JP2007312033A - Image processor and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor which generates suitable dither images for each image that is processed by the image processor. <P>SOLUTION: The image processor which generates the dither images represented by a multi-valued dither method has: a threshold table holding means for holding a table of thresholds for generating the dither images; an addition value register which holds addition values to be added for each element in the threshold table; and a threshold varying means for varying values of the thresholds by adding addition values for each of the elements in the threshold table. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing apparatus and an image processing method.

  2. Description of the Related Art Conventionally, an image processing apparatus sometimes performs a process of reducing the gradation of an image by performing a dither process on the image data. For example, in an image forming apparatus, an image formed on a sheet can be made suitable by performing dither processing on input image data.

  In recent years, the price of printers has been falling, while the price of consumables such as toner or ink cartridges has been maintained without much drop. Get higher. Therefore, a technique of an image processing apparatus that reduces the amount of toner used is disclosed.

For example, in a color image processing apparatus disclosed in Japanese Patent Laying-Open No. 2005-86719 (Patent Document 1), a dither matrix used for dither processing for reducing the gradation of an image is replaced with a dither matrix for normal mode and a toner save. When the dither matrix for the toner save mode is selected, the amount of toner used is reduced.
JP 2005-86719 A Japanese Patent No. 2830690

  However, in the technique disclosed in Patent Document 1, the image processing apparatus holds a dither matrix (dither table) for toner save mode in order to reduce the amount of toner used. Depending on the nature of the image, reducing the amount of toner used may cause image quality problems. For example, in the case of a character image, the amount of toner used is reduced to cause blurring in characters.

  In order to solve this, the dither table used for processing is switched by inputting, for example, whether the image to be formed is a character image or an image such as a photograph or a figure from an operation panel or the like of the apparatus. It is possible. In addition, when a character image and an image such as a photograph or a figure are mixed in one image, the tag bit disclosed in Japanese Patent No. 2830690 (Patent Document 2) is used, and the image is previously stored. By maintaining the property of the area to which each pixel that constitutes belongs, a suitable dither table or the like can be selected for each pixel.

  However, retaining the data for the toner save mode in addition to the data for the normal mode requires providing more memory for the image processing apparatus than in the case of only the normal mode, which reduces the cost of the image processing apparatus. It becomes a factor to raise. One of the purposes for reducing the amount of toner used is to keep the cost for printing as low as possible. Therefore, it is not preferable that the cost of the image processing apparatus be increased.

  The dither processing is not limited to the toner save mode, such as reducing the gradation to add a special effect to the image, or performing dither processing suitable for a high-definition image. Retaining a dither table corresponding to the dither processing of the image is not only expensive due to an increase in memory, but also because other dither tables of the dither table held in advance cannot be used. There was a problem that was limited.

  Therefore, it is possible to switch multiple dither tables with as little memory as possible so as to generate dither images corresponding to the nature of the image or each area constituting the image, and also according to the content of the required processing. However, there has been no such image processing apparatus until now.

  The present invention has been invented in order to solve these problems in view of the above points, and provides an image processing apparatus that generates a suitable dither image for each image processed by the image processing apparatus. It is aimed.

  In order to achieve the above object, the image processing apparatus of the present invention employs the following configuration.

  An image processing apparatus according to the present invention is an image processing apparatus that generates a dither image expressed by a multi-value dither method, and includes a threshold value table holding unit that holds a threshold value table for generating the dither image, and the threshold value An addition value register that holds an addition value that is a value to be added for each element of the table, and a threshold value changing unit that changes the threshold value by adding the addition value for each element of the threshold value table. be able to.

  In this way, by adding the addition value stored in the register to the threshold value for generating the dither image and changing the threshold value, a suitable dither image can be generated for each image processed by the image processing apparatus. .

  In order to achieve the above object, the image processing apparatus according to the present invention further includes a threshold value stored in the threshold value table and a threshold value changed by the threshold value changing unit based on a property of a region to which a pixel to be processed belongs. And a selection unit that selects one of the two.

  As described above, it is possible to provide an image processing apparatus that generates a suitable dither image for each region of an image by selecting a threshold value based on the property of the region to which the pixel belongs.

  In order to achieve the above object, the image processing apparatus according to the present invention may further include a region property holding unit that holds the property of the region to which the pixel belongs.

  Thus, by acquiring the property of the region to which the pixel belongs from the region property holding means, it is possible to provide an image processing apparatus that selects a threshold based on the property.

