JP5740991B2 - Image processing apparatus and image processing method - Google Patents

Description

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

  A color printer analyzes PDL (Page Description Language), draws a multi-valued band image, performs color conversion, gradation processing, and encoding of the drawn band image, and stores the code for one page. After that, decrypt and print. Due to recent developments in semiconductor technology, such processing can be performed by hardware in part of processing performed by a CPU (Central Processing Unit).

  For example, Patent Document 1 discloses a technology that implements plane division processing including color conversion processing for a generated multi-value band image and halftone processing (gradation processing) by hardware. In Patent Documents 2 and 3, the drawing portion of a photographic image is made into hardware, and the speed-up is realized by pipelining the scaling processing and halftone processing of the source image of the photographic image for each horizontal line. Technology is disclosed. Further, in Patent Document 4, the generated multi-value band image is color-converted by a color conversion processing device, and then the halftone processing is pipelined by the halftone processing device, thereby realizing high speed. ing.

  In addition, with the recent development of semiconductor processes, the main memory DRAM (Dynamic Random Access Memory) has been speeded up, and accordingly, the transfer rate between the CPU and the memory controller has been speeded up. Began to require the cost of. Therefore, a manufacturer that manufactures a general-purpose CPU may connect an image processing ASIC to the standard bus of the general-purpose CPU when a general-purpose CPU incorporating a memory controller is used as a printer controller.

  For example, in Patent Document 5, image processing such as color conversion processing and gradation processing is realized by hardware, an RGB band image of a main memory is read through a bus, image processing is performed by pipeline processing, and image processing is performed. A technique for transferring a processing result to a main memory via a bus is disclosed.

  By the way, an image to be printed by a color printer is a white background color, and many portions of a graphics image or the like often have the same color. However, in conventional color printers, image processing is performed for each pixel of a band image, so even if pipeline processing is performed, hardware that performs image processing processes only one pixel per clock. I can't.

  Therefore, it is necessary to increase the clock frequency in order to meet the demand for printing a high-resolution image at high speed. However, in the semiconductor process technology, when the miniaturization advances and the distance between the transistor gates becomes narrower, the through current increases, and when the clock frequency increases, the heat generated by the through current becomes a problem. For this reason, it is difficult to use a high clock frequency in order to suppress current consumption of hardware that performs image processing.

  In addition, there is a method of speeding up the processing by performing parallel image processing using a plurality of logic circuits, but the memory capacity for gradation processing increases, the size of the semiconductor LSI increases, and the cost increases. Becomes higher. Specifically, for example, a color conversion processing apparatus in a color printer needs to have a 17 * 17 * 17 (4,913) word LUT (Look Up Table). In the gradation processing apparatus in the color printer, a total of four 32 * 32 dither size threshold tables are required, one for each CMYK component. Further, when the number of bits for gradation processing is four values, a configuration having three threshold tables requires 32 * 32 * 4 * 3 = 12,288 bytes of memory. When these image processing hardware and a plurality of memories are mounted on the ASIC, the size of the ASIC is increased and the cost is increased.

  Therefore, in Patent Document 6, color space conversion processing is performed on pixel values of even pixels only when even pixels and odd pixels included in the band image have the same pixel value. A technique is disclosed in which the processed pixel values are set as the pixel values of even-numbered pixels and odd-numbered pixels, and gradation processing is performed in parallel on even-numbered pixels and odd-numbered pixels.

  However, according to the technique disclosed in Patent Literature 6, when the pixel values of the even-numbered pixels and the odd-numbered pixels are the same, it is not necessary to perform the color space conversion processing of the odd-numbered pixels, and the image processing speed is increased. However, when the pixel values of even-numbered pixels and odd-numbered pixels are different, such as when the color changes alternately, such as an image where the color changes finely like a photographic image or a graphics brush pattern, etc. However, there is a problem that image processing must be performed for each of even-numbered pixels and odd-numbered pixels, and it is not possible to increase the speed of image processing.

  The present invention has been made in view of the above, and an object thereof is to provide an image processing apparatus and an image processing method capable of speeding up image processing.

In order to solve the above-described problems and achieve the object, the present invention provides a first storage unit that stores a first pixel value that is a pixel value of a pixel included in image data, Second storage means for storing a second pixel value when color space conversion processing is performed, reading means for reading a pixel value of a pixel included in output image data, and the read pixel value are the first storage Determination means for determining at a time whether or not each of the plurality of first pixel values stored in the means matches, and color space conversion processing is performed on pixel values that do not match the first pixel value among the read pixel values. Color conversion processing means to be performed, and second pixel value when color space conversion processing is performed on the first pixel value that matches the read pixel value among the second pixel values stored in the second storage means Color space conversion for the read pixel value And a selection means for selecting a pixel value in the case of performing management, the first memory means and said second storage means, wherein the first pixel value, the second pixel value, the association with each other When the selection means performs a color space conversion process on the read pixel value, the second pixel value stored in association with the first pixel value that matches the read pixel value. The pixel value is selected .

The present invention is also an image processing method executed by an image processing apparatus, wherein the image processing apparatus stores a first pixel value that is a pixel value of a pixel included in image data; Second storage means for storing a second pixel value when a color space conversion process is performed on the first pixel value, wherein the first storage means and the second storage means are the first pixels. A value and the second pixel value are stored in association with each other, and the reading unit reads the pixel value of the pixel included in the image data to be output; and the determining unit reads the pixel value A step of determining at a time whether or not each of the plurality of first pixel values stored in one storage means matches, and a pixel in which the color conversion processing means does not match the first pixel value among the read pixel values The process of performing color space conversion processing on the value and the selection means Of the second pixel value stored in the second storage means, a second pixel value in the case of performing color space conversion processing on the first pixel value matched with the read pixel values, the first pixel Selecting a second pixel value stored in association with the value as a pixel value when color space conversion processing is performed on the read pixel value.

  According to the present invention, when the pixel value of the pixel read from the image data matches the pixel value when the color space conversion process has been performed previously, the color space conversion for the pixel value of the pixel read from the image data is performed. Since there is no need to perform processing, the image processing can be speeded up.

FIG. 1 is a diagram illustrating a configuration example of a mechanism unit of a multicolor image forming apparatus to which an image processing apparatus and an image processing method according to the present invention are applied. FIG. 2 is a diagram illustrating an example of the hardware configuration of the electrical / control unit of the multicolor image forming apparatus according to the present embodiment. FIG. 3 is a flowchart showing an outline of processing in the multicolor image forming apparatus. FIG. 4 is a diagram for explaining a storage area of the main memory. FIG. 5 is a diagram illustrating a hardware configuration of the image processing unit. FIG. 6 is a block diagram illustrating a specific configuration of the matching pixel determination unit. FIG. 7 is a block diagram illustrating a specific configuration of the color restoration processing unit. FIG. 8 is a block diagram showing a specific configuration of the gradation processing unit. FIG. 9 is a diagram illustrating a configuration example of image data. FIG. 10 is a diagram illustrating a configuration example of image data. FIG. 11 is a diagram illustrating an example of a threshold matrix. FIG. 12 is a flowchart showing the flow of color space conversion processing and halftone processing. FIG. 13 is a flowchart for explaining gradation processing by the gradation processing unit.

  Exemplary embodiments of an image processing apparatus and an image processing method according to the present invention are explained in detail below with reference to the accompanying drawings.

  FIG. 1 is a diagram illustrating a configuration example of a mechanism unit of a multicolor image forming apparatus to which an image processing apparatus and an image processing method according to the present invention are applied. In this multicolor image forming apparatus, reference numeral 1 denotes a belt-like photoconductor as an image carrier, and the photoconductor 1 is rotatably supported by rotating rollers 2 and 3. It is rotated in the direction of arrow A by driving. On the outer periphery of the photoreceptor 1, a charging device 4 as a charging unit 4, a static elimination lamp L, and a cleaning blade 15 </ b> A for the photoreceptor 1 are arranged. At the downstream position of the charging device 4, there is an optical writing unit that is irradiated with laser light emitted from a laser writing unit 5 that is optical writing means.

  A multi-color developing device 6 in which a plurality of developing units (developing means) are supported in a switchable manner is disposed downstream of the optical writing unit. The multicolor developing device 6 includes a yellow developing unit, a magenta developing unit, and a cyan developing unit for each color of toner to be accommodated. A black developing unit 7 containing black toner is provided at the top of the multicolor developing device 6.

  Any one of these development units moves to a developable position in synchronization with the development timing of the corresponding color. The multicolor developing device 6 has a function of selecting any developing unit by rotating 120 degrees on the circumference. When these developing units operate, the black developing unit 7 moves to a position separated from the photoreceptor 1. The movement is performed by the rotation of the cam 22.

  The laser writing unit 5 sequentially generates laser light according to image forming signals (writing information) of a plurality of colors from a laser light source (not shown), and periodically uses the polygon mirror 5B rotated by the polygon motor 5A. Then, the surface of the charged photoreceptor 1 is scanned through the fθ lens 5C and the mirror 5D, and an electrostatic latent image is formed on the surface.

  The electrostatic latent image formed on the surface of the photoreceptor 1 is developed with toner from the corresponding developing unit, and a toner image is formed and held. The intermediate transfer belt 21 is adjacent to the photoreceptor 1 and is supported by the rotating rollers 11 and 12 so as to be rotatable in the direction indicated by the arrow B. The toner image on the photoreceptor 1 is transferred onto the surface of the intermediate transfer belt 21 by a transfer brush (first transfer means) 13 on the back side of the intermediate transfer belt 21.

  The surface of the photoreceptor 1 is cleaned for each color by the cleaning blade 15A, and a toner image of a predetermined color is formed on the surface. Each time the intermediate transfer belt 21 is rotated, the toner image on the photoreceptor 1 is transferred to the same position on the surface, and the toner images of a plurality of colors are superimposed and held on the intermediate transfer belt 21. The Thereafter, the toner image is transferred to a recording medium such as paper or plastic.

  At the time of transfer onto the paper, the paper stored in the paper feeding device (paper feeding cassette) 17 is fed out by the paper feeding roller 18 and transported by the transporting roller 19, and is temporarily applied to the registration roller pair 20. After being stopped, the toner image is transferred to the nip between the intermediate transfer belt 21 and the transfer roller (second transfer means) 14 at a timing so that the transfer position of the toner image becomes normal. Then, after the toner images of a plurality of colors on the intermediate transfer belt 21 are collectively transferred by the action of the transfer roller 14, the sheet is sent to the fixing device 23, where the toner image is fixed, and then the paper discharge roller pair 51. As a result, the paper is discharged to the paper discharge stack 52 at the top of the main body frame 9.

  The intermediate transfer belt 21 is provided with a cleaning device 16 for the intermediate transfer belt 21 at a portion of the rotating roller 11 so that the cleaning blade 16A can be contacted and separated via a cleaning blade contacting / separating arm 16C. In the step of receiving the toner image from the photoreceptor 1, the cleaning blade 16A is separated from the intermediate transfer belt 21 and comes into contact after the toner image is transferred from the intermediate transfer belt 21 to the paper. The residual toner after the toner is transferred is scraped off. As already described, there are cleaning blades for the photoreceptor 1 and the intermediate transfer belt 21. Waste toner scraped by these blades is stored in a collection container 15. The collection container 15 is replaced as appropriate. An auger 16B provided inside the cleaning device 16 for the intermediate transfer belt 21 conveys the waste toner scraped off by the cleaning blade 16A and sends it to the collection container 15 by a conveying means (not shown).

  Reference numeral 31 denotes a unitized process cartridge, which includes a photosensitive member 1, a charging device 4, an intermediate transfer belt 21, a cleaning device 16, a conveyance guide 30 that forms a sheet conveyance path, and the like so that they can be replaced when the end of their service life is reached. It is configured. In addition to the replacement of the process cartridge 31, the multi-color developing device 6, the black developing unit 7 and the like are also replaced at the end of their service life. However, in order to facilitate the exchange and handling of jammed paper, Has a structure that can be opened and closed about the support shaft 9A.

  On the left side of FIG. 1, an electrical / control device 26 is accommodated. Above that, a fan 24 is provided, which exhausts air to prevent excessive temperature rise in the machine. On the right side of the figure, another relatively small paper feeder 25 is provided. In this embodiment, the intermediate transfer belt 21 is used as an intermediate transfer member, but an intermediate transfer drum can also be used.

  FIG. 2 is a diagram illustrating an example of the hardware configuration of the electrical / control unit of the multicolor image forming apparatus according to the present embodiment. 2, the printer controller board 10 is connected to a personal computer (hereinafter referred to as a PC) 90 via a network, and is also connected to a printer engine 700.

  The printer controller board 10 includes a CPU 40 with a built-in memory controller, an image processing ASIC 50, and a panel control ASIC 80, which are connected via a bus. The memory controller built-in CPU 40 is further connected to the main memory 60 and the ROM 70.

  The CPU 40 with a built-in memory controller includes a CPU 41, a CPU interface (hereinafter referred to as CPU I / F) 42, a memory arbiter 43, a communication controller 44, a drawing unit 45, a memory controller 46, and a bus controller 49.

  The CPU 41 controls the entire multicolor image forming apparatus. The CPU 41 also analyzes the PDL transmitted from the PC 90, outputs a drawing command to the drawing unit 45, generates parameters for the image processing ASIC 50, and the like. The CPU I / F 42 is an interface of the CPU 41, and is connected to the main memory 60 and other controllers via the memory arbiter 43.

  The memory arbiter 43 arbitrates access to the main memory 60 of each controller included in the CPU 40 with built-in memory controller. The memory controller 46 controls the main memory 60. The memory controller 46 is connected to each controller via the memory arbiter 43.

  The bus controller 49 performs arbitration between the controllers that input and output data to the bus and the bus. The communication controller 44 is connected to a network and receives data, commands, and the like transmitted from the PC 90 or the like connected via the network. Further, the communication controller 44 outputs received data and the like to each controller connected via the memory arbiter 43, and transmits data and the like input from each controller to the PC 90 and the like.

  The drawing unit 45 draws image data using a drawing command generated by analyzing the input PDL. The drawing unit 45 stores the image data to be drawn in the main memory 60.

  The ROM 70 stores computer programs executed by the CPU 41, character font information, and the like. The main memory 60 stores image data, code data obtained by compressing image data, a computer program executed by the CPU 41, and the like. The image data stored in the main memory 60 is obtained by performing predetermined image processing on these image data in addition to the image data input from the PC 90 and the image data output from the printer engine 700. But you can.

  The image processing ASIC 50 includes an image processing unit 500, a bus interface (hereinafter referred to as a bus I / F) 58, and an engine controller 59. The image processing unit 500 receives image processing parameters generated by the CPU 41 and performs image processing according to the parameters. The image processing unit 500 reads image data to be image-processed from the main memory 60 and stores the image processed image data in a predetermined area of the main memory 60.

  The bus I / F 58 is an interface when the image processing ASIC 50 is connected to the bus. The engine controller 59 controls the printer engine 700.

  The panel control ASIC 80 is connected to the panel 81 and controls the panel 81 in accordance with a control command from the CPU 41 or the like. The panel control ASIC 80 has a panel controller 89 and a bus I / F 88. The panel controller 89 performs control of data displayed on the panel 81, acquisition of information input from the panel 81, and the like. The bus I / F 88 is connected to the bus and inputs and outputs data from the CPU 40 with a built-in memory controller.

  The panel 81 displays the state of the multicolor image forming apparatus and receives instructions from the operator for the multicolor image forming apparatus.

  The printer engine 700 forms an image on a medium under the control of the engine controller 59. The PC 90 creates a PDL for an image to be output to the multicolor image forming apparatus, and outputs the PDL to the multicolor image forming apparatus via a network.

  FIG. 3 is a flowchart showing an outline of processing in the multicolor image forming apparatus. In FIG. 3, input image data is analyzed, subjected to image processing, and then output to the printer engine 700. 3 includes a PDL storage step S201, a PDL analysis step S202, a drawing processing step S203, an RGB band image storage step S204, an image processing step S250, and a post-gradation page image storage step S206 in the order described above. Processing of each step is executed.

  In the PDL storage step S201, the main memory 60 stores the PDL data input from the PC 90. In the PDL analysis step S202, the CPU 41 analyzes the PDL data stored in the main memory 60 by executing a computer program.

  In the rendering processing step S203, the CPU 41 renders image data represented in the RGB color space via the rendering unit 45 by a rendering command generated by analyzing the PDL data stored in the main memory 60, and the main processing is performed. Transfer to memory 60. The image data generated here is band data in “band” units, which are units in which the multicolor image forming apparatus processes images. In the RGB band image storage step S <b> 204, band data (RGB data) is stored in the main memory 60.

  The image processing step S250 includes an image reading processing step S251, a color conversion processing step S252, and a gradation processing step S253. In the image reading processing step S251, the image data processed in the RGB band image storing step S204 is read. In the image reading processing step S251, a plurality of pixels that are continuous in raster order among the image data may be read in parallel. Next, in the image reading processing step S251, whether or not the RGB values that are the pixel values (color information) of the read pixels match the pixel values (color information) of the pixels that have been subjected to the color space conversion processing before. Determine. In the image reading processing step S251, the pixel value of the pixel that does not match the pixel value of the pixel that has been subjected to the color space conversion process before and the pixel that has been previously subjected to the color space conversion process among the plurality of read pixels. The result of determining whether the color is the same color as is output.

  In color conversion processing step S252, color space conversion processing is performed on pixel values of pixels that did not match the pixel values of pixels that have been subjected to color space conversion processing previously, and CMYK values are generated. In color conversion processing step S252, if the determination result output in step S251 indicates that the pixel value of the pixel that has been subjected to color space conversion processing is the same as that previously, the color space conversion processing is performed previously. The CMYK value generated at the time of execution is taken as the result of the color space conversion process performed on the pixel value of the read pixel.

  In the gradation processing step S253, the halftone process for the CMYK value generated when the color space conversion process is performed and the halftone process (the gradation process for the CMYK value generated when the color space conversion process is performed previously). ) In parallel.

  In the post-gradation page image storage step S206, the image data obtained by the halftone process in step S253 is stored in the main memory 60. After the process of step S206, the printer engine 700 prints and outputs the image data stored in the main memory 60.

  FIG. 4 is a diagram for explaining a storage area of the main memory. The main memory 60 has a PDL storage memory area, a program area, an RGB band image storage area, an image processing unit parameter area, a gradation processed page memory storage area, and other areas.

  The PDL storage memory area stores PDL data input from the PC 90. The program area stores computer programs executed by the CPU 41. The RGB band image storage area stores the RGB data of the image drawn by the drawing unit 45 in band units.

  The image processing unit parameter area has a lattice point data storage area, a gamma data storage area, and a threshold data storage area. The grid point data storage area and the gamma data storage area store parameters for performing color space conversion in the color conversion processing step S252.

  The threshold data storage area stores a threshold table used when halftone generation processing is performed in the gradation processing step S253. The threshold value table stored in the threshold value data storage area may be provided for each color component constituting the image data to be subjected to halftone processing.

  The post-gradation page memory storage area has a C-page memory area, an M-page memory area, a Y-page memory area, and a K-page memory area. Each storage area of the page memory storage area after gradation processing is preferably provided for each color component after gradation processing. For example, in addition to the CMYK color space, it corresponds to each color component in the RGB color space. May be provided.

