JP5360131B2 - Image processing apparatus and program - Google Patents

Description

  The present invention relates to an image processing apparatus and a program.

  A color image is printed by superimposing a plurality of planes (for example, CMYK planes). At this time, color blur may occur if the overlapping position is shifted between a plurality of planes. This phenomenon is generally referred to as misregistration. In order to suppress this color blur, an image processing apparatus that detects an edge portion of a character or the like, reduces the CMY (cyan, magenta, yellow) component of the detected edge portion, and increases the K (black) component. Known (for example, Patent Document 1).

JP 2000-206756 A

  An object of the present invention is to provide an image processing apparatus and program capable of applying a color blur correction process to a halftone processed N-value image.

According to the first aspect of the present invention, the yellow, magenta, cyan, and black pixel values that are overlaid on the halftone-processed N-value image and that are included in a preset area centered on the target pixel are off. The number of pixels of 1 and the second number of pixels in which pixels having at least one pixel value of yellow, magenta and cyan included in the region overlap with black pixels included in the region, and the halftone processing Whether or not the pixel of interest is to be subjected to color blur correction processing based on the on / off state of the yellow, magenta and cyan pixel values of the pixel corresponding to the pixel of interest in the N-value image Determining means for determining
When the determination unit determines that the target pixel is a pixel to be subjected to color blur correction processing, a target pixel determination for turning off the yellow, magenta, and cyan pixel values of the pixel corresponding to the target pixel An image processing apparatus comprising: a changing unit.

According to a second aspect of the present invention, in the image processing apparatus according to the first aspect, the determination unit is configured such that the first pixel number is equal to or greater than a first threshold value, and the second pixel number is a second threshold value. When the pixel value corresponding to the target pixel in the half-valued N-value image is ON, and the pixel value of any one of yellow, magenta, and cyan is on, the target pixel corrects color blur It is an image processing apparatus characterized by determining that a pixel is to be processed.

According to a third aspect of the present invention, in the image processing apparatus according to the first aspect, the pixel-of-interest determination change means has a black pixel value of a pixel in which the pixel values of the yellow, the magenta, and the cyan are turned off. In this case, the image processing apparatus is characterized in that the black pixel value is turned on.

The invention according to claim 4 is the image processing apparatus according to any one of claims 1 to 3, wherein the N-value image is a binary image.

According to the fifth aspect of the present invention, the yellow, magenta, cyan, and black pixel values that are overlapped with the half-toned N-value image and included in a preset area centered on the target pixel are turned off. A second pixel number in which a pixel having at least one pixel value of yellow, magenta and cyan included in the region overlaps a black pixel included in the region, and the halftone The pixel of interest is a pixel to be subjected to color blur correction processing based on the on / off state of the yellow, magenta, and cyan pixel values of the pixel corresponding to the pixel of interest in the processed N-value image A determination unit that determines whether or not the target pixel is a pixel that should be subjected to a color blur correction process; That pixel of yellow, which is a program for causing to function as a pixel value determining means for turning off the pixel values of the magenta and cyan.

  According to the first aspect of the present invention, color blur correction processing can be applied to an N-value image subjected to halftone processing.

  According to the second aspect of the present invention, it is possible to determine a pixel to be subjected to color blur correction processing by a simple method.

  According to the third aspect of the present invention, when the halftone processed N-value image is black, color bleeding can be suppressed.

  According to the fourth aspect of the present invention, the color blur correction process can be applied to the halftone processed binary image.

  According to the fifth aspect of the present invention, the color blur correction process can be applied to the half-valued N-value image.

FIG. 2A is a block diagram illustrating an example of a configuration of an image processing apparatus according to the present embodiment. FIG. 2B is a diagram illustrating an example of a hardware configuration of the print control unit 3. (A) is a diagram showing a binary image that has been subjected to halftone processing when no color blur has occurred. FIG. 2B is an enlarged view of a part of the character in FIG. (A) is a figure which shows the binary image by which the halftone process in case the color blur has generate | occur | produced. FIG. 3B is an enlarged view of a part of the character in FIG. 3 is a block diagram illustrating a configuration of a color blur correction processing unit 9. FIG. (A) is a figure which shows C (cyan) plane corresponding to a part of character of FIG. 2 (B). (B) is a diagram showing an M (magenta) plane corresponding to a part of the character of FIG. 2 (B). (C) is a diagram showing a Y (yellow) plane corresponding to a part of the character of FIG. 2 (B). (D) is a figure which shows K (black) plane corresponding to a part of character of FIG. 2 (B). (A) is a figure which shows the state of C plane and K plane contained in the process area 50. FIG. FIG. 6B is a diagram illustrating the states of the M plane and the K plane included in the processing area 50. (C) is a diagram showing the states of the Y plane and the K plane included in the processing area 50. It is a figure which shows the pixel determined by the color blur correction determination part 13 that the color blur correction process is required. (A) is a diagram illustrating a state after color blur correction processing of the binary image in FIG. 2 (B). FIG. 6B is a diagram illustrating a state after the color blur correction process of the binary image in FIG. FIG. 8A is a flowchart illustrating processing executed by the color blur correction processing unit 9. FIG. 9B is a flowchart illustrating a modification of part of the process in FIG.

