JP2006159436A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor and an image processing method in which high speed drawing processing is ensured while saving memory by not creating redundant components being removed after rasterization. <P>SOLUTION: The image forming apparatus comprises a means for inputting a drawing instruction, a means for analyzing the drawing instruction being inputted, a means for drawing an image based on the results from the drawing instruction analyzing means, and a means for encoding an image outputted from the drawing means and capable of altering the rate of encoding by parameters wherein the drawing means alters resolution for each color space or color of an image to be outputted by parameters of the encoding means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and an image forming method for interpreting PDL (Page Description Language) and outputting it on a sheet.

  Conventionally, in order to print image information generated using a drawing application executed on a host computer, the image information is converted into a page description language (PDL), and then a communication cable or the like is met. To the printer device. Such a printer apparatus includes a printer controller capable of controlling the entire apparatus and interpreting PDL, receives the PDL transmitted from the host computer by the printer controller, expands the received PDL data into bitmap data, and Processing to send to the interface is performed.

  In general, a host computer expresses a color image on a display, so that image data is handled by RGB expression which is an additive mixed three primary colors. For this reason, drawing information included in the PDL is usually expressed in RGB representation in many cases.

  On the other hand, the printer prints a document on a paper surface using YMC and K expressions, which are three subtractive primary colors. Therefore, it is necessary for the printer controller to convert drawing information from RGB representation to YMC and K representation, and as one method for this, when generating a bitmap from PDL, a bitmap is formed by RGB representation, and the formed bitmap There is known a method of converting the image into CMYK expression. This method has an advantage that drawing fraud does not occur in logical drawing because bitmap conversion is performed after generating bitmap data with the same color representation as that on the host computer.

  However, in order to generate bitmap data in RGB representation, a large-capacity memory is required and the cost tends to increase. For this reason, when generating a bitmap of RGB representation, the paper surface is generated by dividing it into band-like areas (hereinafter referred to as band areas), and the bands are held in the memory in the printer controller by a compression means such as JPEG, for example. A bitmap in RGB representation can be generated even in the memory.

  A conventional example will be described below with reference to FIGS.

  FIG. 10 is a diagram for explaining a conventional example of the above-described printer controller, in which 1001 is a host computer that generates PDL data, 1002 is a printer controller connected to the host computer, for example, via a LAN (Local Area Network) or the like. , 1003 is a PDL interpretation unit that interprets PDL data transmitted from the host computer 1001, and 1004 is a display list generation that generates a command (hereinafter referred to as a display list) that can be read by a rasterizer 1005, which will be described later, according to the interpretation result of the PDL interpretation unit 1003 Reference numeral 1005 denotes a rasterizer that reads the display list generated by the display list generation unit and forms a bitmap image.

  Reference numeral 1006 denotes a JPEG encoding unit that generates a JPEG code by encoding the bitmap generated by the rasterizer 1005 using JPEG encoding. Reference numeral 1007 denotes a JPEG that decodes the JPEG code generated by the JPEG encoding unit 1006 into a bitmap. A decoding unit 1008 is a color conversion unit that converts the color space of the bitmap decoded by the JPEG decoding unit 1007 into CMYK representation, and 1009 is a half of the CMYK bitmap converted by the color conversion unit 1008 A halftone processing unit 1010 that performs tone processing is a DMA (Direct Memory Access) that transmits image data that has been halftone processed in 1009 to the printer engine 1012.

  Reference numeral 1011 denotes a memory mounted on the printer controller. The memory 1010 stores an area for storing a display list generated by the display list generation unit 1004, an area for storing a JPEG code generated by the JPEG encoding unit, Two band buffers (band buffer 1 and band buffer 2) for storing bitmaps to be transferred to the printer engine are defined. Reference numeral 1011 denotes a printer engine for outputting a halftone image generated by the printer controller 1002 on a paper surface.

  The printer controller 1002 and the printer engine 1012 are connected by a high-speed interface, and the printer controller 1002 transmits the generated halftone image to the printer controller via the interface.

