JP6565463B2 - Image processing apparatus, image forming apparatus, and image processing program - Google Patents

Description

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

  For example, in a copying machine, a printer, or the like, which is an image forming apparatus using an electrophotographic system, an inkjet system, or the like, an image is output by an output device after various image processing is performed on input image data. As the image processing, for example, there is area gradation processing (screen processing) in which intermediate gradation is reproduced in a pseudo manner with binary image data. In this area gradation processing, the gradation of an image is converted into a halftone dot area by a regular screen pattern such as a halftone dot pattern or a line pattern.

  Some image data input to the image forming apparatus has an image area (pattern area) that has undergone ROP (Raster Operation) processing. In this ROP process, the original image is used as a background, and the foreground is superimposed on the background in the form of a repetitive pattern. When area gradation processing (screen processing) is performed on an image region that has undergone such ROP processing, the repeated pattern of ROP processing and the screen pattern of screen processing may interfere with each other to cause moire or the like. is there.

  Thus, for example, Patent Document 1 proposes a technique for switching a screen pattern by detecting a pattern area by comparing pixel values of pixels.

JP 2013-48371 A

  However, in the technique of Patent Document 1, when an image having a fine image structure such as a photographic image is used as a background, there are many pattern region detection errors, and a technique with higher detection power is required.

  An object of the present invention is to provide an image processing apparatus, an image forming apparatus, and an image processing program capable of detecting a pattern area even when a photographic image or the like is in the background.

An image processing apparatus according to claim 1 is provided.
Accepting means for accepting an image that is a pixel set expressing gradation by density gradation method;
A detection unit that detects a pattern area including a repetitive pattern according to a predetermined rule and a background that fills a gap between the repetitive patterns, from the image received by the reception unit, and performs detection processing from the image When the target processing range is selected and the first pixel at a predetermined position in the processing range is positioned on the repetitive pattern according to the above rule, the first pixel and the other pixels in the processing range are selected. From the comparison result of the pixel value with each pixel, it is determined whether or not the first pixel is a pixel constituting the pattern area, and when the first pixel is located on the background according to the rule From the comparison result of the pixel values of the second pixel located on the repetitive pattern according to the rule and each of the other pixels in the processing range, whether or not the first pixel is a pixel constituting the pattern area A detection unit for determining whether
An area gradation process using the first repetitive structure is performed on an image region other than the pattern region detected by the detection unit, and a second different from the first repetitive structure is performed on the pattern region. A gradation processing unit that performs area gradation processing by a repetitive structure;
It is provided with.

An image processing apparatus according to claim 2 is provided.
The detection unit compares the first pixel and the second pixel with each pixel located on the repetitive pattern according to the rule, and a pixel value difference larger than a threshold is less than a reference number, above in comparison with the pixel positioned on the background first pixel and the second stroke element and the above rules, if fewer than the number of criteria that the difference between the pixel values is less than the threshold value, the first pixel It is determined that the pixel constitutes the pattern area.

An image processing apparatus according to claim 3 is provided.
The detection unit uses, as the second pixel, a pixel closest to the first pixel among the pixels located on the repetitive pattern.

An image forming apparatus according to claim 4
Accepting means for accepting an image that is a pixel set expressing gradation by density gradation method;
A detection unit that detects a pattern area including a repetitive pattern according to a predetermined rule and a background that fills a gap between the repetitive patterns, from the image received by the reception unit, and performs detection processing from the image When the target processing range is selected and the first pixel at a predetermined position in the processing range is positioned on the repetitive pattern according to the above rule, the first pixel and the other pixels in the processing range are selected. From the comparison result of the pixel value with each pixel, it is determined whether or not the first pixel is a pixel constituting the pattern area, and when the first pixel is located on the background according to the rule From the comparison result of the pixel values of the second pixel located on the repetitive pattern according to the rule and each of the other pixels in the processing range, whether or not the first pixel is a pixel constituting the pattern area A detection unit for determining whether
An area gradation process using the first repetitive structure is performed on an image region other than the pattern region detected by the detection unit, and a second different from the first repetitive structure is performed on the pattern region. A gradation processing unit that performs area gradation processing by a repetitive structure;
A forming unit that forms an image subjected to area gradation processing on the recording material by the gradation processing unit;
It is provided with.