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

  FIG. 1A is a block diagram illustrating a configuration of an image processing apparatus according to this embodiment.

  In FIG. 1, an image processing apparatus 1 is, for example, a printer, a copier, or a multifunction machine. The image processing apparatus 1 includes an input unit 2, a print control unit 3, and an output unit 4. The input unit 2 is an interface for inputting image data. As shown in FIG. 1B, the print control unit 3 includes a CPU 31, a memory 32, and a communication interface (I / F) 33, and executes predetermined image processing on the input image data. The output unit 4 outputs the image data that has been subjected to image processing to a recording sheet.

  The print control unit 3 includes a PDL interpretation unit 5, a color conversion unit 6, an N-value conversion processing unit 7 (N = 2 or more), a drawing unit 8, and a color blur correction processing unit 9. A PDL (Page Description Language) interpreter 5 interprets a page description language and develops image data. The color conversion unit 6 converts RGB data (Red, Green, Blue) of image data into CMYK data (Cyan, Magenta, Yellow, Black). The N-value processing unit 7 performs N-value processing (for example, halftone processing) on the image data. The drawing unit accumulates the N-valued data and creates a bitmap image. The color blur correction processing unit 9 executes color blur correction processing for suppressing color blur caused by color plane registration misalignment.

  FIG. 2A is a diagram illustrating a binary image that has been subjected to halftone processing when no color blur has occurred, and FIG. 2B is an enlarged view of a portion of the character in FIG. is there. FIG. 3A is a diagram showing a binary image that has been subjected to halftone processing in the case where a color blur has occurred, and FIG. 3B is an enlarged view of a part of the character in FIG. is there.

  As shown in FIGS. 2A and 3A, for example, the binary image that has been subjected to the halftone process is a black character “B” in which CYMK components are mixed. Since the binary image is generated by a halftone process such as a dither matrix, the image becomes a halftone dot image as shown in FIGS. 2B and 3B. In such a binary image, color blur occurs when the C (cyan) plane deviates from the other planes. In FIGS. 2A and 2B, the C plane is not displaced from the other planes. On the other hand, in FIGS. 3A and 3B, the C plane is shifted downward by 2 pixels from the other planes. Due to the deviation of the C plane, the edge portion (ie, outline) of the character is blurred. A color plane such as a K plane or C plane is also called a color plate.

  Hereinafter, an example will be described in which the C plane is shifted by two pixels downward from the other planes, and color misregistration correction processing is performed with a 2-dot width along the outline of the character. Further, it is assumed that the image data input to the color misregistration correction processing unit 9 is a binary image subjected to halftone processing.

  FIG. 4 is a block diagram illustrating a configuration of the color blur correction processing unit 9.

  The color blur correction processing unit 9 includes a processing region determination unit 11, a region feature amount calculation unit 12, a color blur correction determination unit 13, and a target pixel value determination unit 14. The color blur correction determination unit 13 functions as a determination unit. The target pixel value determination unit 14 functions as a changing unit.

  When acquiring the binary image, the processing area determination unit 11 determines a 5 (dot) × 5 (dot) area having the center pixel as a target pixel as the processing area 50 as illustrated in FIG. The processing area 50 is not limited to a 5 (dot) x 5 (dot) area, and may be a 3 (dot) x 3 (dot) area or a 7 (dot) x 7 (dot) area.

  A C (cyan) plane, an M (magenta) plane, a Y (yellow) plane, and a K (black) plane corresponding to a part of the character in FIG. 2B are shown in FIGS. . The state of the C plane and the K plane included in the processing area 50 is shown in FIG. 6A, and the state of the M plane and the K plane included in the processing area 50 is shown in FIG. FIG. 6C shows the state of the Y plane and the K plane included in 50.

