JP2006217578A - Image forming apparatus and driver program thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming an image on the basis of image forming data resulting from compressing image data with high image quality. <P>SOLUTION: The image forming apparatus for receiving the image forming data including a command with compression form information and compressed image data 54B, decompresses the compressed image data on the basis of the compression form information, and forming an image depending on the decompressed reproduction image data, includes: a command analysis means for analyzing first number of bit information D8/16 of the command with respect to the number of bits of the original image data; a decompression unit for decompressing the compressed image data on the basis of the compression form information to generate the reproduction image data; and a binary processing means for converting the reproduction image data into binary data corresponding to the pixels, and the decompression unit outputs the reproduction image data in the number of bits corresponding to the first number of bit information D8/16. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and a driver program thereof, and more particularly, by forming original image data format information and compressed data format information in JPEG-compressed image formation data, image formation with higher image quality is achieved. The present invention relates to an enabling image forming apparatus and a driver program thereof.

  2. Description of the Related Art Image forming apparatuses that form images by inkjet are widely used as means for printing photographs taken with a digital camera, designs created on a controller, and the like on a print medium. In particular, by adding light cyan, light magenta, light black, etc. in addition to cyan (C), magenta (M), yellow (Y), and black (K), the reproducible color is improved. This enables high image quality.

  The image forming apparatus is connected to a host computer, receives image forming data from the host computer, performs predetermined image processing, and outputs image reproduction data to a print engine such as an ink head or an electrophotographic engine. With the increase in image quality, the amount of image formation data has increased, and it is necessary to reduce the amount of communication time between the host computer and the image forming apparatus in order to reduce the image formation time.

In order to reduce the amount of communication data, data compression is performed on the host computer side, and data decompression is performed on the image forming apparatus side. There are various data compression methods, and representative methods include the JPEG compression method and the run length compression method. In particular, the JPEG compression method is widely used as a compression method for images such as photographs. In this case, the host computer JPEG compresses image data composed of RGB data of pixels, and the compressed data is transferred to a printer or the like. The data is transmitted to the image forming apparatus via a communication line and decompressed on the image forming apparatus side. The following Patent Document 1 discloses that an image forming apparatus using an ink jet receives JPEG compressed image forming data and generates an image.
JP 2002-187315 A

  Conventional general RGB image data, for example, image data captured from a digital still camera is composed of 8-bit RGB gradation data corresponding to each pixel. The same applies to the image data to be displayed on the monitor screen of the host computer. Therefore, the image forming apparatus performs decompression on the assumption that the original image data of the compressed image formation data is 8-bit RGB data, and performs image processing.

  However, in recent years, it has been proposed to use 12-bit RGB gradation data as higher-quality image data. When such image data is JPEG-compressed, the conventional image forming apparatus can only handle it as 8-bit RGB gradation data after decompression, and the image data on the transmission side has been increased in quality by increasing the number of bits. However, the image forming apparatus on the receiving side cannot cope with it, which hinders the improvement of image quality.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of forming an image based on compressed image forming data of high quality image data.

  In order to achieve the above object, according to a first aspect of the present invention, image forming data having a command including compressed format information and compressed image data is received, and the image forming data is received based on the compressed format information. In an image forming apparatus that decompresses compressed image data and forms an image according to the decompressed reproduced image data, the command includes first bit number information relating to the bit number of the original image data. The image forming apparatus includes a command analysis unit that analyzes the first bit number information of the command, a decompression unit that decompresses the compressed image data based on the compression format information, and generates reproduction image data, Binarization processing means for converting reproduced image data into binarized data corresponding to pixels, and the decompression unit outputs the reproduced image data with a bit number corresponding to the first bit number information. Features.

  According to the first aspect, since the bit number information of the original image data before decompression is included in the command of the image formation data, the reproduced image data after decompression is generated according to the bit number information. Can do. Therefore, even when the original image data has high image quality due to the increase in the number of bits, the image forming apparatus can form an image based on the reproduced image data corresponding to the original image data.

  In the first aspect, in a preferred embodiment, the binarization processing means converts reproduced image data into the binarized data corresponding to the number of bits.

  Furthermore, in the first aspect, in a preferred embodiment, the compression format is a format having a discrete cosine transform for generating a signal of a direct current component and an alternating current component, and the compressed image data includes the direct current component of the direct current component. A second bit number information relating to the number of bits, wherein the decompression unit performs inverse discrete cosine transform from the DC component and the AC component according to the second bit number information to generate the reproduced image data. To do.

  In order to achieve the above object, according to a second aspect of the present invention, image forming data having a command including compression format information and compressed image data is received, and the image forming data is received based on the compression format information. An image compression program that decompresses compressed image data and causes a computer to generate the image formation data for an image forming apparatus that forms an image according to the decompressed reproduction image data. This is a format having a discrete cosine transform for generating an AC component signal. Then, the image compression program includes the first bit number information regarding the bit number of the original image data in the command together with the compression formation information, and compresses the original image data according to the compression formation format. Generating image data, causing the computer to execute a procedure for generating the image forming data and a procedure for transmitting the image forming data to the image forming apparatus; and further, the compressed image data includes the DC component 2nd bit number information on the number of bits, and in the generation procedure, the DC component is generated with the number of bits of the second bit number information.

  According to the second aspect described above, it is possible to perform high-quality image compression using the first bit number information and the second bit number information, and by including such information in the image forming data, the image forming apparatus Can form high-quality images.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof.