  In order to achieve the above object, the image processing method of the present invention includes threshold value table holding means for holding a threshold value table for generating a dither image expressed by a multi-value dither method, and elements of the threshold value table. An image processing method for generating the dither image in an image processing apparatus having an addition value register that holds an addition value that is an addition value every time, and adding the addition value for each element of the threshold value table It can be set as the structure which has the threshold value change step which changes the value of a threshold value.

  In order to achieve the above object, the image processing method of the present invention further includes a threshold value stored in the threshold value table and a threshold value changed in the threshold value changing step based on a property of a region to which a pixel to be processed belongs. And a selection step for selecting one of the two.

  In order to achieve the above object, the image processing method of the present invention is further configured to have a property acquisition step of acquiring the property from a region property holding means for holding the property of the region to which the pixel belongs. be able to.

  According to the image processing apparatus of the present invention, it is possible to provide an image processing apparatus that generates a suitable dither image for each image processed by the image processing apparatus.

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

  In this embodiment, an example of a printer is described as an image processing apparatus. However, the image processing apparatus of the present invention is not limited to a printer, and may be an image processing apparatus that generates a dither image.

  In order to facilitate understanding of the image processing apparatus and the image processing method of the present invention, the image processing apparatus according to the prior art will be described prior to the description of the present invention.

(An example of an apparatus for processing an image formed on a paper surface.)
FIG. 1 shows a process in which image data processed by a personal computer (hereinafter referred to as “PC”) 1 is processed by a printer controller 2, formed on a paper surface by a printer engine 9, and output. It is a figure explaining the process part provided in.

  The printer controller 2 performs a process of expanding the input compressed image data and converting it into image data to be output to the printer engine. The printer controller 2 includes a reception memory 21, a decompression processing unit 22, a frame memory 23, a color conversion unit 24, a black generation / under color removal (hereinafter referred to as “BG / UCR”) unit 25, The γ correction unit 30, the multi-value dither calculation unit 40, the dither table holding unit 50, the pulse width modulation (hereinafter referred to as “PWM”) unit 26, and the line memory 27 are configured.

  The reception memory 21 is a memory that stores compressed image data input to the printer controller 2. The format of the compressed image data received by the reception memory 21 is, for example, a data format generated by JPEG (ISO / ICE IS 10918-1), MH (Modified Huffman) method, or BTC (Block Truncation Coding) method. .

  The decompression processing unit 22 performs a process of decompressing the compressed image data stored in the reception memory 21 and storing it in the frame memory 23. The frame memory 23 is a memory for storing the decompressed image. The image stored in the frame memory 23 has a color bitmap format, and each pixel is expressed in the RGB color space.

  The color conversion unit 24 converts each pixel of the image data stored in the frame memory 23 from an RGB color space to an expression in the CMY color space. This is because a personal computer display or the like uses an RGB color space that is an additive color mixture because the color is recognized when the pixels themselves emit light, whereas an image formed on a sheet of paper contains light including RGB. This is because the CMYK color space, which is a subtractive color mixture, is used because the color is recognized by the reflected light partially absorbed when applied. Black K is generated by the next BG / UCR unit 25.

  The BG / UCR unit 25 generates black (K1) from pixel values (C0, M0, Y0) expressed in the CMY color space, and performs undercolor removal from (C0, M0, Y0) (C1 , M1, Y1) to convert each pixel into a representation in the CMYK color space. In the generation of black, for example, the minimum value of C0, M0, and Y0 is set to K1. In the black generation, the minimum value of C0, M0, and Y0 may be set as m, and a value corresponding to m in a black generation table (not shown) may be acquired and set as K1. For the undercolor removal, for example, the minimum value of C0, M0, and Y0 is m0, and the value obtained by subtracting m0 from C0, M0, and Y0 is C1, M1, and Y1, respectively. Undercolor removal also obtains m1, which is a value corresponding to m0, from a not-shown undercolor removal table, and subtracts m1 from C0, M0, and Y0, respectively, as C1, M1, and Y1. Also good.

  The γ correction unit 30 performs a process of correcting the pixel values determined to correspond to the light emission characteristics of the display so as to correspond to the characteristics of the printer. FIG. 2 shows a principle diagram of γ correction. FIG. 2 shows the correspondence between the input value (X) and the output value (Y). The straight line C0 is the case where the correspondence between X and Y is the best, and X and Y are directly proportional to the slope 1. A curve C1 is an example of the light emission characteristics of the display, and an image handled on the PC is corrected so that the image having the characteristics of the curve C1 is recognized as a straight line C0. The correction is realized by multiplying the value of the curve C2. By giving the pixel the characteristic of the curve C2, it is recognized as a straight line C0 on the display. A curve C2 is a characteristic curve for correcting the curve C1 to be C0.

