JP2012135998A - Image processor and image processing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processor capable of adequately suppressing banding, and an image processing program.SOLUTION: In a case where a significant pixel is included in a region C, banding can be surely suppressed by using an error diffusion parameter C. In addition, in a case where a significant pixel is not included in the region C, but included in a region B, occurrence of granular feeling can be surely suppressed by using an error diffusion parameter B. Further, a significant pixel is not included in the regions C and B, occurrence of granular feeling can be suppressed by using an error diffusion parameter A.

Description

  The present invention relates to a banding suppression technique.

  The line printer includes a long print head 102 as shown in FIG. 10A and can print an image for each line. The print head 102 is provided with a plurality of partial heads 104, and each partial head 104 is provided with a nozzle that ejects ink toward the paper P. The print head 102 is provided such that its longitudinal direction is orthogonal to the paper transport direction T.

  For convenience of explanation, as shown in FIG. 10B, the longitudinal direction of the print head 102 is defined as the X direction, and the direction orthogonal to the X direction is defined as the Y direction. In order to increase the degree of integration of the nozzles 106, the nozzles 106 may be formed such that the positions of the nozzles 106 adjacent to each other in the X direction of the print head 102 are different from each other in the Y direction.

JP 2007-88927 A JP 2007-38435 A JP 2007-196483 A

  When printing an image with such a line printer, it is caused by an installation error of the print head 102, variation in the ink ejection direction of each nozzle 106, variation in the position of the nozzle 106, variation with time, variation in paper conveyance, and the like. There is a risk that streaks called banding may occur in an image printed on paper.

  FIG. 10B is a diagram illustrating the dot row 108 formed on the paper P by the print head 102 attached at an ideal attachment angle, and FIG. 10C includes an error in the attachment angle. FIG. 4 is a diagram illustrating dot rows 108 formed on paper P by a print head 102.

  Ideally, as shown in FIG. 10B, the X direction of the print head 102 and the transport direction T are orthogonal to each other. However, in practice, as shown in FIG. 10C, when the print head 102 is provided at an inclination from an ideal angle, dot density is generated in the dot row 108 formed on the paper P. As a result, in the image printed on the paper P, a thin stripe along the transport direction T is generated in a portion where the distance between the dots is large. On the other hand, a dark streak along the transport direction T occurs in a portion where the distance between dots is small.

  Here, as the pair of nozzles 106 adjacent to each other in the X direction are separated from each other in the Y direction, the distance between the pair of dots formed by the pair of nozzles 106 is deviated from the ideal state, and banding is easily perceived. For example, as shown in FIG. 10C, since the distance in the Y direction is large between the pair of nozzles 106a adjacent to each other at the boundary between the two partial heads 104, banding is easily perceived.

  The present invention has been made to solve the above-described problems, and an object thereof is to appropriately suppress banding.

  In order to achieve this object, an apparatus according to the present invention is for causing a print execution unit including a print head including a plurality of partial heads arranged along a first direction orthogonal to the conveyance direction of a recording medium to execute printing. A generating unit that performs image processing including error diffusion processing on the image data and generates print data; and a supply unit that supplies the print data to the print execution unit. Is a determination to determine whether or not a significant area is included in the specific area corresponding to the boundary between two adjacent partial heads of the plurality of partial heads in the image data And the generation unit uses the first value as the value of the processing parameter in the first case where it is determined that no significant pixel is included in the specific region in the image data. First on data In the second case where the error diffusion process is performed and it is determined that the specific region in the image data includes a significant pixel, the second value is used as the value of the processing parameter, and the image data A second error diffusion process is performed on the.

  According to the above apparatus, since the processing parameters of the error diffusion processing are properly used depending on whether or not a significant pixel is included in a specific area in the image data, banding can be appropriately suppressed.

  In the above apparatus, in the second case, the determination unit determines whether a significant pixel indicating that the density is higher than a reference density is included in the specific region, and the generation unit In the second case, when it is determined that a significant pixel indicating that the density is higher than the reference density is not included in the specific area, the first value is set as the value of the processing parameter. The first error diffusion process is used, and when it is determined that a significant pixel indicating that the density is higher than the reference density is included in the specific region, the value of the processing parameter is It is preferable to execute the second error diffusion process using a second value. In this way, the processing parameters of the error diffusion processing are properly used based on the reference density, so that banding can be suppressed more appropriately.

  In the above apparatus, the plurality of partial heads include two or more first type partial heads arranged in a line along the first direction, and the specific region includes two adjacent first type parts. It is preferable to include a region corresponding to the boundary of the head. In this way, the error diffusion processing parameters are properly used based on whether or not a significant pixel is included in the region corresponding to the boundary between two adjacent first type partial heads. Banding can be suppressed.

  In the above apparatus, the print execution unit can form a first type dot and a second type dot having a smaller size than the first type dot, and the second value is It is preferable that the value be such that more dots of the first type are generated than the first value. In this way, when significant pixels are included in the specific region, banding can be suppressed by executing the second error diffusion process using the second value. On the other hand, when a significant pixel is not included in the specific region, the occurrence of graininess can be suppressed by executing the first error diffusion process using the first value.

  In the above apparatus, the plurality of partial heads may include two or more first type heads arranged in a line along the first direction at a first position in a second direction parallel to the conveyance direction of the recording medium. A partial head, and two or more second type partial heads arranged in a line along the first direction at a second position in the second direction, and the specific region is adjacent to each other. A first type specific region corresponding to a boundary between the two first type partial heads; a second type specific region corresponding to a boundary between the adjacent first type partial head and the second type partial head; It is preferable to contain. In this way, since the processing parameters of the error diffusion process are properly used based on whether or not significant pixels are included in the first type specific area and the second type specific area, more appropriately. Banding can be suppressed.

