed due to erroneous determination, the determination result in the determination step can be corrected with high accuracy. After correcting the determination result in the determination step, by processing the adjacent area in which different image areas are adjacent to each other, the pixels included in the local pixel block can be replaced with the intermediate area. Can be prevented. As a result, it is possible to suppress the gap that has conventionally existed in the adjacent portion where different image areas are adjacent to each other.

Further, according to the present invention, it is possible to change the setting of each threshold value on the basis of a command indicating which one of the image regions is to have the highest reproducibility. By setting each threshold value in the replacement step to a value according to each command, it is possible to improve the detection accuracy of pixels that are isolated and included in the local pixel block, and to accurately correct the determination result in the determination step. You can

Further, according to the present invention, based on the judgment result by the judgment means for judging which one of the plurality of image areas each pixel of the input image belongs to, the adjacent portion where the different image areas are adjacent to each other is the intermediate area. The part is replaced by the replacement means. A new image area is created between different image areas by replacing the adjacent area where different image areas are adjacent to each other with the intermediate area. Each image area determined by the determination means and the image of the newly created intermediate area portion are corrected by the correction means according to the characteristics of each image area and the intermediate area portion. The adjacent portion is replaced with the intermediate area portion, the determination result by the determination means is corrected, and the correction means is only corrected according to the characteristics of each image area and the intermediate area portion, so that complicated processing is not required. , The calculation amount can be suppressed as much as possible.
The newly created image of the intermediate area portion is corrected by the correction unit so that the image having the intermediate characteristics of the image areas adjacent to each other with the intermediate area portion interposed therebetween is obtained. It is possible to suppress the gap generated in the adjacent portion due to the remarkable difference.

Further, according to the present invention, the correction processing of the same processing form with different correction levels is applied to each image area by the correction means. For the intermediate area part, regarding two image areas that are adjacent to each other with the intermediate area part in between,
The correction means performs the correction processing of the same processing form as the correction processing performed on each image area at an intermediate correction level between the correction level applied to one image area and the correction level applied to the other image area. The correction level for the intermediate area,
By setting an intermediate correction level and performing correction as described above, it is possible to suppress the gap existing in the adjacent portion where different image areas are adjacent to each other.

Further, according to the present invention, when one of the two adjacent image areas is a character area and the other of the two adjacent image areas is a halftone dot area, an edge of the halftone dot area adjacent to the character area The area portion is replaced with the intermediate area portion by the replacement means. By replacing the edge area portion with the intermediate area portion, the intermediate area portion functions as a character expansion area that can be regarded as a character area. The extended portion of the character area, that is, the intermediate area portion, is subjected to correction processing at a correction level closer to that of the character than the correction level for the halftone dot area. It is possible to prevent the color from fading.

Further, according to the present invention, when the character area is a black character area, the edge area portion adjacent to the black character area of the halftone dot area is replaced with the black character corresponding intermediate area portion by the replacing means, and the character area is changed. If it is a color character area, the edge area portion adjacent to the color character area of the halftone dot area is
The color character corresponding intermediate area portion is replaced by the replacing means. According to various image areas of the black character area and the color character area, the predetermined intermediate area portions are respectively replaced, and the respective intermediate area portions are subjected to correction processing so that the character area and the halftone dot area are adjacent to each other. The gap that occurs can be suppressed.

For example, when the character area is a black character area, the black generation amount for the black character area is considerably larger than that for the halftone dot area. Therefore, the black generation amount for the black character corresponding intermediate area portion is larger than that for the halftone dot area. By setting so that it is possible to suppress the gap in the adjacent portion where the black character area and the halftone dot area are adjacent to each other. When the character area is a color character area, the black generation amount for the color character area is the same as the amount for the halftone dot area, so the black generation amount for the color character corresponding intermediate area portion is the same as the amount for the halftone dot area. By setting, it is possible to suppress the gap between the adjacent portions where the color character area and the halftone dot area are adjacent to each other.