  FIG. 1 is a configuration diagram of an image forming apparatus according to the present embodiment. As an example, this image forming apparatus is an ink jet printer that enables image formation on large-format paper. The controller 20 receives image forming data from a host computer (not shown), performs image processing on the image forming data, and outputs image reproduction data. The image reproduction signal 38 is output to the print head 10 having a large number of nozzles that generate and eject ink. The controller 20 includes a CPU that controls image processing for generating image reproduction data, its CPU bus CBUS1, and an image processing unit 22 connected to the CPU bus CBUS1. Further, an external CPU memory CPUMEM is connected to the CPU bus CBUS1, and various parameters and control programs are stored in the external CPU memory.

  The CPU bus CBUS1 is connected to the second CPU bus CBUS2 via the CPU interface CPUIF in the image processing unit 22. Further, the image processing unit 22 includes interfaces IF1 to IF3 of various communication channels NET1 to NET3, a path control unit 24 that performs transfer control of input data, a decompression unit group 26 that performs decompression processing, and image reproduction in a raster direction. A dedicated hardware block includes a pass decomposition processing unit 32 that decomposes data for each pass of the print head, and a nozzle order conversion processing unit 34 that changes the order of image reproduction data decomposed for each pass in the order of the nozzles of the print head. It is provided as. Further, the color conversion and binarization processing unit 12 is configured by an external dedicated processor, not dedicated hardware in the controller 20 such as the decompression unit group 26, the pass separation processing unit 32, and the nozzle forward conversion processing unit 34. In addition, color conversion and binarization processing are realized by a program so that changes in those processing can be easily handled.

  Furthermore, the image processing unit 22 has a local bus LBUS for connecting the above-described pass control unit 24, decompression unit group 26, pass decomposition processing unit 32, and nozzle forward conversion processing unit 34. The local bus LBUS includes an external memory. An external large-capacity memory E-MEM is connected via the controller 28. The external memory controller 28 and the external memory E-MEM are connected via a memory bus MBUS. The external large-capacity memory E-MEM temporarily stores input image formation data and has a plurality of buffer areas for temporarily storing data after each process. The local bus LBUS is connected to the binarization interface unit 30 and is connected to the color conversion and binarization processing unit 12 via the binarization bus HTBUS. The local bus LBUS is connected to the print head 10 via the head interface unit 36.

  The CPU buses CBUS1 and CBU2 are used for command interpretation and the like, whereas the local bus LBUS is used for transferring a large amount of image data. Therefore, the buses have a larger capacity than the CPU bus (the local bus has 128 bits). , The CPU bus is formed in 32 bits).

  The operations of the dedicated processing units in the image processing unit 22 are controlled through the CPU and the first CPU bus CBUS1 and the second CPU bus CBUS2. For example, when the CPU writes an operation start flag in the operation start register of each processing unit, each dedicated processing unit executes the corresponding processing, and the CPU receives an operation end interrupt signal when the processing of each processing unit ends. The end of the operation is detected.

Inkjet large format printers are widely used in the printing industry and the like, but in this embodiment, they can receive three types of input formats. First, JPEG compressed data obtained by compressing RGB image data in JPEG format, and second, C (cyan), M (magenta), Y (yellow), K (black) corresponding to the nozzles of the print head 10. , Lc (light cyan), lm (light magenta), lk (light black), llk (second light black) color data of 8 colors and run-length compressed data consisting of binarized data (each color 2 bits) Third, it is RHV2 compressed data in which CMYK 8-bit image data is compared with the previous raster and the difference is obtained.

  In the case of the first JPEG compressed data, the original image data is JPEG compressed on the host computer side, and the compressed data is input to the controller 20 via the communication lines NET1 to NET3. Since the compression rate is high, the amount of communication data can be reduced, and the communication time between the host computer and the printer can be shortened. However, on the printer side, the received JPEG compressed data is decompressed and RGB image data is reproduced, and the reproduced RGB image data is converted into color conversion, binarization processing, and conversion processing (pass decomposition processing) corresponding to the head nozzle. And nozzle forward conversion processing).

  In the case of the second run-length compressed data, since color conversion and binarization processing are performed on the host computer side, decompression processing is performed on the printer side, and after conversion processing to head data, an image is applied to the print head 10. What is necessary is just to output as the reproduction signal 38, and the process in the printer side is simplified.

  Since the third RHV2 compressed data is subjected to color conversion processing on the host computer side, it is necessary to perform decompression processing on the printer side to perform binarization processing and conversion processing corresponding to the nozzles of the head. is there.

  The data input in this way includes decompression (decoding) processing corresponding to each compression format, color conversion and binarization processing as required, and conversion processing to head data, that is, two for each dot. A pass decomposition process for decomposing the digitized data for each pass, and a nozzle order conversion process for rearranging the data arranged in the raster direction decomposed for each pass in the nozzle order of the head are performed.

  Next, a data flow and processing corresponding to input image formation data will be described. The input image formation data is input in the form of a packet via various communication channels NET1 to NET1-3. Each input interface IF1-3 performs processing such as reconstructing the packet into the original data string, Restore original data before transmission. Then, the input data is stored in the first input buffer I-BUF1 constituted by the FIFO memory in the path control unit 24, and the input buffer of the external large-capacity memory E-MEM via the local bus LBUS. Stored in the I-BUF3. The external memory E-MEM is, for example, a double rate synchronous DRAM, and has a large capacity and a high speed. Access to the external memory E-MEM is performed via the memory controller unit E-MC and the memory bus MBUS.

  Then, the head portion of the input data stored in the external memory E-MEM is stored again in the second input buffer I-BUF2 in the path control unit 24 via the local bus LBUS. That is, all the input data is stored in the external memory E-MEM, and only a part of the top of the input data is stored in the second input buffer I-BUF2 in the path control unit 24 and stopped. The first and second input buffers I-BUF1, 2 are FIFO buffers and are controlled by a FIFO controller (not shown).

