JP4080496B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a scanner, and a facsimile.

  Some image forming apparatuses such as copying machines, scanners, and facsimiles perform the following image processing on image data of a document read by a document reading unit.

  That is, first, based on the read image data, it is determined for each pixel whether the pixel data is a pixel area, a halftone dot area, or another area. For example, the pixel data of the character area is subjected to an error diffusion process after a sharpening process such as an edge enhancement process. For example, the pixel data in the halftone dot region is subjected to a smoothing process in order to prevent the occurrence of moire and then a screen process. For example, the pixel data in the other region is subjected to a smoothing process and then a screen process. However, the smoothing process for the pixel data in the other areas is less smoothed than the smoothing process for the pixel data in the halftone area. After the above processing is performed on each of the character area, halftone dot area, and other areas, the data is synthesized.

  Various methods for determining the type of region to which each pixel data belongs have been proposed. For example, in Japanese Patent Application Laid-Open No. 62-147860, a block having a predetermined size is obtained by calculating a difference between the maximum density and the minimum density, so that the block is a photographic part whose gradation changes smoothly. Alternatively, a technique for discriminating whether the character or halftone dot portion is other than that is disclosed. Japanese Patent Application Laid-Open No. 7-26497 discloses a technique for discriminating between a character part and a photographic part even when there is a part where the density change is severe in the photographic part.

However, with these conventional techniques, it is difficult to distinguish between a character portion and a halftone portion when there is a portion where the density change is severe in the halftone document.
Japanese Patent Laid-Open No. Sho 62-147860 Japanese Patent Laid-Open No. 7-26497

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of accurately identifying a character portion and a halftone dot portion even when there is a portion where the density change is severe in the halftone document.

  According to the first aspect of the present invention, a first area for identifying, for each pixel, whether the pixel is a character / halftone area or an area other than a character / halftone area based on input image data. For each pixel determined to be a character / halftone dot area by the identification processing means and the first area identification processing means, it is determined whether the pixel is a character area, a halftone dot area, or a character or halftone dot. The second area identification processing means for identifying whether the area cannot be easily discriminated (character / halftone dot unknown area), and each pixel determined to be a character / halftone unknown area by the second area identification processing means And a third area identification processing means for identifying whether the pixel is a character area or a halftone dot area with reference to the identification result by the first area identification processing means. The identification processing means is a character / halftone unknown area Of the determined pixels, if the pixel of interest is the pixel of interest, a character in the reference area having a predetermined size centered on the pixel of interest is identified using the identification result of the first area identification processing means. The first area determined to be a halftone dot area and the second area determined to be an area other than a character / halftone dot are separated, and the number of pixels included in the first area and the first area are in contact with the second area. Calculating means for calculating the number of pixel units of the side that is present, and the number of pixels included in the first region and the side of the side where the first region is in contact with the second region with one side of one pixel as one unit And determining means for determining whether the target pixel is a character area or a halftone dot area based on the number.

  The invention according to claim 2 is the invention according to claim 1, wherein the discrimination means in the third area identification processing means calculates the fourth threshold value from the number of pixels included in the first area, And the number of sides of the pixel unit in which the first region is in contact with the second region is compared with the fourth threshold value calculated by the threshold value calculation means. If the number of sides is equal to or greater than the fourth threshold value, It is characterized in that there is provided means for determining that the target image is a halftone dot region, and determining that the target image is a character region when the number of sides is smaller than a fourth threshold value.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the first region identification processing unit determines that the pixel of interest in the input image data is the pixel of interest and sets the pixel of interest as the pixel of interest. Differentiating is performed on the image, and it is determined whether the target pixel is a character / halftone dot region or a region other than a character / halftone dot based on whether the obtained image value is equal to or greater than the first threshold value. It is characterized by being.

