JP5656800B2 - Image processing apparatus and image forming apparatus - Google Patents

Description

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

  When a certain image processing apparatus enlarges an image, the level difference of the edge portion in the image is smoothed according to the length of the flat portion before or after the level difference (for example, see Patent Document 1).

  Further, an image processing apparatus determines, for each line, whether or not the image of the line is a pseudo gradation image based on the number of pixel value changes between adjacent pixels in the line. When the image is not a pseudo gradation image, smoothing is performed. When the image is a pseudo gradation image, smoothing is not performed so as not to impair the reproducibility of the gradation (see, for example, Patent Document 2).

JP-A-4-329484 JP 2001-268348 A

  In order to separate the pseudo gradation area and the other areas (character and line drawing areas) more finely, it is determined for each pixel of interest whether the pixel belongs to the pseudo gradation area, and the pseudo gradation area It is conceivable that smoothing is performed if the tone does not belong to, and smoothing is not performed in order not to impair the reproducibility of the tone if it belongs to the pseudo tone area.

  However, when determining whether or not the target pixel belongs to the pseudo gradation area for each target pixel, depending on the distribution of dots around the step, the pixel determined to belong to the pseudo gradation area around the step and The pixels that are determined not to belong to the pseudo gradation region are spatially alternately arranged, and the continuity of the stepped portion after image enlargement may be impaired.

  FIG. 5 is a diagram illustrating an example of a case where it is determined whether or not each pixel belongs to the pseudo gradation region, and whether or not to perform smoothing is determined based on the determination result, and enlargement processing is performed. . FIG. 5A shows an example of the original image. In FIG. 5A, a step 103 is formed by the edges 101 and 102. FIG. 5B shows the number of pairs in which the pixel value of a pair of two pixels adjacent to each other in the eight pixels around the pixel in the original image changes.

  FIG. 5C illustrates an example of a determination result on whether to perform smoothing based on the number of pairs described above for each pixel illustrated in FIG. When it is determined that the number of pairs is 6 or more, in FIG. 5A, the pixel 111 is determined to belong to the pseudo gradation area, and the pixel 112 is included in the pseudo gradation area. It is determined that it does not belong. The pixel 114 is determined to belong to the pseudo gradation area, and the pixel 113 is determined not to belong to the pseudo gradation area. For this reason, as shown in FIG. 5C, the enlargement process is performed without smoothing on the pixels 111 and 114, and the enlargement process is performed with smoothing on the pixels 112 and 113.

  FIG. 5D shows an image when the original image shown in FIG. 5A is enlarged three times vertically and horizontally (that is, when the resolution is tripled). As shown in FIG. 5D, when the enlargement process is performed by determining whether or not smoothing is performed for each pixel, the unevenness of the edge near the step becomes intense, and the continuity of the edge in the step portion after the image enlargement is impaired. .

  The present invention has been made in view of the above problems, and even in an image in which a pseudo gradation area and other areas (character and line drawing areas) are mixed, an edge in a step portion after image enlargement is obtained. An object of the present invention is to obtain an image processing apparatus and an image forming apparatus that maintain the continuity of the image.

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

An image processing apparatus according to the present invention includes a base point specifying unit that specifies an end of an edge constituting a step as a base point, a region type determining unit that determines whether or not each pixel belongs to a pseudo gradation region, a pseudo-level An enlargement processing unit that performs an enlargement process without performing smoothing on the key area and performs an enlargement process while performing smoothing on an area other than the pseudo gradation area. The enlargement processing unit performs an enlargement process on the pixels in a predetermined range around the base point including the base point without performing smoothing on the pixel when the base point belongs to the pseudo gradation area, and the base point Is not belonging to the pseudo gradation area, the enlargement process is performed while smoothing.

  As a result, it is determined whether or not to perform smoothing for pixels near the step (that is, near the base point) as belonging to the same region (pseudo gradation region or other region) as the base point. Therefore, smoothing does not switch near the step (that is, near the base point), so even if the original image contains both pseudo-gradation areas and other areas (character and line drawing areas), The continuity of the edge in the step portion is maintained.

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, for the pixels belonging to a predetermined range around the base point including the base point , the enlargement processing unit does not perform smoothing on the pixel when the base point closest to the pixel belongs to the pseudo gradation area. Enlarging processing is performed, and when the base point closest to the pixel does not belong to the pseudo gradation region, the enlarging processing is performed while performing smoothing.