  Next, the operation of FIG. 10 will be described with reference to the flowchart of FIG.

  The PDL created by the host computer 1001 is transmitted to the printer controller via the network, the PDL interpretation unit 1003 built in the printer controller 1001 is interpreted, and the display list generation unit 1004 is interpreted according to the interpretation result. Generates a display list that can be interpreted by the rasterizer 1005 (S1101). The display list is generated for each band area and stored in the display list area defined in the memory 1011.

  When this process is performed for all the transmitted PDLs and the generation of the display list for one sheet is completed, the rasterizer 1005 forms a bitmap of RGB representation for one band according to the generated display list (S1102). . Subsequently, the JPEG encoding unit 1006 performs JPEG encoding on the bitmap formed in S1102 to generate a JPEG code, and stores the generated JPEG code in the JPEG code area defined in the memory 1011 (S1103). ). JPEG encoding will be described later.

  The above-described processes of S1101 and S1103 are repeated until all the bands have been processed (S1104), thereby generating a JPEG code for one page. When the generation of the JPEG code for one page is completed, the JPEG decoding unit 1006 decodes the first band on the page in the band buffer 1 defined in the memory 1011 (S1105), and performs color conversion on the bitmap of the decoded band. The RGB representation is converted from the RGB representation into the CMYK representation, and the halftone processing unit 1009 performs the halftone processing on the bitmap converted into the CMYK representation (S1106).

  Subsequently, the printer controller 1002 instructs the printer engine 1012 to start feeding (S1107), and transmits the halftone processed image data stored in the band buffer 1 to the printer engine (S1108). Since the DMA 1010 is used for the processing of S1108, if the transfer parameter is set and the start of transfer is instructed in S1108, it is possible to proceed to the next processing without waiting for the transfer processing.

  Subsequently, the band buffer other than the band buffer transferred to the printer engine 1012, that is, when the first S1109 is executed, the next band buffer is decoded into the band buffer 2 (S1109), and the bitmap formed in the band is converted to Then, color conversion and halftone processing are performed (S1110), and the band buffer is transferred to the printer engine by DMA (S1111). In the process of S1111 as well as S1108, the next process can be continued without waiting for the end of the DMA transfer.

  Subsequently, it waits for the end of the DMA transfer started in S1108 or S111 (S1112), and when the DMA transfer ends, the process ends if the band transferred in S1111 is the final band, otherwise In step S1109, the remaining bands are processed. Note that in S1109, decoding is performed to the band buffer that is not being transferred to the printer engine 1012. Therefore, in S1109, decoding is alternately performed on the two band buffers.

  As described above, the printer controller 1002 transfers the halftone-processed image data to the printer controller 1012 in band units, and the printer engine prints the received image data on a sheet.

  Next, JPEG encoding and decoding will be described.

  FIG. 12 is a diagram for explaining JPEG encoding, in which 1201 is a rasterizer that generates an RGB image, 1202 is RGB image data transferred from the rasterizer 1201, Y (lightness), Cr (red difference), A color conversion unit for converting to Cb (blue difference), 1203 is a downsampling unit for changing the resolution for each color in accordance with the sampling rate in JPEG from Y, Cr, Cb signals transferred from the color conversion unit 1202, and 1204 is for downsampling An FDCT unit that converts image information from the image information into frequency information by DCT (Discrete Cosine Transform) on the image data for each color received from the unit 1203, and 1205 quantizes the data received from the DCT unit 1204 Quantization unit 1206 is quantization unit 1 An encoding unit that encodes data received from 205 by entropy encoding, for example, Huffman encoding.

  Next, the operation of FIG. 12 will be described.

