JP2013077870A - Image processing device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform image scaling of non-integer multiple while suppressing image quality deterioration such as thickness unevenness of a thin line portion and shade unevenness of a pseudo gradation region.
In an image processing apparatus, an enlargement processing unit 32 generates an enlarged image obtained by enlarging an image by an integral multiple in a main scanning direction and / or a sub-scanning direction, and a contraction processing unit 34 The downsampling unit 35 downsamples the enlarged image after the shrinking process to an integer of 1 in the main scanning direction and / or the sub scanning direction.
[Selection] Figure 1

Description

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

  There has been proposed an image processing apparatus that scales images such as characters and line drawings by non-integer multiples (see, for example, Patent Documents 1 and 2).

  The technique described in Patent Document 2 performs a magnification process of 3 times while performing smoothing, then performs downsampling of 1/2 and performs non-integer magnification expansion of 1.5 times.

Japanese Patent Laid-Open No. 9-312762 Japanese Patent Laid-Open No. 10-84472

  However, when non-integer multiple enlargement is performed as described above, due to downsampling, unevenness in thickness occurs in the thin line portion in the image after enlargement by non-integer multiples, and uneven grayness occurs in the pseudo gradation region. Sometimes. The shading unevenness in the pseudo gradation area is remarkable in the case of the pseudo gradation area by the error diffusion method.

  In order to eliminate unevenness in thickness, it is conceivable to use the logical sum method during downsampling, but in that case, the thin line part becomes thicker overall, the characters are crushed, and the pseudo gradation is relatively high in density. The area will also be crushed.

  Further, the technique described in Japanese Patent Laid-Open No. 7-28992 is a method of thinning an original image and down-sampling after the thinning, but the thin line between the original image and the image after enlarging the original image Since the image characteristics such as the thickness distribution of the parts are different, even if the technique described in JP-A-7-28992 is applied to the image after enlarging the original image, a good non-integer multiple It is difficult to obtain an image.

  The present invention has been made in view of the above-described problems, and performs image scaling of non-integer multiples while suppressing image quality degradation such as uneven thickness of thin line portions and uneven shading of pseudo gradation regions. The purpose is to obtain.

  In order to solve the above problems, the present invention is configured as follows.

  An image processing apparatus according to the present invention includes an enlargement processing unit that enlarges an image by an integral multiple in the main scanning direction and / or the sub-scanning direction, a contraction processing unit that performs a shrinkage process on the image enlarged by an integral multiple, A down-sampling unit that down-samples the image subjected to the contraction process by the contraction processing unit to an integer.

  As a result, non-integer multiple image scaling is performed while suppressing image quality degradation such as uneven thickness of the thin line portion and uneven shading of the pseudo gradation region.

  In addition to the image processing apparatus described above, the image processing apparatus according to the present invention may be configured as follows. In this case, the image processing apparatus determines that the dot density after down-sampling is constant regardless of the phase of down-sampling in the shape of the pixel set without dots in the image that is enlarged to an integral multiple corresponding to isolated pixels without dots in the image. The image processing apparatus further includes a correction processing unit that corrects the shape to

  Thereby, it is possible to suppress image quality degradation caused by an isolated pixel without dots in the original image (that is, one pixel without dots surrounded by pixels with dots).

  The image processing apparatus according to the present invention may be as follows in addition to any of the image processing apparatuses described above. In this case, the contraction processing unit performs contraction processing so that the dot density after downsampling is constant regardless of the phase of downsampling.

  Thereby, it is possible to suppress image quality deterioration regardless of the phase of downsampling.

  The image processing apparatus according to the present invention may be as follows in addition to any of the image processing apparatuses described above. In this case, the contraction processing unit sequentially scans the pixel of interest along the main scanning direction and the sub-scanning direction in the image magnified to an integral multiple, and among the pixel of interest and the peripheral pixels of the pixel of interest, Presence / absence of a dot of the target pixel is determined from the values of the pixel, the pixel after the target pixel in the main scanning direction in the line with the target pixel, and the pixel value of the line after the line with the target pixel in the sub-scanning direction.

  As a result, the contraction process is performed without using the pixel value before the contraction process (the value indicating the presence / absence of a dot) for the pixel that has been subjected to the contraction process. Overwriting can be performed sequentially, and the storage area required for the shrinking process can be reduced.

