JP2012010171A - Printing employing both irrational number screen and rational number screen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain optimization of rosetta.SOLUTION: Printing employing both a rational number screen and an irrational number screen is performed.

Description

  The present invention relates to printing using an irrational number screen and a rational number screen together.

  An image forming apparatus (printing apparatus) that employs an electrophotographic system has a very high demand for high image quality. Particularly in the high-end market, an image subjected to AM screen processing such as printing is required. The AM screen process is a process for creating a color gradation by using regularly arranged dots and line sizes called halftone dots. For human eyes, the smaller the dot area, the lighter the color, and the larger the area, the darker the color. Using this property, the halftone dot size is controlled for each color plate of cyan (C), magenta (M), yellow (Y), and black (K), and by combining those dots and lines, Expresses full color including tones.

  Further, in this printing industry, it is desirable that C is 15 degrees, K is 45 degrees, M is 75 degrees, and Y is 0 degrees. However, if the CMY 30 degree interval is realized, the CMY angle is It is said that it may be replaced. This is because Rosetta optimization can be achieved. In order to optimize this rosetta, the three color plates of CMK other than the Y plate, which have the highest brightness and are not visually noticeable, are arranged at the same screen line number, and the screen angles of each color plate are arranged at intervals of 30 °. is required. The above points are described in each patent document.

JP 2006-311488 A JP 55-6393 JP 61-137473 A

  However, since tan θ of 15 degrees and 75 degrees is an irrational number, it is impossible to realize this with a rational number screen. On the other hand, if an irrational screen of 45 degrees is to be realized, error rounding frequently occurs and the printing result becomes dirty.

  Therefore, in the present invention, a rational number screen and an irrational number screen are used in combination.

  As an embodiment, for example, an irrational screen is used when realizing 15 degrees and 75 degrees that cannot be realized with a rational screen, and a rational screen is used when realizing 45 degrees that can be realized with a rational screen. To do.

  This makes it possible to use an irrational screen for angles that cannot be achieved while using a rational screen that requires less computation.

  Rosetta can be optimized.

1 is a block diagram illustrating a configuration of an image forming apparatus. 1 is a cross-sectional view of an image forming apparatus. FIG. 3 is a block diagram illustrating image processing for printing. It is an example of a table of halftone dot patterns. It is a schematic diagram of AM screen processing by an irrational tangent method. It is an example of the threshold matrix of a rational tangent method. It is a schematic diagram of AM screen processing using a threshold matrix. It is an example of the AM screen processing result by an irrational tangent method. It is an example of the AM screen processing result by an irrational tangent method. It is an example of the AM screen processing result by an irrational tangent method. It is an example of the AM screen processing result using a threshold value matrix. It is an example of the AM screen processing result of CMYK four colors. It is an example of the AM screen processing result by an irrational tangent method. FIG. 3 is a block diagram illustrating image processing for printing. It is an example of an error diffusion process result. FIG. 3 is a block diagram illustrating image processing for printing. It is an example of the threshold matrix of a rational tangent method. It is a schematic diagram of AM screen processing using a threshold matrix. It is an example of the threshold matrix of a rational tangent method.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic block diagram of the image forming apparatus 100, and is a block diagram of a digital multi-function peripheral having functions such as general copying, printing, and FAX.

  The image forming apparatus 100 according to this embodiment includes a scanner unit 101 that performs document reading processing, and a controller 102 that performs image processing on image data read from the scanner unit 101 and stores the image data in a memory 105. Furthermore, an operation unit 104 for setting various printing conditions for image data read by the scanner unit 101 is provided. In addition, the image forming apparatus includes a printer unit 103 that performs image formation in which image data read from the memory 105 is visualized on a recording sheet in accordance with print setting conditions set by the operation unit 104. The image forming apparatus 100 is connected to a server 108 that manages image data, a personal computer (PC) 107 that instructs the image forming apparatus 100 to execute printing, and the like via a network 106. Further, the controller 102 rasterizes the print data transmitted when printing is instructed from the server 108 or the PC 107 into image data and stores the image data in the memory 105.