  The RGB representation bitmap generated by the rasterizer 1201 is converted into Y, Cr, and Cb by the color space unit 1202. Thereafter, the downsampling unit 1202 converts the resolution of the input image data according to the sampling rate in JPEG. Here, the sampling rate in JPEG indicates the resolution of Y, Cr, and Cb. For example, if the ratio is 4: 4: 4, the resolution of all colors is the same, and if the ratio is 4: 1: 1, the resolution of Cr, Cb. Becomes 1/4 of the resolution of Y.

  The above processing is as shown in FIG. 13, and shows the processing when the sampling rate is 4: 1: 1. Thus, the image data whose resolution is changed for each color is subjected to DCT conversion in accordance with the FDCT equation shown in FIG. Image data converted into the frequency domain by DCT conversion is quantized by the quantization unit 1205. In quantization, a quantization table is usually prepared for each density component (Y) and color difference components (Cr, Cb) as shown in FIG. The data quantized in this way is encoded by entropy encoding in the order shown in FIG. 17, and Huffman encoding is generally used as the JPEG entropy encoding method.

  On the other hand, FIG. 16 is a diagram for explaining JPEG decoding, in which 1601 is a decoding unit that performs entropy decoding, 1602 is an inverse quantization unit that inversely quantizes data received from the decoding unit 1602, and 1603 is An IDCT unit that converts data received from the inverse quantization unit 1602 from frequency components into image information by IDCT (Inverse Discrete Cosine Transform). 1604 is an up-converter that converts the resolution of the signal received from the IDCT unit 1603 A sampling unit 1605 is a color conversion unit that converts the color space of the image information received from the upsampling unit into RGB representation.

  Next, the operation of FIG. 16 will be described.

  Data encoded by the JPEG encoding method described above is first entropy-decoded by the decoding unit 1601. For entropy decoding in JPEG, Huffman decoding is usually used. Subsequently, the data decoded by the decoding unit 1601 is inversely quantized by the inverse quantization unit 1602. Here, as the inverse quantization table used for inverse quantization, the quantization table in the above-described JPEG encoding is used. Subsequently, the data inversely quantized by the inverse quantization unit 1602 is converted from frequency information to image data by the IDCT unit 1603 according to the IDCT conversion formula of FIG. The image data output here is expressed in Y, Cr, Cb.

Subsequently, the upsampling unit 1604 returns the resolution of the image data of each color output from the IDCT unit to the state before encoding. This is synonymous with, for example, when the sampling rate is 4: 2: 2, the Cr and Cb information is expanded by a factor of 4 and matched with the resolution of the Y information. Subsequently, when all the color information constituting a pixel is found by the upsampling unit 1604, the color conversion unit 1605 converts the image data of Y, Cr, Cb expression into a bitmap image of RGB expression.
JP 2001-205860 A

  However, in the above conventional example, since the rasterizer does not take into account that the rasterized bitmap is encoded, redundant components to be removed at the time of encoding are also generated, which increases the processing speed and the amount of memory used. There was no use.

  The present invention has been made to solve the above problem, and provides an image forming apparatus and an image forming method capable of saving memory and performing high-speed drawing processing by not generating redundant components that are removed after rasterization. Objective.

  In order to achieve the above object, an image forming apparatus of the present invention includes a drawing command input unit that inputs a drawing command, a drawing command analysis unit that analyzes an input drawing command, and an analysis result of the drawing command analysis unit. A drawing unit that draws an image based on the image; and an encoding unit that encodes an image output by the drawing unit that can change a coding rate according to a parameter. It is characterized by changing the space.

  The image forming apparatus of the present invention is characterized in that the drawing unit changes the resolution of an image to be output for each color according to the parameters of the encoding unit.

  In the image forming apparatus of the present invention, the drawing command analyzing unit generates a drawing command that can be executed by the drawing unit, and the drawing command analyzing unit is executable by a drawing unit that outputs according to a parameter of the encoding unit. It is characterized by changing the format of the drawing command.

  The image forming method of the present invention includes a drawing command input step for inputting a drawing command, a drawing command analyzing step for analyzing the inputted drawing command, and a drawing step for drawing an image based on the analysis result of the drawing command analyzing step. And an encoding step for encoding the image output by the drawing step, the encoding rate of which can be changed by a parameter, wherein the drawing step changes a color space of the output image according to the parameter of the encoding step. It is said.