  The area feature quantity calculation unit 12 calculates the feature quantity of the processing area 50. The color blur correction determination unit 13 determines whether or not the target pixel is a pixel to be subjected to color blur correction processing based on the feature amount of the processing region 50. The target pixel value determination unit 14 determines the target pixel value to be output based on the pixel value corresponding to the target pixel in the input binary image and the output value from the color blur correction determination unit 13.

  Here, a method for determining the size of the processing region 50 will be described.

  In the processing area 50 of 5 (dots) × 5 (dots), when the target pixel is placed at the position of the inner end of the character, it can be used if there is a color blur (registration misalignment) of 2 dots or less. However, it cannot be used when there is a color blur of 3 dots or more. In this case, when there is a color blur of 2 dots or less, cyan pixels are included in the processing region 50, but when there is a color blur of 3 dots or more, cyan pixels are included in the processing region 50. Because it is not possible. Accordingly, the processing area 50 of 5 (dots) × 5 (dots) can be used when correction processing of color blur having a width of 2 dots or less is performed on the outline of a character.

  Similarly, when the processing area 50 is an area of 3 (dots) × 3 (dots), the processing area 50 can be used when correction processing for color blur having a 1-dot width is performed on the contour portion. When the processing area 50 is an area of 7 (dots) × 7 (dots), the processing area 50 can be used when correction processing for color blur having a width of 3 dots or less is performed on the outline of a character.

  As described above, the dot width for performing the color blur correction process can be changed according to the size of the processing area 50. When color blur correction processing is performed, it is necessary to determine a dot width for performing color blur correction processing. This dot width can be set in advance with the size of the registration shift assumed from the specifications of the output unit 4. Accordingly, the processing area determination unit 11 receives the notification of the specification from the output unit 4 and determines the size of the processing area 50. Further, the processing area determination unit 11 may determine the size of the processing area 50 based on an input from the user (for example, an instruction to select a 5 (dot) × 5 (dot) area).

  Next, the operation of the region feature amount calculation unit 12 will be described.

The region feature calculation unit 12 refers to the processing region 50 and calculates the feature amount of the processing region 50 shown below.
(1) Number of white pixels (all components of CMYK = off): This is referred to as “the number of white pixels”.
(2) Coefficient of pixels in which one of K and CMY overlaps: This is referred to as “the number of overlapping pixels”.
(3) Information on whether or not any of CMY of the target pixel (hereinafter referred to as “target CMY”) is on: The output of the target CMY is turned on when any of the target CMY is on, Turns off when all of CMY are off.

  For example, when the region feature calculation unit 12 calculates the feature amounts of the processing regions in FIGS. 5A to 5D, the calculation result is the number of white pixels = 14, the number of overlapping pixels = 5, and the target CMY = on. This calculation result is sent to the color blur correction determination unit 13.

  Next, the operation of the color blur correction determination unit 13 will be described.

  The color blur correction determination unit 13 determines whether or not “the number of white pixels is equal to or greater than a white pixel number threshold, the number of overlapping pixels is equal to or greater than the overlapping pixel number threshold, and any one of CMY of interest is ON”, When this condition is satisfied, it is determined that the pixel of interest is a pixel to be subjected to color blur correction processing.

  The threshold for the number of white pixels and the threshold for the number of overlapping pixels are determined in advance according to the characteristics of the binarized halftone process and the conditions of the color blur correction process. The characteristics of binarization halftone processing are, for example, the type of screen used in binarization and the periodic structure of the screen. The condition for color blur correction processing includes, for example, the size of the processing region 50 and the distribution state of each pixel of CMYK. That is, the white pixel count threshold and the overlap pixel count threshold depend on the type of screen used for binarization, the periodic structure of the screen used for binarization, the size of the processing region 50, or the distribution state of each pixel of CMYK. Changed. In this embodiment, the white pixel number threshold = 8 and the overlapping pixel number threshold = 3. FIG. 7 shows the determination results of all the pixels in FIG. 2B when these two threshold values are used. As illustrated in FIG. 7, the color blur correction determination unit 13 detects a target pixel for color blur correction at the boundary between the character and the background of the binary image, and transmits the detection result to the target pixel value determination unit 14.

  Next, a method for determining a target pixel value will be described.