Further, according to the present invention, the number of pixels belonging to each image area in the local pixel block including a plurality of pixels and the threshold value set in advance for each image area based on the judgment result by the judging means. Are compared with each other, and the replacement unit determines whether or not the local pixel blocks are formed of the same image area. When the replacement unit determines that the local pixel blocks are formed of the same image area, the replacement unit determines the result of the determination by the determination unit so as to unify the image areas to which the pixels in the local pixel block belong. Will be corrected. By unifying the image area to which each pixel in the local pixel block belongs, it is possible to prevent a plurality of pixels belonging to another image area different from the desired image area from being isolated and contained in the local pixel block. You can For the local pixel block, the same image area and 2
Since the determination as to which of the image areas of the type or more is configured is made by considering all the information about each pixel in the local pixel block, other image areas may be mixed in the same image area due to an erroneous determination. However, the determination result by the determination unit can be corrected with high accuracy. After correcting the determination result by the determination means, if processing is performed so as to replace the adjacent portion where different image areas are adjacent to the intermediate area portion,
It is possible to prevent isolated pixels included in the local pixel block from being replaced by the intermediate area portion. As a result, it is possible to suppress the gap that has conventionally existed in the adjacent portion where different image areas are adjacent to each other.

Further, according to the present invention, it is possible to change the setting of each threshold value on the basis of a command indicating which one of the image regions has the highest reproducibility. By setting each threshold value used by the replacement means to a value according to each command, the detection accuracy of the pixels isolated in the local pixel block is improved, and the judgment result by the judgment means is accurately corrected. can do.

Further, according to the present invention, a plurality of image regions can be accurately extracted from the input image by correcting the determination result by the determination means so that the local pixel block is composed of the same image region. At the same time, an adjacent portion where different image areas are adjacent to each other can be replaced with an intermediate area portion, and a correction process according to the intermediate area portion can be performed. Since the correction process is performed according to the image of each image region and the intermediate region, it is possible to form an image in which the reproducibility of the image of the input image is improved at the time of image formation.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a configuration of a character edge determination unit 12.

FIG. 3 is a block diagram showing a configuration of a chromatic / achromatic determination unit 13.

FIG. 4 is a diagram showing an example of a local pixel block, FIG. 4 (1) shows an image region when an isolated character region portion 40 exists in a halftone dot region, and FIG. 4 (2) shows The corrected halftone dot area is shown.

FIG. 5 is a diagram showing an example of a local pixel block, FIG. 5 (1) shows an image area in the case where an isolated halftone dot area portion 41 exists in a character area, and FIG. 5 (2) shows The corrected character area is shown.

FIG. 6 is a diagram showing an example of a block of 5 rows and 5 columns in which an edge area portion adjacent to a black character area of a halftone dot area is replaced with a black character corresponding intermediate area portion.

FIG. 7 is a diagram showing an example of a block of 5 rows and 5 columns in which an edge area portion adjacent to a color character area of a halftone dot area is replaced with a color character corresponding intermediate area portion.

8 is a graph showing a correction level applied to each image area in the black generation undercolor removal unit 18. FIG.

9A and 9B are diagrams showing an example of a filter in the spatial filter processing unit 19, FIG. 9A shows a halftone dot area filter 50, and FIG. 9B shows a photographic area filter 51.
9 (3) shows a character area filter 52, and FIG. 9 (4) shows a character corresponding intermediate area filter 5
3 is shown.

10A and 10B are diagrams showing an example of a dither matrix in the gradation reproduction processing unit 21, FIG. 10A shows a 1 × 1 dither matrix 54, and FIG. 10B shows a 2 × 2 dither matrix. 55, and FIG. 10C shows a 4 × 4 dither matrix 56.

FIG. 11 is a flowchart showing a processing procedure of an isolated area portion determination step included in the replacement step in the embodiment of the present invention.

FIG. 12 is a flowchart showing a processing procedure of an intermediate area part determination step included in the replacement step in the embodiment of the present invention.

[Explanation of symbols]

1 Image forming device 2 Image input device 3 Image processing device 4 Image output device 8 Area separation processing section 9 Judgment means 10 Character area determination unit 11 Halftone dot area determination unit 12 Character edge determination section 13 Chromatic achromatic judgment section 14 Replacement means 15 Isolated area part determination unit 16 Intermediate area part determination unit 18 Black generation undercolor removal unit 19 Spatial filter processing unit 21 gradation reproduction processing unit 40 Isolated character area 41 Isolated halftone dot area 50 Halftone filter 51 Filter for photo area 52 Filter for character area Filter for intermediate area part corresponding to 53 characters 54 1 x 1 dither matrix 55 2 x 2 dither matrix 56 4 × 4 dither matrix