An image processing program according to claim 5 includes:
Accepting means for accepting an image that is a pixel set expressing gradation by density gradation method;
A detection unit that detects a pattern area including a repetitive pattern according to a predetermined rule and a background that fills a gap between the repetitive patterns, from the image received by the reception unit, and performs detection processing from the image When the target processing range is selected and the first pixel at a predetermined position in the processing range is positioned on the repetitive pattern according to the above rule, the first pixel and the other pixels in the processing range are selected. From the comparison result of the pixel value with each pixel, it is determined whether or not the first pixel is a pixel constituting the pattern area, and when the first pixel is located on the background according to the rule From the comparison result of the pixel values of the second pixel located on the repetitive pattern according to the rule and each of the other pixels in the processing range, whether or not the first pixel is a pixel constituting the pattern area A detection unit for determining whether
An area gradation process using the first repetitive structure is performed on an image region other than the pattern region detected by the detection unit, and a second different from the first repetitive structure is performed on the pattern region. A gradation processing unit that performs area gradation processing by a repetitive structure;
An information processing apparatus is operated as an image processing apparatus including

  According to the image processing apparatus according to claim 1, the image forming apparatus according to claim 4, and the image processing program according to claim 5, a pattern region can be detected even if a photographic image or the like is a background.

  According to the image processing apparatus of the second aspect, it is possible to easily detect the pattern region as compared with the case where the determination method of the present configuration is not used.

  According to the image processing apparatus of the third aspect, the determination can be made more accurately than in the case where the second pixel that is not closest is used.

1 is a schematic configuration diagram of a printer corresponding to a specific embodiment of an image forming apparatus. It is the block diagram which showed roughly the hardware structure of the control part. FIG. 3 is a block diagram illustrating a software structure of a signal processing system in a printer control unit. It is a figure which shows the ROP pattern made into a detection target in this embodiment. It is a figure which shows an example of a screen pattern. It is a figure which shows typically interference with a ROP pattern and a screen pattern. It is a figure which shows the image disturbance resulting from the phase of a ROP pattern and a screen pattern. It is the figure explaining the functional structure of the detection part in more detail. It is the flowchart explaining the procedure in which a detection part detects a pattern area | region. It is a flowchart which shows the detection procedure in a 2dotx2dot staggered pattern. It is a figure which shows each phase of a 2dotx2dot staggered pattern. It is a figure which shows a 1st Example. It is a figure which shows a 2nd Example.

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

<Overall configuration of image forming apparatus>
FIG. 1 is a schematic configuration diagram of a printer corresponding to a specific embodiment of an image forming apparatus.

  The printer 1 includes, for example, a plurality (four in this embodiment) of image forming units 10 (specifically, 10Y (yellow), 10M (magenta), 10C) in which each color component toner image is formed by electrophotography. (Cyan), 10K (black)). In addition, the printer 1 includes an intermediate transfer belt 20 that sequentially transfers (primary transfer) and holds each color component toner image formed by each image forming unit 10. The printer 1 further includes a secondary transfer device 30 that collectively transfers (secondary transfer) the toner image transferred to the intermediate transfer belt 20 onto the paper P. Furthermore, the printer 1 includes a fixing device 50 that fixes the second-transferred toner image on the paper P, and a control unit 70 that controls each mechanism unit of the printer 1.

  Each image forming unit 10 (10Y, 10M, 10C, 10K) has the same configuration except for the color of the toner used. Therefore, the yellow image forming unit 10Y will be described as an example. The yellow image forming unit 10Y includes a photosensitive drum 11 that rotates in the direction of arrow A. Around the photosensitive drum 11, a charging roll 12, an exposure device 13, a developing device 14, a primary transfer roll 15, and a drum are provided. A cleaner 16 is provided.

  The charging roll 12 charges the photosensitive drum 11 to a predetermined potential, and the exposure unit 13 writes the electrostatic latent image on the surface of the photosensitive drum 11 by exposing the charged photosensitive drum 11. The developing device 14 stores toner of a color corresponding to the image forming unit (yellow toner in the yellow image forming unit 10Y), and develops the electrostatic latent image on the photosensitive drum 11 with this toner. The primary transfer roll 15 primarily transfers the toner image formed on the photosensitive drum 11 to the intermediate transfer belt 20. The drum cleaner 16 removes residues (toner and the like) on the photosensitive drum 11 after the primary transfer.

  The intermediate transfer belt 20 is an endless belt member stretched and supported by the drive roll 21, the stretch rolls 22 and 25, the correction roll 23, and the backup roll 24, and circulates and moves in the direction of arrow B. Further, a belt cleaner 26 that removes residues (toner and the like) on the intermediate transfer belt 20 after the secondary transfer is disposed at a position facing the stretching roll 25 with the intermediate transfer belt 20 interposed therebetween.

  A secondary transfer roll 50 is provided at a location facing the backup roll 24 with the intermediate transfer belt 20 in between, and the backup roll 24 and the secondary transfer roll 50 function as a secondary transfer device.

  Further, the printer 1 is provided with a paper transport system 80 for transporting paper as a recording material. The paper transport system 80 includes a paper tray T, a pickup roll 81, a transport roll 82, a registration roll 84, And a discharge roll 86 is provided.

  In this embodiment, the paper P is stacked and accommodated in the paper tray T as the recording material. However, in addition to the paper, an OHP sheet, a plastic paper, an envelope, or the like may be accommodated as the recording material. Even when such a recording material is accommodated, the basic operation of the printer 1 is the same.