  The target pixel value determination unit 14 determines the target pixel value to be output based on the pixel value corresponding to the target pixel in the input binary image and the output value from the color blur correction determination unit 13. Specifically, the target pixel value determination unit 14 determines and outputs a target pixel value according to the following conditions (1) and (2).

(1) When the color blur correction determination unit 13 determines that the target pixel is not a target pixel for color blur correction processing, the target pixel value determination unit 14 corresponds to the target pixel in the input binary image. The pixel value is output as the target pixel value as it is.
(2) When the color blur correction determination unit 13 determines that the target pixel is a target pixel for color blur correction processing, the target pixel value determination unit 14 corresponds to the target pixel in the input binary image. The CMY component of the pixel value is set to OFF, and only the K component of the pixel value is output as the target pixel value.

  Note that when the K component of a pixel that is determined as a target pixel for color blur correction processing and the CMY component is set to OFF is OFF, the target pixel value determination unit 14 may turn ON the K component. In this case, since the same K component as the character color is turned on, color blur does not occur. Further, when the CMY component is turned off at a time, the character density is reduced (decreased), but the K component is turned on to suppress the reduction in the character density.

  FIGS. 8A and 8B show the state of the binary image after the color blur correction process. FIG. 8A shows a state after the color blur correction process of the binary image in FIG. 2B (that is, a binary image in which the C plane is not shifted from other planes). FIG. 8B shows a state after the color blur correction process of the binary image in FIG. 3B (that is, a binary image in which the C plane is shifted by two pixels below the other plane). .

  As shown in FIG. 8A, in the binary image in which the C plane is not shifted from the other planes, no color blur occurs before or after the color blur correction process. On the other hand, in the binary image in which the C plane is shifted to the right by two pixels with respect to the other planes, as shown in FIG. 8B, color blur does not occur after the color blur correction process.

  FIG. 9A is a flowchart illustrating processing executed by the color blur correction processing unit 9. FIG. 9B is a flowchart showing a modification of part of the process of FIG.

  9A, first, the processing area determination unit 11 acquires a binary image (step S1), and sets a processing area 50 (step S2). The region feature amount calculation unit 12 calculates the number of white pixels, the number of overlapping pixels, and the on / off state of the target CMY in the processing region 50 (step S3). The color blur correction determination unit 13 determines whether or not the number of white pixels is equal to or greater than the white pixel number threshold, the number of overlapping pixels is equal to or greater than the overlapping pixel number threshold, and any of the target CMY is on (step S4). ). Here, the color blur correction determination unit 13 determines whether or not the target pixel is a target pixel for the color blur correction process.

  If YES in step S4, the target pixel value determination unit 14 sets the CMY component of the pixel value corresponding to the target pixel in the input binary image to off, and only the K component of the pixel value is the target pixel. It outputs as a value (step S5), and this process is complete | finished. On the other hand, in the case of NO in step S4, the target pixel value determination unit 14 outputs the pixel value corresponding to the target pixel in the input binary image as the target pixel value as it is (step S6), and ends this processing. To do.

  As shown in FIG. 9B, after the process of step S5, the target pixel value determination unit 14 determines whether or not the K component of the pixel in which the CMY component is set to off is off. Good (step S7). If YES in step S7, the target pixel value determination unit 14 sets the K component to ON, outputs only the K component as the target pixel value (step S8), and ends this process. If NO in step S7, the process ends.

  As described above, according to the present embodiment, the color blur correction determination unit 13 turns off the pixel values of yellow, magenta, cyan, and black included in the processing area 50 set in advance with the pixel of interest at the center. The number of white pixels, the number of pixels that have at least one pixel value of yellow, magenta, and cyan included in the processing region 50 overlapped with the black pixels included in the processing region 50, and halftone processing has been performed. Determine whether the pixel of interest is a pixel to be subjected to color blur correction processing based on the on / off state of the pixel values of yellow, magenta, and cyan corresponding to the pixel of interest in the binary image To do. Then, when the color blur correction determination unit 13 determines that the target pixel is a pixel to be subjected to color blur correction processing, the target pixel value determination unit 14 determines yellow, magenta, and cyan of the pixel corresponding to the target pixel. Turn off pixel values. Accordingly, it is possible to apply color blur correction processing to a halftone processed binary image.