Therefore, the CPU accesses the second input buffer I-BUF2 via the CPU buses CBUS1 and CBUS2 and analyzes the command at the head portion of the input data. The input data command includes compression format information for specifying the compression format. The command describes the data amount (how many bytes) in the case of the JPEG compression format and the RHV compression format, and the subsequent data amount can be recognized. In the case of the run-length compression format, the command does not describe the amount of data. When the CPU analyzes the command and recognizes the format type (compression format information) and the amount of data, the external memory E-MEM The input data stored in the three input buffers I-BUF3 are successively transferred to the second input buffer I-BUF2, from which the decompression units JPEGU, RLEU, RHVU corresponding to the format type in the decompression unit group 26 are transferred. To transfer data. This data transfer is performed via the dedicated line from the second input buffer I-BUF2 without passing through the local bus LBUS.

  In the case of the JPEG format, the image data is decompressed (decoded) by the corresponding decompression unit JPEGU, and the decompressed reproduced image data is stored in the RGB buffer RGB-BUF of the external memory E-MEM. This reproduced image data is 8-bit or 16-bit RGB gradation data corresponding to pixels of a predetermined resolution. The RGB reproduced image data stored in the RGB buffer is transferred to the color conversion & binarization processing unit 12 via the binarization interface unit 30, where it is subjected to color conversion processing, and the color space CMYK of the printer ink. Further, binarization processing is performed on the ink ejection data (2 bits) from the nozzles of the print head 10 and stored in the plane buffer PL-BUF of the external memory E-MEM. The 2-bit ink ejection data is binarized data indicating whether or not there is ejection for large dot printing and whether or not ejection for small dot printing is performed on each of the eight colors of ink described above. The binarization processing unit 12 performs resolution conversion for converting the resolution of the decompressed reproduced image data to a higher resolution as necessary. As a result, binarization processing results in binarized data indicating whether or not dots are ejected at a resolution of pixel density printed by the printer head.

  The CMYK binarized data stored in the plane buffer PL-BUF is decomposed into binarized data for each path of the head 10 by the path decomposition process 32 and stored in the path buffer MW-BUF in the external memory E-MEM. Stored. The binarized data decomposed for each pass is rearranged in the nozzle order of the head by the nozzle order conversion processing unit 34, and the nozzle order binarized data is stored in the head buffer HD-BUF in the external memory E-MEM. Stored. Finally, the binarized binarized data rearranged in the nozzle order is transferred to the printer head 10 as the image reproduction data 38 via the head control unit 36.

  When the input image formation data is in the run length compression format, it is obtained by compressing the binarized data of eight colors that have been subjected to the color conversion process and the binarization process on the host computer side. Therefore, the input image formation data is transferred from the second input buffer I-BUF2 to the run length decompression unit RLEU via a dedicated line, decompressed there, and stored in the plane buffer PL-BUF of the external memory E-MEM. . The subsequent processing is the same as the JPEG compression format.

  In the case of the RHV compression format, color conversion from RGB data to CMYK data is performed on the host computer side, and the CMYK four-color image data is RHV compressed. Therefore, the input image formation data is transferred from the second input buffer I-BUF2 to the RHV decompression unit RHVU via a dedicated line, where it is decompressed, and as CMYK image data, RGB buffer RGB- of the external memory E-MEM. Stored in BUF. Thereafter, the CMYK image data is transferred to the binarization processing unit 12, where binarization processing is performed to generate the above-described eight-color binarization data. The binarized data of the eight colors is stored in the plane buffer PL-BUF of the external memory E-MEM. The subsequent steps are the same as in the JPEG compression format.

  As described above, input data of different compression formats are transferred to and stored in the first input buffer I-BUF1, the third input buffer I-BUF3 in the external memory E-MEM3, and the second input buffer I-BUF2. Is done. Then, the command located at the head of the input data stored in the second input buffer I-BUF2 is analyzed by the CPU, and the compression format information is detected. Further, the CPU transfers the compressed data from the second input buffer I-BUF2 to the decompression units JPEGU, RLEU, RHVU corresponding to the detected compression format information via a dedicated line. After decompression by each decompression unit, the color conversion and binarization processing is performed by the processing unit 12, the pass division processing is performed by the processing unit 32, and the nozzle forward conversion processing is performed by the processing unit 34 as necessary. The binarized data to be output to the printer head 10 is stored in the head buffer HD-BUF. The binarized data rearranged in the order of the nozzles of the head is transmitted to the printer head 10 as an image reproduction signal 38.

  FIG. 2 is a diagram showing a configuration of image formation data in the case of the JPEG compression format. The image formation data 50 transmitted from the host computer side includes a command 52 having compression format information FMT and first bit number information D8 / 16 relating to the bit number of the original image data, and JPEG compressed image data 54. Composed. The command 52 is analyzed by the CPU, the compression format is detected, and it is detected whether the original RGB image data is 8-bit gradation data or 16-bit gradation data. Further, the compressed image data 54 includes a JPEG marker 54A and compressed data 54B, and the JPEG marker 54A includes information DC8 / 16 indicating whether or not the extension of the number of bits of the DC component is included. That is, when the number of bits is not expanded, the DC component is composed of 8 bits, and when the number of bits is expanded, the DC component is composed of 16 bits. Therefore, the JPEG decompression unit JPEGU analyzes this JPEG marker 54A and detects the number of effective bits of the DC component.