  FIG. 5 is a diagram illustrating a hardware configuration of the image processing unit. 5 includes an image reading unit 510, a color conversion processing unit 520, a gradation processing unit 530, a color restoration processing unit 540, a parameter address generation unit 541, an image processing parameter reading unit 542, and a DMA parameter storage unit 543. , Lattice point data storage unit 551, gamma table storage unit 552, halftone parameter storage unit 561, odd threshold matrix storage unit 562, even threshold matrix storage unit 563, post image processing image address generation unit 581, post image processing image writing unit 582, a post-image processing image buffer 583, and a bus arbiter interface (hereinafter referred to as bus arbiter I / F) 590.

  The bus arbiter I / F 590 performs arbitration when the image reading unit 510, the image processing parameter reading unit 542, and the post-image processing image writing unit 582 input / output data to / from the bus via the bus I / F 58. Do.

  The parameter address generation unit 541 generates addresses of various parameters stored in the image processing unit parameter area on the main memory 60. The image processing parameter reading unit 542 reads out various parameters stored in the main memory 60 based on the address generated by the parameter address generation unit 541.

  The DMA parameter storage unit 543 receives parameters such as an address used when the image processing parameter reading unit 542 reads the image processing parameters from the image processing parameter reading unit 542 and stores them. The parameters stored in the DMA parameter storage unit 543 are a multi-value RGB band width that is a band width, a multi-value RGB band height that is a band height, and an RGB band start that is a start address of the band data on the main memory 60. Address, CMYK band width after gradation processing and CMYK band height after gradation processing, which are the width and height of the band after gradation processing, and band data of each color component of C, M, Y, and K Is a start address or the like when the data is stored in the main memory 60.

  The image reading unit 510 includes a band image address generation unit 511, an RGB band image reading unit 512 in units of words, an RGB data cutout unit 513, and a matching pixel determination unit 514.

  The band image address generation unit 511 generates an address when reading band data from the main memory 60. The band image address generation unit 511 generates an address for reading the band data based on the address for each horizontal line of the image data in the main memory 60.

  The word-unit RGB band image reading unit 512 reads band data (RGB data) from the RGB band image storage area on the main memory 60. The RGB band image reading unit 512 in units of words uses, for example, band data for two adjacent pixels based on the addresses for each horizontal line generated by the band image address generation unit 511 and the addresses in units of words in the main memory 60. Read at the same time. More specifically, the odd-numbered pixels and the even-numbered pixels in the horizontal line are read by one request. When image data in the RGBA color space is stored in the RGB band image storage area of the main memory 60, the band data for two pixels is 64 bits.

  In the present embodiment, band data for two pixels is read. However, the present invention is not limited to this. For example, band data for four pixels may be read, or band data for other pixels may be read. good. When band data for four pixels is read, color space conversion processing is performed for one of the four pixels, and the other pixels are obtained by performing color space conversion processing previously. The pixel value (the pixel value stored in the storage area 706 (see FIG. 7)) is set as the result of the color space conversion process for the pixel values of the other pixels.

  The RGB data cutout unit 513 cuts the band data read by the RGB band image read unit 512 in units of words into data for each pixel. The RGB data cutout unit 513 divides the read pixel data into two 32-bit pixels (even-numbered image data and odd-numbered image data) when the read-out pixel data is two-pixel and 64-bit.

  The matching pixel determination unit 514 converts the RGB values (color information) of the two pixels cut out by the RGB data cutout unit 513 into the RGB values (storage area 608 ( It is determined whether or not it matches the RGB value stored in FIG. In the present embodiment, the matching pixel determination unit 514 outputs even pixels (even RGB pixels) out of the two pixels cut out by the RGB data cutout unit 513. Then, the matching pixel determination unit 514 determines that the RGB value of the odd pixel (odd RGB pixel) out of the two pixels cut out by the RGB data cutout unit 513 is the same as the pixel that has been subjected to the color space conversion process and the RGB value. It is determined whether or not.

  FIG. 6 is a block diagram illustrating a specific configuration of the matching pixel determination unit. The matching pixel determination unit 514 includes an RGB_FIFO storage processing unit 601, a pixel value comparison unit 602, an OR circuit 603, a matching flag register 604, a matching address generation unit 605, a matching address register 606, and an even RGB pixel register 607.

  The RGB_FIFO storage processing unit 601 (first storage unit) is a pixel value of two pixels (even RGB pixels and odd RGB pixels) cut out by the RGB data cutout unit 513 (pixels that have been previously subjected to color space conversion processing) RGB values are stored in the FIFO (First In First Out) format in the order read by the RGB band image reading unit 512 in units of words. In the present embodiment, the RGB_FIFO storage processing unit 601 has a storage area (FIFO) 608 to which addresses from “0” to “31” are assigned, and the RGB data cutout unit 513 uses an even number of two pixels. The RGB values of the RGB pixels are stored in the storage area 608 with even addresses, and the RGB values of the odd RGB pixels are stored in the storage area 608 with odd addresses. The RGB_FIFO storage processing unit 601 sequentially reads the RGB values of the even RGB pixels from the storage area 608 assigned with the lowest even address: “0” every time the RGB band image reading unit 512 reads the word unit. The highest even address: Stored while shifting toward the storage area 608 to which “30” is attached. The RGB_FIFO storage processing unit 601 sequentially converts the RGB values of the odd RGB pixels from the storage area 608 to which the lowest odd address: “1” is assigned each time the word is read by the RGB band image reading unit 512 in units of words. The data is stored while being shifted toward the storage area 608 with the highest odd address: “31”.

  The pixel value comparison unit 602 compares the RGB values of the odd RGB pixels extracted by the RGB data extraction unit 513 with the RGB values stored in all the storage areas 608 included in the RGB_FIFO storage processing unit 601.

  The OR circuit 603 is a match flag that indicates whether or not the RGB value of the odd RGB pixel is the same as the RGB value of the pixel that has been previously subjected to the color space conversion processing, according to the comparison result by the pixel value comparison unit 602. Is output. Specifically, the OR circuit 603, when the RGB values of the odd RGB pixels cut out by the RGB data cutout unit 513 match at least one RGB value among the RGB values stored in all the storage areas 608, The value of the match flag is “1”, which is “ON”. On the other hand, when the RGB values of the odd RGB pixels cut out by the RGB data cutout unit 513 do not match the RGB values stored in all the storage areas 608, the OR circuit 603 sets the value of the match flag to “0”. ”And“ OFF ”. The match flag output from the OR circuit 603 is held by the match flag register 604.

  The coincidence address generation unit 605 is an address of the storage area 608 that stores RGB values that match the RGB values of the odd RGB pixels cut out by the RGB data cutout unit 513 in the storage area 608 of the RGB_FIFO storage processing unit 601. Generate a match address. The match address generation unit 605 holds the generated match address in the match address register 606.