  FIG. 2 is a cross-sectional view of the image forming apparatus 100. A more detailed configuration of the image forming apparatus 100 described with reference to FIG. 1 will be described with reference to FIG. The image forming apparatus 100 has copy, print, and fax functions. In FIG. 2, the image forming apparatus according to the present embodiment includes a scanner unit 101, a document feeder (DF) 202, and a printer unit 103 for print recording including a color four-color drum.

  First, a copy reading operation performed mainly by the scanner unit 101 will be described. When a document is set on the document table 207 and read, the user sets the document on the document table 207 and closes the DF 202. Then, the open / close sensor 224 detects that the document table 207 is closed, and then detects the document size on which the light reflection type document size detection sensors 226 to 230 in the housing of the scanner unit 101 are set. Starting from this size detection, the light source 210 irradiates the document, and a CCD (charge-coupled device) 231 receives the reflected light from the document via the reflector 211 and the lens 212 to read the image. Then, the controller 102 of the image forming apparatus 100 converts the data read by the CCD 231 into digital image data, performs image processing for the scanner, and stores the image data in the memory 105 in the controller 102. The image data is an RGB color space composed of three image signals, and holds a value of 8 bits (256 gradations) for each image signal for each pixel.

  Next, a print rasterizing operation performed mainly by the PC 107 will be described. Print data such as PDL (Page Description Language) data and a display list is transmitted from the PC via the network 106. The print data is vector information, and holds data indicating attributes such as characters, lines, figures, and images in units of objects in addition to information such as colors, shapes, and coordinates for drawing. The controller 102 receives the print data, rasterizes it based on the print data, and generates image data and attribute data for each pixel. The print data has a color space composed of a plurality of image signals such as gray scale, RGB, and CMYK, and the image data has a value of 8 bits (256 gradations) per image signal for each pixel. The attribute data holds values representing attributes such as characters, lines, graphics, and images of the object, and is handled in the image processing unit 301 together with the image data.

  Next, a copy / print printing operation performed mainly by the printer unit 103 will be described. The image data and the attribute data once stored in the memory 105 in the controller 102 are transferred to the printer unit 103 after image processing for printing described later is performed again in the controller 102. In the printer unit 103, it is converted into a pulse signal by PWM control in the printer unit 103, and in the laser recording unit, recording lasers of four colors of cyan (C), magenta (M), yellow (Y), and black (K) are used. Converted to light. Then, the recording laser light is applied to the photosensitive members 214 of the respective colors, and an electrostatic latent image is formed on each photosensitive member. The printer unit 103 performs toner development on each photoconductor with toner supplied from the toner cartridge 215, and the toner image visualized on each photoconductor is primarily transferred to the intermediate transfer belt 219. The intermediate transfer belt 219 rotates in the clockwise direction in FIG. 2, and when the recording paper fed from the paper cassette 216 through the paper feed conveyance path 217 reaches the secondary transfer position 218, the recording is performed from the intermediate transfer belt 219. The toner image is transferred to the paper.

  The recording paper onto which the image has been transferred is fixed with toner by pressurization and heat in the fixing device 220 (this causes the CMYK four color materials to adhere to the paper) and is conveyed through the paper discharge conveyance path. Then, the sheet is discharged to the face-down center tray 221 or the face-up side tray 222.

  The color material is not limited to toner, and any color material may be used as long as it contains a component for coloring the paper such as ink.

  Next, the above-described image processing for printing will be described in detail with reference to FIG.

  In FIG. 3, reference numeral 301 denotes an image processing unit that performs image processing for printing in the controller 102. The image data input from the memory 105 is subjected to color correction processing in a color correction unit 302 and converted into a CMYK color space having a density composed of four image signals by a color conversion LUT or matrix calculation. The converted image data has an 8-bit value for each image signal for each pixel, and then gamma correction processing is performed in the gamma correction unit 303. The irrational screen processing units 304 to 306 and the rational screen processing unit 307 perform AM screen processing, which will be described later, to convert the pixel value from 8 bits to 1-bit image data that can be printed by the printer unit 103. Thereafter, the data is sent to the printer unit 103. Reference numeral 309 denotes a CPU that operates as a computer for image processing, and controls the entire operation of the image processing unit 301 based on a control program held in the ROM 308. A RAM 310 is used as a work area for the CPU 309. Further, the RAM 310 stores a threshold value matrix and a halftone dot pattern table which will be described later.