  FIG. 3 is a diagram showing the flow of processing in the host computer and printer in the case of the JPEG compression format. The original image data 60 stored in the host computer PC is 8-bit RGB image data or 16-bit (or more than 8 bits) RGB data, respectively. Therefore, 16-bit RGB data has higher gradation resolution and higher image quality. The original image data 60 is JPEG compressed by the printer driver program of the host computer PC (S62). In the JPEG compression process, the first bit number information D8 / 16 regarding the bit number of the original image data is stored in the command 52 of the image formation data compressed by JPEG (S64). Also, second bit number information DC8 / 16 relating to the effective number of bits of the DC component generated by JPEG compression discrete cosine conversion is stored in the marker 54A of the JPEG compression data.

  FIG. 4 is a flowchart showing JPEG compression processing by the printer driver. In response to the print request for the original image data, the driver program analyzes the original image data 60 (S80) and detects whether the RGB data is 8 bits or 16 bits (or more than 8 bits), respectively. The number of detected bits is set as the first bit number information D8 / 16 (S84, S86). Furthermore, the driver program sets the number of bits of the DC component after discrete cosine conversion to 8 bits or 16 bits depending on whether or not a high-quality print request is made (S88, S90, S92). Then, JPEG compression processing is performed corresponding to the first and second bit number information (S94).

  The JPEG process generates a DC component and an AC component of image data by a discrete cosine conversion process. At this time, if the second bit number information DC8 / 16 is 8 bits, a direct current component including more image features is generated with 8 bits, and if the second bit number information is 16 bits, the direct current component is Generated to 16 bits. Since the direct current component contains more image features, it is possible to improve the quality of the decompressed image while avoiding a reduction in compression rate by extending this component to 16 bits. Since the AC component does not include so much image feature, it is generated with 8 bits regardless of the second bit number information. The JPEG process includes a quantization process for the direct current component and the alternating current component, and an encoding process for Huffman encoding the quantized data.

  Then, the driver program generates a command 52 having the first bit number information D8 / 16 and the compression format information FMT (S96), and also includes the marker including the second bit number information DC8 / 16 and the compressed data having the compressed data. 54 is generated (S98). As a result, image formation data 50 is generated. Thereafter, the driver program transmits the image forming data 50 to the printer via a predetermined communication path.

  Returning to FIG. 3, the image forming data 50 is transmitted from the host computer to the printer (S66). In the printer, as described above, the input image formation data is stored in the first input buffer I-BUF1, the external memory E-MEM, and the second input buffer I-BUF2, and the commands stored in the second input buffer I-BUF2 are stored. Are read and analyzed by the CPU (S68). In the case of JPEG-compressed image formation data, the CPU detects that it is in JPEG compression format, and the compressed data 54 is transferred to the JPEG decompression unit JPEGU, where it is decompressed (S70).

  FIG. 5 is a diagram showing the configuration of the JPEG decompression unit and the reproduction image data generated by it. The JPEG decompression unit JPEGU is composed of dedicated hardware and includes a JPEG decoder 40 and a data selector 42. The JPEG decoder 40 further includes a Huffman decoder 44, an inverse quantizer 46, and an inverse discrete cosine. It comprises a converter (inverse DCT) 48, and decodes the image formation data 50 to generate RGB image data with 16 effective bits as reproduced image data 60A. The inverse DCT 48 is given the second bit number information DC8 / 16 stored in the JPEG marker 54A, and the DC component and the AC component are inversely DCT converted in accordance with the second bit number information. As a result, 16-bit RGB reproduction image data 60A is generated. Since the DCT conversion is an irreversible conversion, the reproduced image data 60A is not necessarily the same as the original image data 60, but is 16-bit RGB data.

  The data selector 42 of the JPEG decompression unit is provided with the first bit number information D8 / 16 and is generated by the JPEG decoder 40 corresponding to the effective bit number (8 bits or 16 bits) of the original image data. The effective portion of the 16-bit reproduction image data 60A is selected, and the effective reproduction image data 60A is output to the 128-bit local bus LBUS. The RGB buffer RGB- of the external memory via the external memory control unit E-MC Store in BUF. That is, as shown in FIG. 5, when the first bit number information D8 / 16 is 8 bits, 8-bit RGB data is sent to the local bus LBUS, and the first bit number information S8 / 16 is In the case of 16 bits, 16-bit RGB data is sent to the local bus LBUS.

  In this way, the JPEG decompression unit performs inverse DCT processing according to the second bit number information DC8 / 16, and reproduces image data consisting of bits selected according to the first bit number information D8 / 16 to the local bus LBUS. Output.

  Returning to FIG. 3, the printer controller 20 converts the reproduction image data of the RGB buffer RGB-BUF in the external memory into a color conversion and binarization processing unit via the binarization interface unit 30 and the binarization bus HTBUS. 12 for transfer. The color conversion and binarization processing unit 12 executes the firmware, performs color conversion processing from RGB to CMYK on the reproduced image data, and binarized data corresponding to whether or not eight colors of ink are ejected. Execute binarization processing to generate At this time, the color conversion and binarization processing unit 12 is provided with first bit number information D8 / 16 indicating the number of effective bits of RGB data. In accordance with this information, the processing unit 12, which is a dedicated processor, performs color conversion and binarization processing on 8-bit RGB data or 16-bit RGB data. The binarized data is stored in the plane buffer PLBUF of the external memory. The color conversion and binarization processing unit 12 includes a dedicated processor, and a processing program for 8-bit RGB data and a processing program for 16-bit RGB data are stored in memory as firmware. Therefore, the corresponding processing program is executed in accordance with the given first bit number information D8 / 16.

  Further, the printer controller 20 converts the binarized data into head data by the pass separation processing unit 32 and the nozzle forward conversion processing unit 34 (S74). Then, the converted head data is output to the printer head 10 as the image reproduction signal 38 (S76).