  The matching pixel determination unit 514 does not perform processing on the even RGB pixels cut out by the RGB data cutout unit 513, and causes the even RGB pixel register 607 to hold the even RGB pixels (RGB image data).

  Returning to FIG. 5, the color conversion processing unit 520 receives even RGB pixels (RGB image data) from the matching pixel determination unit 514, and performs RGB to CMY color space conversion processing and BG for the RGB values of the even RGB pixels. / Color space conversion processing including UCR processing is performed. Accordingly, the color conversion processing unit 520 converts the received even RGB pixels from the RGBA color space to the even CMYK pixels (CMYK image data) in the CMYK color space. In addition, the color conversion processing unit 520 receives the matching flag and the matching address from the matching pixel determination unit 514, and transfers the received matching flag and matching address to the color restoration processing unit 540.

  Note that the color conversion processing unit 520 indicates that the match flag received from the match pixel determination unit 514 indicates that the RGB value of the odd RGB pixel does not match the RGB value stored in the storage area 608 ( That is, when the value of the match flag is “0”), odd RGB pixels are received from the match pixel determination unit 514, and color space conversion processing is performed on the RGB values of the odd RGB pixels. The color conversion processing unit 520 then converts the CMYK values of the odd CMYK pixels obtained by performing the color space conversion processing on the RGB values of the odd RGB pixels, via the color restoration processing unit 540, to the gradation processing unit 530. Output to.

  The color conversion processing unit 520 performs processes such as under color removal and color correction in addition to color space conversion. The color conversion processing unit 520 acquires parameters used for processing from the lattice point data storage unit 551 and the gamma table storage unit 552.

  In the present embodiment, an example in which color space conversion processing is performed on RGB values of even RGB pixels (or odd RGB pixels) to CMYK values will be described. However, the present invention is not limited to this. Color space conversion processing to values, color space conversion processing from RGB values to CMY values, and color space conversion processing from Lab values to CMYK values can also be performed.

  The lattice point data storage unit 551 stores the lattice point data input from the image processing parameter reading unit 542. The gamma table storage unit 552 stores a gamma table including parameters for gamma correction input from the image processing parameter reading unit 542.

  The color restoration processing unit 540 receives the match flag and the match address via the color conversion processing unit 520. Then, the color restoration processing unit 540 indicates that the match flag indicates that the RGB value of the odd RGB pixel matches the RGB value stored in the storage area 608 (that is, the value of the match flag is “1”). CMYK values when color space conversion processing is performed on the RGB values stored in the storage area 608 assigned with the coincidence address among the RGB values stored in the storage area 608, the color of the odd RGB pixels This is selected as a CMYK value, which is the pixel value of odd-numbered CMYK pixels when a spatial conversion process is performed. In addition, the color restoration processing unit 540 transfers the CMYK values (CMYK image data) of the even CMYK pixels received from the color conversion processing unit 520 to the gradation processing unit 530.

  FIG. 7 is a block diagram illustrating a specific configuration of the color restoration processing unit. The color restoration processing unit 540 includes a CMYK_FIFO storage processing unit 701, an odd pixel generation unit 702, an odd CMYK pixel register 703, an even CMYK pixel register 704, and a match flag register 705.

  The CMYK_FIFO storage processing unit 701 (second storage unit) causes the even CMYK pixel register 704 to hold the CMYK values of the even CMYK pixels received from the color restoration processing unit 520.

  Further, the CMYK_FIFO storage processing unit 701 converts the CMYK values of the even CMYK pixels received from the color restoration processing unit 520 and the CMYK values of the odd CMYK pixels selected by the odd pixel generation unit 702, which will be described later, in the order in which the color space conversion processing is performed. Store in FIFO format. In the present embodiment, the CMYK_FIFO storage processing unit 701 has a storage area (FIFO) 706 to which addresses from “0” to “31” are attached, and CMYK of even CMYK pixels received from the color conversion processing unit 520. The value is stored in the storage area 706 to which the even-numbered address is assigned, and the CMYK value of the selected odd-numbered CMYK pixel is stored in the storage area 706 to which the odd-numbered address is assigned. The CMYK_FIFO storage processing unit 701 receives the even CMYK pixel from the color restoration processing unit 520 (or every time the CMYK value of the odd CMYK pixel is selected), and sets the CMYK value of the even CMYK pixel to the lowest even CMYK value. The data is stored while being shifted from the storage area 706 to which the address: “0” is assigned in order toward the storage area 706 to which the highest even-numbered address: “30” is assigned. Further, every time the CMYK_FIFO storage processing unit 701 receives even CMYK pixels from the color restoration processing unit 520 (or every time a CMYK value of odd CMYK pixels is selected), the CMYK value of odd CMYK pixels is set to the lowest odd number. The addresses are sequentially shifted from the storage area 706 assigned “1” to the storage area 706 assigned the highest odd address: “31”.

  In the present embodiment, the RGB values of even RGB pixels and odd RGB pixels stored in the RGB_FIFO storage processing unit 601 and the CMYK values of even CMYK pixels and odd CMYK pixels when color space conversion processing is performed on the RGB values. Are stored in storage areas 608 and 706 having the same address. Thereby, the RGB values of the even RGB pixels and the odd RGB pixels stored in the RGB_FIFO storage processing unit 601 are stored in association with the CMYK values of the even CMYK pixels and the odd CMYK pixels stored in the CMYK_FIFO storage processing unit 701. ing.

  The odd pixel generation unit 702 reads the CMYK value from the storage area 706 assigned the same address as the matching address received from the color restoration processing unit 540, and performs a color space conversion process on the read CMYK value to the odd RGB pixel. Generated (selected) as CMYK values of odd CMYK pixels. Then, the odd pixel generation unit 702 holds the selected CMYK value in the odd CMYK pixel register 703.

  The color restoration processing unit 540 holds the match flag and match flag register 705 received from the color conversion processing unit 520.

  Returning to FIG. 5, when the value of the match flag received from the color restoration processing unit 540 is “0”, the gradation processing unit 530 receives the CMYK value (CMYK0 image data) of the even CMYK pixels from the color conversion processing unit 520 and The CMYK values (CMYK1 image data) of the odd CMYK pixels are received, and the threshold matrix is read from the odd threshold matrix storage unit 562 and the even threshold matrix storage unit 563. Then, the gradation processing unit 530 performs halftone processing by comparing the received CMYK values of even CMYK pixels and CMYK values of odd CMYK pixels with predetermined threshold values included in the threshold value matrix.