  Thereby, it is determined whether or not smoothing is appropriately performed for each pixel.

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 enlargement processing unit does not perform smoothing on a pixel in a predetermined range in a direction parallel to the edge from the base point including the above-described base point when the base point belongs to the pseudo gradation area. If the base point does not belong to the pseudo gradation area, the enlargement process is performed while performing smoothing.

  As a result, regarding the pixels near the base point in the direction parallel to the edge from the base point, whether to perform smoothing is determined as belonging to the same region as the base point. Therefore, since smoothing is not switched in the direction parallel to the edge in the vicinity of the base point, even if the image includes a pseudo gradation region and other regions (character or line drawing region), The continuity of the edge in the step portion is maintained.

  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 area type determination unit determines that the base point does not belong to the pseudo gradation area when there is no dot other than the two edges constituting the step in the peripheral area of the base point.

  Thereby, in order to express an oblique edge, when the vertical edge or the horizontal edge is arranged in an oblique direction and a step is formed, the step is appropriately smoothed.

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, for the pixels in a predetermined range around the base point including the above-described base point , when the base point does not belong to the pseudo gradation area, the enlargement processing unit determines the edge length and the edge of the pixel. The enlargement process is performed while performing smoothing according to the distance from the end.

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

  As a result, even if the image handled by the image forming apparatus (for example, a facsimile received image) is an image in which a pseudo gradation area and other areas (character and line drawing areas) are mixed, the stepped portion after image enlargement The continuity of the edges at is maintained.

  According to the present invention, even in an image in which a pseudo gradation area and other areas (character and line drawing areas) are mixed, the continuity of the edge in the stepped portion after the image enlargement is maintained.

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 diagram for explaining determination of whether or not the target pixel belongs to the pseudo gradation region by the region type determination unit in FIG. FIG. 3 is a flowchart for explaining enlargement processing by the image processing apparatus in FIG. FIG. 4 is a diagram illustrating an example of enlargement processing by the image processing apparatus in FIG. FIG. 5 is a diagram illustrating an example of a case where it is determined whether or not each pixel belongs to the pseudo gradation region, and whether or not to perform smoothing is determined based on the determination result, and enlargement processing is performed. .

  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 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 1200 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, a base point specifying unit 32, an area type determination unit 33, and an enlargement processing unit 34 as processing units.

  The control unit 31 controls the base point specifying unit 32, the region type determination unit 33, and the enlargement processing unit 34, and in the image data of the binary image, the pixels are selected in order along the main scanning direction and the sub scanning direction. Scan as.

  The base point specifying unit 32 specifies the end of the edge constituting the step in the image as a base point by pattern matching.

  Here, the step is a portion where two edges are in contact with each other in the horizontal direction (main scanning direction) or the vertical direction (sub-scanning direction) while being shifted by one pixel, and the edge portion of the edge is horizontal (main scanning direction). Alternatively, it is a pixel at the end of a pixel row arranged in a straight line in the vertical direction (sub-scanning direction).

  The area type determination unit 33 determines whether each pixel belongs to the pseudo gradation area. 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.

  The region type determination unit 33 determines whether or not the target pixel belongs to the pseudo gradation region from the values of the pixels in the peripheral region of the target pixel.

  FIG. 2 is a diagram for explaining determination by the region type determination unit 33 in FIG. 1 whether or not the target pixel belongs to the pseudo gradation region. As shown in FIG. 2, the region type determination unit 33 performs, for each pixel, a ratio of a pair in which the pixel value of a pair of two adjacent pixels in eight pixels around the pixel changes or a pair in which the pixel value changes. Is greater than a predetermined threshold value, it is determined that the pixel belongs to the pseudo gradation area.

  In the case of FIG. 2, the number of pairs in which the pixel value changes is 6 among the pair (eight) of two adjacent pixels in the eight pixels around the target pixel.

  In this embodiment, when the pixel value is changed in 6 or more of the 8 pairs in FIG. 2 (that is, the pixel values of the two pixels constituting the pair are different from each other), the pixel is It is determined that it belongs to the pseudo gradation area.