  The pick-up roll 81 is for taking out the paper P from the paper tray T, and the transport roll 82 is for transporting the picked-up paper P along the transport path R in the direction of arrow C. The registration roll 84 stops the conveyed paper P at one end and sends it to the secondary transfer device at a timing suitable for secondary transfer.

  On the transport path R, a fixing device 60 having a heating roll 61 and a pressure roll 62 is provided, and an image on the passing paper P is fixed to the paper P.

  The discharge roll 86 sends out the fixed paper P to a stacking tray (not shown) outside the apparatus.

<Image forming process of image forming apparatus>
Next, a basic image forming process of the printer 1 will be described.

  For example, when a digital image signal is sent to the printer 1 from an external device such as a PC (personal computer) or the like, the digital image signal is received by the control unit 70 and four colors (Y color, M color, C color, K) are received. The control unit 70 performs image processing, which will be described in detail later, on the (color) digital image signal. Then, a digital image signal of a corresponding color is input from the control unit 70 to the exposure device 13 of each image forming unit 10 (specifically, 10Y, 10M, 10C, 10K), and an electrostatic latent image is formed on the photoconductor 11. Is formed. Then, a toner image of each color is formed on the photoreceptor 11 by development, and a color toner image is formed by primary transfer sequentially onto the surface of the intermediate transfer belt 20 by the primary transfer roll 15.

  The color toner image on the intermediate transfer belt 20 is transported to the secondary transfer position as the intermediate transfer belt 20 rotates, and is superimposed on the paper P sent from the registration roll 84. The toner image superimposed on the paper P in this way is transferred to the paper P by the action of transfer electrolysis in the secondary transfer device.

  The paper P onto which the toner image has been transferred is conveyed to the fixing device 60, where the toner image on the paper P is heated and pressurized and fixed by the fixing device 50, and then sent out of the apparatus.

  The control unit 70 corresponds to an embodiment of the image processing apparatus of the present invention, and a portion from each image forming unit 10 that obtains a digital image signal from the control unit 70 to the fixing device 50 and the discharge roll 86 is on the recording material. This corresponds to an example of a forming portion according to the present invention that forms an image.

<Control part structure>
Here, the hardware structure of the control unit 70 will be described.

  FIG. 2 is a block diagram schematically showing the hardware structure of the control unit.

  The control unit 70 is a type of information processing apparatus, and is used for processing in the main CPU 701 that executes digital arithmetic processing according to a predetermined program, a RAM 702 that is used as a working memory for the main CPU 701, and the main CPU 701. ROM 703 for storing various setting values, non-volatile memory (NVM) 704 such as a flash memory backed up by a battery that can be rewritten and can retain data even when power supply is interrupted, and control unit 70 An interface (I / F) unit 705 that inputs and outputs signals to and from each component (for example, the image forming unit 10) to be connected is provided.

  Then, the main CPU 701 reads an embodiment of the image processing program of the present invention from an external storage device (not shown) into the main storage device (RAM 702) and executes it, so that the control unit 70 is the image processing apparatus of the present invention. It functions as one embodiment.

  In addition, as another provision form regarding this control program, there is a form that is provided in the state stored in the ROM 703 in advance and loaded into the RAM 702. Further, when a rewritable ROM 703 such as an EEPROM is provided, after the main CPU 701 is set, only a program is installed in the ROM 703 and loaded into the RAM 702. Further, there is a form in which a program is transmitted to the control unit 70 via a network such as the Internet, installed in the ROM 703 of the control unit 70, and loaded into the RAM 702. Furthermore, there is a form in which the RAM 702 is loaded from an external recording medium such as a DVD-ROM or a flash memory.

<Signal processing system>
Next, the signal processing system in the control unit 70 will be described.

  FIG. 3 is a block diagram illustrating a software structure of a signal processing system in the control unit 70 of the printer 1.

  3 illustrates not only the signal processing system in the control unit 70 but also the PC 90 that is an external device of the printer 1 and the printer driver 100 that is a function incorporated in the PC 90 as software.

  Hereinafter, the flow of processing of an image signal will be described with reference to FIG.

  The printer driver 100 receives print data and converts it into a page description language (PDL), a rasterization unit 102 that creates a raster image from the PDL generated by the PDL generation unit, and RGB data Are converted into YMCK data, and a raster image adjustment unit 104 that adjusts the raster image converted by the color conversion processing unit 103 is provided.

  In this embodiment, first, the PDL generation unit 101 receives print data from the PC 90 (internal word processor software, drawing software, etc.). This image data is image data that the user who uses the PC 90 wants to print using the printer 1. Upon receiving the image data, the PDL generation unit 101 converts this into code data described in PDL and outputs the code data.

  The rasterizing unit 102 converts the code data described in PDL output from the PDL generating unit 101 into raster data for each pixel, and forms a raster image. The rasterizing unit 102 outputs the converted raster data as RGB (red, green, blue) video data (RGB video data). At this time, the rasterizing unit 102 outputs RGB data for each page.