  In the above apparatus, in the second case, the generation unit does not include a significant pixel in the second type specific area, and includes a significant pixel in the first type specific area. In this case, the second type of second error diffusion process is performed on the image data using the second type of the first value as the second value, and the second type of specific region is significant. In the case where a pixel is included, it is preferable to execute a second type of second error diffusion process on the image data by using a second type of second value as the second value. . In this way, banding can be suppressed more appropriately.

  In the above apparatus, in the second case, the determination unit determines whether or not the first type specific area includes a significant pixel indicating that the density is higher than the first type reference density. Determining whether or not the second type specific area includes a significant pixel indicating that the density is higher than the reference density of the second type, and the generation unit is configured to perform the determination in the second case. The second type specific area does not include a significant pixel indicating that the density is higher than the second type reference density, and the first type specific area is higher than the first type reference density. When the image data includes a significant pixel indicating that the density is high, the second error diffusion process of the first type is executed on the image data using the second value of the first type. However, it is indicated that the concentration in the specific area of the second type is higher than the reference density of the second type. If a pixel is included, with the second type of the second value, it is preferable to perform the second error diffusion processing of the second type with respect to the image data. In this way, banding can be suppressed more appropriately.

  In the above apparatus, it is preferable that the first type reference concentration is higher than the second type reference concentration. In this way, banding can be suppressed more appropriately.

  In the above apparatus, the printing execution unit can form a first type of dot and a second type of dot having a smaller size than the first type of dot, and the second type of second dot. The value and the second value of the first type are values that generate more dots of the first type than the first value, and the second value of the second type is the value It is preferable that the value is such that more dots of the first type are generated than the second value of the first type. In this way, banding can be reliably suppressed by executing the error diffusion process using the second type second value. By executing the error diffusion process using the first type second value, it is possible to suppress the occurrence of graininess while suppressing banding. By executing the error diffusion process using the first value, the occurrence of graininess can be suppressed.

  The present invention can be implemented in various modes such as a control device that controls an image processing device, an image processing method, an image processing program that controls the image processing device, and a recording medium that records the program.

It is a fragmentary sectional view of a printer provided with the control part of a 1st embodiment of the present invention. (A) is the figure which showed the relationship between the structure of a print head, and the printing range, (b) is an enlarged view which shows a partial head. FIG. 2 is a block diagram schematically illustrating an electrical configuration of a printer. (A) is a figure which shows typically the structure of an error diffusion parameter memory, (b) is a table | surface explaining the printing result in the case of performing an error diffusion process using each error diffusion parameter. It is a flowchart which shows the printing process performed by a control part. It is a flowchart which shows the error diffusion process performed by the control part. It is a figure which shows typically the structure of the error diffusion parameter memory provided in the control part of 2nd Embodiment. In 3rd Embodiment, it is an example of the chart used in order to determine a reference | standard density | concentration. It is a flowchart which shows the printing process performed by the control part of 3rd Embodiment. (A) is a figure which shows typically the print head provided in a line printer, (b), (c) is a figure explaining the relationship between the attachment angle of a print head, and the dot row | line | column formed. is there.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a partial cross-sectional view of a printer 1 equipped with a control unit 10 according to a first embodiment of the image processing apparatus of the present invention. The control unit 10 is configured to suppress banding of an image printed by the printer 1.

  The printer 1 is a line printer, and an image is formed by the control unit 10, the print head 2, a transport mechanism 21 that transports the paper P, a paper feed mechanism 30 that feeds the paper P to the transport mechanism 21, and the print head 2. A paper discharge unit 90 that discharges the paper P is mainly provided.

  The transport mechanism 21 includes belt rollers 6 and 7 and a transport belt 8 wound around the belt rollers 6 and 7. A conveyor motor 22 (FIG. 3) is connected to the belt roller 7 and rotates in the direction of arrow R in FIG. 1 by the rotational force from the conveyor motor 22. At this time, the transport belt 8 travels so as to transport the paper P in the transport direction T, and the belt roller 6 that is a driven roller also rotates.

  A nip roller 4 is disposed at a position facing the belt roller 6 with the conveyance belt 8 interposed therebetween. The nip roller 4 presses the paper P sent by the paper feed mechanism 30 against the outer peripheral surface 8 a of the transport belt 8 and holds it on the outer peripheral surface 8 a of the transport belt 8. On the other hand, a platen 19 is disposed on the inner peripheral side of the conveyor belt 8 and supports the conveyor belt 8 from the inner peripheral side.

  The print head 2 is provided for each of the four ink colors C, M, Y, and K (cyan, magenta, yellow, and black), is supported by the frame 3 of the frame, and is provided in the conveyance direction T of the paper P. Has been. Each print head 2 is connected to the ink reservoir 60 via a tube. The ink storage unit 60 is provided with an ink cartridge 61 that stores ink for each color, and each print head 2 is supplied with ink of a corresponding color.

  The paper P held on the transport belt 8 passes through the four print heads 2 in order, whereby an image is formed on the paper P. Each print head 2 forms a dot row on the paper P by ejecting ink droplets from the nozzle 2d (FIG. 2) of the ink ejection surface 2a and landing on the paper P as dots. The printer 1 prints an image by repeating the formation of dot rows and forming a large number of dot rows on the paper P. The paper P on which the image is printed is transported to the downstream paper discharge unit 90 by the transport mechanism 21. The discharge mechanism 90 transports the paper P transported from the transport mechanism 21 upward and discharges it.