  The image processing apparatus according to the present invention may be as follows in addition to any of the image processing apparatuses described above. In this case, the image processing apparatus further includes a pseudo gradation area specifying unit that specifies a pseudo gradation area in the image. The enlargement processing unit enlarges the image by the nearest neighbor method without performing smoothing on the pseudo gradation area, and enlarges the image while performing smoothing on the area other than the pseudo gradation area.

  Thereby, since the enlargement process is performed without performing smoothing for the pseudo gradation area, a dot pattern unique to the pseudo gradation area is maintained, and shading unevenness in the pseudo gradation area is suppressed.

  The image processing apparatus according to the present invention may be as follows in addition to any of the image processing apparatuses described above. In this case, the image after downsampling is a non-integer multiple of the image before enlargement.

  An image forming apparatus according to the present invention includes any of the image processing apparatuses described above.

  As a result, non-integer multiple image scaling is performed on an image (for example, a facsimile received image) handled by the image forming apparatus while suppressing image quality deterioration such as uneven thickness of a thin line portion and uneven shading of a pseudo gradation region. .

  According to the present invention, non-integer multiple image scaling is performed while suppressing image quality degradation such as uneven thickness of a thin line portion and uneven shading of a pseudo gradation region.

FIG. 1 is a block diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart for explaining the operation of the image processing apparatus in FIG. FIG. 3 is a diagram for explaining the correction of white isolated points by the white isolated point correcting unit in FIG. FIG. 4 is a diagram illustrating a case where white isolated points are not corrected. FIG. 5 is a diagram for explaining an example of pattern matching of contraction processing by the contraction processing unit in FIG. FIG. 6 is a diagram illustrating an example in which a thin line image is enlarged 1.5 times in the main scanning direction and the sub-scanning direction by the image processing apparatus illustrated in FIG. 1. FIG. 7 is a diagram illustrating an image after downsampling when downsampling is performed at different phases in the case illustrated in FIG. 6. FIG. 8 is a diagram illustrating an image after downsampling when the contraction process is not performed in the case illustrated in FIG. 6. FIG. 9 is a diagram showing another example in which a thin line image is enlarged 1.5 times in the main scanning direction and the sub-scanning direction by the image processing apparatus shown in FIG. FIG. 10 is a diagram illustrating an image after downsampling when downsampling is performed at different phases in the case illustrated in FIG. 9. FIG. 11 is a diagram illustrating an image after downsampling when the contraction process is not performed in the case illustrated in FIG. 9. FIG. 12 is a diagram illustrating an example in which the pseudo gradation area is enlarged 1.5 times in the main scanning direction and the sub-scanning direction by the image processing apparatus illustrated in FIG. 1. FIG. 13 is a diagram illustrating an image after downsampling when the contraction process is not performed in the case illustrated in FIG. 12.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of an image forming apparatus 1 according to an embodiment of the present invention. An image forming apparatus 1 shown in FIG. 1 is a multifunction machine. However, the image forming apparatus 1 may be a printer, a copier, a facsimile machine, or the like.

  The image forming apparatus 1 includes a printing device 11, an image reading device 12, a facsimile device 13, and an image processing device 14.

  The printing device 11 is an internal device that prints a document image based on raster image data. For example, the printing apparatus 11 prints a document image based on the image data enlarged by the image processing apparatus 14.

  The image reading device 12 is an internal device that optically reads a document image from a document and generates image data of the document image.

  The facsimile machine 13 is an internal device that generates a facsimile signal from image data of a document image to be transmitted and transmits it via a predetermined communication path, and receives the facsimile signal via a predetermined communication path and converts it into image data. is there.

  The image processing device 14 performs image processing such as enlargement processing on the image data generated by the image reading device 12, the facsimile device 13, or the like. In particular, the image processing device 14 enlarges the binary image by a non-integer multiple in the main scanning direction and / or the sub-scanning direction. For example, the image processing apparatus 14 converts the resolution of an image of 400 dpi (dot per inch) received by the facsimile apparatus 13 into 600 dpi for printing.

  The image processing device 14 includes an arithmetic processing device 21 and a memory 22. The arithmetic processing unit 21 is realized by an application specific integrated circuit (ASIC) or a microcomputer, and has various processing units. The memory 22 is a rewritable storage device such as a RAM (Random Access Memory). The memory 22 temporarily stores image data before image processing such as enlargement processing, data during image processing, image data after image processing, and the like.