  Next, AM screen processing by the irrational tangent method performed by the irrational screen processing units 304 to 306 will be described in detail with reference to FIGS.

  FIG. 4 is an example of a halftone dot pattern, which is a table in which threshold values representing one halftone dot are two-dimensionally arranged in a grid pattern, and has a table length of D. In the table, there are square grid points of the table length D corresponding to the threshold value. FIG. 5 is a diagram schematically showing AM screen processing by the irrational tangent method. In FIG. 5, the X axis and the Y axis indicate recording pixel coordinates in the main scanning direction and the sub scanning direction of the image data, and the U axis and V axis indicate address coordinates of the halftone dot pattern.

  The irrational screen processing units 304 to 306 receive the value of one pixel as an input pixel sequentially from the image data 501 in which pixels having an 8-bit value per image signal are arranged in a grid at equal intervals. Thereafter, the value is compared with a threshold value read from the halftone dot pattern 401 by an irrational tangent method described later. As a result, “1” is output if the pixel value is the same or larger than the threshold value, and “0” is output otherwise. In the present embodiment, the image data has 8 bits, that is, 256 gradations having a value of 0 to 255. Therefore, the threshold value to be compared with the image data may have a value of 0 to 254. Therefore, the table length D of the halftone dot table in this embodiment is 16, and the number of grid points (threshold number) of the halftone dot table is 256.

  Next, referring to FIGS. 4 and 5, the threshold value reading method by the above-described irrational tangent method in the halftone processing unit 302 of this embodiment will be described in detail.

  First, the coordinates of the pixel coordinate system XY corresponding to the input target pixel are acquired. Here, the pixel of interest is assumed to be A (Ay, Ax) as an example.

Next, the acquired pixel of interest A (Ay, Ax) is converted into A (Av, Au) in the address coordinate system U-V of the halftone dot pattern 401. Conversion can be performed by coordinate conversion of the following equation.
Au = (Ax · cos θ + Ay · sin θ) · p
Av = (Ay · cos θ−Ax · sin θ) · p
p = table length of halftone dot pattern D / (resolution / number of screen lines)
At this time, p is an address coordinate conversion value in one pixel of the image data. For example, when the screen pattern number 170 lpi (line per inch) is processed on image data having a resolution of 1200 dpi (dot per inch) using the halftone dot pattern 401 of FIG. 5, the address coordinate conversion value is approximately 2.27. . Θ is the screen angle (°).

  Next, a random number is generated and added to each coordinate of A (Av, Au). The random number added at this time is a uniform random number, and it is desirable that the maximum value be smaller than the absolute value of the increase amount of the address coordinate that changes in one pixel, that is, the address coordinate converted value p. Further, this random number may be added to the coordinates Ax and Ay of the target pixel, and the maximum value of the random number in this case is preferably less than 1.

Next, a threshold value is acquired from the halftone dot pattern 401 using the integer part of the target pixel A (Av, Au). In the address coordinate system UV, a halftone dot pattern 401 is arranged on a tile with a table length D as shown in FIG. Therefore, when the threshold value is TH (THv, THu) in the halftone dot pattern 401,
THu = MOD (INT (Au), D)
THv = MOD (INT (Av), D)
It is calculated by. Here, INT is an operation that gives an integer part with the fractional part rounded down, and MOD is an arithmetic operation that returns a remainder obtained by dividing the first argument by the second argument. That is, the coordinate obtained by adding the integer part on the address coordinate by the table length D corresponds to the lattice point of the halftone dot pattern 401, and the threshold value TH is acquired from the corresponding lattice point.

  Next, AM screen processing using a rational tangent threshold matrix performed by the rational number screen processing unit 307 will be described in detail with reference to FIGS.

  FIG. 6 is an example of a threshold matrix of the rational tangent method, and FIG. 7 is a diagram schematically showing AM screen processing using the threshold matrix.