  FIG. 2A is a diagram illustrating the relationship between the configuration of the print head 2 and the print range. The one-color print head 2 includes two head units 2b. One head unit 2b is provided at a first position L1 in a direction parallel to the transport direction T, and the other head unit 2b is provided at a second position L2 in a direction parallel to the transport direction T. A plurality of trapezoidal partial heads 2c are provided on the ink ejection surface 2a of each head unit 2b. The plurality of partial heads 2 c are arranged along the main scanning direction S orthogonal to the transport direction T.

  In the following description, the longitudinal direction of the print head 2 is the X direction, and the direction orthogonal to the X direction is the Y direction. Ideally, as shown in FIG. 2A, the print head 2 is attached to the frame 3 (FIG. 1) so that the X direction of the print head 2 and the main scanning direction S are parallel to each other. However, in actuality, in consideration of mounting errors and variations with time in the manufacturing stage, the X direction of the print head 2 may be inclined with respect to the main scanning direction S as long as the printer 1 is practically acceptable. good.

  In the following description, the print range in the main scanning direction S that can be printed by the print head 2 is classified into an A area, a B area, and a C area. The area A is an area corresponding to the central part of the partial head 2c. The image of area A is formed by the nozzle 2d provided on one partial head 2c. The area B is an area corresponding to the boundary between two adjacent partial heads 2c in one head unit 2b, and the area C is a boundary between two adjacent partial heads 2c provided in different head units 2b. Is an area corresponding to. The images in the B area and the C area are formed by the nozzles 2d provided in two different partial heads 2c.

  FIG. 2B is an enlarged view showing the partial head 2c. As shown in FIG. 2B, a number of nozzles 2d are formed in the partial head 2c. Each nozzle 2d is configured to be able to form three types of dots (large dots, medium dots, and small dots) having different sizes on the paper P.

  In the print head 2, nozzles 2d are formed so that the nozzles 2d adjacent to each other in the X direction are arranged at different positions in the Y direction. Here, when banding occurs in an image, the banding becomes more conspicuous as the distance in the Y direction between adjacent nozzles 2d in the X direction increases. In particular, in the B region and the C region, the Y-direction distance between the nozzles 2d adjacent in the X direction may be larger than that in the A region, and banding is easily noticeable. For example, in the region B, as shown in FIG. 2B, a pair of nozzles 2d1 formed on different partial heads 2c may be adjacent to each other in the X direction.

  Further, although not shown, in the region C, a pair of nozzles 2d formed in different head units 2b may be adjacent to each other in the X direction. Therefore, banding is more conspicuous in the C region than in the B region.

  FIG. 3 is a block diagram schematically showing the main electrical configuration of the printer 1. As shown in FIG. 3, the printer 1 includes a control unit 10, an interface 16 (I / F 16), a print head 2, and a carry motor 22.

  The control unit 10 includes a CPU 11, a ROM 12, a RAM 13, a flash memory 14, and an ASIC 15, which are connected to each other via a bus line. The control unit 10, the I / F 16, the print head 2, and the transport motor 22 are connected to each other via the ASIC 15.

  The CPU 11 controls each function of the printer 1 and each unit connected to the ASIC 15 according to fixed values and programs stored in the ROM 12 and the flash memory 14. The ROM 12 is a non-rewritable memory that stores a control program 12a, an error diffusion parameter memory 12b, a color profile memory 12c, and the like. The control program 12a is a program for causing the CPU 11 to execute the processing shown in the flowcharts of FIGS.

  The error diffusion parameter memory 12b stores three types of error diffusion parameters. The error diffusion parameter will be described later with reference to FIG. The color profile memory 12c is a predetermined correspondence for color-converting R (red), G (green), and B (blue) pixel values into C, M, Y, and K pixel values. Stores relationships (color profiles). Similar to the error diffusion parameter memory 12b, the color profile memory 12c also stores three types of color profiles in advance.

  The RAM 13 is a rewritable volatile memory, and is provided with an image data memory 13a, an error diffusion parameter setting memory 13b, a color profile setting memory 13c, a random number table 13d, and a random number counter 13e.

  The image data memory 13a stores image data to be processed. In the error diffusion parameter setting memory 13b, one type of error diffusion parameter selected from the three types of error diffusion parameters stored in the error diffusion parameter memory 12b is set. For details, refer to FIG. It will be described later. The color profile setting memory 13c has one type of color profile to be used in combination with the error diffusion parameter set in the error diffusion parameter setting memory 13b among the three types of color profiles stored in the color profile memory 12c. Is set. The flash memory 14 is a rewritable nonvolatile memory.

  The random number table 13d stores a plurality of (for example, 512) pseudo random numbers generated using a known algorithm. Note that random numbers in the range of −8 to 8 are stored in the random number table 13d of the first embodiment. The random number counter 13e is a counter indicating a random number reading position. The value of the random number counter 13e is incremented by “1” every predetermined time, and is set to “1” when the value reaches the number of random numbers stored in the random number table 13d. The control unit 10 executes error diffusion processing using the random numbers read from the random number table 13d, and details will be described later with reference to FIG.

  The control unit 10 performs image processing including error diffusion processing on the image data, generates print data, and supplies the print data to the ASIC 15. The ASIC 15 prints an image on the paper P by controlling the print head 2 and the conveyance motor 22 based on the print data.

  FIG. 4A is a diagram schematically showing the configuration of the error diffusion parameter memory 12b. FIG. 4A shows three types of error diffusion parameters. Various error diffusion parameters include three values: a large dot reference value (threL), a medium dot reference value (threM), and a small dot reference value (threS). As shown in FIG. 4A, the various error diffusion parameters are different from each other only in threL. In the following description, they are referred to as error diffusion parameter A, error diffusion parameter B, and error diffusion parameter C, respectively, in order from the largest threL.