  The multi-value dither calculation unit 40 performs processing for reducing the gradation of each pixel constituting the image. The multi-value dither calculation unit 40 reads the threshold value corresponding to the coordinates of each pixel from the dither table holding unit 50 and performs dither processing.

  FIG. 3 shows a configuration example of a circuit that realizes the dither processing. In FIG. 3, the threshold value B stored in the dither table holding unit 50 and the halftone delta value holding unit 59 are stored for the pixel (value A) expressed by 8 bits output from the γ correction unit 30. The processing based on the halftone delta value D is performed, and a pixel represented by 4 bits is output. The output value I is 0x0 when the value A is less than or equal to the threshold B, and when the value A is greater than or equal to the value obtained by adding the network delta value D to the threshold B, the maximum value 0xF and the value A are When the value is larger than the threshold value B and less than the value obtained by adding the network delta value D to the threshold value B, the value is greater than 0 and less than 0xF.

  3 subtracts a value C obtained by subtracting a threshold value B corresponding to the coordinates of the pixel stored in the dither table holding unit 50 from the value A of the 8-bit pixel output from the γ correction unit 30. Generate. An example of the dither table stored in the dither table holding unit 50 is shown in FIG. The dither matrix in FIG. 4 is a dot dispersion type.

  In FIG. 4, four cells D1 to D4 are arranged. This is called a dither matrix with a variance of 4. In FIG. 4, when 20 pixels are defined as one block in the vertical and horizontal directions, the blocks satisfy the periodic boundary condition. The periodic boundary condition is, for example, that α with f (x) = f (x + α) exists for a certain function f (x).

  Each cell has a threshold value corresponding to 20 pixels. The threshold value is a multiple of 16, or a number obtained by adding a constant to a multiple of 16, or a maximum value of 255, and the constant is a value common to the threshold values in the cell.

  The subtractor 41 also compares the pixel value A with the threshold value B, and outputs 1b when A> B and 0b when A ≦ B as the value G. Note that “b” at the end of the numeric string indicates that the numeric string is in binary notation.

  The comparator 42 compares the output value C of the subtractor 41 with the network delta value D stored in the network delta value holding unit 59. When C ≧ D, 1b is set, and when C <D, 0b is set. , Output as value F. Here, the halftone delta value D is a value obtained by multiplying the dispersion of the dither matrix and the number of stages of pulse width modulation described later, and represents the number of gradations of pixels generated by the dither processing.

  The OR circuit 43 performs arithmetic processing on the value E, which is the lower n bits of the value C output from the subtractor 41, and the 1-bit value F output from the comparator 42. The bit number n of the value E is based on the number of gradations determined by the network delta value D, and is 4 here. The OR circuit 43 performs an OR operation between 0000b and the value E when the value F is 0b, and performs an OR operation between 1111b and the value E when the value F is 1b.

  The AND circuit 44 performs an arithmetic process on the value G (0b or 1b) output from the subtractor 41 and the value H output from the OR circuit 43, and outputs a 4-bit value I. When the value G is 0b, an AND operation of 0000b and the value H is performed, and when the value G is 1b, an AND operation of 1111b and the value H is performed.

  The PWM unit 26 performs a process of converting the pixel value expressed by 4 bits output from the multi-value dither calculation unit 40 into a PWM signal that is a signal expressed by a pulse width. FIG. 5 shows an example of pixel values, PWM signals, and dots printed by the PWM signals. When the pixel value is 0, there are no dots to be printed, and when the pixel value is 0x3, a ¼ width pulse is generated. Similarly, when the pixel value is 0x4, a 1/2 width pulse is generated, when the pixel value is 0xB, a 3/4 width pulse is generated, and when the pixel value is 0xF, a full width pulse is generated. .

  The line memory 27 is a memory for storing image data to be transmitted to the printer engine 9, and stores an image corresponding to the scanning direction of the printer engine 9. Thereby, the printer engine 9 can process the received image data in a pipeline manner.

  The printer engine 9 receives the image data transmitted from the printer controller 2, forms it on a paper surface, and outputs it.