The color conversion processing unit 103 converts the RGB data input from the rasterizing unit 102 into device-independent color values (color values) such as [XYZ], [L ^* a ^* b ^* ], and [L ^* u ^* v ^* ]. Is converted into YMCK data which is the reproduction color (yellow, magenta, cyan, black) of the printer 1 and output. This YMCK data is a set of Y color data, M color data, C color data, and K color data separated for each color.

  The raster image adjustment unit 104 performs adjustments such as γ conversion, definition processing, and halftone processing on the YMCK data input from the color conversion processing unit 103 so that a better image quality can be obtained by the printer 1.

  The control unit 70 receives the raster data from the printer driver 100, and detects the image area (pattern area) that has undergone ROP (Raster Operation) processing from the image represented by the raster data received by the receiving unit 71. And a screen processing unit 73 that performs screen processing and outputs an image signal to the image forming unit 10.

  The receiving unit 71 corresponds to an example of a reception unit according to the present invention, the detection unit 72 corresponds to an example of a reception unit according to the present invention, and the screen processing unit 73 is an example of a gradation processing unit according to the present invention. It corresponds to.

  The screen processing unit 73 changes the screen pattern between the pattern region and the other image regions according to the detection result by the detection unit 72, and suppresses image disturbance such as moire described later. Therefore, the detection accuracy of the pattern area in the detection unit 72 greatly contributes to the suppression of the final moire and the like. Hereinafter, detection of the pattern area in the detection unit 72 will be described in detail.

<Detection target of detection unit>
The pattern area detected by the detection unit 72 is an image area that has undergone ROP processing in the present embodiment, and what corresponds to the repetitive pattern referred to in the present invention is a so-called ROP pattern. In this ROP process, as described above, the original image is used as the background, and the foreground is superimposed on the background in the shape of the repeated pattern, so that an image structure in which the background is filled between the foreground of the repeated pattern is generated. Further, since this repeated pattern itself is fine and cannot be recognized by the observer, it is recognized as a translucent image in which the background can be seen through the foreground.

  There are various types of ROP patterns. In this embodiment, some of these typical patterns are to be detected.

  FIG. 4 is a diagram showing ROP patterns to be detected in the present embodiment.

  In the present embodiment, a houndstooth pattern and a line ladder pattern are to be detected.

  4A and 4B show a staggered pattern, and FIG. 4A is a pattern in which a square pattern having a size of 2 dots × 2 dots is repeated in a staggered pattern. FIG. 4B is a pattern in which a square pattern having a size of 4 dots × 4 dots is repeated in a zigzag pattern.

  4 (c) and 4 (d) show a line ladder pattern. FIG. 4 (c) is a pattern in which vertical lines having a width of 2 dots are repeated in the horizontal direction, and FIG. Is a pattern in which horizontal lines having a width of 2 dots are repeated in the vertical direction.

  When ROP processing is performed with these ROP patterns, the foreground remains in the hatched (ON) portion of the pixel 210 shown in FIG. 4, and the white background (OFF) portion of the pixel 220 is filled with the background.

  Any of the ROP patterns illustrated in FIG. 4 is a detection target of the detection unit 72 because there is a possibility of causing interference as described below with the screen pattern.

  FIG. 5 is a diagram illustrating an example of a screen pattern.

  In the example shown here, a uniform image having a density of 50% is shown as the input image 230. A halftone dot pattern 240 is shown as an example of the screen pattern. The halftone dot pattern 240 is a halftone dot pattern with a screen angle of 30 degrees, and the halftone dots are two-dimensionally arranged in directions of 30 degrees and 120 degrees. By combining the input image 230 and the halftone dot pattern 240, the output result 250 has a two-dimensional array of dots in the directions of 30 degrees and 120 degrees as in the halftone dot pattern 240. The image structure is such that (ON) is 1: 1. Since the arrangement of the points included in the image structure of the output result 250 is fine, it cannot be recognized by the observer, and the output result 250 is recognized by the observer as a uniform image having a density of 50%.

  FIG. 6 is a diagram schematically showing interference between the ROP pattern and the screen pattern.

  In the example shown here, an image having a staggered ROP pattern is shown as the input image 260, and a halftone dot pattern 240 similar to that in FIG. 5 is shown as the screen pattern. When the input image 260 of the staggered lattice and the halftone dot pattern 240 are combined, a complicated pattern in which the houndstooth lattice and the halftone dot pattern interfere with each other is generated in the output result 270. This complex interference pattern causes a shading pattern image disturbance called moire when the period of the staggered lattice and the halftone dot pattern is shifted. This image disturbance has a magnitude that can be recognized by an observer, resulting in image degradation of the output image.

  As described above, when the ROP pattern interferes with the screen pattern, it may cause image disturbance. Furthermore, image disturbance may occur due to the positional relationship between the ROP pattern and the screen pattern (hereinafter, this positional relationship may be referred to as “phase”).