  On the other hand, when the value of the match flag received from the color restoration processing unit 540 is “1”, the gradation processing unit 530 receives the CMYK value of even CMYK pixels from the color conversion processing unit 520, and the color restoration processing unit 540 The CMYK value of the selected odd CMYK pixel is received. Further, the gradation processing unit 530 reads the threshold matrix from the odd threshold matrix storage unit 562 and the even threshold matrix storage unit 563. Then, the gradation processing unit 530 receives the CMYK value of the even CMYK pixel received from the color conversion processing unit 520, the CMYK value of the odd CMYK pixel selected by the color restoration processing unit 540, and a predetermined threshold value included in the threshold value matrix. A halftone process is performed by comparison.

  Then, the gradation processing unit 530 outputs gradation-processed word data, which is a plurality of pixel data (even CMYK pixels and odd CMYK pixels) after halftone processing, in units of words in the main memory 60. Note that the odd threshold matrix storage unit 562 and the even threshold matrix storage unit 563 respectively generate threshold matrices for halftone processing corresponding to odd CMYK pixels and even CMYK pixels based on the position of the horizontal line of the pixel data. Remember.

  FIG. 8 is a block diagram showing a specific configuration of the gradation processing unit. The gradation processing unit 530 is connected to the odd threshold matrix storage unit 562 and the even threshold matrix storage unit 563. The gradation processing unit 530 includes a threshold matrix address generation unit 801, CMYK comparison units 802 and 803, and a fixed length data generation unit 804.

  The threshold matrix address generation unit 801 corresponds to pixels to be processed (even CMYK pixels and odd CMYK pixels) in the threshold table (threshold matrix) stored in the odd threshold matrix storage unit 562 and the even threshold matrix storage unit 563. A threshold address is generated.

  The CMYK comparison unit 803 compares the threshold value for the pixel at the odd position acquired from the odd threshold matrix storage unit 562 with the CMYK value that is the pixel value of the input odd CMYK pixel, and outputs the comparison result. Thereby, the pixel value corresponding to the halftone is obtained.

  Similarly, the CMYK comparison unit 802 compares the threshold value for the pixel at the even position acquired from the even threshold value matrix storage unit 563 with the CMYK value that is the pixel value of the input even CMYK pixel, and outputs the comparison result. . Thereby, the pixel value of the pixel corresponding to a halftone is obtained.

  The fixed length data generation unit 804 converts the CMYK values of the odd CMYK pixels (odd CMYK comparison results) and the CMYK values of the even CMYK pixels (even CMYK comparison results) output from the CMYK comparison units 802 and 803 to a fixed length of 32 bits. Convert.

  9 and 10 are diagrams showing examples of the structure of image data. FIG. 9 is a diagram illustrating a configuration example of band data, in which 6774 pixels are arranged in the band width direction, and 256 lines are arranged in the band height direction. In FIG. 9, pixels with an odd address in the width direction are “odd pixels” (odd RGB pixels), and pixels with an even address in the width direction are “even pixels” (even RGB pixels).

  FIG. 10 is a diagram illustrating an example of data for one word in the main memory 60. FIG. 10 shows an example of data for two pixels, that is, 64 bits. One word of data is a set of even and odd pixels. Therefore, the RGB band image reading unit 512 in units of words can read pixel data for two pixels by one access by reading data for one word.

  FIG. 11 is a diagram illustrating an example of a threshold matrix. FIG. 11A is a diagram illustrating the pixels of the band data. In the figure, a pixel whose line address is “0” and whose horizontal line direction address is “1” is expressed as “0-1”.

  FIG. 11B is a diagram illustrating a threshold matrix corresponding to four pixels in the vertical and horizontal directions. A threshold matrix for four pixels in the vertical and horizontal directions is expressed as “4 * 4 matrix”. FIG. 11C is a diagram showing an odd pixel threshold table and an even pixel threshold table corresponding to the threshold matrix of FIG.

  The threshold value matrix of the even-numbered pixels in FIG. 11C includes threshold values corresponding to the pixels whose horizontal addresses are even among the elements of the matrix in FIG. In addition, the threshold value matrix for odd pixels in FIG. 11C includes threshold values corresponding to pixels whose addresses in the horizontal direction are odd among the elements of the matrix in FIG.

  Returning to FIG. 5, the halftone parameter storage unit 561 stores parameters read from the main memory 60 when the gradation processing unit 530 performs halftone processing.

  The post-image processing image buffer unit 583 is a pixel for which halftone processing has been performed by the gradation processing unit 530 in order to efficiently perform burst transfer of a plurality of pixel data subjected to halftone processing by the gradation processing unit 530. Retain data.

  The post-image processing image writing unit 582 stores the plurality of pieces of pixel data subjected to halftone processing temporarily stored in the post-image processing image buffer unit 583 through the bus arbiter I / F 590. Write to the page memory storage area after adjustment processing. At this time, in order to efficiently perform burst transfer of pixel data, a plurality of pieces of pixel data written at consecutive addresses in the main memory 60 are transferred.

  The post-image processing image address generation unit 581 generates an address when the post-image processing image writing unit 582 stores the pixel data in the main memory 60. In this embodiment, since the RGB image reading unit 512 in units of words reads band data in units of horizontal lines, the post-image processing image address generation unit 581 uses the post-image processing image buffer unit 583 to perform post-halftone processing pixels. For data, an address is generated in units of horizontal lines.

  FIG. 12 is a flowchart showing the flow of color space conversion processing and halftone processing. In FIG. 12, color space conversion processing and halftone processing are performed on band data for two pixels. First, the RGB band image reading unit 512 in units of words reads band data for two pixels of 64 bits out of band data in the RGB color space (step S101).

  Next, the RGB data cutout unit 513 cuts the read band data for two pixels into an odd RGB pixel and an even RGB pixel (step S102). Next, the pixel value comparison unit 602 compares the RGB values of the separated odd RGB pixels with all the RGB values stored in the storage area 608 (FIFO), and the match address generation unit 605 performs the separation. The coincidence address, which is the address of the storage area 608 storing the RGB values that coincide with the RGB values of the odd RGB pixels, is obtained (step S103).

  Here, when the same RGB value as that of the separated odd RGB pixel is stored in the storage area 608 (step S104: Yes), the color conversion processing unit 520 performs the color space conversion process (RGB to CMYK) of the even RGB pixel. In addition, the color restoration processing unit 540 uses the CMYK values stored in the storage area 706 of the match address obtained by the match address generation unit 605 among the CMYK values stored in the storage area 706 to color the odd RGB pixels. The CMYK value of the odd CMYK pixel when the space conversion process is performed is selected (step S105).

