JP5644230B2 - Image processing apparatus and image processing method - Google Patents

Description

  The present invention relates to an image processing apparatus and an image processing method.

  Conventionally, in an image forming apparatus employing an electrophotographic method or an inkjet method, a screen of about 100 to 200 lines is usually used. However, in such an image forming apparatus, halftone characters or fine lines are printed. The edges of characters and fine lines may not be printed smoothly, and so-called jagged edges may be noticeable.

  Therefore, in an image forming apparatus adopting the above-described electrophotographic method or inkjet method, as a technique for reducing the jagged edge called jaggy appearing in halftone characters or fine lines, for example, edge detection of image data is performed. An image processing technique for expanding the edge region by performing expansion processing for expanding the edge portion of the image and reducing the jaggy feeling has been proposed (Japanese Patent Laid-Open No. 2006-262204).

  An image processing apparatus according to Japanese Patent Laid-Open No. 2006-262204 is an image processing apparatus that switches image processing for image data according to whether it is an edge part or another non-edge part. Edge extracting means to extract, re-determination means for receiving the processing result of the edge extracting means and expanding the edge region to determine an edge portion, or an edge portion determined by the edge extracting means and the re-determination means or And a processing means for performing image processing according to the non-edge portion.

Japanese Patent No. 2006-262204

  By the way, the problem to be solved by the present invention is image processing that can reduce the jaggy feeling of halftone characters and thin line images while suppressing the collapse of characters and thin line images in a high density region near 100%. An apparatus and an image processing method are provided.

That is, the invention described in claim 1 is an edge determination means for determining whether or not the image data is an edge portion;
Based on the determination result of the edge determination means, and the edge portion and the re-determining edge redetermination unit pixel of interest in the image data to expand the edge regions of said image data,
Processing means for performing different processing between the image data determined to be an edge portion by the edge determination means and the edge redetermination means and the image data determined to be a non-edge portion;
When the image density of the target pixel is equal to or higher than the first value, the target pixel is less likely to be re-determined as an edge portion, and the image density of the target pixel is equal to or lower than the first value The image processing apparatus further includes a changing unit that changes the content of the redetermination process by the edge redetermination unit so that the target pixel is easily determined again as an edge portion .

According to a second aspect of the present invention, the edge re-determination means is configured such that, for the target pixel, the number of edge pixels in a determination region including a plurality of pixels around the target pixel is greater than or equal to a threshold value. While re-determining the target pixel as an edge portion, if the number of edge pixels in the determination area is less than or equal to the threshold value, re-determine the target pixel as a non-edge portion
When the image density of the target pixel is equal to or higher than the first value , the changing unit increases the threshold used by the edge redetermining unit, and the image density of the target pixel is equal to or lower than the first value. The image processing apparatus according to claim 1, wherein the threshold used by the edge re-determination means is lowered .

Further, in the invention described in claim 3, when the image density of the target pixel is equal to or higher than the first value , the changing unit performs a process of re-determining an edge portion by the edge re-determination unit. The image processing apparatus according to claim 1 , wherein when the image density of the target pixel is equal to or less than the first value, the edge redetermination unit performs redetermination as an edge portion. is there.

The invention described in claim 4 is an edge determination step for determining whether or not the edge portion is from image data;
Based on the determination result of the edge determination step, and the edge portion and the re-determining edge redetermination process the target pixel in the image data to expand the edge regions of said image data,
A processing step of performing different processing between the image data determined to be an edge portion by the edge determination step and the edge redetermination step and the image data determined to be a non-edge portion;
When the image density of the target pixel is equal to or higher than the first value, the target pixel is less likely to be re-determined as an edge portion, and the image density of the target pixel is equal to or lower than the first value The image processing method further includes a changing step of changing the content of the redetermination process in the edge redetermination step so that the target pixel is easily judged again as an edge portion .

  According to the first aspect of the present invention, halftone characters and fine line images are suppressed while suppressing the collapse of characters and fine line images in a high density region near 100% as compared with the case without this configuration. The jaggy feeling can be reduced.

  Further, according to the invention described in claim 2, it is possible to easily change the image density for suppressing the collapse of characters and thin line images.

  Furthermore, according to the third aspect of the invention, the configuration of the edge redetermining means can be simplified.