  The PC 1 performs processing for generating image data and transmitting it to the printer controller 2. The PC 1 is configured to include an image data generation unit 11, a compression processing unit 12, and a transmission memory 13. The image data generation unit 11 is a device or application that generates image data. The image data generated by the image data generation unit 11 is expressed in the RGB color space, but may be data expressed in other color spaces.

  The compression processing unit 12 compresses the image data generated by the image data generation unit 11 and generates compressed image data. The compression processing unit 12 compresses image data by JPEG, MH, BTC, or other methods.

  The transmission memory 13 is a memory for storing the compressed image data compressed and generated by the compression processing unit 12, and the image data stored in the transmission memory 13 is transmitted to the printer controller 2.

(Example of a device that realizes a toner save mode by γ correction.)
FIG. 6 shows an example of an apparatus that realizes the toner save mode by γ correction. In FIG. 6, as in FIG. 1, the image data processed by the PC 1 is processed by the printer controller 2, formed on the paper surface by the printer engine 9, and output. In FIG. 6, description of an apparatus having the same configuration and function as in FIG. 1 is omitted here.

  The PC 1 in FIG. 6 is configured to include an image data generation unit 11, a compression processing unit 12, and a transmission memory 13. In the image data generation unit 11, image data is generated, and attribute determination is performed for each region included in the image data. The attribute is divided into, for example, a character area, a photograph area, or a drawing area. Then, for each pixel constituting the image data, a tag bit that is a bit representing the attribute of the region to which the pixel belongs is generated. For example, in the case of a character area, the tag bit value is 1b, and in the case of a non-character area that is not a character, the tag bit value is 0b.

  The tag bits generated in the image data generation unit 11 are stored in the transmission memory 13 and transmitted to the printer controller 2 in the same manner as the compressed image data.

  The printer controller 2 in FIG. 6 includes a selection circuit 33 and tag bit storage means 60 in addition to the printer controller 2 in FIG. The printer controller 2 in FIG. 6 further includes a normal γ correction unit 31 and a toner save γ correction unit 32 as a γ correction unit.

  The reception memory 21 of the printer controller 2 stores compressed image data and tag bits. The compressed image data is decompressed by the decompression processing unit 22, the image data is stored in the frame memory 23, and the tag bit is stored in the tag bit storage unit 60. Note that the compressed image data and the tag bit may be configured as one file. Thereby, the operator can handle the compressed image data without being aware of the correspondence between the compressed image data and the tag bit. The compressed image data and the tag bit may be configured as separate files, and may be associated with each other according to a predetermined rule.

  The image data stored in the frame memory 23 is converted into image data expressed by the CMYK color space in the color conversion unit 24 and the BG / UCR unit 25. Image data expressed by the CMYK color space is subjected to γ correction in the normal γ correction unit 31 and the toner save γ correction unit 32. Here, the normal γ correction unit 31 performs the same processing as the γ correction unit 30 of FIG. 1, and the toner save γ correction unit 32 uses the toner value rather than the pixel value based on the output of the normal γ correction unit 31. Γ correction is performed so as to reduce the amount of use.

  The selection circuit 33 acquires the tag bit corresponding to the pixel to be processed from the tag bit storage unit 60, and based on the contents of the tag bit, outputs the normal γ correction unit 31 and the toner save γ correction unit 32. Select. For example, if the pixel is included in the character area when the tag bit is 1b, the output of the normal γ correction unit 31 is selected for the pixel with the tag bit 1b, and the pixel with the tag bit 0b is selected. The output of the toner saving γ correction unit 32 is selected.

  The selection circuit 33 may be provided in front of the γ correction unit so that the process of the γ correction unit selected from the normal γ correction unit and the toner saving γ correction unit is executed. Good. Thereby, for example, when the printer controller is realized by software, the processing speed can be increased.

  The output of the selection circuit 33 is processed by the multi-value dither calculation unit 40 and the PWM unit 26 and stored in the line memory 27.

(Example of a device that realizes a toner save mode by dithering.)
FIG. 7 is a diagram illustrating an example of an apparatus included in a printer controller that is an image processing apparatus of the present invention, and is an example of an apparatus that realizes a toner save mode by dither processing. In FIG. 7, as in FIG. 1, the image data processed by the PC 1 is processed by the printer controller 2, formed on the paper surface by the printer engine 9, and output. In FIG. 7, description of devices having the same configurations and functions as those in FIG. 1 is omitted here.