  According to a fourth aspect of the present invention, in the first to third aspects of the present invention, the second region identification processing unit is configured to detect pixels that are determined to be character / halftone regions by the first region identification processing unit. Of these, if the pixel of interest is the pixel of interest, smoothing processing using a Gaussian filter is performed on the pixel of interest and then obtained by smoothing / differential processing means and smoothing / differential processing means for performing differential processing. When the pixel value of the target pixel obtained by the smoothing / differential processing means is smaller than the second threshold, the pixel value of the target pixel obtained is compared with the second threshold and the third threshold greater than the second threshold. The pixel is determined to be a halftone dot region, and when the pixel value of the pixel of interest obtained by the smoothing / differential processing means is larger than the third threshold value, the pixel of interest is determined to be a character region, and smoothing / differential processing is performed. By means When the obtained pixel value of the target pixel is equal to or larger than the second threshold value and equal to or smaller than the third threshold value, the pixel of interest includes a determination unit that determines that the target pixel is a character / halftone unknown region. To do.

  According to the present invention, even when there is a portion where the density change is severe in the halftone original, the character portion and the halftone portion can be accurately identified.

  Embodiments of the present invention applied to a digital copying machine will be described below with reference to the drawings.

  FIG. 1 shows a schematic configuration of a digital copying machine.

  The digital copying machine includes a scanner unit 10, a control unit 20 including an image processing unit, a hard disk device (HDD) 30, an image forming unit 40, and a user operation unit 50. The scanner unit 10 includes a document feeder (DF) 11, a scanner 12, and an image reading CCD 13. The control unit 20 includes a CPU, a ROM, a RAM, and the like.

  The image forming unit 40 includes a laser scanning unit (LSU) 41 and an electrostatic copying mechanism including a photosensitive drum. The user operation unit 50 includes a key input unit 51 including various keys such as a numeric keypad, a start button, and an interrupt button, a liquid crystal display unit 52 with a touch panel, and an LED display unit 53.

  A document fed onto a contact glass (not shown) by a document feeder (DF) 11 is optically scanned by a scanner 12 and a document image is read by an image reading CCD 13. Image data obtained by the image reading CCD 13 is sent to the control unit 20 and subjected to predetermined image processing, and then stored in the HDD 30. The image data stored in the HDD 30 is sent to the LSU 41 via the control unit 20. The LSU 41 generates laser light in accordance with the sent image data, modulates and deflects it to form an electrostatic latent image pattern on the photosensitive drum. This electrostatic latent image pattern is transferred onto a recording sheet.

  Image processing performed by the control unit 20 will be described. First, based on the image data obtained by the image reading CCD 13, it is determined for each pixel whether the pixel data is the pixel data of a character area, a halftone dot area, or another area. That is, first, region separation processing is performed.

  Then, for each region separated by the region separation process, image processing adapted to that region is performed. That is, region adaptation processing is performed. Specifically, for example, the pixel data of the character area is subjected to an error diffusion process after being subjected to a sharpening process such as an edge enhancement process. For example, the pixel data in the halftone dot region is subjected to a smoothing process in order to prevent the occurrence of moire and then a screen process. For example, the pixel data in the other region is subjected to a smoothing process and then a screen process. However, the smoothing process for the pixel data in the other areas is less smoothed than the smoothing process for the pixel data in the halftone area.

  When image processing adapted to each region is performed in this way, those image data are synthesized. The feature of the present invention is the region separation process.

  FIG. 2 shows a procedure of region separation processing performed by the control unit 20.

  Here, it is assumed that the image data is 8 bits, the light side (white side) is “0”, and the dark side (black side) is “255”.

  First, based on the read image data, for each pixel, the pixel is a character / halftone dot region (either a character or halftone dot region) or other region (a region other than a character / halftone dot) ) Is performed (step S1), and the identification result is stored (step 2). For the pixels identified as other regions in the first region identification process, the identification result is the final identification result.

  In the first region identification processing, differentiation processing is performed on the pixel of interest, and whether the pixel of interest is a character / halftone dot region based on whether the obtained image value is equal to or greater than the first threshold th1. It is determined whether the area is other area.

  When the differentiation process is performed on the character / halftone dot area, the pixel value becomes large because there are many edge portions, whereas when the differentiation process is performed on the other area, the pixel value becomes small because there are few edge portions. Assuming that the pixel value of the target pixel obtained by the differentiation process is X, if X ≧ Th1, it is determined that the target pixel is a character / halftone dot region, and if X <Th1, the target pixel is another region. Is determined.