  In this embodiment, a binary image subjected to halftone processing is used as an input image. However, an N-value image (N = 2 or more) subjected to halftone processing may be used as an input image. For example, when the input image is a quaternary image, all components of CMYK are represented by “00”, “01”, “10”, and “11”. “00” indicates a state where the density is 0, and the density increases in the order of “01”, “10”, and “11”. In the above description, for example, C being off corresponds to the C component of the quaternary image being “00”. “C” is ON corresponds to the C component of the quaternary image being “01”, “10”, or “11”. The same applies to the components of MYK. In this case, a color blur correction process can be applied to an N-value image that has been subjected to halftone processing.

  In the conventional color blur correction process, it is assumed that an 8-bit input image is used. For this reason, as a memory saving measure, the input image is binarized, an image processing apparatus that stores the binary image, or an application performs N-value harp tone processing on the input image, and the N-value image is output to the output unit. A conventional color blur correction process cannot be applied to an image processing apparatus to be sent. Therefore, the above-described embodiment is particularly effective for these image processing apparatuses.

  In the present embodiment, the color blur correction process is realized using the determination of the combination condition of the pixel values of the color plane (that is, the number of white pixels and the number of overlapping pixels). Therefore, it is not necessary to detect a region where color bleeding occurs with high accuracy using a large region. Therefore, since a large memory or circuit is not required for the color blur correction process, it can be realized at a low cost.

  The above-described implementation can also be realized by supplying a recording medium in which a software program for realizing the functions of the image processing apparatus 1 is recorded to the image processing apparatus 1 and the CPU 31 reads and executes the program stored in the storage medium. The same effect as that of the embodiment is produced. Examples of the storage medium for supplying the program include a CD-ROM, a DVD, or an SD card. In addition, the CPU 31 executes the software program for realizing the functions of the image processing apparatus 1, and the same effects as those of the above-described embodiment can be obtained.

  The present invention is not limited to the above-described embodiment, and can be implemented with various modifications within a range not departing from the gist thereof.

DESCRIPTION OF SYMBOLS 1 Image processing apparatus 2 Input part 3 Print control part 4 Output part 5 PDL interpretation part 6 Color conversion part 7 N-value conversion part 8 Drawing part 9 Color blur correction process part 11 Processing area determination part 12 Area | region feature-value calculation part 13 Color Smudge correction determination unit 14 Attention pixel value determination unit

Claims (5)

A first pixel number which is overlaid on a halftone-processed N-value image and which is included in a predetermined area centered on the pixel of interest and whose pixel values of yellow, magenta, cyan and black are off; A second pixel number in which a pixel having at least one pixel value of yellow, magenta, and cyan included in the region overlaps a black pixel included in the region; and the target pixel in the halftone processed N-value image Determination means for determining whether or not the pixel of interest is a pixel to be subjected to color blur correction processing based on an ON or OFF state of pixel values of yellow, magenta, and cyan of pixels corresponding to
When the determination unit determines that the target pixel is a pixel to be subjected to color blur correction processing, the target pixel determination change for turning off the yellow, magenta, and cyan pixel values of the pixel corresponding to the target pixel And an image processing apparatus.   The determination unit includes the target pixel in the N-valued image in which the first pixel number is equal to or greater than a first threshold, the second pixel number is equal to or greater than a second threshold, and the halftone process is performed. The pixel according to claim 1, wherein when the pixel value of any one of yellow, magenta, and cyan is on, it is determined that the pixel of interest is a pixel to be subjected to color blur correction processing. The image processing apparatus described. The pixel-of- interest determination change unit turns on a black pixel value when a black pixel value of a pixel in which the yellow, magenta, and cyan pixel values are off is off. The image processing apparatus according to claim 1.   The image processing apparatus according to claim 1, wherein the N-value image is a binary image. Computer
A first pixel number which is overlaid on a halftone-processed N-value image and which is included in a predetermined area centered on the pixel of interest and whose pixel values of yellow, magenta, cyan and black are off; A second pixel number in which a pixel having at least one pixel value of yellow, magenta, and cyan included in the region overlaps a black pixel included in the region; and the target pixel in the halftone processed N-value image Determination means for determining whether or not the pixel of interest is a pixel to be subjected to color blur correction processing based on an ON or OFF state of pixel values of yellow, magenta, and cyan corresponding to the pixel, and When the determination unit determines that the target pixel is a pixel for which color blur correction processing is to be performed, the yellow, magenta, and shear of the pixel corresponding to the target pixel are determined. A program that functions as a pixel value determining means for turning off a pixel value of a screen.

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