  FIG. 6 is a diagram for explaining a process of converting the binarized data in the raster direction in the plane buffer into head data. The binarized data 100 in the plane buffer PL-BUF are arranged in the raster direction (row direction) of rows L1 to L4 of the print medium. That is, after the binarized data “A1B1A1B1...” Of the row L1, the binarized data “A2B2A2B2...” Of the row L2, and then the binarized data “A3B3A3B3. Followed by "A4B4A4B4 ..." in row L4. Assume that the printer head 10 is composed of four nozzles and prints four rasters L1 to L4 in two passes A and B. That is, “A” of the binarized data 100 is printed in pass A, and “B” of the binarized data 100 is printed in the next pass B.

  First, the binarized data 100 arranged in the raster direction is divided into data for each path of the head by processing by the path division processing unit 32. In other words, the binarized data 102 of the path A includes “A1A1A1A1...” In the row L1, “A2A2A2A2. The binarized data 104 of the path B are rearranged in the same manner. Next, the binarized data 102 and 104 of each pass are rearranged in the order of the nozzles 1 to 4 of the printer head 10 by the nozzle order conversion processing unit 34. This nozzle forward conversion process is a so-called horizontal / vertical conversion process in which the binarized data 102 and 104 in the horizontal direction are rearranged in the order of the nozzles 10 in the nozzle direction. As a result, the binarized data 102 of pass A is rearranged as “A1A2A3A4A1A2A3A4...” Like the nozzle order data 106 by the nozzle order conversion process. Similarly, the binarized data 104 of pass B is rearranged as “B1B2B3B4B1B2B3B4...” Like the nozzle order data 108 by the nozzle order conversion process.

  In the first pass A in which the printer head 10 moves on the recording paper, the head control unit 36 generates an image reproduction signal 38 from the nozzle order data 106 and supplies it to the printer head 10 as a nozzle drive signal. The image reproduction signal 38 is supplied in the order of the nozzles 1 to 4 of the head 10. Similarly, in the next pass B of the printer head 10, the image reproduction signal 38 generated from the nozzle order data 108 is supplied to the printer head 10.

  As described above, according to the present embodiment, when image formation data compressed with JPEG is transmitted from a host computer to a printer and an image is formed after image processing by the printer, the original image data is included in the compressed data. First bit number information indicating the number of bits and second bit number information indicating the number of effective bits of the DC component after DCT conversion generated by JPEG compression are included. Thus, the printer controller 20 can detect the first bit number information and reflect it in the image processing, and can detect the second bit number information and reflect it in the inverse DCT conversion processing. Thereby, high-quality image formation is enabled. In the embodiment, the color conversion and binarization processing unit 12 is described as an example of a dedicated processor. However, as a dedicated processor, a general-purpose processor may be used exclusively for color conversion and binarization processing. A processor dedicated to image processing such as a DSP may be used.

  Based on the above embodiment, image compression means for generating image formation data by JPEG compression of 8-bit or 16-bit image data, decompressing the JPEG compression data to generate reproduction image data, Based on this, a specific example of compression / decompression processing in an image forming system including image forming means for forming an image will be described. First, JPEG compression processing by discrete cosine (DCT) in an image compression printer driver as image compression means will be described. Next, the decompression process in the JPEG decompression unit of the image forming apparatus as the image forming unit will be described.

  FIG. 7 is a diagram illustrating a configuration example of image formation data generated by JPEG compression processing of the image compression printer driver. As described with reference to FIG. 2, the image forming data 50 includes the command 52 having the compression format information FMT and the first bit number information D8 / 16 relating to the bit number of the original image data, the compressed image data 54 compressed with JPEG, Consists of.

  The JPEG marker 54A constituting the compressed image data 54 includes component bit number information DA11 / 15 relating to the DC component generated by DCT conversion and the effective bit number of the AC component. Here, the DC component and the AC component are composed of 11 bits when not bit-extended and 15 bits when bit-extended. Also, as will be described later, the number of bits of the AC component is expanded only when the number of bits of the DC component is expanded. Therefore, the component bit number information DA11 / 15 is composed of 15 bits when the direct current component and the alternating current component are both expanded and configured with 15 bits, or when both are not expanded with 11 bits, or the direct current component is expanded with 15 bits. This is information for identifying one of the cases where the AC component is not expanded and is composed of 11 bits.

  The compressed image data 54B constituting the compressed image data 54 includes a quantization coefficient table Q-TBL, a Huffman table H-TBL, and Huffman code data H-DT used for JPEG compression / decompression. It is. The quantization coefficient table Q-TBL is a table containing coefficients for quantizing a DC component and an AC component generated by DCT conversion. The Huffman table H-TBL is a table that stores associations between components and codes when the quantized DC component and AC component are replaced with Huffman codes. The Huffman code data H-DT is a series of reference information for referring to the Huffman table H-TBL.

  In a JPEG decompression unit to be described later, in decompression processing, the image data 54B compressed based on the Huffman table H-TBL, the quantization coefficient table Q-TBL, and the Huffman code data H-DT is decompressed. After the JPEG marker 54A is analyzed by the JPEG decompression unit, the component bit number information included therein is referred to by the color conversion & binarization processing unit 12 (FIG. 1) that performs processing such as halftoning.

  FIG. 8 is a flowchart showing the JPEG compression process of the image compression printer driver in the case where the bit expansion of the DC component and the AC component is included. In response to the print request for the original image data, the driver program analyzes the original image data 60 (S80) and detects whether the RGB data is 8 bits or 16 bits (or more than 8 bits), respectively. Then, the number of detected bits is set in the first bit number information D8 / 16 (S84, S86). The first bit number information is referred to when the JPEG decompression unit on the image forming apparatus side performs decompression processing.