  Although details will be described later with reference to FIG. 6, the smaller the value set as threL, the more large dots are generated (that is, the occurrence frequency of large dots is increased) and the value set as threL is increased. , It is possible to generate fewer large dots (that is, to reduce the frequency of large dots). Therefore, when the error diffusion parameter C is set, the largest number of large dots can be generated, and when the error diffusion parameter A is set, the largest number of large dots can be generated.

  FIG. 4B is a table in which banding and graininess appearing in the print result are evaluated and set when various error diffusion parameters are set. When error diffusion processing is performed using the error diffusion parameter A, in which large dots are least likely to occur, evaluation results indicate that banding is bad (banding is easily noticeable) and graininess is good (occurrence of graininess is suppressed). was gotten. On the other hand, when error diffusion processing using the error diffusion parameter C in which large dots are most likely to occur is performed, the evaluation result is that banding is good (banding is suppressed) and graininess is bad (graininess is easily noticeable). Obtained.

  The control unit 10 of this embodiment suppresses banding by using different error diffusion parameters depending on whether or not significant pixels are included in the B region or C region of the image data. Here, a significant pixel means a pixel that contributes to dot formation. In the present embodiment, pixels other than white pixels (pixels whose R, G, and B pixel values are all 255) are treated as significant pixels.

  FIG. 5 is a flowchart illustrating a printing process executed by the control unit 10. In this process, image data including an error diffusion process is performed on the image data to generate print data, and the image is printed. This process is executed when a print instruction is input from an external device such as a personal computer.

  First, the CPU 11 inputs image data and stores it in the image data memory 13a (S502). It is assumed that R, G, and B pixel values included in the image data are 0 or more and 255 or less. Next, the CPU 11 analyzes the image data (S504), and determines whether or not a significant pixel is included in the C area in the image data (S506). Specifically, it is determined whether or not the pixel values of R, G, and B are all 255 for each pixel constituting the C region. When it is determined that the R, G, and B pixel values included in the C area are all 255, the CPU 11 determines that no significant pixel is included in the C area (S506: No).

  On the other hand, when any one of the R, G, and B pixel values included in the C region is not 255, the CPU 11 determines that a significant pixel is included in the C region (S506: Yes). Then, the CPU 11 reads the error diffusion parameter C from the error diffusion parameter memory 12b and sets it in the error diffusion parameter setting memory 13b (S508). Further, the CPU 11 reads the color profile C from the color profile memory 12c and sets it in the color profile setting memory 13c (S510). The color profile C is prepared in advance as a color profile optimal for color conversion of image data when error diffusion processing using the error diffusion parameter C is performed on the image data.

  Next, the CPU 11 performs color conversion processing on the image data stored in the image data memory 13a using the color profile C set in the color profile setting memory 13c (S522). The R, G, B pixel values included in the image data are converted into C, M, Y, K pixel values by color conversion processing.

  Next, the CPU 11 performs error diffusion processing using the error diffusion parameter C set in the error diffusion parameter setting memory 13b on the color-converted image data to generate print data (S524). Details of the error diffusion processing will be described later with reference to FIG. Next, the CPU 11 supplies the generated print data to the ASIC 15, prints an image (S526), and ends the process.

  In this way, the image data determined to include significant pixels in the C region is subjected to error diffusion processing using the error diffusion parameter C, so that other error diffusion parameters are set. More large dots can be generated than in FIG. As a result, banding can be reliably suppressed when significant pixels are included in the C region in which banding is particularly conspicuous.

  On the other hand, when no significant pixel is included in the C area (S506: No), the CPU 11 next determines whether or not a significant pixel is included in the B area (S512). For the B area, similarly to the C area, it is determined whether or not the R, G, and B pixel values included in the B area include values other than 255.

  When it is determined that the B area includes a significant pixel (S512: Yes), the CPU 11 reads the error diffusion parameter B from the error diffusion parameter memory 12b and sets it in the error diffusion parameter setting memory 13b (S514). . The CPU 11 reads the color profile B from the color profile memory 12c and sets it in the color profile setting memory 13c (S516). The color profile B is prepared in advance as a color profile optimal for color conversion of image data when error diffusion processing using the error diffusion parameter B is performed on the image data.

  Next, the CPU 11 performs color conversion processing on the image data using the color profile B (S522), and performs error diffusion processing using the error diffusion parameter B on the color-converted image data (S524). . In this way, error diffusion processing using the error diffusion parameter B is performed on image data that is determined to include no significant pixels in the C region and include significant pixels in the B region. Therefore, more large dots can be generated than when the error diffusion parameter A is set. Further, compared to the case where the error diffusion parameter C is set, fewer large dots can be generated. Therefore, it is possible to suppress the occurrence of graininess while suppressing banding.

  When it is determined that no significant pixel is included in the B area (S512: No), the CPU 11 reads the error diffusion parameter A from the error diffusion parameter memory 12b and sets it in the error diffusion parameter setting memory 13b (S518). Further, the CPU 11 reads the color profile A from the color profile memory 12c and sets it in the color profile setting memory 13c (S520). The color profile A is prepared in advance as a color profile optimum for color conversion of image data when error diffusion processing using the error diffusion parameter A is performed on the image data.

  Next, the CPU 11 performs color conversion processing on the image data using the color profile A (S522), and performs error diffusion processing using the error diffusion parameter A on the color-converted image data (S524). . In this way, error diffusion processing using the error diffusion parameter A is performed on image data that is determined not to include significant pixels in both the B area and the C area. Therefore, compared to the case where other error diffusion parameters are set, it is possible to generate fewer large dots and suppress the occurrence of graininess.

  FIG. 6 is a flowchart showing the error diffusion process (S524) executed by the CPU 11. This processing is processing for generating print data indicating formation of any of large, medium, and small dots or non-formation of dots based on the color-converted image data. This process is executed for each color of C, M, Y, and K, but for the sake of simplicity, only the process for one color will be described in the flowchart of FIG.

  First, the CPU 11 selects a target pixel (S602) and determines a correction input value I '(S604). The corrected input value I ′ is a value obtained by adding the error e of the peripheral pixel to the pixel value of the target pixel. Since the calculation method of the correction input value I ′ in the error diffusion process is known, a detailed description thereof will be omitted.

  Next, the CPU 11 acquires a random number T (S606). Specifically, the value N of the random number counter 13e is acquired, and the random number T stored in the Nth of the random number table 13d is acquired. In the first embodiment, random numbers in the range of −8 to 8 are acquired. Next, the CPU 11 determines a value obtained by adding the random number T to threL among the error diffusion parameters set in the error diffusion parameter setting memory 13b as a large dot threshold (S608).

  Next, the CPU 11 determines whether or not the correction input value I ′ is larger than the large dot threshold (S612). When it is determined that the corrected input value I ′ is larger than the large dot threshold value (S612: Yes), the CPU 11 sets the value of the target pixel as a value indicating the formation of large dots, and the large dot relative density from the corrected input value I ′. A value obtained by subtracting (DotL) is calculated as an error e of the target pixel (S614). Then, the CPU 11 stores the calculated error e in an error buffer (not shown) (S630), and determines whether it is the last pixel (S632). If the determination in S632 is negative (S632: No), the CPU 11 repeats the process from S602.

  On the other hand, when it is determined that the corrected input value I ′ is equal to or smaller than the large dot threshold (S612: No), the CPU 11 adds a random number T to threM among the error diffusion parameters set in the error diffusion parameter setting memory 13b. The determined value is determined as the medium dot threshold value (S616).

  Next, the CPU 11 determines whether or not the correction input value I ′ is larger than the medium dot threshold value (S618). When it is determined that the correction input value I ′ is larger than the medium dot threshold value (S618: Yes), the CPU 11 sets the value of the target pixel as a value indicating the formation of the medium dot, and the medium dot relative density from the correction input value I ′. A value obtained by subtracting (DotM) is calculated as an error e of the target pixel (S620).

  On the other hand, when it is determined that the corrected input value I ′ is equal to or less than the medium dot threshold (S618: No), the CPU 11 adds a random number T to threS among the error diffusion parameters set in the error diffusion parameter setting memory 13b. The determined value is determined as a small dot threshold value (S622).

  Next, the CPU 11 determines whether or not the correction input value I ′ is larger than the small dot threshold (S624). When it is determined that the correction input value I ′ is larger than the small dot threshold (S624: Yes), the CPU 11 sets the value of the target pixel as a value indicating the formation of a small dot, and uses the correction input value I ′ as a small dot relative density ( A value obtained by subtracting DotS) is calculated as an error e of the target pixel (S626). On the other hand, when it is determined that the corrected input value I ′ is equal to or smaller than the small dot threshold value (S624: No), the CPU 11 sets the value of the target pixel as a value indicating no dot formation, and sets the corrected input value I ′ as the error e. (S628). When the process is completed up to the final pixel while the process is repeated in this way (S632: Yes), the CPU 11 ends the error diffusion process.

  According to the error diffusion process (S524), the smaller the error diffusion parameter threL set in the error diffusion parameter setting memory 13b, the smaller the large dot threshold value is determined. As a result, the generation of large dots can be increased and banding can be suppressed.

  According to the first embodiment, depending on whether or not a significant pixel is included in a specific area in the image data, the error diffusion parameter is properly used and banding can be appropriately suppressed. That is, when a significant pixel is included in the C region where banding is most conspicuous, the error diffusion parameter C can be used to reliably suppress banding. Further, when no significant pixels are included in the C region and significant pixels are included in the B region, the occurrence of graininess can be suppressed while suppressing banding using the error diffusion parameter B. Further, when no significant pixel is included in any of the B region and the C region, the occurrence of graininess can be suppressed using the error diffusion parameter A.

  Further, according to the present embodiment, even when banding occurs due to fluctuations that are difficult to predict, such as aging fluctuations and paper conveyance deviations, banding can be appropriately suppressed by properly using error diffusion parameters. Robust image processing is realized. Further, according to the present embodiment, banding can be suppressed without detecting the uneven position, so that the printer 1 can be configured at a lower cost than when the uneven position detecting means is provided in the printer.

  Furthermore, according to the present embodiment, one image data is subjected to error diffusion processing using one type of error diffusion parameter. In other words, error diffusion processing using the same error diffusion parameter is performed on the A region, the B region, and the C region of one image data. Therefore, the occurrence of an unnatural boundary at the boundary of each region is suppressed.

  A second embodiment will be described with reference to FIG. In the first embodiment, threL used for determining the large dot threshold is changed depending on whether or not a significant pixel is included in the B area or the C area. On the other hand, in the second embodiment, the range of the random number T used for determining the large dot threshold value, the medium dot threshold value, and the small dot threshold value is changed depending on the case.

  FIG. 7 is a diagram schematically illustrating a configuration of information stored in the error diffusion parameter memory 12b of the control unit 10 according to the second embodiment. In the second embodiment, the error diffusion parameter defines a range of random numbers to be stored in the random number table 13d.

  In the second embodiment, the error diffusion parameter memory 12b stores three types of error diffusion parameters. The range of random numbers defined by these three types of error diffusion parameters has the same upper limit value and different lower limit values. In the second embodiment, the error diffusion parameter A, the error diffusion parameter B, and the error diffusion parameter C are referred to in descending order of the lower limit value of the random number.

  Next, the process which the control part 10 of 2nd Embodiment performs is demonstrated. The flowcharts of FIG. 5 and FIG. 6 that have already been referred to can be used to describe the processing executed by the control unit 10 of the second embodiment. Therefore, referring to FIG. 5 and FIG. Processing executed by the unit 10 will be described. Of the processing shown in the flowcharts of FIGS. 5 and 6, description of the same processing as in the first embodiment is omitted.

  When the control unit 10 according to the second embodiment executes the printing process illustrated in FIG. 5, when it is determined that a significant pixel is included in the C region (S506: Yes), the CPU 11 illustrated in FIG. The error diffusion parameter C of the second embodiment is set in the error diffusion parameter setting memory 13b (S508). Further, when the C area does not include a significant pixel (S506: No) and the B area includes a significant pixel (S512: Yes), the CPU 11 uses the error diffusion parameter B of the second embodiment as the error diffusion. The parameter setting memory 13b is set (S514). If the B area and the C area do not contain significant pixels (S506: No, S512: No), the CPU 11 sets the error diffusion parameter A of the second embodiment in the error diffusion parameter setting memory 13b (S518). ).

  In the control unit 10 of the second embodiment, the CPU 11 executes a random number generation process independent of the printing process (FIG. 5). The random number generation process is a process of generating a random number within the range set in the error diffusion parameter setting memory 13b and storing it in the random number table 13d. However, since it can be realized by a known algorithm, illustration and detailed description are omitted. To do.

  With reference to FIG. 6, the error diffusion process (S524) executed by the control unit 10 of the second embodiment will be described. The CPU 11 acquires a random number T within the range set in the error diffusion parameter setting memory 13b from the random number table 13d (S606).

  Next, the CPU 11 determines a large dot threshold value by adding a random number T to threL (S608). In the first embodiment, threL is read from the error diffusion parameter setting memory 13b. On the other hand, in the second embodiment, this threL is a fixed value (for example, 128) stored in advance in the ROM 12 or the like, for example.

  Here, the error diffusion parameter A [−8 to 8] has a larger lower limit value of the random number T than the error diffusion parameter B [−16 to 8] or the error diffusion parameter C [−32 to 8]. Therefore, when the error diffusion parameter A is set in the error diffusion parameter setting memory 13b, the large dot threshold value tends to take a larger value. Therefore, when the error diffusion process using the error diffusion parameter A is executed, it is difficult to generate large dots and the occurrence of graininess can be suppressed.

  The error diffusion parameter C [−32 to 8] has a lower lower limit value of the random number T than the error diffusion parameter A [−8 to 8] or the error diffusion parameter B [−16 to 8]. Therefore, when the error diffusion parameter C is set in the error diffusion parameter setting memory 13b, the large dot threshold value tends to take a smaller value. Therefore, when error diffusion processing using the error diffusion parameter C is executed, large dots can be easily generated and banding can be suppressed.

  In the second embodiment, the CPU 11 determines a value obtained by adding a random number T to threM and threS as a medium dot threshold value and a small dot threshold value (S616, S622). Similar to threL described above, threM and threS are fixed values (for example, 65, 2) stored in advance in the ROM 12 or the like, and the same random number T as threL is added.

  According to the control part 10 of 2nd Embodiment, the effect similar to 1st Embodiment is acquired.

  A third embodiment of the present invention will be described with reference to FIGS. The control part 10 of the said 1st Embodiment and 2nd Embodiment judged whether the significant pixel was contained in the specific area | region of image data. The control unit 10 of the third embodiment further determines whether or not a significant pixel indicating that the density is higher than the reference density is included in the specific region.

  FIG. 8 is a diagram illustrating an example of a chart used for determining the reference density. This chart is obtained by causing the printer 1 to print a gradation image in which the luminance gradually decreases (the density increases) as it goes downward. In addition, this chart includes at least one area A, area B, and area C in the print range (FIG. 2A) in the main scanning direction S that can be printed by the print head 2.

  Here, banding is difficult to perceive at a low concentration, and is likely to be perceived in a region where the concentration is higher than a certain concentration. Therefore, the designer (or the user of the printer 1) visually checks the chart and determines the density (reference density) at which banding adversely affects the image quality. This reference density is determined for each of the B region and the C region. As described above, since banding is less likely to be perceived in the B area than in the C area, the first type reference density determined for the B area is higher than the second type reference density determined for the C area. Is a value indicating

  In the third embodiment, the luminance value is used to determine whether or not a pixel having a higher density than the reference density exists in the specific area. Specifically, a luminance value T1 corresponding to the first type reference density determined for the B region is obtained, and it is determined whether or not a pixel having a luminance equal to or lower than the luminance value T1 exists in the B region. Similarly, a luminance value T2 corresponding to the second type reference density determined for the C region is obtained, and it is determined whether or not a pixel having a luminance equal to or lower than the luminance value T2 exists in the C region.

  FIG. 9 is a flowchart illustrating print processing executed by the control unit 10 according to the third embodiment. Among the processes shown in the flowchart of FIG. 9, the same processes as those shown in the flowchart of FIG. 5 are denoted by the same step numbers, and detailed description thereof is omitted.

  As shown in FIG. 9, the CPU 11 determines whether or not a pixel having a luminance value Y equal to or lower than the luminance value T2 is in the C region (S902). Note that the CPU 11 performs the determination in S902 by using the smallest value among the pixel values of the R, G, and B colors of the target pixel as the luminance value Y of the target pixel. When it is determined that there is a significant pixel in the area C and the luminance value Y of the pixel is equal to or lower than the luminance value T2 (that is, the density is higher than the second type reference density) (S902). : Yes), the CPU 11 sets the error diffusion parameter C (FIG. 4A) described in the first embodiment in the error diffusion parameter setting memory 13b (S508).

  On the other hand, when it is not determined that the pixel indicating the luminance value Y equal to or lower than the luminance value T2 is in the C region (S902: No), the CPU 11 determines whether the pixel indicating the luminance value Y equal to or lower than the luminance value T1 is in the B region. Is determined (S904). When it is determined that there is a significant pixel in the area B and the luminance value Y of the pixel is equal to or lower than the luminance value T1 (that is, the density is higher than the first type reference density) (S904). : Yes), the CPU 11 sets the error diffusion parameter B described in the first embodiment in the error diffusion parameter setting memory 13b (S514).

  On the other hand, when the pixel having the luminance value Y equal to or lower than the luminance value T2 is not in the C region and the pixel having the luminance value Y equal to or lower than the luminance value T1 is not present in the B region (S902: No, S904: No), the CPU 11 performs the first implementation. The error diffusion parameter A described in the embodiment is set in the error diffusion parameter setting memory 13b (S518).

  According to the third embodiment, when a pixel indicating that the density is higher than the second type reference density is included in the C region, the error diffusion process using the error diffusion parameter C is executed. Therefore, when there is a high possibility that banding will adversely affect image quality, it is possible to reliably suppress banding using the error diffusion parameter C.

  Further, a pixel indicating that the density is higher than the second type reference density is not included in the C area, and a pixel indicating that the density is higher than the first type reference density is included in the B area. Then, an error diffusion process using the error diffusion parameter B is executed. Therefore, when there is a high possibility that banding will adversely affect image quality, the error diffusion parameter B is used to suppress the occurrence of graininess while suppressing banding.

  Further, by setting the first type reference density determined for the B area to a value indicating a higher density than the second type reference density determined for the C area, the C area has a lower density than the B area. In consideration of the characteristic that banding is conspicuous, the error diffusion parameter can be used properly, and banding can be suppressed more appropriately.

  Further, according to the third embodiment, even when significant pixels are included in the B region and the C region, error diffusion is performed when the density is lower than the reference density determined for each region. Since parameter A is set, the occurrence of graininess can be reliably suppressed.

  In the printing process (FIG. 9) of the third embodiment, the error diffusion parameter (FIG. 4) described in the first embodiment is used. Instead, the error described in the second embodiment is used instead. The third embodiment may be configured to use diffusion parameters (FIG. 7).

  In the above embodiment, the printing mechanism including the print head 2 in the printer 1 is an example of the print execution unit. The control program 12a is an example of an image processing program. The main scanning direction S is an example of the first direction. The area B is an example of the first type of specific area, and the area C is an example of the second type of specific area. The error diffusion parameter A is an example of a first value, the error diffusion parameter B is an example of a first type of second value, and the error diffusion parameter C is an example of a second type of second value. A large dot is an example of a first type dot, and a medium dot and a small dot are examples of a second type dot. The CPU 11 that executes S524 is an example of a generation unit, and the CPU 11 that executes S526 is an example of a supply unit.

  Although the present invention has been described based on the embodiments, the present invention is not limited to the above-described embodiments, and various improvements and modifications can be easily made without departing from the spirit of the present invention. Can be inferred.

  For example, in the above-described embodiment, the control unit 10 in the printer 1 is an example of an image processing apparatus. However, an external device such as a personal computer that is communicably connected to the printer 1 is an example of the image processing apparatus of the present invention. Can be.

  In the above embodiment, each color print head 2 includes two rows of head units 2 b and includes two rows of partial heads 2 c arranged in the main scanning direction S. However, the present invention can also be applied to the case where the print head 2 is composed of a plurality of partial heads 2 c arranged in a line along the main scanning direction S. In that case, the B region corresponding to the boundary between the two adjacent partial heads 2c corresponds to an example of the specific region.

  Even in this case, banding can be appropriately suppressed by using at least two types of error diffusion parameters depending on whether or not a significant pixel is included in the specific region, as in the above embodiment. For example, when significant pixels are included in a specific area, banding is performed by executing error diffusion processing using a second error diffusion parameter that generates more large dots than the first error diffusion parameter. Can be suppressed. On the other hand, when a significant pixel is not included in the specific area, the occurrence of graininess can be suppressed by using the first error diffusion parameter.

  In the case where the print head 2 is configured by the partial heads 2c arranged in a line, the specific area includes significant pixels and the density is higher than the reference density in the specific area, as in the third embodiment. The second error diffusion parameter may be used on the condition that it is determined that the pixel indicating is included. In this way, it is possible to suppress the occurrence of graininess while suppressing banding that adversely affects image quality.

  In the above embodiment, the color profile is changed according to the type of the error diffusion parameter. However, the color conversion process may be executed using the same color profile regardless of the type of error diffusion parameter.

  Moreover, in the said embodiment, it was judged whether the specific area | region contains a significant pixel based on the R, G, B pixel value. However, instead of this, for example, this determination may be made using pixel values of C, M, Y, K, or luminance values calculated from R, G, B pixel values.

  In the first embodiment (FIG. 4A), the plurality of types of error diffusion parameters differ from each other only in threL for determining the large dot threshold, but threM and threS are also different from each other. Also good.

  In the second embodiment (FIG. 7), the CPU 11 has been described as storing a random number within the range set in the error diffusion parameter setting memory 13b in the random number table 13d. However, a plurality of types of random number tables may be provided in the control unit 10 in advance, and each random number table may store different ranges of random numbers. In that case, the error parameter may be a value indicating from which of a plurality of types of random number tables a random number should be read.

  Moreover, you may combine the said 1st Embodiment and 2nd Embodiment. That is, both threL for determining the large dot threshold and the value that the random number T can take may be changed depending on whether or not a significant pixel is included in the specific area.

  In the third embodiment, the luminance value Y is used to determine whether or not there is a pixel indicating that the density is higher than the reference density. For example, C, M, Y, and K are used. You may comprise so that it may judge using a pixel value.

DESCRIPTION OF SYMBOLS 1 Printer 2 Print head 10 Control part 12a Control program

Claims (10)

An image processing apparatus for causing a print execution unit including a print head including a plurality of partial heads arranged along a first direction orthogonal to a conveyance direction of a recording medium to execute printing,
A generation unit that performs image processing including error diffusion processing on the image data and generates print data;
A supply unit for supplying the print data to the print execution unit;
With
The generator is
A determination unit configured to determine whether or not a significant area is included in the specific area in the image data, the specific area corresponding to a boundary between two adjacent partial heads of the plurality of partial heads; Prepared,
The generator is
In the first case where it is determined that no significant pixel is included in the specific area in the image data, the first error diffusion is performed on the image data using the first value as the value of the processing parameter. Execute the process,
In the second case where it is determined that a significant pixel is included in the specific area in the image data, a second error diffusion is performed on the image data by using the second value as the value of the processing parameter. An image processing apparatus that executes processing. The determination unit determines whether or not a significant pixel indicating that the density is higher than a reference density is included in the specific region in the second case;
In the second case, the generation unit is
When it is determined that no significant pixel indicating that the density is higher than the reference density is included in the specific area, the first error diffusion is performed using the first value as a value of a processing parameter. Execute the process,
When it is determined that a significant pixel indicating that the density is higher than the reference density is included in the specific area, the second error diffusion is performed using the second value as a value of a processing parameter. The image processing apparatus according to claim 1, wherein the processing is executed. The plurality of partial heads include two or more first type partial heads arranged in a line along the first direction,
The image processing apparatus according to claim 1, wherein the specific area includes an area corresponding to a boundary between two adjacent first type partial heads. The print execution unit is capable of forming a first type of dot and a second type of dot having a smaller size than the first type of dot,
The image processing apparatus according to claim 1, wherein the second value is a value that generates more of the first type of dots than the first value. The plurality of partial heads are
Two or more first type partial heads arranged in a line along the first direction at a first position in a second direction parallel to the conveyance direction of the recording medium;
Two or more second type partial heads arranged in a line along the first direction at the second position in the second direction;
Contains
The specific area is
A first type specific region corresponding to a boundary between two adjacent first type partial heads;
A second type specific region corresponding to a boundary between the adjacent first type partial head and the second type partial head;
The image processing apparatus according to claim 1, comprising: In the second case, the generation unit is
When no significant pixel is included in the second type specific area and a significant pixel is included in the first type specific area, the second value of the first type is used as the second value. To perform a first type of second error diffusion process on the image data,
When a significant pixel is included in the second type of specific area, a second type of second value is used as the second value, and a second type of second is used for the image data. The image processing apparatus according to claim 5, wherein error diffusion processing is executed. In the second case, the determination unit determines whether or not the first type specific region includes a significant pixel indicating that the density is higher than the first type reference density, and Determining whether or not the two specific regions include significant pixels indicating that the density is higher than the second type reference density;
In the second case, the generation unit is
The second type of specific area does not include a significant pixel indicating that the density is higher than the second type of reference density, and the first type of specific area is higher than the first type of reference density. When a significant pixel indicating that the density is high is included, the second error diffusion process of the first type is performed on the image data using the second value of the first type. ,
When the second type specific area includes a significant pixel indicating that the density is higher than the second type reference density, the second type second value is used to generate the image. The image processing apparatus according to claim 6, wherein the second type of second error diffusion process is performed on data.   The image processing apparatus according to claim 7, wherein the first type of reference density is higher than the second type of reference density. The print execution unit is capable of forming a first type of dot and a second type of dot having a smaller size than the first type of dot,
The second type second value and the first type second value are values that generate more dots of the first type than the first value, and the second type 9. The image processing apparatus according to claim 6, wherein the second value is a value that generates more dots of the first type than the second value of the first type. . An image processing program,
An image processing apparatus for causing a print execution unit including a print head including a plurality of partial heads arranged along a first direction orthogonal to a conveyance direction of a recording medium to execute printing,
A generation unit that performs image processing including error diffusion processing on the image data and generates print data;
A supply unit for supplying the print data to the print execution unit;
To function,
The generator is
A determination unit configured to determine whether or not a significant area is included in the specific area in the image data, the specific area corresponding to a boundary between two adjacent partial heads of the plurality of partial heads; Prepared,
The generator is
In the first case where it is determined that no significant pixel is included in the specific area in the image data, the first error diffusion is performed on the image data using the first value as the value of the processing parameter. Execute the process,
In the second case where it is determined that a significant pixel is included in the specific area in the image data, a second error diffusion is performed on the image data by using the second value as the value of the processing parameter. An image processing program that executes processing.