  The arithmetic processing device 21 includes a control unit 31, an enlargement processing unit 32, a white isolated point correction unit 33, a contraction processing unit 34, and a downsampling unit 35 as processing units.

  The control unit 31 controls the enlargement processing unit 32, the white isolated point correction unit 33, the contraction processing unit 34, and the downsampling unit 35, and in the image data of the binary image, along the main scanning direction and the sub scanning direction. The pixels are sequentially scanned as the target pixel.

  In this embodiment, the control unit 31 specifies a pseudo gradation region in the original image. Note that the pseudo gradation area is an area obtained by an error diffusion method, a screen method, or the like and expressing a gradation with the size and density of dots. For example, the control unit 31 determines whether or not the target pixel belongs to the pseudo gradation area from the values of pixels in a predetermined range around the target pixel. Specifically, whether or not the pixel of interest belongs to the pseudo gradation region is determined based on the number of locations where the values of two adjacent pixels are different within a predetermined range.

  The enlargement processing unit 32 enlarges the original image by an integral multiple in the main scanning direction and / or the sub-scanning direction, and generates an enlarged image. In this embodiment, the enlargement processing unit 32 enlarges the original image while performing smoothing on areas (thin line drawings, characters, etc.) other than the above-described pseudo gradation area, and performs smoothing on the pseudo gradation area. Enlarge the original image using the nearest neighbor method.

  The white isolated point correction unit 33 converts the shape of the pixel set without dots in the enlarged image corresponding to isolated pixels without dots in the original image (hereinafter referred to as white isolated points) after downsampling regardless of the phase of downsampling. Modify the shape so that the dot density is constant.

  The contraction processing unit 34 performs contraction processing on the enlarged image. In this embodiment, the contraction processing unit 34 performs contraction processing on the enlarged image after the white isolated point correction unit 33 corrects the white isolated point.

  In this embodiment, the contraction processing unit 34 sequentially scans the target pixel in the enlarged image along the main scanning direction and the sub-scanning direction. Among the target pixel and the peripheral pixels of the target pixel, Presence / absence of a dot of the target pixel is determined from the values of the target pixel, the pixel after the target pixel in the main scanning direction in the line with the target pixel, and the pixel value of the line after the line with the target pixel in the sub-scanning direction.

  In this embodiment, the contraction processing unit 34 performs contraction processing so that the dot density after downsampling is constant regardless of the phase of downsampling. In this embodiment, the contraction processing unit 34 performs contraction processing so that two thin lines (vertical thin lines and / or horizontal thin lines) connected in the original image are connected also in the downsampled image.

  The down-sampling unit 35 down-samples the image that has been subjected to the contraction processing by the contraction processing unit 34 to 1 / integer. In this embodiment, the image after downsampling is a non-integer multiple of the original image before enlargement.

  Next, the operation of the image processing apparatus will be described. FIG. 2 is a flowchart for explaining the operation of the image processing apparatus 14 in FIG.

  First, the control unit 31 sets a target pixel (step S1). In the first case, the first pixel in the main scanning direction in the first line is selected as the target pixel. Next, the next pixel in the main scanning direction in the first line is selected as the target pixel. Then, after the last pixel in the main scanning direction in the first line, the first pixel in the main scanning direction in the second line is selected as the target pixel.

  Next, the control unit 31 determines whether or not the target pixel belongs to the pseudo gradation region (step S2).

  If it is determined that the pixel of interest does not belong to the pseudo gradation region, the enlargement processing unit 32 performs enlargement processing of an integral multiple (N times) in the main scanning direction and the sub-scanning direction while smoothing the pixel. (Step S3). On the other hand, when it is determined that the target pixel belongs to the pseudo gradation region, the enlargement processing unit 32 performs integer multiple (N times) in the main scanning direction and the sub scanning direction by the nearest neighbor method without smoothing the pixel. An enlargement process is performed (step S4).

  When the enlargement process for the target pixel is completed, the control unit 31 determines whether the target pixel has reached the last pixel of the last line (step S5), and the target pixel reaches the last pixel of the last line. If not reached, the next pixel of interest is set (step S1).

  Thereafter, the processes in steps S1 to S5 are repeated as appropriate until the enlargement process for the entire image is completed.