  In FIG. 6, a rational tangent threshold matrix 601 is a threshold matrix having a screen line number of about 169.71 lpi and a screen angle of 45 ° in an image forming apparatus having a resolution of 1200 dpi. The threshold value matrix 601 is composed of four halftone dot cells (602 to 605) each having 50 threshold values, and is an array of threshold values having a width of 20 and a height of 10. The halftone cells 602 to 605 are all the same size (threshold number) but have different threshold values. Since gradations can be expressed not in halftone cells but in the entire threshold matrix, this is an effective method when using small halftone cells, and is generally called a submatrix method.

  In AM screen processing using a threshold matrix, the pixels of the image data 501 correspond to the thresholds of the threshold matrix 601. When a pixel value is sequentially received from the image data 501 as a pixel of interest, a corresponding threshold value is acquired from the threshold matrix 601 and the pixel and the threshold value are compared. As shown in FIG. 7, the threshold matrix 601 is arranged (tiled) in a tile shape with respect to the image data 501 while shifting the threshold matrix 601 so that four halftone cells 602 to 605 are continuous. The threshold matrix 601 is formed so that four halftone cells 602 to 605 are continuous by shifting 10 pixels in the X-axis direction every 10 pixels in the Y-axis direction continuously in the X-axis direction. . In this way, the value of the target pixel is compared with the corresponding threshold value, and as a result, “1” is output if the pixel value is the same or larger than the threshold value, and “0” is output otherwise. Convert from bit to 1 bit.

  Next, with reference to FIGS. 8, 9, 10, 11, 12, and 13, the CMYK total four-color color screen set according to the present embodiment will be described in detail.

  FIG. 8 shows an example of the processing result of the C plate generated by the AM screen processing by the irrational tangent method in this embodiment. The screen line number is about 169.71 lpi and the screen angle is 15 °. FIG. 9 shows an example of the processing result of the M plate generated by the AM screen processing by the irrational tangent method in the present embodiment. The screen line number is about 169.71 lpi and the screen angle is 75 °. FIG. 10 is an example of the processing result of the Y plate generated by the AM screen processing by the irrational tangent method in this embodiment, and the screen line number is about 183.28 lpi and the screen angle is 30 °. FIG. 11 is an example of the processing result of the K version generated by the AM screen processing using the rational tangent threshold matrix 601 in the present embodiment. The processing result of FIG. 11 is that the number of screen lines is approximately 169.71 lpi and the screen angle is 45 ° as described above. FIG. 12 is a graph in which the processing results of the four color plates of CMYK in FIGS. FIG. 13 is an example of a processing result of generating a screen having a screen line number of about 169.71 lpi and a screen angle of 45 ° using AM screen processing by an irrational tangent method.

  In this embodiment, as shown in FIGS. 8 to 11, the K plate is processed by AM screen processing using the threshold matrix 601 of FIG. 6, and the other three CMY color plates are processed by AM screen processing by the irrational tangent method. The screen lines of the C and M plates are set to about 169.71 lpi, which is the same as that of the K plate, and the screen angles are set to 15 ° and 75 ° which are 30 degrees apart from the K plate. In addition, the Y version, which has the highest brightness and is visually inconspicuous, has a screen line count of approximately 183.28 lpi, which is 1.08 times higher than the other colors, and a screen angle of 30 ° more than 15 degrees away from the other colors. Set to The Y version is set at an angle of 15 ° that is likely to cause interference with other colors due to its visually inconspicuous characteristics. However, by using a higher number of lines than other colors, the interference is released to a higher frequency. Making it more difficult to see visually.

  Usually, when the threshold matrix of the above condition is created using the supercell method, the size of the matrix becomes very large, so that the memory capacity for storing it becomes enormous. On the other hand, if the size of the threshold matrix is limited, the number of screen lines and the angles that can be created are far from the above conditions, and the optimization of the rosette becomes insufficient. However, in the present embodiment, as can be seen from the processing result of FIG. 12, it can be seen that the rosette, which is the minimum period of moire that appears when multiple colors overlap, is optimized regardless of the memory capacity. FIG. 13 shows the result of AM screen processing by the irrational tangent method having the same screen line number and angle as when the threshold matrix of the rational tangent method of FIG. 11 is used. It can be seen that there are many variations in halftone dot size and surrounding irregularities. If this is used for the K version, which has the lowest brightness and is visually noticeable, the entire image may appear to be cluttered. In this embodiment, the threshold of the rational tangent method in FIG. Since the matrix is used, the roughness of the entire image can be minimized.