  The image forming method of the present invention is characterized in that, in the drawing step, the resolution of an image to be output is changed for each color according to the parameters of the encoding step.

  In the image forming method of the present invention, the drawing command analysis step generates a drawing command that can be executed by the drawing step, and the drawing command analysis step can execute a drawing step that is output according to parameters of the encoding step. It is characterized by changing the format of the drawing command.

  According to the first aspect of the present application, since the color space to be output is switched with reference to the encoding parameter before rasterization, a bitmap suitable for the encoding method can be directly generated at the time of rasterization.

  In addition, according to the second invention of the present application, since the resolution to be output is switched for each color space with reference to the encoding parameter before rasterization, image information to be removed at the time of encoding is not generated at the time of rasterization. Therefore, high speed and memory saving can be realized.

  Further, according to the third invention of the present application, the format of the display list generated by referring to the encoding parameter when the display list is generated can be changed, for example, a display list can be created for each color space. It becomes possible to change the resolution for each space.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

  FIG. 1 is a diagram that best represents the features of the present invention. In FIG. 1, 101 is a PDL interpretation unit that interprets PDL transmitted from a host computer (not shown), and 102 is a display list based on the interpretation of the PDL interpretation unit 101. 103 is a rasterizer that performs rasterization based on the display list created by the display list generation unit 102, and 104 is an RGB bitmap that has been input into a bitmap of Y, Cr, Cb representation. A color conversion unit for conversion, 105 is an FDCT unit that converts the input bitmap into a frequency signal by DCT for each 8 × 8 window region, and 106 is a quantization unit that quantizes the frequency signal output by the FDCT unit 105 107 represent the signal quantized by the quantization unit 106 as Huffman Encoding unit for encoding at-coding, 108 is a compression parameter supply section for supplying a compression parameter later in the display list generation unit 102 and the quantization unit 106.

  Next, the operation of FIG. 1 will be described with reference to the flowchart of FIG.

  First, the compression parameter supply unit 106 determines a compression parameter (S201). In this example, the compression parameters are the sampling rate and quantization table in JPEG encoding, and these parameters are determined from the available memory size. Subsequently, the PDL interpretation unit 101 interprets the PDL transmitted from the host computer (S202).

  Subsequently, the display list generation unit 102 refers to the sampling rate determined in S201 notified from the compression parameter supply unit 108, and if the sampling rate is 1: 1: 1, that is, if there is no downsampling, RGB is displayed. A display list having attributes is created (S205). When downsampling is performed other than 1: 1: 1, display lists having Y, Cr, and Cb attributes are created (S204).

  Subsequently, it is checked whether or not all PDL interpretations have been completed (S206). If not, the process returns to S202 to continue interpretation of the remaining PDLs. When interpretation of all PDLs is completed in S206, the rasterizer 103 performs rasterization in band units based on the display list generated in S204 or S205 (S207).

  Here, when the display list is generated in S204, the rasterizer 103 performs rasterization by changing the output resolution for each color based on the sampling rate notified from the compression parameter supply unit 108. For example, when the output resolution of the printer engine is 600 DPI and the sampling rate is 4: 1: 1, rasterization is performed at 600 DPI for the Y plane and 300 DPI for the CrCb plane. On the other hand, when the display list is generated in S205, rasterization is performed with RGB representation at the resolution of the printer engine.

  Subsequently, if the band raster generated in S207 is RGB representation, the color conversion unit 104 converts the band raster from RGB representation to Y, Cr, Cb representation (S209). Subsequently, the band raster converted into Y, Cr, Cb representation by the color conversion unit 104 is processed by the FDCT unit 105 for each Y, Cr, Cb plane and for each 8 × 8 pixel processing unit (hereinafter abbreviated as MCU). DCT conversion is performed (S210).

  On the other hand, if the band buffer generated in S208 is Y, Cr, Cb representation, the process proceeds to S210, and DCT conversion is performed for each color plane. At this time, when the rasterizer 103 is rasterized with RGB, the number of MCUs DCTed with Y, Cr, and Cb is the same for each color, but when rasterized with the rasterizer 103 with Y, Cr, and Cb, Therefore, the number of MCUs differs depending on the output resolution of each color. For example, when the Y plane is rasterized at 600 DPI and the CrCb plane is 300 DPI, if the MCU on the Y plane is 4 × n (where n is an integer), the MCU on the CrCb plane is n.

  Subsequently, the result of the DCT conversion by the FDCT unit 105 is transferred to the quantization unit 106 and quantized (S211). Subsequently, the quantized result is encoded by the encoding unit 107 by entropy encoding, for example, Huffman encoding (S212).

  Subsequently, it is determined whether or not the MCU encoded in S212 is the last MCU in the band rasterized in S207 (S213). If it is not the last MCU, the process returns to S208 and the above-described processing is repeated. If it is the final MCU, it is determined whether or not the band rasterized in S207 is the last band on the paper (S214). If it is not the last band, the process returns to S207 for the remaining band. The process is repeated, and if it is the last band, the process ends. Since the subsequent processing is the same as the conventional example, the description thereof is omitted.

  Next, the display list generated in S204 and S205 will be described. FIG. 3 shows an example of the display list created in S204. 301 is a display list for each drawing object. The display list includes header information, drawing position information, and S (Source: transfer source bitmap). An ID for specifying, an ID for specifying P (pattern), and ROP information are included. Reference numeral 302 denotes a transfer destination bitmap, which can be obtained from the position information of the display list 301, 303 is the entity of the transfer source bitmap, 304 is the entity of the pattern, and 305 is the reverse Polish notation. A raster operation code 306 is a bitmap generated in the display list.

  An example of the header of the display list 301 is shown in FIG. In FIG. 4, 401 is an enlargement ratio of S specified in the display list 301, 402 is an enlargement ratio of the same P, 403 is an output color space to be drawn in the display list, and the rasterizer 103 has a header. By examining it, the color space to be output can be determined.

  On the other hand, the display list created in S205 is as shown in FIG. 5, in which 501 is a display list for the Y plane, 502 is a display list for the Cr plane, and 503 is a display list for the Cb plane. Here, P in each display list is obtained by changing P in FIG. 304 to Y, Cr, Cb expression.

  In FIG. 5, the transfer destination bitmap and pattern entities are prepared for each color, but the others are shared. By creating the display list in S205 as described above, the rasterizer 103 can perform rasterization for each color space, and it is easy to change the resolution of the bitmap generated for each color plane. Become.

  FIG. 6 illustrates examples of bitmaps output at different resolutions for each color space in S208. In FIG. 6, reference numeral 601 denotes an RGB representation bitmap, 602 denotes a Y plane bitmap, and 603 denotes a Cr plane. 604 is a bitmap of the Cb plane. Since each pixel is represented by 24 bits in 601, the size of the bitmap of 601 is 768 bytes, but each pixel is represented by 8 bits in 602, 603, and 604, so that the sum of them is 384 It can be seen that the same drawing object is generated with a size smaller than the RGB representation.

  The JPEG code generated as described above can be handled in the same manner as the JPEG code described in the conventional example, and the subsequent processing has been described in the conventional example, and thus the description thereof is omitted.

  As described above, since it is determined whether to create a display list for each of Y, Cr, and Cb by referring to the compression parameter before generating the display list, the resolution for each color space can be easily changed. It becomes possible to do.

  In the first embodiment, the method for changing the resolution for each region by generating the display list for each color by referring to the compression parameter before generating the display list has been described. A means for changing the resolution for each color by referring to the compression parameter will be described. In this embodiment, the process up to the creation of the display list is the same as that in the prior art, and the description thereof is omitted. The display list created in the present embodiment is the same as that shown in FIG.

  FIG. 7 is a diagram for explaining the rasterizer according to the present embodiment. In FIG. 7, reference numeral 701 denotes color conversion for converting input RGB values (24-bit length) into Y, Cr, and Cb (each 8-bit length). 702, an address generation unit for generating an address for drawing an object according to the input position information, and 703 for the color of each pixel of S (transfer source bitmap), P (pattern), and D (transfer destination bitmap). A logical operation unit that performs a logical operation with the specified ROP parameter, 704 is a resolution conversion unit that converts the resolution of an input signal, and 705 is a buffer in which D is stored. A logical operation unit 703 is prepared for each color of Y, Cr, and Cb.

  The rasterizer shown in FIG. 7 reads the display list of FIG. 3 and receives S, P, and D for one pixel from the display list. Here, to receive D, the address generation unit 702 converts the position information described in the display list into an offset address from the head of the band buffer 705, and reads the pixel value of the offset from the band buffer 705.

  Subsequently, S and P are converted from the RGB color space to the Y, Cr, and Cb color space by the color conversion unit 701 and input to the logic operation unit 703 together with D input as described above. The logical operation unit 703 performs a logical operation according to the ROP information described in the display list from which the input S, P, and D values have been read, and the Y logical operation unit addresses the logical operation result as described above. The data is stored in the address D calculated by the generation unit 702, and the logical operation unit of Cr and Cb transmits the logical operation result to the resolution conversion unit 704.

  The resolution conversion unit 704 scales the input color information according to the input compression parameter, here, the sampling rate, and stores the scaled color information in the band buffer 705 in the same manner as Y. For example, when the sampling rate input to the resolution conversion unit 704 is 4: 1: 1, the magnification of the resolution conversion unit may be 1/4 as shown in FIG. Needless to say, when the sampling rate is 4: 4: 4, the scaling factor may be set to 1.

  By performing the above processing on the input object for one band, Y, Cr, and Cb bitmaps for one band are generated.

  Subsequently, the bitmap for each color generated by the above processing is JPEG-encoded, but this processing only needs to omit the down-sampling processing from the encoding processing described in the conventional example, so the description is omitted.

  By performing the above processing for all the bands on the paper, a JPEG code for one paper is generated.

  The JPEG code generated as described above can be handled in the same manner as the JPEG code described in the conventional example, and the subsequent processing has been described in the conventional example, and thus the description thereof is omitted.

  As described above, by referring to the compression parameter at the time of rasterization, only image information that is not deleted at the time of compression can be rasterized, and the amount of memory used for rasterization can be reduced.

  Note that the compression parameters described in the first and second embodiments may be changed during processing of one sheet.

  FIG. 9 is a flowchart showing a process when the memory for storing the display list is exhausted when the display list is generated. The third embodiment according to the present invention will be described below with reference to FIG.

  First, a flag for determining whether or not the memory is depleted and a JPEG encoding parameter are initialized (S901). Here, JPEG encoding parameters are selected so that image quality deterioration due to encoding is reduced, for example, the sampling rate of JPEG encoding is set to 4: 4: 4. Subsequently, the PDL transmitted from the host computer is interpreted (S902), and a display list is generated (S903). Subsequently, it is determined whether or not the generated display list can be stored in the memory (S904). If the display list cannot be stored in the memory, the flag is set to 1 (S905).

  Subsequently, the compression parameter, in this example, the sampling rate in JPEG encoding is changed to, for example, 4: 1: 1. Subsequently, referring to the changed compression parameter, rasterization is performed as described in the second embodiment, and a JPEG code is generated (S907).

  Subsequently, the rasterized display list is deleted from the memory (S908), the display list that could not be stored in the memory in S904 is stored in the memory, and the process returns to S902. If the display list can be stored in the memory in S904, it is determined whether or not all PDL interpretations have been completed. If not, the process returns to S902 to interpret the remaining PDLs and generate a display list. To do. If the compression parameter has been changed at this time, the output of the display list may be changed as described in the first embodiment. Subsequently, when all PDL interpretations are completed in S909, the above-described flag is checked. If the flag is 1, the JPEG code already encoded in S907 is decoded in the band to be rasterized. And stored in the band buffer (S911).

  When decoding a JPEG code as described above, decoding is performed with an output resolution suitable for each color plane as a compression parameter. Subsequently, as described in the second embodiment, rasterization and JPEG encoding processing are performed (S912), and the above processing is performed for all the bands on the paper (S913).

  The JPEG code generated as described above can be handled in the same manner as the JPEG code described in the conventional example, and the subsequent processing has been described in the conventional example, and thus the description thereof is omitted.

  As described above, by changing the compression parameter during the processing of one page, a bitmap in which the output resolution is changed for each color is created only when the memory is exhausted, so when the memory is not exhausted. The image quality can be prevented from deteriorating.

1 is a diagram illustrating a printer controller according to a first embodiment of the present invention. FIG. It is a flowchart explaining the 1st Example concerning the present invention. It is a figure which shows an example of the display list which concerns on 1st Example of this invention. It is a figure which shows an example of the header information of the display list of FIG. It is a figure which shows an example of the display list which concerns on 1st Example of this invention. It is a figure which shows an example of the bit map from which resolution differs for every Y, Cr, and Cb. It is a figure explaining the rasterizer which concerns on 2nd Example of this invention. It is a figure which shows an example of the resolution conversion which concerns on 2nd Example of this invention. It is a flowchart explaining the 3rd Example of the present invention. It is a figure explaining a prior art example. It is a flowchart explaining a prior art example. It is a figure explaining JPEG encoding. It is a figure explaining the color conversion and downsampling in JPEG encoding. It is a formula for DCT conversion and IDCT conversion. It is a figure which shows an example of a quantization table. It is a figure explaining JPEG decoding. It is a figure which shows the encoding order of entropy encoding.

Explanation of symbols

101 PDL interpretation unit 102 display list generation unit 103 rasterizer 104 color conversion unit 105 FDCT unit 106 quantization unit 107 encoding unit 108 compression parameter supply unit 701 color conversion unit 702 address generation unit 703 logical operation unit 704 resolution conversion unit 705 band buffer

Claims (6)

  A drawing command input unit for inputting a drawing command, a drawing command analyzing unit for analyzing the input drawing command, a drawing unit for drawing an image based on an analysis result of the drawing command analyzing unit, and a coding rate is changed by a parameter An image forming apparatus comprising encoding means for encoding an image output by the drawing means, wherein the drawing means changes a color space of an image to be output according to a parameter of the encoding means.   The image forming apparatus according to claim 1, wherein the drawing unit changes a resolution of an image to be output for each color according to a parameter of the encoding unit.   3. The image forming apparatus according to claim 2, wherein the drawing command analyzing unit generates a drawing command that can be executed by the drawing unit, and the drawing command analyzing unit is executed by a drawing unit that outputs according to a parameter of the encoding unit. An image forming apparatus characterized by changing a format of a possible drawing command.   A drawing command input step for inputting a drawing command, a drawing command analyzing step for analyzing the inputted drawing command, a drawing step for drawing an image based on the analysis result of the drawing command analyzing step, and changing the coding rate according to parameters An image forming method comprising: an encoding step of encoding an image output by the drawing step, wherein the drawing step changes a color space of the output image according to a parameter of the encoding step.   5. The image forming method according to claim 4, wherein in the drawing step, the resolution of an image to be output is changed for each color according to the parameters of the encoding step.   6. The image forming method according to claim 5, wherein the drawing command analyzing step generates a drawing command that can be executed by the drawing step, and the drawing command analyzing step is executed by a drawing step that is output according to a parameter of the encoding step. An image forming method characterized by changing a format of a possible drawing command.

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