  Next, the driver program sets the bit number of the DC component of the component bit number information to 11 bits or 15 bits depending on whether or not a high-quality print request is made (S880, S890, S892). Further, when the DC component is set to be expanded to 15 bits (S892), the bit number of the AC component of the component bit number information is required when higher image quality is requested according to the degree of the high image quality print request. Is similarly set to 11 bits or 15 bits (S900, S910, S912).

  Further, the driver program performs JPEG compression processing (S920) corresponding to the component bit number information. Then, a command having first bit number information and compression format information is generated (S940), compressed image data having component bit number information and compressed data is generated (S960), and the JPEG compression process is terminated.

  FIG. 9 is a diagram for explaining a change in data and a change in the number of bits associated with the JPEG compression processing of the printer driver.

  First, the original image data stored in the host computer PC is RGB data D502 of 8 bits or 16 bits (or more than 8 bits), respectively. In the JPEG compression process, the original image data is converted into YUV data D504 expressed by the luminance component (Y), the difference between the luminance component and the blue component (U), and the difference between the luminance component and the red component (V). (S941). Here, the 8-bit RGB image data is converted into 8-bit data, and the 16-bit RGB image data is converted into 16-bit YUV data D504.

  The following processing is performed on the YUV data D504 for each component of the luminance component (Y), the difference between the luminance component and the blue component (U), and the difference between the luminance component and the red component (V).

  First, DCT conversion is performed on 8-bit or 16-bit YUV data D504 (S942), and a DC component and an AC component D506 are generated. Regardless of the number of bits of the YUV data D504, the DC component and the AC component are generated as floating point type data having an integer part of 11 bits in the driver program of the host computer PC. Therefore, in JPEG compression processing after DCT conversion (S942), the floating-point type with an integer part of 11 bits is used regardless of whether the number of bits of the original image data is 8 bits or 16 bits (or more than 8 bits). It is possible to perform the same processing on the DC component or AC component that is data.

  In the DCT conversion, the two-dimensional pixel of the image data is divided into blocks each of 64 pixels of 8 pixels × 8 pixels, and all the pixels are performed in this block unit. When DCT conversion is performed on the YUV values of 64 pixels in one block, 64 DCT coefficients arranged two-dimensionally are obtained. FIG. 10A shows a block DB composed of 64 DCT coefficients obtained as a result of the DCT transformation. Here, the DCT coefficients are one DC component D which is a low frequency component including the most image features of the block and 63 AC components A1 to A63 which are high frequency components.

  Each of these components is arranged so that it contains more high-frequency horizontal frequency components as it goes from left to right, and more high-frequency vertical frequency components as it goes from top to bottom, and as it contains more high-frequency components. , The absolute value of the DCT coefficient of the component is small.

  Returning to FIG. 9, the DC component and AC component D506 generated in units of blocks as described above are quantized (S944) using the quantization coefficient table Q-TBL, and the quantized DC component and AC component are converted. Component D508 is obtained. The data obtained as a result of quantization is also configured as floating point type data having an integer part of 11 bits.

  The quantization coefficient table Q-TBL used for quantization is a table storing a DC component and a divisor for each AC component. The quantization is performed by dividing the DCT coefficient of each component in the block by each divisor of the quantization coefficient table Q-TBL and converting the result value to an integer part nearest to the integer. The quantization coefficient table Q-TBL is sent to the image forming apparatus as part of the compressed data, and is referred to when the JPEG decompression unit performs decompression processing.

  FIG. 10A shows a block BB obtained by quantizing each component of the block DB. The block BB includes a quantized DC component D1 and quantized AC components A11, A21, A31, This means that the high-frequency part, which is composed of... And has a small absolute value of the coefficient, is converted to an integer of “0”.

  Returning to FIG. 9, zigzag conversion, zero run length conversion, and Huffman coding are performed on the quantized DC component and AC component D508 configured as floating point type data having an integer part of 11 bits (S945). A table H-TBL and Huffman code data H-DT are obtained.

  In the zigzag transformation, the quantized direct current component and alternating current component arranged two-dimensionally in the block BB shown in FIG. 10A are converted from the direct current component D1 to the direct current components A11, A21, A31,..., A71, A81. , A, 91,..., 0, 0, 0 are read in a zigzag manner and rearranged into a one-dimensional bit string BS.

  Then, since the bit string BS is configured so that “0” continues at the end, the number of consecutive “0” values is collectively converted into one Huffman code by zero run length conversion. Thereby, redundant data can be compressed.

  In Huffman coding, a quantized DC / AC component configured as a bit string BS is associated with a Huffman code having the number of bits corresponding to the appearance frequency. That is, the data amount as a whole can be compressed by associating a component with high appearance frequency with a smaller number of bits. As a result of this processing, a Huffman table H-TBL storing a correspondence between Huffman data H-DT, which is a series of Huffman codes, and Huffman codes and quantized DC / AC components is generated from the bit string BS. .

  An example of the Huffman data H-DT and the Huffman table H-TBL generated in this way is shown in FIG. The Huffman code constituting the Huffman code data H-DT is configured as reference information HC1, HC2, HC3,... Referring to the Huffman table H-TBL, and the Huffman table H-TBL is a DC component quantized with these reference information. The correspondence between D1 and AC components A11, A21,... Is stored. Therefore, the Huffman code data HD and the Huffman table H-TBL have a relationship of reference data and a referenced table. The Huffman table H-TBL is sent to the image forming apparatus as a part of the compressed data, and is referred to when the JPEG decompression unit performs decompression processing.

  Returning to FIG. 9, through the above zigzag transformation, zero run length transformation, and Huffman coding, the DC component and the AC component are configured as floating point type data having an integer part of 11 bits. However, when expanding the number of bits of a DC component or AC component in response to a high-quality print request, floating-point type data in which the integer part is expanded to 15 bits by shifting the decimal point by 4 bits at the Huffman encoding stage. Is stored in the Huffman table H-TBL.

  Thus, in the driver program, bit expansion is performed at the time of storing the quantized DC component and AC component data in the Huffman table H-TBL, but until that point, each of the DCT conversion, quantization, zigzag conversion, etc. The processing can be uniformly performed on a DC component and an AC component, which are floating point type data of 11 bits in the integer part.

  Returning to FIG. 9 again, finally, compressed image data 54B including Huffman code data H-DT, Huffman table H-TBL, and quantization coefficient table Q-TBL for each YUV component is generated.

  As described above, the printer driver of the host computer PC JPEG compresses 8-bit or 16-bit image data as an 11-bit DC component and an AC component, and has image formation data 50 having a Huffman table corresponding to the presence or absence of bit expansion. To the image forming apparatus. In the image forming apparatus that has received this, the JPEG decompression unit performs decompression processing and performs image formation based on the generated reproduced image data.

  FIG. 11 is a diagram for explaining the configuration of the JPEG decompression unit and the number of bits of decompressed data and reproduced image data generated by the unit. The JPEG decompression unit JPEGU of the image forming apparatus includes dedicated hardware, and includes a JPEG header analysis unit J10, a storage unit MEM, a Huffman decoding unit J12, a zero run length decoding unit J14, an inverse quantization unit J16, and an inverse discrete cosine. A conversion (inverse DCT conversion) unit J18, a YUV / RGB conversion unit J20, and buffer memories FIFO1 to FIFO4 are provided, which are connected by a local bus LBUS1. Such a JPEG decompression unit JPEGU performs each process according to a reference clock CLK supplied from a clock generator (not shown), and stores the result of the process in an external register (not shown) as appropriate via the register interface RegI / F.

  With the above configuration, the JPEG decompression unit JPEGU decodes the JPEG-compressed image formation data 50 sent from the host computer PC, and converts the RGB image data having 8 or 16 effective bits into the local bus as the reproduction image data 60A. LBUS is output and stored in the RGB buffer RGB-BUF (FIG. 1) of the external memory via the external memory control unit E-MC.

  First, the JPEG header analysis unit J10 analyzes the command 52 and the marker 54A of the image formation data 50, and extends the first bit number information D8 / 16 regarding the number of bits of the original image data, the number of bits of the DC component and the AC component. Read component bit number information DA11 / 15 regarding non-expansion. Further, the quantization coefficient table Q-TBL and the Huffman table H-TBL included in the compressed image data 54B are read and stored in the storage unit MEM, and the Huffman code data H-DT is stored in the buffer FIFO1.

  Next, the Huffman decoding unit J12 reads the Huffman data H-DT from the buffer FIFO1, and decodes the quantized DC component and AC component with reference to the Huffman table H-TBL in the storage unit MEM. That is, based on the reference information of the Huffman code data H-DT with respect to the Huffman table H-TBL, the quantized DC component or AC component associated with the reference information is read from the Huffman table H-TBL and arranged in one dimension. The direct current component and the alternating current component in the quantized state are stored in the buffer FIFO 2. However, at this time, the AC component quantized to the continuous “0” value is still converted into one Huffman code.

  Here, paying attention to the quantized DC component and AC component stored in the Huffman table H-TBL, these components are originally 11 bits in the case of non-expansion on the printer driver side, and in the case of expansion. It was configured as floating point type data with an integer portion of 15 bits. However, since the JPEG decompression unit JPEGU processes the DC component and the integer part of the AC component as effective bits, the expanded component is composed of 15 effective bits and the unexpanded component is composed of 11 effective bits. Will be.

  Therefore, in the JPEG decompression unit JPEGU, decoding is performed according to the data stored in the Huffman table H-TBL, so that the automatically expanded bit component is the expanded bit number without depending on the component bit number information. Non-extended components can be decoded with unextended bits.

  Next, the zero run length decoding unit J14 reads the above data stored in the buffer FIFO2, decodes the continuous "0" value, and a bit string BS in which the quantized DC component and AC component are continuous (see FIG. 10 (A)) is reproduced and stored in the buffer FIFO 3.

  Next, the inverse quantization unit J16 reads the bit string BS stored in the buffer FIFO 3 while performing inverse zigzag conversion, rearranges it in a two-dimensional form, and reproduces the block BB (FIG. 10A). Then, each coefficient of the quantization coefficient table Q-TBL is multiplied by each corresponding component of the block BB, and the block DB composed of the DC component and the AC component before quantization is reproduced to the inverse DCT transform unit J18. Output.

  Then, the inverse DCT conversion unit J18 performs inverse DCT conversion on the direct current component and the alternating current component constituting the block DB, and reproduces the YUV value of 64 pixels of 8 pixels × 8 pixels as an integer of 12 bits, respectively. Store in FIFO4. The buffer FIFO 4 stores the decoded YUV data for every 64 pixels. This YUV data corresponds to decompressed data.

  In the above-described processing from Huffman decoding to inverse quantization, the direct current component and the alternating current component are composed of the number of bits corresponding to the number of bits of data stored in the Huffman table, that is, 11 bits or 15 bits. However, at the stage of inverse DCT conversion, the generated YUV data is composed of 12 effective bits.