  In this embodiment, the number of screen lines of the Y plate is set to 1.08 times higher than that of the other colors. However, the number of screen lines is not limited to this, and other colors are used to release interference to a higher frequency. It goes without saying that a higher number of lines is sufficient.

  In addition, the screen number of screens of the K plate is 169.71 lpi and the screen angle is 45 °, but this is not restrictive, and it goes without saying that the number of lines and angles that can be generated by the threshold matrix by the rational tangent method are sufficient. Yes. Further, it goes without saying that the K-threshold threshold matrix may be created using the supercell method as long as the memory capacity of the image forming apparatus permits. Of course, in these cases, the number of lines and the angle of the three color plates of CMY are set so as to satisfy the above-mentioned conditions for the screen of the K plate.

  The value output from the intermediate length processing unit 302 is 1 bit. For example, if the halftone dot pattern 501 has a plurality of hierarchies according to the output gradation value, multilevel output is possible. The number of output bits is not limited.

  From the above, according to the present embodiment, in the color plate using the AM screen processing by the irrational tangent method, the necessary memory capacity is constant regardless of the number of lines and the angle of the screen, and the number of screen lines of the K plate It is possible to set the number of lines and the angle of the screen of the color plate according to the. Therefore, it is possible to optimize the rosetta for various screen lines without increasing the memory capacity. Furthermore, the visually conspicuous K version uses a rational tangent threshold matrix with no variation in halftone dot size, so that the entire image can be minimized.

  In this embodiment, only the partial configuration of the image processing for printing in FIG. 3 is different from the above-described embodiment. Therefore, the same parts as those of the above-described embodiment are designated by the same reference numerals and omitted, and only different parts will be described below.

  First, image processing for printing in the present embodiment will be described in detail with reference to FIG. In this embodiment, the image processing unit 1401 is obtained by replacing the irrational screen processing unit 306 of the image processing unit 301 with an error diffusion processing unit 1402.

  In FIG. 14, reference numeral 1401 denotes an image processing unit that performs image processing for printing in the controller 102. The image data and attribute data input to the image processing unit 1401 are subjected to color correction processing in the color correction unit 302 and gamma correction processing in the gamma correction unit 303. Thereafter, the above-described AM screen processing is performed in the irrational screen processing units 304 and 305 and the rational screen processing unit 307, and the error diffusion processing described later is performed in the error diffusion processing unit 1402. As a result, the pixel value is converted from 8-bit image data to 1-bit printable data and sent to the printer unit 103.

  Next, the error diffusion processing performed by the error diffusion processing unit 1402 of the previous operation will be described in detail with reference to FIG.

  The error diffusion processing unit 1402 receives the value of one pixel as an input sequentially from the image data 501 in which pixels having an 8-bit data amount are arranged in a grid at equal intervals. Thereafter, it is compared with a predetermined threshold value (127 in the present embodiment). As a result, “1” is output if the pixel value is equal to or larger than the threshold value, and “0” is output otherwise. Convert to 1 bit. At the same time, the difference between the pixel value and the threshold value is diffused to the surrounding pixels.

  Next, a screen set of four color plates of CMYK in this embodiment will be described in detail with reference to FIGS.

  FIG. 15 is an example of the processing result of the Y version generated by the error diffusion processing in this embodiment.

  As mentioned above, the screen number of the K plate is about 169.71 lpi, the screen angle is 45 °, the C plate and the M plate have the same number of lines as the K plate, and the screen angles are set to 30 ° apart. The In addition, in the present embodiment, as shown in the processing result of FIG. 15, the Y plate uses an error diffusion process with less periodicity and relatively dispersed dots. Thereby, since the periodicity of the Y plate is reduced, it is possible to eliminate interference caused by a 15 ° relationship with other colors.