  Next, for each pixel determined to be a character / halftone dot region by the first region identification processing, it is easy to determine whether the pixel is a character region, a halftone dot region, or a character or halftone dot. A second area identification process is performed to identify whether the area cannot be identified (character / halftone unknown area) (step S3), and the identification result is stored (step S4). For the pixel identified as the character area and the pixel identified as the halftone dot area in the second area identification process, the identification result is the final identification result.

  In the second region identification processing, first, smoothing processing using a Gaussian filter is performed on the target pixel, and then differentiation processing is performed. Then, by comparing the obtained pixel value of the target pixel with two threshold values th2 and th3 (th3> th2), it is determined whether the target pixel is a character region, a halftone dot region, or a character / halftone dot. Determine whether it is an unknown area.

  When a smoothing process using a Gaussian filter is applied to the halftone dot area, a solid image is obtained. On the other hand, even if a smoothing process using a Gaussian filter is performed on the character region, an edge portion remains to some extent. For this reason, if a differentiation process is performed after the smoothing process using the Gaussian filter, the pixel value becomes small in the halftone area and the pixel value becomes large in the character area.

  If the pixel value of the target pixel obtained when the differentiation process is performed after the smoothing process using the Gaussian filter is Y, it is determined that the target pixel is a halftone dot region if Y <th2. If Y> th3, it is determined that the target pixel is a character area. If th2 ≦ Y ≦ th3, it is determined that the target pixel is a character / halftone unknown region.

  Next, with respect to each pixel determined to be a character / halftone unknown region by the second region identification processing, the result of the first region identification processing is referred to to determine whether the pixel is a character region A third area identification process for identifying the above is performed (step S5), and the identification result is stored (step S6). Details of the third region identification processing will be described later.

  For the pixel identified as the character area and the pixel identified as the halftone dot area in the third area identification process, the identification result is the final identification result. As described above, a character, halftone dot, or other region identification result is obtained for each pixel.

  FIG. 3 shows the procedure of the process (third area identification process) in step 5 of FIG. FIG. 3 shows a third region identification process procedure for one pixel (a pixel of interest) determined to be a character / halftone unknown region.

  The reference area consisting of N × N blocks centered on the target pixel is determined as the area A determined as the character / halftone dot area and other areas using the result of the first area identification processing. The area B is divided (step S11). N is set to 11, for example.

  The number K of pixels included in the area A is calculated (step S12). For example, the threshold th4 is calculated from the number of pixels K based on a table prepared in advance (step S13). FIG. 4 shows the relationship between the number of pixels K and the threshold value th4. As the image number K increases, the threshold th4 also increases.

  Next, using one side of one pixel as one unit, the number W of sides where the region A is in contact with the region B is calculated (step S14). The number of sides W is calculated with the length of one side of the pixel being 1. And it is discriminate | determined whether W is more than th4 (step S15). If W ≧ th4 (YES in step S15), it is determined that the target pixel is a halftone dot region (step S16). If W <th4 (NO in step S15), it is determined that the target pixel is a character region (step S17).

  FIG. 5 shows an example of an 11 × 11 block centering on the target pixel C when one pixel (target pixel) C determined to be a character / halftone unknown region exists in the halftone area. Is shown. When an 11 × 11 block is a halftone dot area, the area A (area shown by hatching) determined as a character / halftone dot area is often finely dispersed. Therefore, for the number K of pixels included in the area A determined as the character / halftone area, the number W of the sides where the area A determined as the character / halftone area is in contact with the other determined area B Is a relatively large value.

  For example, the number K of pixels included in the region A is 42, and the number W of sides where the region A is in contact with the region B is 90. The threshold Th4 is calculated from the number of pixels K, and is assumed to be 70, for example. In this case, W ≧ th4, and it is determined that the target pixel C is a halftone dot region.

  FIG. 6 shows an example of an 11 × 11 block centered on the target pixel C when one pixel (target pixel) C determined to be a character / halftone unknown region exists in the character region. Show. When an 11 × 11 block is a character area, the area A (hatched area) determined as a character / halftone area is often clustered. Therefore, the number W of the sides where the region A is in contact with the region B is a relatively small value with respect to the number K of pixels included in the region A.