  FIG. 7 is a diagram illustrating image disturbance due to the phase between the ROP pattern and the screen pattern.

  In FIG. 7, 2 dot × 2 dot houndstooth patterns 310, 320, and 330 are shown as ROP patterns, and a halftone dot pattern 340 with a screen angle of 45 degrees is shown as a screen pattern. The halftone dot pattern 340 with a screen angle of 45 degrees has the same image structure as the houndstooth pattern when the density is 50%. In particular, in the example shown here, the square pattern forming the houndstooth lattice has a size of 2 dots × 2 dots. The number of screen lines is used.

  The houndstooth pattern 310 shown in FIG. 7A has the same shape and position as the halftone dot pattern 340 (the phases are aligned). For this reason, the output result 350 is in a state where the houndstooth pattern 310 is output as it is.

  On the other hand, the houndstooth pattern 320 shown in FIG. 7B has the same pattern shape as that of the halftone dot pattern 340, but the phase is shifted by 1 dot in the left direction of the figure. For this reason, in the output result 360, the square pattern forming the houndstooth check pattern 320 is halved.

  Further, the houndstooth pattern 330 shown in FIG. 7C has the same pattern shape as that of the halftone dot pattern 340, and the phase is shifted by 2 dots (that is, a half cycle) in the left direction in the figure. For this reason, the output results 370 are all white and the ROP pattern disappears.

  As described above, image disturbance may occur due to a difference in phase. Therefore, the detection unit 72 sets each phase of the ROP pattern to be detected as a detection target.

<Detection method of ROP pattern>
Next, a method for detecting a pattern area by the detection unit 72 will be described.

  FIG. 8 is a diagram illustrating the functional structure of the detection unit 72 in more detail.

  The detection unit 72 illustrated in FIG. 8 sets a target pixel selection unit 721 that selects a target pixel from the image received by the reception unit 71, and pixels in a predetermined range with respect to the target pixel as a detection window. A detection window setting unit 722; a pattern storage unit 723 that stores an ROP pattern; a determination unit 724 that applies the ROP pattern to the detection window to determine whether the pixel of interest forms a pattern region; and And a tag setting unit 725 for setting a tag indicating that the pixel is a pattern area when the pixel is an area.

  The target pixel selection unit 721 selects one pixel as the target pixel from the rasterized image received by the receiving unit 71.

  The detection window setting unit 722 selects a pixel in a predetermined range centering on the target pixel, and sets this range as a detection window for determining whether the target pixel is a pixel constituting the pattern region. .

  A pattern region detection procedure by the detection unit 72 having such a functional configuration will be described below with reference to flowcharts.

  FIG. 9 is a flowchart illustrating a procedure in which the detection unit 72 detects a pattern area.

  The procedure shown in the flowchart of FIG. 9 is started when the receiving unit 71 shown in FIG. 3 receives an image. The initial setting at the start (not shown) is performed by the target pixel selecting unit 721 and the detection window setting unit 722. And a detection window (in this embodiment, a 7 × 7 square centered on the pixel of interest) are set.

  Thereafter, for each of the four types of ROP patterns shown in FIG. 4, the determination unit 724 determines whether or not the target pixel is a pixel that forms a pattern region that has undergone the ROP process.

  First, in step S101, the 2 dot × 2 dot houndstooth pattern shown in FIG. 4A is read from the pattern storage unit 723 and applied to the detection window to perform pattern detection. Details of pattern detection will be described later.

  In step S102, the 4 dot × 4 dot houndstooth pattern shown in FIG. 4B is read from the pattern storage unit 723 and applied to the detection window to perform pattern detection.

  In step S103, the 2-dot vertical line ladder pattern shown in FIG. 4C is read from the pattern storage unit 723 and applied to the detection window to perform pattern detection.

  In step S104, the 2-dot horizontal line ladder pattern shown in FIG. 4D is read from the pattern storage unit 723 and applied to the detection window to perform pattern detection.

  When the ROP pattern is detected in any of these steps S101 to S104, it is determined that the target pixel at the center of the detection window is a pixel forming the pattern area, and the process proceeds to step S105. The tag setting unit 725 sets a tag that means a pattern area for the target pixel.

  On the other hand, when no ROP pattern is detected in any of steps S101 to S104 (step S104; No), it is determined that the target pixel is not a pixel forming the pattern region.

  Regardless of which of the target pixels is determined, the process advances to step S106 to determine whether or not there is a pixel not selected as the target pixel in the image. If there is a pixel to be selected (step S106; Yes), the process proceeds to step S107, and the target pixel is moved to the next pixel. Then, the process returns to step S101, and further determination is performed for the next target pixel. On the other hand, when there is no pixel to select (step S106; No), the process in the detection part 72 is complete | finished.