  In this embodiment, the error diffusion processing unit uses an error diffusion method, but is not limited thereto. For example, the average error minimization method, the average density preservation method, the blue noise mask method, etc. have little periodicity and dots are compared. Needless to say, any method that distributes automatically can be used.

  From the above, according to the present embodiment, it is possible to optimize the rosette for various screen lines without increasing the memory capacity, and the rational tangent threshold matrix is used for the visually prominent K version. Therefore, the roughness of the entire image can be minimized. In addition, by applying an error diffusion process with less periodicity to the Y plate, it is possible to eliminate interference caused by a 15 ° relationship with other colors.

  In this embodiment, only the partial configuration of the image processing for printing in FIG. 3 is different from the above-described embodiment. Therefore, the same parts as those of the above-described embodiment are designated by the same reference numerals and omitted, and only different parts will be described below.

  First, image processing for printing in the present embodiment will be described in detail with reference to FIG. In this embodiment, the image processing unit 1601 is obtained by changing the irrational screen processing unit 306 of the image processing unit 301 to a rational number screen processing unit 1602.

  In FIG. 16, an image processing unit 1601 performs image processing for printing in the controller 102. The image data and attribute data input to the image processing unit 1601 are subjected to color correction processing in the color correction unit 302 and gamma correction processing in the gamma correction unit 303. Thereafter, the screen processing described above is performed in the irrational screen processing units 304 and 305 and the rational number screen processing units 307 and 1402. As a result, the pixel value is converted from 8-bit image data to 1-bit printable data and sent to the printer unit 103.

  Next, AM screen processing using a rational tangent threshold matrix performed by the rational number screen processing unit 1602 will be described in detail with reference to FIGS.

  FIG. 17 is an example of a rational tangent threshold matrix, and FIG. 18 is a diagram schematically showing AM screen processing using the threshold matrix of FIG.

  In FIG. 17, a rational tangent threshold matrix 1701 is a threshold matrix having a screen line number of 300 lpi and a screen angle of 90 ° in an image forming apparatus having a resolution of 1200 dpi. The threshold matrix 1701 is composed of 16 halftone dot cells (1702 to 1717) each having 16 threshold values, and is an array of threshold values having a width of 16 and a height of 16. The halftone cells 1702 to 1717 are all the same size (threshold number) but have different threshold values.

  Similar to the rational number screen processing unit 307, the rational number screen processing unit 1602 receives pixel values as sequential pixels of interest from the image data 501, acquires corresponding threshold values from the threshold value matrix 1701, and compares the pixel values with the threshold value values. To do. As shown in FIG. 18, the threshold matrix 1701 is tiled (tiled) with respect to the image data 501 such that 16 halftone cells 1702 to 1717 are continuous. In this way, the value of the target pixel is compared with the corresponding threshold value, and as a result, “1” is output if the pixel value is the same or larger than the threshold value, and “0” is output otherwise. Convert from bit to 1 bit.

  Next, a screen set of four color plates of CMYK in this embodiment will be described in detail with reference to FIGS.

  FIG. 19 shows an example of the processing result of the Y plate generated by the AM screen processing using the threshold matrix 1701 in this embodiment.

  As mentioned above, the screen number of the K plate is about 169.71 lpi, the screen angle is 45 °, the C plate and the M plate have the same number of lines as the K plate, and the screen angles are set to 30 ° apart. The In addition, in this embodiment, as shown in the processing result of FIG. 19, the Y matrix uses a rational tangent threshold matrix with little variation in halftone dot size. As a result, although it is not visually conspicuous, artifacts such as roughness due to variation in halftone dot size when using AM screen processing by irrational tangent method for Y plate and worm noise when using error diffusion processing are used. Occurrence can be prevented. Furthermore, by using a sufficiently higher number of lines than the other color plates, the interference caused by the 15 ° relationship with other colors can be released to a higher frequency, making it more difficult to see visually.