  For example, the number K of pixels included in the region A is 42, and the number W of sides where the region A is in contact with the region B is 52. The threshold Th4 is calculated from the number of pixels K, and is assumed to be 70, for example. In this case, W <th4, and it is determined that the target pixel C is a character area.

1 is a block diagram illustrating a schematic configuration of a digital copying machine. 5 is a flowchart showing a procedure of region separation processing performed by a control unit 20; It is a flowchart which shows the procedure of the process (3rd area | region identification process) of step 5 of FIG. It is a graph which shows the relationship between the pixel number K and threshold value th4. FIG. 11 is a schematic diagram showing an 11 × 11 block centered on a target pixel C when one pixel (target pixel) C determined to be a character / halftone unknown region exists in the halftone dot region. . It is a schematic diagram showing an 11 × 11 block centered on the target pixel C when one pixel (target pixel) C determined to be a character / halftone unknown region exists in the character region.

Explanation of symbols

10 Scanner unit 10
20 control unit 30 hard disk drive (HDD)
40 Image forming unit 50 User operation unit

Claims (4)

First region identification processing means for identifying, for each pixel, whether the pixel is a character / halftone dot region or a region other than a character / halftone dot, based on input image data;
For each pixel determined to be a character / halftone area by the first area identification processing means, it cannot be easily determined whether the pixel is a character area, a halftone area, or a character or halftone dot. A second region identification processing means for identifying a region (character / halftone unknown region), and
For each pixel determined to be a character / halftone unknown region by the second region identification processing means, refer to the identification result by the first region identification processing means to determine whether the pixel is a character region or not. A third region identification processing means for identifying whether the region is a region;
The third area identification processing means
Of the pixels determined to be a character / halftone unknown region, if the pixel of interest is the pixel of interest, the first region identification process is performed within a reference region of a predetermined size centered on the pixel of interest. Using the identification result of the means, the first area determined as the character / halftone area and the second area determined as the area other than the character / halftone area are divided, and the number of pixels included in the first area, The calculation means for calculating the number of sides where the first area is in contact with the second area, with one side of one pixel as one unit, the number of pixels included in the first area, and the first area as the second area An image forming apparatus comprising: discrimination means for discriminating whether the pixel of interest is a character area or a halftone dot area based on the number of sides of a pixel unit in contact with the pixel area. The discriminating means in the third area identification processing means includes means for calculating a fourth threshold value from the number of pixels included in the first area, and the number of sides of the pixel unit in which the first area is in contact with the second area. And the fourth threshold value calculated by the threshold value calculation means, and if the number of sides is equal to or greater than the fourth threshold value, it is determined that the target image is a halftone dot region, and the number of sides is The image forming apparatus according to claim 1, further comprising a unit that determines that the target image is a character area when the threshold value is smaller than four threshold values. The first area identification processing means performs a differentiation process on the pixel of interest when the currently focused pixel of the input image data is the pixel of interest, and whether the obtained image value is equal to or greater than the first threshold value. 3. The image according to claim 1, wherein it is determined whether the pixel of interest is a character / halftone dot region or a region other than a character / halftone dot based on whether or not the pixel of interest is a character / halftone dot region. Forming equipment. The second region identification processing unit is configured to gauss the target pixel with respect to the pixel of interest as a pixel of interest among the pixels determined to be a character / halftone dot region by the first region identification processing unit. Smoothing / differential processing means for performing differential processing after performing smoothing processing using a filter, and a pixel value of a pixel of interest obtained by the smoothing / differential processing means is set to a second threshold value and a third threshold value greater than the second threshold value. When the pixel value of the target pixel obtained by the smoothing / differential processing means is smaller than the second threshold value compared with the threshold value, it is determined that the target pixel is a halftone dot region, and obtained by the smoothing / differential processing means When the pixel value of the target pixel is larger than the third threshold value, it is determined that the target pixel is a character region, and the pixel value of the target pixel obtained by the smoothing / differential processing means is equal to or larger than the second threshold value and the third threshold value. In If there is, a discrimination means for discriminating that the target pixel is a character / halftone unknown region,
The image forming apparatus according to claim 1, further comprising:

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