  Further, the RGB_FIFO storage processing unit 601 stores the separated RGB values of the odd RGB pixels in the storage area 608 of the address “1”, and increases the already stored RGB values of the odd RGB pixels by one higher odd number. Shift to the storage area 608 of the address (step S106). In addition, the RGB_FIFO storage processing unit 601 stores the RGB values of the separated even RGB pixels in the storage area 608 of the address: “0”, and increases the already stored RGB values of the even RGB pixels by one higher Shift to the storage area 608 of the address (step S106).

  Next, the gradation processing unit 530 performs halftone processing (gradation processing) on the CMYK0 image data (CMYK values of even CMYK pixels) after the color space conversion processing using a threshold matrix, and thereby performs even CMYK. Word data is generated after pixel gradation processing (step S107). Further, the gradation processing unit 530 uses a threshold matrix for the CMYK values of the odd CMYK pixels selected by the color restoration processing unit 540 (that is, the CMYK values stored in the storage area 706 indicated by the coincidence address). Halftone processing (gradation processing) is performed to generate post-gradation word data for odd CMYK pixels (step S108).

  Further, the CMYK_FIFO storage processing unit 701 stores the CMYK value of the odd CMYK pixel selected by the color restoration processing unit 540 in the storage area 706 of the address: “1” and also stores the CMYK value of the odd CMYK pixel already stored. Is shifted to the storage area 706 of the odd address which is one higher (step S109). Further, the CMYK_FIFO storage processing unit 701 stores the CMYK values of the even CMYK pixels after the color space conversion processing in the storage area 706 of the address: “0”, and sets the already stored CMYK values of the even CMYK pixels. The storage area 706 of the next higher even address is shifted (step S109).

  On the other hand, if the same RGB value as that of the separated odd RGB pixel is not stored in the storage area 608 (step S104: No), the color conversion processing unit 520 performs color space conversion processing (RGB to CMYK) for even RGB pixels. Is performed (step S110).

  Further, the RGB_FIFO storage processing unit 601 stores the separated RGB values of the odd RGB pixels in the storage area 608 of the address “1”, and increases the already stored RGB values of the odd RGB pixels by one higher odd number. To the address storage area 608 (step S111). In addition, the RGB_FIFO storage processing unit 601 stores the RGB values of the separated even RGB pixels in the storage area 608 of the address: “0”, and increases the already stored RGB values of the even RGB pixels by one higher To the address storage area 608 (step S111).

  Next, the gradation processing unit 530 performs halftone processing (gradation processing) on the CMYK0 image data (CMYK values of even CMYK pixels) after the color space conversion processing using a threshold matrix, and thereby performs even CMYK. Word data is generated after pixel gradation processing (step S112).

  Next, the color conversion processing unit 520 performs color space conversion processing (RGB to CMYK) for odd RGB pixels (step S113). Next, the gradation processing unit 530 performs halftone processing (gradation processing) on the CMYK1 image data (CMYK values of the odd CMYK pixels) after the color space conversion processing using the threshold value matrix, and generates the odd CMYK. Word data is generated after pixel gradation processing (step S114).

  Thereafter, the CMYK_FIFO storage processing unit 701 stores the CMYK values of the odd CMYK pixels after the color space conversion processing in the storage area 706 of the address: “1”, and sets the CMYK values of the odd CMYK pixels already stored. A shift is made to the storage area 706 of the next higher odd address (step S115). Further, the CMYK_FIFO storage processing unit 701 stores the CMYK values of the even CMYK pixels after the color space conversion processing in the storage area 706 of the address: “0”, and sets the already stored CMYK values of the even CMYK pixels. A shift is made to the storage area 706 of the next higher even address (step S115).

  Then, the post-image processing image writing unit 582 stores the post-gradation word data of odd-numbered CMYK pixels and even-numbered CMYK pixels in the main memory 60 in units of words (step S116). The image processing unit 500 repeats the processing from step S103 to step S116 until it is performed on the band data of one band (step S117: No). When the process for the band data for one band is completed (step S117: Yes), the image processing unit 500 ends the process.

  FIG. 13 is a flowchart for explaining gradation processing by the gradation processing unit. In FIG. 13, for example, the threshold matrix shown in FIG. 11C is applied to the input image data (CMYK0 image data and CMYK1 image data).

  The gradation processing unit 530 calculates a vertical address corresponding to the threshold matrix (step S1301). More specifically, when the 4 * 4 matrix shown in FIG. 11B is used, the vertical address is an integer from 0 to 3. Here, the vertical address corresponding to the threshold matrix is called a Y dither address, and the horizontal address is called an X dither address.

  Therefore, the Y dither address is a remainder obtained by dividing the address of the horizontal line being processed, that is, the Y coordinate in the image data by the dither size in the Y direction. The dither size is the size of the threshold matrix.

  Next, the gradation processing unit 530 initializes the X dither address to “0” (step S1302). The X dither address corresponds to the horizontal address of the threshold matrix.

Next, the gradation processing unit 530 receives CMYK1 image data and CMYK0 image data from the color conversion processing unit 520 and the color restoration processing unit 540 (step S1303). Then, the threshold matrix address generation unit 801 generates a threshold matrix address (step S1304). Here, the address is calculated by the following equation (1).
Threshold matrix address = (Y dither address) * (X dither size) + (X dither address) (1)

  The gradation processing unit 530 reads the odd threshold data and the even threshold data as the threshold matrix from the odd threshold matrix storage unit 562 and the even threshold matrix storage unit 563 based on the threshold matrix address generated in step S1304 ( Step S1305).

  The CMYK comparison unit 802 compares the input CMYK0 image data of the even CMYK pixels with the even threshold data, and generates an even CMYK comparison result (step S1306).

  Further, the CMYK comparison unit 803 determines whether or not the input CMYK value (color) of the even CMYK pixel and the input odd CMYK pixel are the same color (step S1307). . If the color of the even CMYK pixel and the color of the odd CMYK pixel are not the same color (step S1307: No), the CMYK comparison unit 803 receives the input CMYK1 image data of the odd CMYK pixel (step S1308). The input CMYK1 image data of the odd CMYK pixels is compared with the odd threshold data to generate an odd CMYK comparison result (step S1309).

  When the color of the even CMYK pixel and the color of the odd CMYK pixel are the same color (step S1307: Yes), the CMYK comparison unit 803 converts the even CMYK comparison result generated by the CMYK comparison unit 802 into the odd CMYK comparison result. The comparison result. Accordingly, when the color of the even CMYK pixel and the color of the odd CMYK pixel are the same color, it is not necessary to perform the halftone process on the odd CMYK pixel, and the halftone process on the even CMYK pixel and the odd CMYK pixel. Therefore, the gradation processing in the gradation processing unit 530 can be speeded up.