  The printer controller 2 in FIG. 7 includes a register 51, an arithmetic circuit 52, a selection circuit 53, and tag bit storage means 60 in addition to the printer controller 2 in FIG. The register 51 is a register that stores an addition value to be added to the threshold for dither processing stored in the dither table holding unit 50. The added value stored in the register 51 may be changed according to the nature of the image area. Thus, toner save processing corresponding to the nature of the image area can be performed.

  The arithmetic circuit 52 is a circuit that adds the addition value stored in the register 51 to the threshold value stored in the dither table holding unit 50. Thereby, the threshold value used for dither processing can be changed.

  The selection circuit 53 is means for selecting one of the threshold value stored in the dither table holding unit 50 and the threshold value output by the arithmetic circuit 52. The selection circuit 53 may perform selection based on the content of the bit corresponding to the pixel to be processed among the tag bits stored in the tag bit storage unit 60. Thereby, the threshold value used for the dither process can be selected based on the property of the region to which the pixel belongs.

(The figure of the example of a function structure of the image processing apparatus of this invention.)
FIG. 8 is a diagram illustrating an example of a functional configuration of the image processing apparatus according to the present invention. The image processing apparatus of the present invention is an image processing apparatus that performs multi-value dither processing, and is configured to perform different dither processing in, for example, toner save mode and normal mode. The image processing apparatus of FIG. 8 is configured to include a multi-value dither operation unit 400, a dither table holding unit 500, an addition value register 510, a threshold value changing unit 520, a selection unit 530, and an area property holding unit 600.

  The multi-value dither calculation unit 400 is a unit that performs dither processing on each pixel of the input image data based on the threshold value stored in the dither table holding unit 500. The dither table holding unit 500 is a unit that holds a threshold value used for dither processing. The threshold value used for the dither processing is configured to correspond to the coordinates of the pixels constituting the image.

  The addition value register 510 is a register that stores an addition value to be added to the threshold value stored in the dither table holding unit 500. The added value stored in the added value register 510 may be changed according to the nature of the image or the area of the image.

  The threshold value changing means 520 is a means for changing the threshold value used for the dither processing by adding the addition value stored in the addition value register 510 to the threshold value stored in the dither table holding means 500.

  The selection unit 530 is a unit that selects one of the threshold value stored in the dither table holding unit 500 and the threshold value output by the threshold value changing unit 520. The selection unit 530 may perform selection based on the property of the region to which the pixel to be processed belongs. The property of the region to which the pixel to be processed belongs may be acquired from information held by the region property holding unit 600.

  The area property holding unit 600 is a unit that holds the property of each area of the image. The region property holding unit 600 may hold the property of the region to which the target pixel belongs by using a tag bit corresponding to each pixel constituting the image data. The area property holding means 600 may also hold the property of the area of the image divided by performing predetermined processing on the image data in association with the area range.

  The multi-value dither calculation means 400 is a means for performing dither processing on the image data, and performs dither processing based on the threshold selected by the selection means 530. The multi-value dither operation means 400 may be constituted by a circuit shown in FIG. 3, for example.

(The flowchart of the process of the image processing method of this invention.)
FIG. 9 is a diagram for explaining an example of the processing flow of the image processing method of the present invention. In FIG. 9, in the toner save mode, the threshold value used for dither processing is changed for the pixels in the area excluding the character area.

  In step S201 in FIG. 9, the selection unit 530 determines whether the toner save mode is selected. The selection of the toner save mode may be performed, for example, by inputting from an input unit (not shown) by the operator. The selection of the toner save mode may also be performed based on the detection of the remaining amount of toner by the image processing apparatus. If the toner save mode is selected, the process proceeds to step S202. If the toner save mode is not selected, the process proceeds to step S205.

  In step S202, the region property holding unit 600 determines the attribute of the region to which the pixel to be processed belongs. If the area to which the pixel belongs is a character area, the process proceeds to step S205, and if not, the process proceeds to step S203. Note that the attribute of the region to which the pixel belongs may distinguish a region having a small number of colors such as computer graphics or a region such as a photograph in addition to the character region. Thereby, for example, a suitable dither process can be performed for each of a character region, a computer graphics region, and a region such as a photograph.

  In step S203, the threshold value changing unit 520 changes the threshold value by adding the addition value stored in the addition value register 510 to the threshold value stored in the dither table holding unit 500. Note that a plurality of addition values stored in the addition value register 510 may be held corresponding to the attribute of the region to which the pixel belongs. Further, it may be changed according to the attribute of the region to which the pixel belongs. Thereby, suitable dither processing corresponding to the attribute of the region to which the pixel belongs can be performed.

  In step S204, the selection unit 530 selects the threshold value changed in step S203. In step S205, the selection unit 530 selects a threshold value stored in the dither table holding unit.

  With the above processing, it is possible to perform dither processing according to the attribute of the region to which the pixel belongs.

  In the above embodiment, the image data expressed by the RGB color space generated by the PC 1 is compressed, the image data is expanded by the printer controller, converted into image data expressed by the CMYK color space, and γ correction is performed. However, the image processing apparatus or image processing method of the present invention is not limited to this configuration or method.

  The color system may be any of an RGB color space, a CMY color space, a CMYK color space, or another color space. The image data may not be subjected to compression and expansion processing. Further, γ correction may not be performed.

  The attribute of the area to which the pixel belongs is expressed by a tag bit, and the attribute of each area may be determined by the multi-value dither calculator 40.

  Further, the multi-value dither processing may be performed by an application or a device included in the PC 1 in addition to being performed by the printer controller 2.

  In the above embodiment, the dither image generated in each of the two modes of the toner save mode and the normal mode is described as an example. However, the image processing apparatus and the image processing method of the present invention are described above. In addition to the two modes, for example, by changing the addition value stored in the register, dither images generated in a plurality of toner save modes can be made suitable.

  Furthermore, the suitable and adaptive generation of the dither image is not limited to the toner save mode, but is an image processing apparatus or an image processing method for generating a dither image by changing the gradation, depending on various purposes. The present invention can be suitably or adaptively applied to an apparatus or method for generating a dither image. For example, this is effective when performing dither processing for adding a special effect to an image or performing dither processing suitable for a high-definition image.

Although the best mode for carrying out the invention has been described above, the present invention is not limited to the embodiment described in the best mode. Modifications can be made without departing from the spirit of the present invention.

The figure of the example of the apparatus which processes the image formed on a paper surface. The principle figure of (gamma) correction. The figure of the structural example of the circuit which implement | achieves a dither process. An example of a dot dispersion type dither table. An example of a PWM signal corresponding to a pixel value and dots printed by the PWM signal. The figure of the example of the apparatus which implement | achieves toner save mode by (gamma) correction. 1 is a diagram illustrating an example of an apparatus included in a printer controller that is an image processing apparatus of the present invention. The figure of the example of a function structure of the image processing apparatus of this invention. The figure of the example of the flow of a process of the image processing method of this invention.

Explanation of symbols

2 Printer Controller 40 Multilevel Dither Calculation Unit 50 Dither Table Holding Unit 51, 510 Addition Value Register 52 Calculation Circuit 53 Selection Circuit 60 Tag Bit Storage Unit 400 Multilevel Dither Calculation Unit 500 Dither Table Holding Unit
520 threshold value changing means 530 selection means 600 area property holding means

Claims (6)

An image processing apparatus for generating a dither image expressed by a multi-value dither method,
Threshold value table holding means for holding a table of threshold values for generating the dither image;
An addition value register that holds an addition value that is a value to be added for each element of the threshold table;
An image processing apparatus comprising: a threshold value changing unit that changes the value of the threshold value by adding the addition value for each element of the threshold value table.   The apparatus according to claim 1, further comprising a selection unit that selects one of a threshold value stored in the threshold value table and a threshold value changed by the threshold value changing unit based on a property of a region to which a pixel to be processed belongs. The image processing apparatus according to 1.   3. The image processing apparatus according to claim 2, further comprising region property holding means for holding the property of the region to which the pixel belongs. Threshold value table holding means for holding a threshold value table for generating a dither image expressed by a multi-value dither method;
An image processing method for generating the dither image in an image processing apparatus having an addition value register that holds an addition value that is a value to be added for each element of the threshold table,
An image processing method comprising: a threshold value changing step of changing a threshold value by adding the added value for each element of the threshold value table.   2. The method according to claim 1, further comprising a selection step of selecting one of a threshold value stored in the threshold value table and a threshold value changed in the threshold value changing step based on a property of a region to which a pixel to be processed belongs. 5. The image processing method according to 4.   6. The image processing method according to claim 5, further comprising a property acquisition step of acquiring the property from a region property holding unit that holds a property of the region to which the pixel belongs.

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