  Further, according to the invention described in claim 4, compared to the case without the present configuration, halftone characters and characters in a high density region near 100% are suppressed while suppressing collapse of characters and fine line images. It is possible to reduce the jaggy feeling of the fine line image.

It is a flowchart which shows operation | movement of the image processing apparatus which concerns on Embodiment 1 of this invention. 1 is a configuration diagram illustrating an image forming apparatus to which an image processing apparatus according to Embodiment 1 of the present invention is applied. 1 is a block diagram showing an image processing apparatus according to Embodiment 1 of the present invention. It is a graph which shows the tag information according to a drawing object. It is a graph which shows an edge detection filter. It is a schematic diagram which shows operation | movement of the image processing apparatus which concerns on Embodiment 1 of this invention. It is a figure explaining the difference of the image processing based on image density. It is a schematic diagram which shows the conventional image processing. It is a schematic diagram which shows the conventional image processing. It is a schematic diagram which shows operation | movement of the image processing apparatus which concerns on Embodiment 2 of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1
FIG. 2 shows an electrophotographic image forming apparatus to which the image processing apparatus according to Embodiment 1 of the present invention is applied. In addition to the function as a printer for printing image data sent from a personal computer (PC) (not shown), this image forming apparatus includes a copying machine for copying an image of a document (not shown) read by the image reading device, and an image. It is also configured to function as a facsimile that transmits and receives information.

  As shown in FIG. 2, the image forming apparatus 1 includes, for example, an image processing apparatus 3 according to the present embodiment inside an image forming apparatus main body 2, and image processing is performed by the image processing apparatus 3. An image output unit 106 that outputs an image based on the applied image data is arranged. The image forming apparatus main body 2 includes image forming units 4Y, 4M, 4C as image forming units corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (K). It has 4K. These four image forming units 4Y, 4M, 4C, and 4K are basically configured in the same manner except for the color of the image to be formed, and are roughly rotated at a predetermined speed along the arrow A direction. A photosensitive drum 5 as an image carrier, a primary charging scorotron 6 for uniformly charging the surface of the photosensitive drum 5, and an image based on image data corresponding to each color on the surface of the photosensitive drum 5. An image exposure device 7 that performs exposure to form an electrostatic latent image, a developing device 8 that develops the electrostatic latent image formed on the photosensitive drum 5 with toner of a corresponding color, and the surface of the photosensitive drum 5 And a cleaning device 9 for cleaning toner remaining on the toner.

  As shown in FIG. 2, the image processing apparatus 3 exposes the image forming units 4Y, 4M, 4C, and 4K for each color of yellow (Y), magenta (M), cyan (C), and black (K). Corresponding color image data is sequentially output to the devices 7Y, 7M, 7C, and 7K, and laser light LB emitted according to the image data from these image exposure devices 7Y, 7M, 7C, and 7K corresponds. The surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are scanned and exposed to form electrostatic latent images. The electrostatic latent images formed on the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are respectively yellow (Y), magenta (M), and cyan (C) by the developing devices 8Y, 8M, 8C, and 8K. , And developed as a toner image of each color of black (K).

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images are primarily transferred onto the intermediate transfer belt 10 in a multiplex manner and then transferred from the intermediate transfer belt 10 to the recording paper 11. The recording sheet 11 on which a full-color image or a monochrome image is formed is output.

  Incidentally, the image processing apparatus 3 according to this embodiment may of course be configured as an independent apparatus. For example, the image processing apparatus 3 is built in the electrophotographic image forming apparatus 1 in advance as hardware, or the image forming apparatus 1. Are installed as programs (software).

  FIG. 3 is a block diagram showing an image processing apparatus according to Embodiment 1 of the present invention.

  As shown in FIG. 3, the image processing apparatus 3 includes an image data input unit 101 to which image data to be processed having a resolution of about 300 to 600 dpi and a number of gradations of about 256 gradations (8 bits) is input. An edge determination unit 102 as an edge determination unit that determines whether or not the image data is input to the image data input unit 101, and an edge region of the image data based on the determination result of the edge determination unit 102 An edge redetermining unit 103 as an edge redetermining means for re-determining an edge part, image data determined to be an edge part by the edge determining part 102 and the edge redetermining part 103, and the edge determination As processing means for performing different processing on image data determined to be a non-edge portion by the section 102 and the edge redetermining section 103 A screen processing unit 105 is configured to include a changing unit 104 as a change means for changing the contents of the re-determination processing by the edge re-determination unit 103 on the basis of the density information of a target pixel of the image data. The input image data is not limited to a resolution of about 300 to 600 dpi, but may be a higher or lower resolution, and the number of gradations is not limited to 256 gradations (8 bits). Of course not.