  Next, the fixed length data generation unit 804 adds the even CMYK comparison result generated in step S1306 and the odd CMYK comparison result generated in step S1306 or step S1309 to the fixed length data (step S1310).

  Further, the fixed length data generation unit 804 determines whether or not the fixed length data to which the CMYK comparison result is added in step S1310 has a predetermined fixed length (step S1311). When it is a predetermined fixed length (step S1311: Yes), the fixed length data generation unit 804 outputs fixed length data (step S1312). The bit length of the fixed length data is, for example, 32 bits.

  If the predetermined fixed length is not reached (step S1311: No) or if fixed length data is output, the gradation processing unit 530 increments the value of the X dither address by 1 (step S1313). The gradation processing unit 530 determines whether or not the X dither address is smaller than the dither size in the X direction (step S1314). When the X dither address is not smaller than the dither size in the X direction (step S1314: NO), the gradation processing unit 530 sets the value of the X dither address to 0 (step S1315). On the other hand, when the X dither address is smaller than the dither size in the X direction (step S1314: Yes), the gradation processing unit 530 determines whether or not the processing for the horizontal line has been completed (step S1316). When the processing has been completed (step S1316: Yes), the gradation processing unit 530 determines whether or not processing of band data for one band has been completed (step S1317). If it has been completed (step S1317: Yes), the process is terminated. If not completed (step S1317: NO), the process returns to step S1301 and the process is repeated.

  As described above, according to the multicolor image forming apparatus according to the present embodiment, the RGB_FIFO storage processing unit that stores the RGB value that is the pixel value of the pixel that has been previously subjected to the color space conversion process, and the stored RGB value A CMYK_FIFO storage processing unit that stores CMYK values that are pixel values of pixels when color space conversion processing is performed, and RGB values of pixels cut out from the band data are stored in the RGB_FIFO storage processing unit It is determined whether or not it matches the RGB value, and color space conversion processing is performed on the RGB value that does not match the RGB value stored in the RGB_FIFO storage processing unit among the RGB values of the pixels cut out from the band data, and the CMYK_FIFO storage processing unit Color space conversion for RGB values that match the RGB values of the pixels cut out from the band data among the CMYK values stored in By selecting the CMYK value when the processing is performed as the CMYK value when the color space conversion process is performed on the pixel cut out from the band data, the RGB value of the pixel cut out from the band data is stored in the RGB_FIFO storage processing unit. When the stored RGB values match, it is not necessary to perform color space conversion processing on the RGB values of the pixels cut out from the band data, so that the image processing can be speeded up.

  The program executed by the multicolor image forming apparatus of the present embodiment is provided by being incorporated in advance in the ROM 70 or the like, but is not limited to this, and is a file in an installable format or an executable format. May be provided by being recorded on a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, a DVD (Digital Versatile Disk).

  Furthermore, the program executed by the multicolor image forming apparatus of the present embodiment may be provided by being stored on a computer connected to a network such as the Internet and downloaded via the network. The program executed by the multicolor image forming apparatus of the present embodiment may be provided or distributed via a network such as the Internet.

  The program executed by the multicolor image forming apparatus according to the present embodiment has a module configuration including the above-described units (such as the image processing unit 500). As actual hardware, the CPU 41 reads the program from the ROM 70. By executing the above, the above-described units may be loaded onto the main storage device, and the image processing unit 500 or the like may be generated on the main storage device.

  In the above embodiment, the image processing apparatus and the image processing method of the present invention are applied to a multicolor image forming apparatus having at least two functions among a copy function, a printer function, a scanner function, and a facsimile function. However, the present invention can be applied to any image processing apparatus such as a multifunction machine, a copying machine, a printer, a scanner device, and a facsimile machine.

10 Printer controller board 40 CPU with built-in memory controller
41 CPU
45 Drawing unit 50 Image processing ASIC
60 Main memory 70 ROM
500 Image processing unit 510 Image reading unit 511 Band image address generation unit 512 RGB band image reading unit in units of words 513 RGB data cutout unit 514 Matched pixel determination unit 520 Color conversion processing unit 540 Color restoration processing unit 601 RGB_FIFO storage processing unit 602 pixel Value comparison unit 603 OR circuit 605 match address generation unit 608, 706 storage area 701 CMYK_FIFO storage processing unit 702 odd pixel generation unit

JP 2001-18455 A JP 2003-208608 A JP 2004-282239 A JP 2004-242213 A JP 2008-023959 A JP 2010-074445 A

Claims (3)

First storage means for storing a first pixel value that is a pixel value of a pixel included in the image data;
Second storage means for storing a second pixel value when color space conversion processing is performed on the first pixel value;
Reading means for reading pixel values of pixels included in image data to be output;
Determination means for determining at a time whether the read pixel value matches each of the plurality of first pixel values stored in the first storage means;
Color conversion processing means for performing color space conversion processing on pixel values that do not match the first pixel value among the read pixel values;
Of the second pixel values stored in the second storage means, the second pixel value obtained when color space conversion processing is performed on the first pixel value that matches the read pixel value is the read pixel value. Selecting means for selecting as a pixel value when color space conversion processing is performed on
Equipped with a,
The first storage unit and the second storage unit store the first pixel value and the second pixel value in association with each other,
The selection unit is a pixel when the second pixel value stored in association with the first pixel value that matches the read pixel value is subjected to color space conversion processing on the read pixel value. An image processing apparatus characterized by selecting as a value . The first storage means stores the read pixel values in the order read from the image data,
The image processing apparatus according to claim 1 , wherein the second storage unit stores pixel values subjected to color space conversion processing by the color conversion processing unit in an order in which the color space conversion processing is performed. An image processing method executed by an image processing apparatus,
The image processing apparatus includes: a first storage unit that stores a first pixel value that is a pixel value of a pixel included in image data; and a second pixel when a color space conversion process is performed on the first pixel value. Second storage means for storing values, wherein the first storage means and the second storage means store the first pixel value and the second pixel value in association with each other,
A step of reading a pixel value of a pixel included in image data to be output;
A step of determining at a time whether or not the read pixel value matches each of the plurality of first pixel values stored in the first storage unit;
A step of performing color space conversion processing on a pixel value that does not match the first pixel value among the read pixel values;
Selection means, among the second pixel values stored in said second storage means, a second pixel value in the case of performing color space conversion processing on the first pixel value matched with the read pixel values Selecting a second pixel value stored in association with the first pixel value as a pixel value when color space conversion processing is performed on the read pixel value;
An image processing method comprising:

Images