  When the enlargement process is completed, the control unit 31 searches the pixel area corresponding to the white isolated point in the image after the enlargement process. In the image after the enlargement process, the pixel area corresponding to the white isolated point is a pixel area having no dots of N × N pixels. When the control unit 31 finds a pixel area corresponding to the white isolated point, the control unit 31 notifies the white isolated point correction unit 33 of the position of the pixel area, and corrects the white isolated point. The white isolated point correcting unit 33 identifies the pixel area corresponding to the white isolated point from the notified position, and corrects the shape of the pixel area (step S6). In other words, the white isolated point correction unit 33 sets the values of some pixels in the pixel region corresponding to the white isolated points to no dots so that the dot density after downsampling is constant regardless of the phase of downsampling. Change from the value shown to the value showing the presence of dots. The pixel for changing the presence / absence of a dot is determined according to the subsequent contraction process and downsampling.

  FIG. 3 is a diagram for explaining the correction of white isolated points by the white isolated point correcting unit 33 in FIG. FIG. 3A is a diagram showing a pixel area without dots of 3 × 3 pixels corresponding to white isolated points. FIG. 3B is a diagram showing the shape of a pixel area without dots after correcting a white isolated point for the pixel area shown in FIG. FIG. 3C is a diagram showing an image after performing a later-described shrinkage process (shrinkage process by pattern matching shown in FIG. 5) on the corrected image shown in FIG. 3B. FIGS. 3D to 3G are diagrams showing images after down-sampling the image shown in FIG. 3C with different phases and a half in the main scanning direction and the sub-scanning direction. is there.

  As shown in FIGS. 3D to 3G, the dot density of the image after down-sampling is constant regardless of the down-sampling phase due to the correction of the white isolated point.

  3 (H) and 3 (I) show different phases when the resolution of the original image in the sub-scanning direction (for example, 400 dpi) is twice the resolution in the main scanning direction (for example, 200 dpi). FIG. 4 is a diagram showing an image after down-sampling the image shown in FIG. 3C in the main scanning direction and the sub-scanning direction. In this case, down-sampling in half is performed only in the sub-scanning direction without down-sampling in the main scanning direction.

  As shown in FIGS. 3H and 3I, even in this case, the dot density of the image after down-sampling is constant regardless of the down-sampling phase due to the correction of the white isolated point.

  On the other hand, FIG. 4 is a diagram illustrating a case where white isolated points are not corrected. FIG. 4A is a diagram showing an image after performing a later-described shrinkage process (shrinkage process by pattern matching shown in FIG. 5) on the image shown in FIG. 3A. FIGS. 4B to 4E are diagrams showing images after down-sampling the image shown in FIG. 4A at different phases and in half in the main scanning direction and the sub-scanning direction. is there. As shown in FIGS. 4B to 4E, when the white isolated point is not corrected, the dot density of the image after down-sampling changes depending on the down-sampling phase.

  4 (F) and 4 (G) show different phases when the resolution of the original image in the sub-scanning direction (for example, 400 dpi) is twice the resolution in the main scanning direction (for example, 200 dpi). FIG. 5 is a diagram showing an image after down-sampling the image shown in FIG. 4A in the main scanning direction and the sub-scanning direction. As shown in FIGS. 4F and 4G, even in this case, when the white isolated point is not corrected, the dot density of the image after down-sampling changes depending on the down-sampling phase.

  After the correction of the white isolated point is completed, the control unit 31 causes the contraction processing unit 34 to execute a contraction process on the enlarged image after the white isolated point correction. If there is no white isolated point, the control unit 31 immediately causes the contraction processing unit 34 to perform contraction processing on the enlarged image.

  The contraction processing unit 34 scans the pixels in the enlarged image along the main scanning direction and the sub-scanning direction, sequentially sets the target pixel, and determines the presence or absence of the dot of the target pixel by pattern matching (step S7). ). In the first case, the first pixel in the main scanning direction on the first line in the enlarged image is selected as the target pixel. Next, the next pixel in the main scanning direction in the first line is selected as the target pixel. Then, after the last pixel in the main scanning direction in the first line, the first pixel in the main scanning direction in the second line is selected as the target pixel.

  FIG. 5 is a diagram for explaining an example of pattern matching of contraction processing by the contraction processing unit 34 in FIG. As shown in FIG. 5, the target pixel, the pixel next to the target pixel in the main scanning direction (first peripheral pixel), the pixel next to the target pixel in the sub scanning direction (second peripheral pixel), and the first in the sub scanning direction. In accordance with the patterns 51 to 66 of pixel values (that is, presence / absence of dots) in the four pixels including the pixel next to the peripheral pixel, that is, the pixel next to the second peripheral pixel (third peripheral pixel) in the main scanning direction. The pixel value of the target pixel (that is, the presence / absence of a dot) is determined.