  The image data input unit 101 receives and interprets image data described in PDL (page description language) as a drawing command from a personal computer (not shown), for example, performs drawing processing, and outputs an image in the image output unit 106 Bit map image data for each color of yellow (Y), magenta (M), cyan (C), and black (K) is generated. Further, the image data input unit 101 interprets the PDL as necessary, and performs drawing processing for each drawing object in accordance with the interpreted PDL to generate an intermediate code. As shown in FIG. 4, tag information indicating the type of a drawing object such as image / text / graphics is added to the generated intermediate code as an attribute of the drawing object. In the image data input unit 101, yellow (Y), magenta (M), cyan (C), and black (K), which are color materials used in the image output unit 106 from the color signal (RGB) specified by PDL. Are converted to the respective color signals, and the image output unit 106 is converted to an optimal resolution as necessary.

  Further, the image data input unit 101 corresponds to each color of yellow (Y), magenta (M), cyan (C), and black (K) suitable for the image output unit 106 based on the generated intermediate code. Bitmap data is created. At that time, the image data input unit 101 adds tag information as shown in FIG. 4 for each pixel or every several pixels of the beat map data.

  Image data that has been subjected to predetermined image processing by the image data input unit 101 as necessary is input to the edge determination unit 102 and the change unit 104, respectively, as shown in FIG.

  The edge determination unit 101 determines whether or not the pixel to be determined is an edge part from the bitmap data generated by the image data input unit 101. In the edge determination unit 101, for example, an edge detection filter as shown in FIG. 5 is used to determine whether the input image data consisting of bitmap data is an edge portion or a non-edge portion other than the edge portion. As shown in FIG. 4, tag information “11” indicating an edge portion is added to the pixel determined to be an edge portion by the edge determination unit 101.

  The edge re-determination unit 103 receives the processing result of the edge determination unit 102 and performs a process of re-determination of the edge part by expanding the edge region. In this edge re-determination unit 103, as shown in FIG. 6, each pixel of the bitmap data is set as a target pixel in order, and a plurality of (for example, 3 × 3 = 9) predetermined pixels around the target pixel. The number of edge pixels (the number of pixels to which tag information indicating an edge portion is added) in the determination area is counted. If the count value is equal to or greater than a predetermined threshold param_rejudge, the pixel of interest is re-determined as an edge portion, and the tag information is added as an edge portion. If the count value is less than a predetermined threshold param_rejudge, the target pixel is determined again as a non-edge portion, and the fact that it is an edge portion is not added to the tag information.

  Here, in the edge re-determination unit 103, as will be described later, the change unit 104 changes the value of the threshold param_rejudge according to the image density of the target pixel.

  The screen processing unit 105 receives bitmap data and tag information from the edge re-determination unit 103, performs screen processing on the bitmap data according to the tag information, and forms a pseudo halftone image. The screen processing unit 105 basically performs screen processing on a pixel determined to be an edge portion (including redetermination) using, for example, a 600-line screen as shown in FIG. The edge portion is smoothly formed to reduce the jaggy feeling. Further, the screen processing unit 105 performs screen processing selected by the user on the pixels determined to be non-edge portions (including redetermination), or, for example, as shown in FIG. The screen processing is set in advance according to the type of drawing object such as image / text / graphics. Note that the content of the screen processing for pixels determined to be non-edge portions (including redetermination) can be arbitrarily set by the user via a user interface (not shown), for example. Further, when the user does not set, screen processing that is set in advance according to the type of drawing object such as image / text / graphics is performed.

  FIG. 4 is an explanatory diagram illustrating an example of a relationship between tag information and a screen to be used.

  The screen processing unit 105 switches the screen for each drawing object, and performs an optimal screen process for each drawing object. For example, text needs to be high definition, so a 300-line screen is used, and images and graphics do not need to be very high definition. A 150-line screen is used. Further, the edge portion uses a 600-line screen, which is the resolution of the image output unit 106, in order to reproduce a clean edge by reducing jaggy. As described above, the screen is switched between the edge portion and the non-edge portion, and the non-edge portion for each drawing object. By doing so, it is possible to perform optimum screen processing in each part.

  In the screen processing unit 105, a pulse signal for forming dots is generated by the image exposure devices 7Y, 7M, 7C, and 7K of the image output unit 106 based on the image data subjected to the screen processing. It is output to the output unit 106.

  As described with reference to FIG. 2, the image output unit 106 is a full-color or monochrome image on the recording paper 11 based on the image data including the pulse signal output from the screen processing unit 105 of the image processing apparatus 3. Is formed and output.

  In the changing unit 104, the content of redetermination processing by the edge redetermining unit 103 is changed based on the density information of the target pixel of the image data. Specifically, the changing unit 104 according to the first embodiment expands the edge area of the image data by the edge re-determination unit 103 based on the density information of the target pixel of the image data and re-determines the threshold value param_rejudge. Processing to change is performed.

  As shown in FIG. 6, the changing unit 104 determines whether the image density of the target pixel of the image data is equal to or higher than a density threshold Cin (for example, 100%), and the image density of the target pixel of the image data is When the density threshold Cin (for example, 100%) or more, the value of the threshold param_rejudge is changed to a first threshold param_rejudge-1 (9 in the illustrated example), which makes the image difficult to expand. When the image density of the pixel is less than the density threshold Cin (for example, 100%), the value of the threshold param_rejudge is changed to a second threshold param_rejudge-2 (2 in the illustrated example) that the image is likely to expand. Processing is performed.

  The density threshold Cin is set to 100% (255), for example, but the density threshold Cin is not limited to 100% (255), and other values may be used. That is, when the image data is classified by image density, as shown in FIG. 7, from the low density side to the vicinity of approximately 90% of the image density is an image density area where emphasis is placed on eliminating the jaggy feeling. The density area where the image density exceeds 100% and reaches 100% is an image density area where emphasis is placed on eliminating the collapse of characters and lines. However, not all density regions that exceed the image density of 90% and reach the image density of 100% are image density regions where emphasis is placed on eliminating the crushing of characters and lines, and the image density is about 100% to 90%. For example, in an area of about 96 to 97% or less and 90% or more, there are areas where it is desirable to optimize according to the characteristics of the image output unit 106 rather than to eliminate the collapse of characters and lines. This is known by the present inventors' research. Therefore, the density threshold Cin may be set to about 96 to 97%, for example.

  In addition, the image output unit 106 is not limited to an image forming apparatus that employs an electrophotographic system, but may be an apparatus that employs an inkjet system or the like.

  In the above configuration, in the image forming apparatus to which the image processing apparatus according to this embodiment is applied, the halftone image is suppressed in the following manner while suppressing the collapse of characters and thin line images in a high density region near 100%. It is possible to reduce the jaggy of characters and fine line images.

  That is, in the image processing apparatus 3, as shown in FIG. 3, after predetermined processing is performed on the image data input by the image data input unit 101, the image data is converted into the edge determination unit 102. Is input.

  Then, in the edge determination unit 102, as shown in FIG. 1, edge determination processing (background determination) is performed using an edge detection filter or the like (step 101), and pixels determined to be edge portions include As shown in FIG. 4, a value “11” indicating the result of the edge determination process is added as tag information.

  If the edge determination unit 102 determines that the image is a non-edge portion, the edge re-determination unit 103 expands the edge area of the image data based on the determination result of the edge determination unit 102 and re-determination is performed. Processing is performed (step 102). In this edge redetermining unit, as shown in FIG. 6, it is determined whether or not the number of pixels determined to be an edge in a determination region (for example, 3 × 3 = 9) composed of a plurality of pixels is equal to or greater than a threshold parameter_rejudge. When the number of pixels determined to be an edge portion in the determination region is equal to or greater than the threshold param_rejudge, the determination result that the target pixel is located at the center of the determination region is a non-edge portion (“ 1 "). On the other hand, when the number of pixels determined to be the edge portion in the determination region is less than the threshold param_rejudge, the determination result that the target pixel is located at the center of the determination region is a non-edge portion. ("0") is determined again, and the non-edge determination result is turned ON.

  Further, the density of the pixel of interest is determined for the pixel determined to be an edge by the edge determination unit 102 and the pixel re-determined to be an edge by the edge redetermination unit 103 (step 103).

  In this embodiment, as shown in FIG. 1, it is determined whether or not the image density of the pixel of interest is equal to or higher than a predetermined density threshold Cin, which is 100% (the number of gradations corresponds to 255). (Step 103). When the image density of the pixel of interest is 100% or more, which is a predetermined density threshold Cin, the threshold param_rerange is set to a parameter that is difficult to expand, for example, the threshold param_rerange = 9, and the image density of the pixel of interest is set in advance. When the predetermined density threshold Cin is less than 100%, the threshold param_rejudge is set to a parameter that easily expands, for example, the threshold param_rejudge-2 = 2.

  Image data of pixels determined to be edge portions by the edge determination unit 102 and edge redetermination unit 103, and image data of pixels determined to be non-edge portions by the edge determination unit 102 and edge redetermination unit 103 As shown in FIG. 1, data selection (selection) processing is performed (step 104), and the image data of the edge portion and the non-edge portion is selected.

Then, the image data of the pixel determined as the edge portion is determined whether or not the image density of the pixel is equal to or higher than a predetermined second image density value Cin ₂ (step 105), and the image density of the pixel is determined. If it is equal to or higher than the predetermined second image density value Cin ₂ , after changing to the character sharpness correction density value (step 106), screen processing corresponding to the edge portion is performed. Here, as the screen processing corresponding to the edge portion, processing using a 600-line screen is performed with emphasis on reducing jaggy.

  The character sharpness correction density value converts the image density value of the input image data into an appropriate image density value Cin ′ so that the image of the character or line with the image density of 100% or near 100% is not crushed. It is a value for. As the character sharpness correction density value, for example, an image density value with an image density of 100% (255) is converted into an image density value of about “204”. As described above, when the image density of the pixel determined to be the edge portion is 100%, the character sharpness correction of “204”, which is an image density value lower than 100% (255), is set for the pixel density of the edge portion. By converting to a density value, the image of characters and lines is prevented from being crushed.

  Further, when the image density Cin of the pixel is lower than the predetermined image density Cin, the edge screen and the user (or the image output unit 106 automatically) are selected using an EELUT (lookup table). After the image density conversion to match the density characteristics of the screen (for example, 200 lines) is performed (step 107), the edge portion screen processing is performed, and a density step is formed at the boundary between the edge portion screen and the selected screen. It is possible to reduce the jaggy feeling at the edges of characters and lines without occurring.

  The EELUT is an LUT that matches the gradation characteristics of the edge screen portion and the selection screen portion. This EELUT is, for example, a digital image density value when the print density when the digital image density value of the edge screen portion is “128” and the print density when the digital image density value of the selected screen portion is “152” are the same. This is for rewriting “152” to “128”.

  As described above, according to the above-described embodiment, it is possible to reduce the jaggy of halftone characters and thin line images while suppressing the collapse of characters and thin line images in a high density region near 100%.

Comparative Example As a comparative example, after determining the edge portion that has been performed in the past, it is redetermined to expand the area determined to be the edge portion, and a screen with a high line number is adopted to smooth the edge portion. However, when the processing for reducing the density of the edge portion is uniformly performed, as shown in FIG. 8B, all pixels determined to be the edge portion are high for a halftone linear image. Although it is processed with a screen having the number of lines and the jaggy feeling can be reduced, as shown in FIG. 8A, the density of a linear image with an image density of about 100% decreases for all pixels. As a result, the image density is extremely lowered, and the image quality is lowered.

  On the other hand, after determining the edge portion that has been conventionally performed, the processing of expanding the region determined to be the edge portion is not performed, and a screen with a high number of lines is adopted to smooth the edge portion, When the density reduction processing is uniformly performed, as shown in FIG. 9A, the center portion of the linear image remains at a density of 100% in a linear image having an image density of about 100%. Therefore, although it is good without causing an extreme decrease in density, as shown in FIG. 9B, the effect of improving the jaggy feeling is reduced and the image quality is deteriorated for a halftone linear image.