  After the above processing is performed for all blocks to generate YUV data for all pixels, the YUV / RGB conversion unit J20 reads the YUV data from the buffer FIFO 4, converts it to RGB data, and converts it to the local bus LBUS to reproduce image data 60A. Output as. Here, each 12-bit YUV data is converted into 12-bit RGB image data, and thereafter, the effective bit number is scaled based on the first bit number information. That is, when the original image data is RGB data each composed of 8 bits, the effective bit number is shifted up by 4 bits, and 8-bit RGB image data is output. Alternatively, when the original image data is RGB data composed of 16 bits, the effective bit number is expanded by 4 bits, and 16-bit RGB data is output.

  Thus, in the JPEG decompression unit JPEGU, decompression data that is 12-bit YUV data is once generated by inverse DCT conversion at the final stage of the JPEG decompression process, and the first is performed when the YUV data is converted into RGB data. Based on the bit number information, the reproduced image data is configured with the same number of bits as the original image data. Therefore, JPEG-compressed data can be decompressed by a process using the same circuit configuration regardless of whether the DC component and AC component are bit-extended.

  As described above, in the image forming system of this embodiment, on the printer driver side, whether the image data has a normal bit number (8 bits) or a multi-bit number (16 bits), It is converted into 11-bit DC / AC components by DCT conversion. This makes it possible to perform JPEG compression with the same processing procedure. Further, the printer driver includes information on the number of bits of the original image data in the command as the first bit number information. As a result, the JPEG decompression unit side of the image forming apparatus refers to the first bit number information at the stage of generating reproduced image data as RGB data after decompressing JPEG-compressed data by the process with the same circuit configuration. The number of bits of the original image data can be reflected. Therefore, high-quality image formation is possible based on such reproduced image data.

1 is a configuration diagram of an image forming apparatus in the present embodiment. It is a figure which shows the structure of the image formation data in the case of a JPEG compression format. FIG. 5 is a diagram showing a processing flow in a host computer and a printer in the case of a JPEG compression format. FIG. 10 is a flowchart illustrating JPEG compression processing by a printer driver. It is a figure which shows the structure of a JPEG decompression | decompression unit and the reproduction | regeneration image data which it produces | generates. It is a figure explaining the process converted into head data. FIG. 4 is a diagram illustrating a configuration example of image formation data generated by JPEG compression processing of an image compression printer driver. FIG. 10 is a flowchart showing JPEG compression processing of an image compression printer driver in the case of including bit extension of a DC component and an AC component. It is a figure explaining the change of the data accompanying the JPEG compression process of a printer driver, and the change of the bit number. It is a figure explaining the structure of the various data produced | generated in the process of a JPEG compression process. It is a figure explaining the structure of a JPEG decompression | decompression unit, and the bit number of the decompression data and reproduction | regeneration image data which it produces | generates.

Explanation of symbols

50: Image formation data 52: Command 54: Compression data 54A: JPEG marker 54B: Compressed image data FMT: Compression format information D8 / 16: First bit number information DC8 / 16: Second bit number information

Claims (7)

Image forming data having a command including compression format information and compressed image data is received, the compressed image data is decompressed based on the compression format information, and an image is extracted according to the decompressed reproduction image data. In the image forming apparatus to be formed,
The command includes first bit number information regarding the number of bits of the original image data,
Command analysis means for analyzing the first bit number information of the command;
A decompression unit for decompressing the compressed image data based on the compression format information and generating reproduced image data;
Binarization processing means for converting the reproduced image data into binarized data corresponding to the pixels,
The image forming apparatus, wherein the decompression unit outputs the reproduced image data with a bit number corresponding to the first bit number information. In claim 1,
The binarization processing unit converts the reproduced image data into the binarized data in accordance with the number of bits of the first bit number information. In claim 1,
The compression format is a format having a discrete cosine transform for generating a DC component signal and an AC component signal;
The compressed image data has second bit number information related to the number of bits of the DC component, and the decompression unit performs inverse discrete cosine conversion from the DC component and the AC component according to the second bit number information. And generating the reproduced image data. In claim 3,
2. The image forming apparatus according to claim 1, wherein the second bit number information of the DC component is information indicating whether or not the extension of the bit number of the DC component is included. Image forming data having a command including compression format information and compressed image data is received, the compressed image data is decompressed based on the compression format information, and an image is extracted according to the decompressed reproduction image data. In an image compression program for causing a computer to generate the image formation data for an image forming apparatus to be formed,
The compression format is a format having a discrete cosine transform for generating a DC component signal and an AC component signal;
First bit number information relating to the number of bits of the original image data is included in the command together with the compression formation information, and the original image data is compressed according to the compression formation format to generate the compressed image data, A procedure for generating image formation data;
Causing the computer to execute a procedure for transmitting the image forming data to the image forming apparatus;
Further, the compressed image data has second bit number information relating to the number of bits of the DC component, and in the generation procedure, the DC component is generated with the number of bits of the second bit number information. An image compression program. In an image forming system having image compression means for compressing image data and outputting image forming data having the compressed image data, and image forming means,
The image data is image data having a first bit number or a second bit number larger than the first bit number;
The image compression means compresses the image data by discrete cosine transformation that generates a DC component and an AC component with a predetermined number of bits regardless of the number of bits of the image data, and generates the image formation data. An image forming system, wherein the data further includes first bit number information relating to the number of bits of the original image data, and is sent to the image forming means. In claim 6,
The image forming means receives the image forming data, performs inverse discrete cosine transformation from the DC component and AC component of the compressed image data to generate decompressed data with a predetermined number of bits, and then extracts the decompressed data from the decompressed data. A reproduction image data is generated with the first or second bit number based on the first bit number information, and an image is formed according to the reproduction image data.

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