  In the present embodiment, the screen line number of the Y plate is 300 lpi and the screen angle is 90 °. However, the present invention is not limited to this, and the threshold matrix has a line number higher than other colors and is based on the rational tangent method. It goes without saying that the number of lines and the angles that can be generated by the above are sufficient. Further, it goes without saying that the Y-threshold threshold matrix may be created using the supercell method within the range allowed by the memory capacity of the image forming apparatus.

  From the above, according to the present embodiment, it is possible to optimize the rosette for various screen lines without increasing the memory capacity, and the rational tangent threshold matrix is used for the visually prominent K version. Therefore, the roughness of the entire image can be minimized. In addition, by performing AM screen processing using the threshold matrix of the rational tangent method on the Y version, it is possible to prevent further reduction in roughness and generation of artifacts such as worm noise. In addition, by setting the number of screen lines of the Y plate sufficiently higher than that of other colors, it is possible to release interference caused by the relationship with other colors to a higher frequency and make it difficult to see visually.

(Other embodiments)
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

102 Controller unit 103 Printer unit 105 Memory 301 Image processing unit 302 Color correction unit 303 Gamma correction unit 304 Irrational screen processing unit 305 Irrational screen processing unit 306 Irrational screen processing unit 307 Rational number screen processing unit

Claims (13)

A printing apparatus that performs screen processing on first image data, second image data, and third image data, and prints a result of the screen processing using three color materials,
Means for performing rational screen processing with a screen angle of 45 degrees on the first image data;
And a means for performing irrational screen processing with a screen angle other than 45 degrees on the second and third image data. A printing apparatus that performs screen processing on first image data, second image data, and third image data, and prints a result of the screen processing using three color materials,
Means for performing rational screen processing on the first image data;
Means for performing irrational screen processing with a screen angle different from the screen angle of the rational number screen processing on the second and third image data;
A printing apparatus comprising: printing means for printing a result obtained by performing rational screen processing on the first image data with a black color material, and printing the remaining image data with a cyan and magenta color material. .   The screen angles of the irrational screen processing performed on the second and third image data are different from each other, and both screen angles are the rational screen processing performed on the first image data. The printing apparatus according to claim 1, wherein the screen angle is 30 degrees apart.   The printing apparatus according to claim 3, wherein the number of lines of screen processing performed on the first image data, the second image data, and the third image data is the same.   Furthermore, the screen processing is performed on the fourth image data, and the result of the screen processing is printed with the corresponding color material, so that it is a device that performs printing with a total of four color materials. The printing apparatus according to claim 1, wherein the printing apparatus is a printer.   The screen processing performed on the fourth image data has a screen angle of 15 degrees or more and a higher number of lines than screen processing performed on other image data. The printing apparatus according to claim 5, wherein: A printing method in which screen processing is performed on first image data, second image data, and third image data, and a result of the screen processing is printed with three color materials,
Performing rational screen processing having a screen angle of 45 degrees on the first image data;
And an irrational screen process having a screen angle other than 45 degrees with respect to the second and third image data. A printing method in which screen processing is performed on first image data, second image data, and third image data, and a result of the screen processing is printed with three color materials,
Performing rational number screen processing on the first image data;
Performing irrational screen processing having a screen angle different from the screen angle of the rational number screen processing on the second and third image data;
And a printing step of printing a result obtained by performing rational screen processing on the first image data with a black color material and the remaining image data with a cyan and magenta color material. .   The screen angles of the irrational screen processing performed on the second and third image data are different from each other, and both screen angles are the rational screen processing performed on the first image data. The printing method according to claim 7 or 8, wherein the screen angle of the screen is 30 degrees apart.   The printing method according to claim 9, wherein the number of lines of screen processing performed on the first image data, the second image data, and the third image data is the same.   Furthermore, the screen processing is performed on the fourth image data, and the result of the screen processing is printed with the corresponding color materials, so that printing is performed with a total of four color materials. The printing method according to claim 7, wherein the printing method is any one of claims 7 to 10.   The screen processing performed on the fourth image data has a screen angle of 15 degrees or more and a higher number of lines than screen processing performed on other image data. The printing method according to claim 11, wherein:   A computer-readable program for causing a computer to execute the printing method according to any one of claims 7 to 12.

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