  Here, the details of the pattern detection performed in steps S101 to S104 will be described using the pattern detection in step S101 as a representative.

  FIG. 10 is a flowchart showing a detection procedure in a 2 dot × 2 dot staggered pattern, and FIG. 11 is a diagram showing each phase of a 2 dot × 2 dot staggered pattern.

  The procedure of the flowchart shown in FIG. 10 is the procedure executed in step S101 of FIG. 9. First, in step S201, pattern detection is performed for the first phase. The first phase is the phase shown in FIG. 11A, and a 2 dot × 2 dot foreground pixel 410 comes to the lower right of the 7 × 7 detection window. Then, the target pixel 430 positioned at the center of the detection window is positioned on the foreground pixel 410.

  In this way, when the target pixel 430 is located on the foreground pixel 410, the pixel value of the target pixel 430 is compared with the pixel values of the foreground pixels 410 and the background pixels 420, and the determination is performed according to the first determination rule. Is called. That is, the number of foreground pixels 410 whose pixel value difference from the target pixel 430 exceeds a predetermined threshold is less than a predetermined reference number, and the pixel value difference from the target pixel 430 Is less than a predetermined reference number, it is determined that the pixel of interest 430 is a pixel in the pattern area (that is, a pattern has been detected).

  In step S202, pattern detection is performed for the second phase. The second phase is the phase shown in FIG. 11B, and a 2 dot × 2 dot foreground pixel 410 comes to the lower left of the 7 × 7 detection window. Even in the second phase, the target pixel 430 located at the center of the detection window is located on the foreground pixel 410, and therefore, the determination is performed according to the first determination rule.

  In step S203, pattern detection is performed for the third phase. The third phase is the phase shown in FIG. 11C, and a 2 dot × 2 dot foreground pixel 410 comes to the upper right of the 7 × 7 detection window. Even in the third phase, the target pixel 430 located at the center of the detection window is located on the foreground pixel 410, and therefore, the determination is performed according to the first determination rule.

  In step S204, pattern detection is performed for the fourth phase. The fourth phase is the phase shown in FIG. 11 (d), and a 2dot × 2dot foreground pixel 410 comes to the upper left of the 7 × 7 detection window. Even in the fourth phase, the target pixel 430 located at the center of the detection window is located on the foreground pixel 410, and therefore, the determination is performed according to the first determination rule.

  Next, in step S205, pattern detection is performed for the fifth phase. The fifth phase is the phase shown in FIG. 11 (e), and has a relationship in which the positions of the foreground pixels 410 and the background pixels 420 are interchanged with respect to the first phase shown in FIG. 11 (a). ing. Therefore, the target pixel 430 located at the center of the detection window is located on the background pixel 420.

  As described above, when the target pixel 430 is positioned on the background pixel 420, the substitute pixel 440 that replaces the target pixel 430 is selected from the foreground pixels 410. In the present embodiment, the foreground pixel 410 closest to the target pixel 430 is selected as the substitute pixel 440. In the case of the fifth phase shown in FIG. The pixel is a substitute pixel 440. Then, the pixel value of the substitute pixel 440 is compared with the pixel values of the foreground pixels 410 and the background pixels 420, and the determination is performed according to the second determination rule. That is, the number of foreground pixels 410 whose pixel value difference with the substitute pixel 440 exceeds a predetermined threshold is less than a predetermined reference number, and the difference in pixel value with the substitute pixel 440. Is less than a predetermined reference number, it is determined that the pixel of interest 430 is a pixel in the pattern area (that is, a pattern has been detected).

  The target pixel 430 is a target for determining whether or not it is a pixel in the pattern area, but the substitute pixel 440 is used for comparing pixel values. When the target pixel 430 is positioned on the background pixel 420, the pixel value is compared between the background pixels 420 when the pixel value is compared with each pixel in the target pixel 430. For example, a photographic image is used as the background. If it is, it is difficult to determine the presence or absence of the ROP pattern from the comparison result. Therefore, the pixel of interest 430 located on the background pixel 420 is not used for pixel value comparison, but the substitute pixel 440 that is the foreground pixel 410 is used for pixel value comparison. As a result, accurate determination is realized even if the background is a photographic image or the like. Even when the alternative pixel 440 is compared in this way, the range of the other pixels being compared is a 7 × 7 range centered on the target pixel 430, and therefore the determination target pixel is the target pixel. A pixel 430 is formed.

  In step S206, pattern detection is performed for the sixth phase. The sixth phase is the phase shown in FIG. 11 (f), and has a relationship in which the positions of the foreground pixels 410 and the background pixels 420 are interchanged with respect to the second phase shown in FIG. 11 (b). ing. Accordingly, the target pixel 430 located at the center of the detection window is located on the background pixel 420, and the alternative pixel 440 is selected. In the case of the sixth phase, the pixel on the right side of the target pixel 430 is the substitute pixel 440. Then, the determination is performed according to the second determination rule.