  For example, the horizontal line is contracted by the pattern 56, the vertical line is contracted by the pattern 59, and the vertical line and the horizontal line are contracted by the pattern 57. Further, for example, when the thin lines are arranged diagonally as shown in FIGS. 6 and 7 to be described later by the patterns 60 to 65, the continuity of the arranged thin lines is reduced even after contraction and downsampling. Maintained.

  After the contraction process is completed, the control unit causes the downsampling unit 35 to perform a downsampling of 1 / (integer 1) of the enlarged image after the contraction process. The downsampling unit 35 downsamples the enlarged image by 1 / M (M / 1) and generates an image that is a non-integer multiple of the original image (step S8).

  In this manner, a non-integer multiple (N / M) image is obtained with respect to the original image.

  FIG. 6 is a diagram illustrating an example in which the thin line image is enlarged 1.5 times in the main scanning direction and the sub-scanning direction by the image processing device 14 illustrated in FIG. 1. FIG. 7 is a diagram illustrating an image after downsampling when downsampling is performed at different phases in the case illustrated in FIG. 6.

  FIG. 6A shows an original image. In this original image, 1-dot horizontal thin lines are diagonally arranged to represent diagonal lines.

  FIG. 6B is a diagram illustrating an enlarged image in which the image in FIG. 6A is tripled in the main scanning direction and the sub-scanning direction, respectively.

  FIG. 6C is an image (enlarged image) after the contraction process is performed on the enlarged image of FIG. 6B by pattern matching shown in FIG. Here, it is assumed that there are no white isolated points.

  FIG. 6D is a diagram illustrating an image obtained by down-sampling the enlarged image of FIG. 6C by half in the main scanning direction and the sub-scanning direction, respectively.

  FIGS. 7A to 7C are diagrams showing images obtained by down-sampling the enlarged image of FIG. 6C with phases different from those in FIG. 6D.

  In this manner, by performing the contraction process with the pattern matching shown in FIG. 5, as shown in FIGS. 6D and 7A to 7C, even if downsampling is performed at different phases, Thin line thickness unevenness does not occur.

  On the other hand, FIGS. 8A to 8D are diagrams illustrating images down-sampled at different phases when the contraction process is not performed in the case illustrated in FIG. 6. As shown in FIGS. 8A to 8D, when the above-described contraction process is not performed, thickness unevenness occurs in the thin line depending on the phase during downsampling.

  FIG. 9 is a diagram showing another example in which a thin line image is enlarged 1.5 times in the main scanning direction and the sub-scanning direction by the image processing apparatus 14 shown in FIG. FIG. 10 is a diagram illustrating an image after downsampling when downsampling is performed at different phases in the case illustrated in FIG. 9.

  FIG. 9A shows an original image. In this original image, 1-dot horizontal thin lines are diagonally arranged to represent diagonal lines.

  FIG. 9B is a diagram showing an enlarged image in which the image of FIG. 9A is tripled in the main scanning direction and the sub-scanning direction, respectively.

  FIG. 9C is an image (enlarged image) after the contraction process is performed by the pattern matching shown in FIG. 5 on the enlarged image of FIG. 9B. Here, it is assumed that there are no white isolated points.

  FIG. 9D is a diagram showing an image obtained by down-sampling the enlarged image of FIG. 9C by half in the main scanning direction and the sub-scanning direction, respectively.

  FIGS. 10A to 10C are diagrams showing images obtained by down-sampling the enlarged image of FIG. 9C with phases different from those in FIG. 9D.

  In this manner, by performing the contraction process with the pattern matching shown in FIG. 5, as shown in FIGS. 9D and 10A to 10C, even if downsampling is performed at different phases, Thin line thickness unevenness does not occur.

  On the other hand, FIG. 11 (A) to FIG. 11 (D) are diagrams showing images down-sampled at different phases when the contraction process is not performed in the case shown in FIG. As shown in FIGS. 11A to 11D, when the above-described contraction process is not performed, thickness unevenness occurs in the thin line depending on the phase during downsampling.

  FIG. 12 is a diagram illustrating an example in which the pseudo gradation area is enlarged 1.5 times in the main scanning direction and the sub-scanning direction by the image processing apparatus 14 illustrated in FIG. 1.