Continued front page    (72) Inventor Hiroshi Kono             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Mihoko Tanimura             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Shinji Imagawa             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company F term (reference) 5C077 LL05 LL06 LL19 MP02 MP06                       MP07 MP08 NN08 PP27 PP28                       PP33 PP38 PP47 PP68 PQ12                       PQ17 PQ20                 5L096 AA02 AA06 EA05 EA43 FA06                       FA42 FA43 FA44 GA07 GA12                       GA19 GA28 GA51 JA11

Claims (13)

[Claims] 1. A determination step of determining which of a plurality of image areas each pixel of an input image belongs to, and an adjacent area where different image areas are adjacent to each other is defined as an intermediate area based on the determination result in the determination step. A replacement step for replacing and a correction step for correcting the image of each image area and the intermediate area portion according to the characteristics of each image area and the intermediate area portion And a correction step of correcting the image in the intermediate region so as to obtain an image having specific characteristics. 2. In the correction step, correction processing is performed on each image area in the same processing mode with different correction levels, and one of two image areas adjacent to each other with the intermediate area portion interposed therebetween is applied to the intermediate area portion. 2. The correction processing of the same processing mode as the correction processing applied to each image area is performed at an intermediate correction level between the correction level applied to the image area of 1 and the correction level applied to the other image area. Image processing method. 3. In the replacing step, when one of the two adjacent image areas is a character area and the other of the two adjacent image areas is a halftone dot area, an edge area adjacent to the character area of the halftone dot area. 3. The image processing method according to claim 1, wherein the portion is replaced with the intermediate area portion. 4. In the replacing step, when the character area is a black character area, the edge area portion adjacent to the black character area of the halftone dot area is replaced with a black character corresponding intermediate area portion, and the character area is a color character area. 4. The image processing method according to claim 3, wherein the edge area portion adjacent to the color character area of the halftone dot area is replaced with the color character corresponding intermediate area portion. 5. In the replacing step, the number of pixels belonging to each image region in the local pixel block is compared with a threshold value set in advance for each image region based on the determination result in the determining process. , It is determined whether or not the local pixel blocks are configured with the same image area, and if it is determined that the local pixel blocks are configured with the same image area, the image areas to which the pixels in the local pixel block belong are unified. The determination result in the determination step is corrected.
The image processing method according to any one of 1. 6. The setting of each threshold can be changed based on a command indicating which one of the image regions has the highest reproducibility. The described image processing method. 7. A determination unit that determines which one of a plurality of image regions each pixel of the input image belongs to, and an adjacent region where different image regions are adjacent to each other is defined as an intermediate region based on the determination result by the determination unit. A replacement unit that replaces and a correction unit that corrects the image of each image region and the intermediate region portion in accordance with the characteristics of each image region and the intermediate region portion. An image processing apparatus, comprising: a correction unit that corrects an image in an intermediate region so that the image has a characteristic. 8. The correction means performs correction processing on each image area in the same processing mode with different correction levels, and one of two image areas adjacent to each other with the intermediate area portion interposed therebetween with respect to the intermediate area portion. 8. The correction processing of the same processing mode as the correction processing applied to each image area is performed at an intermediate correction level between the correction level applied to the image area and the correction level applied to the other image area. Image processing device. 9. The replacing means, when one of the two adjacent image areas is a character area and the other of the two adjacent image areas is a halftone dot area, an edge area adjacent to the halftone dot character area. 9. The image processing apparatus according to claim 7, wherein the portion is replaced with the intermediate area portion. 10. When the character area is a black character area, the replacing means replaces an edge area portion adjacent to the black character area of the halftone dot area with a black character corresponding intermediate area portion, and the character area is a color character area. 10. The image processing apparatus according to claim 9, wherein the edge area portion adjacent to the color character area of the halftone dot area is replaced with the color character corresponding intermediate area portion. 11. The replacement means compares the number of pixels belonging to each image area in a local pixel block with a threshold value preset for each image area based on the result of the judgment by the judgment means. , It is determined whether or not the local pixel blocks are configured with the same image area, and if it is determined that the local pixel blocks are configured with the same image area, the image areas to which the pixels in the local pixel block belong are unified. The image processing apparatus according to any one of claims 7 to 10, wherein the determination result by the determination unit is corrected. 12. The setting of each threshold can be changed based on a command indicating which one of the image regions has the highest reproducibility. The image processing device described. 13. An image forming apparatus comprising the image processing apparatus according to claim 7.