  In step S207, pattern detection is performed for the seventh phase. The seventh phase is the phase shown in FIG. 11G, and the positions of the foreground pixels 410 and the background pixels 420 are interchanged with respect to the third phase shown in FIG. 11C. ing. Accordingly, the target pixel 430 located at the center of the detection window is located on the background pixel 420, and the alternative pixel 440 is selected. In the case of the seventh phase, the pixel on the left side of the target pixel 430 is the substitute pixel 440. Then, the determination is performed according to the second determination rule.

  In step S208, pattern detection is performed for the eighth phase. The eighth phase is the phase shown in FIG. 11 (h), and has a relationship in which the positions of the foreground pixels 410 and the background pixels 420 are interchanged with respect to the fourth phase shown in FIG. 11 (d). ing. Accordingly, the target pixel 430 located at the center of the detection window is located on the background pixel 420, and the alternative pixel 440 is selected. In the case of the eighth phase, the pixel on the right side of the target pixel 430 is the substitute pixel 440. Then, the determination is performed according to the second determination rule.

  In this way, the determination is made for each phase, and when the pattern is detected in any of steps S201 to S208, the flow returns to the flowchart shown in FIG. 9 as detection Yes. On the other hand, if no pattern is detected in any of steps S201 to S208, the flow returns to the flowchart shown in FIG.

  After the pattern area is detected and the tag is set in this way, the screen processing unit 73 shown in FIG. 3 has a pixel for which a tag is set (that is, a pixel in the pattern area) and a pixel for which no tag is set. Moire and the like are suppressed by performing screen processing by switching the screen with (that is, pixels in the image area other than the pattern area). Specifically, screen processing by a normal screen is performed in an image region other than the pattern region, and screen processing by a screen having a higher number of lines or an FM (Frequency Modulation) screen than the normal screen is performed in the pattern region, for example. As a result, interference between the ROP pattern and the screen pattern is suppressed, and a phenomenon in which image information is lost or moire occurs is suppressed.

<Example>
Here, the Example which confirmed the effect of this invention is described.

  FIG. 12 is a diagram illustrating the first embodiment.

  In the example shown in FIG. 12, the photographic image shown in FIG. 12A was used as the background, and the 100% density houndstooth pattern shown in FIG. 12B was used as the foreground. A translucent image combining these foregrounds and backgrounds is shown in FIG.

  FIG. 12D shows a comparative example in which pattern detection is performed on the semi-transparent image by the technique of Patent Document 1 described above, and a black spot is a place where a pattern is detected. In the technique of Patent Document 1, pattern detection fails except for a part of the upper part.

  In contrast, FIG. 12E shows an example in which pattern detection is performed on the translucent image in FIG. 12C in the above-described embodiment. Also in this embodiment, it can be seen that the black spot is the place where the pattern is detected, and the pattern is detected almost completely over the entire screen. In addition, although illustration is abbreviate | omitted here, when pattern detection was performed in the embodiment mentioned above with respect to the photographic image shown to Fig.12 (a), it also confirmed that pattern non-detection was carried out almost completely over the whole screen. .

  FIG. 13 is a diagram showing a second embodiment.

  In the example shown in FIG. 13, a random pattern image shown in FIG. 13A was used as the background, and a 50% density houndstooth pattern shown in FIG. 13B was used as the foreground. A translucent image in which these foregrounds and backgrounds are combined is shown in FIG. 13C, but it is difficult to distinguish visually from the background-only image shown in FIG.

  FIG. 13D shows a comparative example in which pattern detection is performed on the translucent image by the technique of Patent Document 1 described above, and the black spot is the place where the pattern is detected. In this technique, pattern detection fails for the entire image.

  In contrast, FIG. 13E shows an example in which pattern detection is performed on the translucent image in FIG. 13C in the above-described embodiment. In this embodiment as well, the black spot is the place where the pattern is detected, and the pattern is successfully detected over the entire screen despite the fact that it is difficult to discriminate visually.

  Thus, it was confirmed that the pattern area was detected with high accuracy by the present invention.

  In the above description, an electrophotographic color printer is exemplified as an embodiment of the image forming apparatus. However, the image forming apparatus of the present invention may be applied to a facsimile, a copier, or a multifunction peripheral, and is a monochrome apparatus. The present invention may be applied to an inkjet type apparatus or a thermal transfer type apparatus.

  In the above description, the first determination rule and the second determination rule are exemplified as the detection condition (determination condition) in the detection unit according to the present invention. However, the detection unit according to the present invention includes a pixel of interest. If the pixel is a pixel on the repetitive pattern, the pixel value is compared with each other pixel. If the target pixel is a pixel on the background, the pixel value is compared between the alternative pixel and each other pixel. Of course, it is not limited to the first determination rule and the second determination rule described above. For example, the comparison condition between foreground pixels may be that there are many differences in pixel values, and the comparison condition between foreground pixels and background pixels may be that there are many differences in pixel values. Good.