Embodiment 2
FIG. 10 shows a second embodiment of the present invention. The same reference numerals are given to the same parts as those in the first embodiment. In the second embodiment, the changing means is the Based on the density information of the pixel of interest of the image data, the edge re-determination means expands the edge area of the image data and changes whether or not to re-determine the edge portion.

  That is, in the second embodiment, as shown in FIG. 10, the changing unit 104 widens the edge area of the image data by the edge re-determination means 103 based on the density information of the target pixel of the image data, and re-determines the edge portion. It is configured to change whether or not to perform processing.

  More specifically, as shown in FIG. 10, the changing unit 104 is based on the density information of the target pixel of the image data, and the image density of the target pixel is 100% (the number of gradations is set to 255) which is the density threshold Cin. If the density threshold Cin is 100% (the number of gradations is equivalent to 255) or more, the edge region of the image data is widened and re-determined as an edge portion. Only when the density threshold value Cin is less than 100% (corresponding to the number of gradations is equivalent to 255), the edge region of the image data is expanded and the determination as the edge portion is performed again.

  Therefore, in the second embodiment, when the image density of the target pixel of the image data is equal to or greater than 100% (the number of gradations is equivalent to 255) which is the density threshold Cin, the edge area of the image data is widened to the edge. The determination result of the edge determination unit 102 is sent to the screen unit 105 as it is.

  On the other hand, in the second embodiment, when the image density of the target pixel of the image data is less than 100% (the number of gradations is equivalent to 255) which is the density threshold Cin, the edge area of the image data is widened to the edge. The determination result of the edge determination unit 102 and the edge redetermination unit 103 is sent to the screen unit 105.

  In the second embodiment, the edge redetermination unit 103 may have only one threshold, and the configuration of the edge redetermination unit 103 can be simplified.

  Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.

  3: image processing apparatus, 101: image data input unit, 102: edge determination unit, 103: edge redetermination unit, 104: change unit, and 105: screen processing unit.

Claims (4)

Edge determination means for determining whether or not an edge portion from image data;
Based on the determination result of the edge determination means, and the edge portion and the re-determining edge redetermination unit pixel of interest in the image data to expand the edge regions of said image data,
Processing means for performing different processing between the image data determined to be an edge portion by the edge determination means and the edge redetermination means and the image data determined to be a non-edge portion;
When the image density of the target pixel is equal to or higher than the first value, the target pixel is less likely to be re-determined as an edge portion, and the image density of the target pixel is equal to or lower than the first value The image processing apparatus further comprises: a changing unit that changes a content of the redetermination process by the edge redetermination unit so that the target pixel is easily redetermined to be an edge portion . The edge re-determination means re-determines that the pixel of interest is an edge portion when the number of edge pixels in a determination area composed of a plurality of pixels around the pixel of interest is equal to or greater than a threshold for the pixel of interest. , If the number of edge pixels in the determination area is less than or equal to the threshold value, the target pixel is determined again as a non-edge part,
When the image density of the target pixel is equal to or higher than the first value , the changing unit increases the threshold used by the edge redetermining unit, and the image density of the target pixel is equal to or lower than the first value. The image processing apparatus according to claim 1, wherein the threshold used by the edge re-determination means is lowered . When the image density of the target pixel is equal to or higher than the first value , the changing unit does not perform the process of redetermining the edge portion by the edge redetermining unit, and the image density of the target pixel is the first density. 2. The image processing apparatus according to claim 1 , wherein, when the value is equal to or smaller than the value, the edge re-determination unit performs re-determination as an edge portion . An edge determination step for determining whether or not an edge portion from image data;
Based on the determination result of the edge determination step, and the edge portion and the re-determining edge redetermination process the target pixel in the image data to expand the edge regions of said image data,
A processing step of performing different processing between the image data determined to be an edge portion by the edge determination step and the edge redetermination step and the image data determined to be a non-edge portion;
When the image density of the target pixel is equal to or higher than the first value, the target pixel is less likely to be re-determined as an edge portion, and the image density of the target pixel is equal to or lower than the first value The image processing method further includes a changing step of changing the content of the redetermination process in the edge redetermination step so that the target pixel is easily judged again as an edge portion .

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