  FIG. 12A is a diagram illustrating an original image in a pseudo gradation area. In this original image, dots are arranged every other pixel, and a predetermined density is expressed.

  FIG. 12B is a diagram illustrating an enlarged image in which the image of FIG. 12A is tripled in the main scanning direction and the sub-scanning direction, respectively. Note that since the original image in FIG. 12A is an image in a pseudo gradation area, smoothing is not performed.

  FIG. 12C is an image (enlarged image) after the contraction process is performed on the enlarged image of FIG. 12B by pattern matching shown in FIG. Here, it is assumed that there are no white isolated points.

  FIG. 12D is a diagram illustrating an image obtained by down-sampling the enlarged image of FIG. 12C by half in the main scanning direction and the sub-scanning direction, respectively. FIGS. 12E to 12G are diagrams illustrating images obtained by down-sampling the enlarged image in FIG. 12C with phases different from those in FIG.

  In this way, by performing the contraction process with the pattern matching shown in FIG. 5, even if downsampling is performed at different phases as shown in FIGS. Does not occur.

  On the other hand, FIGS. 13A to 13D are diagrams showing images down-sampled at different phases when the contraction process is not performed in the case shown in FIG. As shown in FIGS. 13A to 13D, in the case where the above-described shrinkage processing is not performed, shading unevenness occurs in the pseudo gradation depending on the phase during downsampling.

  As described above, according to the above embodiment, the enlargement processing unit 32 generates an enlarged image obtained by enlarging the image by an integral multiple in the main scanning direction and / or the sub-scanning direction, and the contraction processing unit 34 A contraction process is performed on the image, and the down-sampling unit 35 down-samples the enlarged image after the contraction process to 1 / integer in the main scanning direction and / or the sub-scanning direction.

  As a result, non-integer multiple image scaling is performed while suppressing image quality degradation such as uneven thickness of the thin line portion and uneven shading of the pseudo gradation region.

  The above-described embodiments are preferred examples of the present invention, but the present invention is not limited to these, and various modifications and changes can be made without departing from the scope of the present invention. is there.

  For example, in the above embodiment, the enlargement processing unit 32 may enlarge only one of the main scanning direction and the sub-scanning direction to a non-integer multiple.

  The present invention is applicable to image resolution conversion in, for example, a multifunction machine.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 14 Image processing apparatus 31 Control part (an example of a pseudo gradation area | region identification part)
32 enlargement processing unit 33 white isolated point correction unit (an example of a correction processing unit)
34 Shrinkage processing unit 35 Downsampling unit

Claims (7)

An enlargement processing unit that enlarges an image by an integral multiple in the main scanning direction and / or the sub-scanning direction;
A contraction processing unit for performing a contraction process on the image enlarged to the integer multiple;
A downsampling unit that downsamples the image subjected to the contraction process by the contraction processing unit to an integer of 1 in the main scanning direction and / or the sub-scanning direction;
An image processing apparatus comprising:   The shape of the pixel set without dots in the image expanded to the integer multiple corresponding to the isolated pixel without dots in the image is a shape in which the dot density after the down sampling is constant regardless of the phase of the down sampling. The image processing apparatus according to claim 1, further comprising a correction processing unit for correcting.   The image processing apparatus according to claim 1, wherein the contraction processing unit performs the contraction processing so that the dot density after the downsampling is constant regardless of the phase of the downsampling.   The contraction processing unit sequentially scans the pixel of interest along the main scanning direction and the sub-scanning direction in the image enlarged to the integral multiple, and among the pixel of interest and the peripheral pixels of the pixel of interest, From the value of the pixel of interest, the pixel after the pixel of interest in the main scanning direction in the line with the pixel of interest, and the pixel value of the line after the line with the pixel of interest in the sub-scanning direction, the dot of the pixel of interest The image processing apparatus according to claim 1, wherein presence or absence is determined. A pseudo gradation area specifying unit for specifying a pseudo gradation area in the image;
The enlargement processing unit enlarges the image by a nearest neighbor method without performing smoothing on the pseudo gradation area, and enlarges the image while performing smoothing on an area other than the pseudo gradation area. about,
The image processing apparatus according to claim 1.   The image processing apparatus according to claim 1, wherein the image after downsampling is a non-integer multiple of the image before enlargement.   An image forming apparatus comprising the image processing apparatus according to claim 1.

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