  In the above-described embodiment, the region type determination unit 33 does not include dots other than the two edges constituting the step in the peripheral region of the base point (the same region as the peripheral region for the region type determination unit 33). Is configured to determine that the base point does not belong to the pseudo gradation region. For example, when there are no dots other than the two edges forming the step around the above-described base point, the above-described predetermined threshold is set so as to determine that the base point does not belong to the pseudo gradation region. The

  The enlargement processing unit 34 performs enlargement processing without performing smoothing on the pseudo gradation region, and performs enlargement processing while performing smoothing on regions other than the pseudo gradation region. However, when the base point belongs to the pseudo gradation area, the enlargement processing unit 34 performs the enlargement process without performing smoothing for the pixel in the predetermined range around the base point. If it does not belong to the key area, the enlargement process is performed while smoothing. That is, the region type of a pixel in a predetermined range around the base point is regarded as the same as the region type of the base point.

  In this embodiment, the enlargement processing unit 34 does not perform smoothing on a pixel in a predetermined range in the direction parallel to the edge from the above base point when the base point belongs to the pseudo gradation area. When the enlargement process is performed and the base point does not belong to the pseudo gradation area, the enlargement process is performed while performing the smoothing.

  The enlargement processing unit 34 performs smoothing (for example, when the base point does not belong to the pseudo gradation area for the pixels in the predetermined range around the base point), from the edge length and the edge end of the pixel. The enlargement process is performed while performing smoothing according to the distance. The enlargement processing unit 34 performs enlargement processing by the nearest neighbor method when smoothing is not performed. Note that the enlargement process is synonymous with an increase in resolution.

  Next, the operation of the image processing apparatus 14 will be described. FIG. 3 is a flowchart for explaining enlargement processing by the image processing apparatus 14 in FIG. FIG. 4 is a diagram illustrating an example of enlargement processing by the image processing apparatus 14 in FIG.

  First, the control unit 31 causes the base point specifying unit 32 to specify the base point in the original image. The base point specifying unit 32 scans the entire area of the original image, detects a step in the image by pattern matching, and specifies a pixel at one end of two edges constituting the step as a base point (step S1).

  FIG. 4A shows an example of the original image. In FIG. 4A, a step 53 is formed by the edges 51 and 52. In the original image shown in FIG. 4A, the pixel 61 is specified as the base point.

  After the base point is specified, the control unit 31 sequentially moves the target pixel in the main scanning direction and the sub-scanning direction, and performs an enlargement process for each pixel.

  First, the control unit 31 sets a target pixel (step S2). 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 is within a predetermined range around any base point (step S3).

  Here, in the direction parallel to the edge 52 to which the base point (pixel 61) belongs, the base point (pixel 61), the pixel 62 on the edge 52 adjacent to the base point, the pixel 63 outside the edge 52 adjacent to the base point, and the pixel It is determined that the pixel 64 adjacent to 63 is within a predetermined range around the base point (pixel 61).

  When it is determined that the pixel of interest is within a predetermined range around the base point, the region type determination unit 33 determines the region type of the pixel of interest without determining the region type of the pixel of interest. If it is determined that the target pixel is not within the predetermined range around the base point, the region type of the target pixel is determined and the region type of the target pixel is specified (step S5).

  When it is determined that the target pixel belongs to the pseudo gradation area, the enlargement processing unit 34 executes the enlargement process without smoothing (step S7), and when it is determined that the target pixel does not belong to the pseudo gradation area. The enlargement process is executed while smoothing (step S8).

  When executing the enlargement process while performing smoothing, the enlargement processing unit 34 specifies the edge length and the distance from the step to the target pixel by pattern matching, and responds to the edge length and the distance from the step to the target pixel. Smoothing is performed to determine the pixel value (with or without dots) after the enlargement process.

  When the enlargement process (step S7 or step S8) for the target pixel is completed, the control unit 31 determines whether or not the enlargement process for all pixels in the original image is completed (step S9). The pixel of interest is moved until the enlargement process for that pixel is completed, and the above-described processes (steps S2 to S8) are executed for each pixel.

  FIG. 4B shows the number of pairs in which the pixel value of a pair of two adjacent pixels in each of the pixels in the original image shown in FIG. . FIG. 4C illustrates an example of a determination result of whether or not smoothing is performed by the region type determination unit 33. In FIG. 4C, when the number of pairs described above is 6 or more, it is determined that the pixel belongs to the pseudo gradation region. Accordingly, since the base pixel 61 is determined to belong to the pseudo gradation region, the pixels 61 to 64 that are pixels within a predetermined range around the base point are not smoothed.

  FIG. 4D is an image when the original image shown in FIG. 4A is enlarged three times vertically and horizontally (that is, when the resolution is tripled). As shown in FIG. 4D, in the vicinity of the step, the presence or absence of smoothing is not switched between adjacent pixels, so that the unevenness of the edge around the step does not become severe, and the continuity of the edge in the step portion after image enlargement is improved. Secured.

  In FIG. 4A, when there is no dot (pixel 71) other than the two edges constituting the step around the base pixel 61, the base pixel 61 belongs to the pseudo gradation region. It is determined that there is no. When there is no dot in the pixel 71, the number of pairs described above is 4, and it is determined that the base pixel 61 does not belong to the pseudo gradation region. In that case, the edges 51 and 52 around the step 53 are all smoothed.

  As described above, according to the above embodiment, the base point specifying unit 32 specifies the edge of the edge constituting the step as the base point, and the region type determination unit 33 belongs to the pseudo gradation region for each pixel. The enlargement processing unit 34 performs an enlargement process without performing smoothing on the pseudo gradation area and performs an enlargement process while performing smoothing on areas other than the pseudo gradation area. However, when the base point belongs to the pseudo gradation area, the enlargement processing unit 34 performs the enlargement process without performing smoothing for the pixel in the predetermined range around the base point. If it does not belong to the key area, the enlargement process is performed while smoothing.

  As a result, it is determined whether or not to perform smoothing for pixels near the step (that is, near the base point) as belonging to the same region (pseudo gradation region or other region) as the base point. Therefore, smoothing does not switch near the step (that is, near the base point), so even if the original image contains both pseudo-gradation areas and other areas (character and line drawing areas), The continuity of the edge in the step portion is maintained.

  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 34 performs smoothing on a pixel belonging to a predetermined range around a plurality of base points when the base point closest to the pixel belongs to the pseudo gradation area. If the base point closest to the pixel does not belong to the pseudo gradation area, the enlargement process may be performed while performing smoothing. In such a case, it is determined whether or not smoothing is appropriately performed for each pixel.

  In addition, the method for determining the region type (pseudo gradation region or other region) in the above embodiment is not limited to the above.

  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 32 Base point specific | specification part 33 Area | region classification determination part 34 Enlargement process part 51,52 Edge 53 Level | step difference 61 Pixel (an example of a base point)

Claims (6)

A base point specifying part that specifies the end of the edge constituting the step as a base point;
An area type determination unit that determines whether or not each pixel belongs to a pseudo gradation area;
An enlargement processing unit that performs enlargement processing without performing smoothing on the pseudo gradation region and performs enlargement processing while performing smoothing on regions other than the pseudo gradation region;
The enlargement processing unit performs an enlargement process without performing smoothing on a pixel in a predetermined range around the base point including the base point without performing smoothing on the pixel when the base point belongs to the pseudo gradation area, and the base point Is not belonging to the pseudo gradation area, performing an enlargement process while performing smoothing,
An image processing apparatus. For the pixel belonging to a predetermined range around the base point including a plurality of the base points , the enlargement processing unit does not perform smoothing on the pixel when the base point closest to the pixel belongs to the pseudo gradation area. 2. The image processing apparatus according to claim 1, wherein enlargement processing is performed, and if the base point closest to the pixel does not belong to the pseudo gradation region, the enlargement processing is performed while performing smoothing. The enlargement processing unit enlarges a pixel in a predetermined range in a direction parallel to the edge from the base point including the base point without performing smoothing on the pixel when the base point belongs to the pseudo gradation region. 3. The image processing apparatus according to claim 1, wherein when the base point does not belong to the pseudo gradation area, the enlargement process is performed while performing the smoothing.   The region type determination unit determines that the base point does not belong to a pseudo gradation region when there are no dots other than two edges forming a step in a peripheral region of the base point. The image processing device according to any one of claims 1 to 3. If the base point does not belong to the pseudo gradation region for a pixel in a predetermined range around the base point including the base point , the enlargement processing unit performs the length of the edge and the edge of the edge for the pixel. The image processing apparatus according to claim 1, wherein the enlargement process is performed while performing smoothing according to the distance from the unit.   An image forming apparatus comprising the image processing apparatus according to claim 1.

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