  In the above description, the target pixel at the center of the detection window is shown as an example of the first pixel according to the present invention. However, the first pixel according to the present invention is located at a position shifted from the center of the processing range. It may be a pixel.

  In the above description, as an example of the second pixel according to the present invention, the substitute pixel closest to the target pixel among the foreground pixels is shown. However, the second pixel according to the present invention is a target of detection processing. Any pixel may be used as long as it is a pixel on the repetitive pattern existing within the processing range. However, a pixel at a position close to the first pixel is preferable to a pixel at a far position.

  In the above description, a square detection window is shown as an example of the processing range according to the present invention, but the processing range according to the present invention may be a range such as a rectangle.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Image forming unit, 70 ... Control part, 71 ... Reception part, 72 ... Detection part, 73 ... Screen processing part, 721 ... Attention pixel selection part, 722 ... Detection window setting part, 723 ... Pattern Storage unit 724 ... determination unit 725 ... tag setting unit 410 ... foreground pixel 420 420 background pixel 430 pixel of interest 440 alternative pixel 100 printer driver P paper

Claims (5)

An accepting unit that accepts an image that is a pixel set that expresses a gradation by a density gradation method;
A detection unit that detects a pattern region including a repetitive pattern according to a predetermined rule and a background that fills a gap between the repetitive patterns, from the image received by the reception unit, the detection unit performing detection processing from the image When a target processing range is selected, and the first pixel at a predetermined position in the processing range is positioned on the repetitive pattern according to the rule, the first pixel,
From the comparison result of the pixel value with each other pixel in the processing range, it is determined whether or not the first pixel is a pixel constituting the pattern area, and the first pixel is on the background according to the rule. The first pixel constitutes the pattern region based on the comparison result of the pixel values of the second pixel located on the repetitive pattern according to the rule and each of the other pixels in the processing range. A detection unit that determines whether or not the pixel is
The image area other than the pattern area detected by the detection unit is subjected to area gradation processing by the first repetitive structure, and the pattern area is subjected to a second different from the first repetitive structure. A gradation processing unit that performs area gradation processing by a repetitive structure;
An image processing apparatus comprising: The detection unit compares the first pixel and the second pixel with each pixel located on the repetitive pattern according to the rule, and a pixel value difference larger than a threshold is less than a reference number, and compares the pixel located on the background the said first pixel and the second stroke element rules, if fewer than smaller ones reference number than the difference threshold pixel value, the second The image processing apparatus according to claim 1, wherein one pixel is determined to be a pixel constituting the pattern area.   The image processing apparatus according to claim 1, wherein the detection unit uses, as the second pixel, a pixel closest to the first pixel among pixels located on the repetitive pattern. . An accepting unit that accepts an image that is a pixel set that expresses a gradation by a density gradation method;
A detection unit that detects a pattern region including a repetitive pattern according to a predetermined rule and a background that fills a gap between the repetitive patterns, from the image received by the reception unit, the detection unit performing detection processing from the image When a target processing range is selected, and the first pixel at a predetermined position in the processing range is positioned on the repetitive pattern according to the rule, the first pixel,
From the comparison result of the pixel value with each other pixel in the processing range, it is determined whether or not the first pixel is a pixel constituting the pattern area, and the first pixel is on the background according to the rule. The first pixel constitutes the pattern region based on the comparison result of the pixel values of the second pixel located on the repetitive pattern according to the rule and each of the other pixels in the processing range. A detection unit that determines whether or not the pixel is
The image area other than the pattern area detected by the detection unit is subjected to area gradation processing by the first repetitive structure, and the pattern area is subjected to a second different from the first repetitive structure. A gradation processing unit that performs area gradation processing by a repetitive structure;
A forming unit that forms an image subjected to area gradation processing on the recording material by the gradation processing unit;
An image forming apparatus comprising: A reception unit for receiving an image expressed by a set of pixels by density gradation method;
A detection unit that detects a pattern region including a repetitive pattern according to a predetermined rule and a background that fills a gap between the repetitive patterns, from the image received by the reception unit, the detection unit performing detection processing from the image When a target processing range is selected, and the first pixel at a predetermined position in the processing range is positioned on the repetitive pattern according to the rule, the first pixel,
From the comparison result of the pixel value with each other pixel in the processing range, it is determined whether or not the first pixel is a pixel constituting the pattern area, and the first pixel is on the background according to the rule. The first pixel constitutes the pattern region based on the comparison result of the pixel values of the second pixel located on the repetitive pattern according to the rule and each of the other pixels in the processing range. A detection unit that determines whether or not the pixel is
The image area other than the pattern area detected by the detection unit is subjected to area gradation processing by the first repetition structure, and the pattern area is subjected to a second repetition different from the first repetition structure. A gradation processing unit that performs area gradation processing according to a structure;
An image processing program for operating an information processing apparatus as an image processing apparatus comprising: