JP2009232303A - Image processing system, image processing apparatus, image processing method and image processing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing technology capable of reducing a processing load for color-converting image data subjected to variable length coding. <P>SOLUTION: A printer 30 of a printing system 10 includes: a decoding table generating section 314 for generating a decoding table 325 obtained by color-converting an encoding table 224 acquired from a personal computer 20 from RGB value into CMYK value; and a decoding section 316 for generating CMYK raster data 328 by decoding encoded data 226 acquired from the PC 20 using the decoding table 325. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image processing technique for processing image data, and more particularly, to a technique for processing image data using variable length encoding such as Huffman encoding or Shannon-Fano encoding.

  In a printing system in which image data transmitted from a personal computer is printed by a printer, the throughput in the printing process can be improved by variable-length encoding the image data transmitted from the personal computer to the printer. In general, image data processed by a printing system is handled by an RGB color system when acquired by a digital camera or a scanner or displayed on a display, and from an RGB format when printed. The color is converted to the color system of the CMYK format. Patent Document 1 below discloses an image processing technique for compressing image data by Huffman coding.

JP 2006-58749 A

  Although the conventional image processing technique can reduce the processing load in variable-length encoding, it has not sufficiently considered the handling of image data that requires color conversion. For example, in a conventional printing system, after decoding variable length encoded image data, it is necessary to further color-convert the decoded image data.

  An object of the present invention is to provide an image processing technique capable of reducing the processing load for color-converting variable-length-encoded image data based on the above-described problems.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  Application Example 1 An image processing system of Application Example 1 is an image processing system that performs color conversion on image data, and includes a first image processing device that processes first raster data in a first color system, A second image processing device that processes second raster data obtained by color-converting the first raster data into a second color system, and the first image processing device includes the first raster data. Generated by the encoding table generation unit that generates an encoding table in which variable-length codes are assigned to pixel values in the first color system according to the appearance frequency of the pixel value in An encoding unit that generates encoded data obtained by variable-length encoding the first raster data using an encoding table; and a data reference that transfers the encoding table and the encoded data to the second image processing apparatus. The second image processing apparatus performs color conversion of pixel values in the encoding table delivered from the first image processing apparatus from the first color system to the second color system. A decoding table generating unit that generates the decoded decoding table, and decoding the encoded data delivered from the first image processing apparatus using the decoding table generated by the decoding table generating unit. And a decoding unit for generating the second raster data. According to the image processing system of Application Example 1, the second raster data can be directly generated from the encoded data using the decoding table obtained by color-converting the encoding table. As a result, it is possible to reduce the processing load for color conversion of variable length encoded image data.

  Application Example 2 In the image processing system according to Application Example 1, the encoding table generation unit of the first image processing apparatus includes: a pixel value of the first color system in the first raster data; An upper color specifying unit that specifies a predetermined number of pixel values as higher pixel values from the higher frequency, and a pixel value according to the first color system in the first raster data is different from the upper pixel value A lower color specifying unit that specifies a plurality of other pixel values, and a predetermined number of variable length codes are assigned to a predetermined number of upper pixel values specified by the upper color specifying unit, and specified by the lower color specifying unit. In addition, a code allocating unit that generates the encoding table by allocating a single variable length code to a plurality of other pixel values may be provided. According to the image processing system of the application example 2, since a single variable length code can be assigned to a plurality of other pixel values different from the upper pixel having a high appearance frequency, each of these other pixel values has a variable length. Compared to the case where a code is assigned, the data amount of the encoding table can be suppressed.

  [Application Example 3] In the image processing system of Application Example 2, the encoding unit of the first image processing apparatus may be configured such that a pixel value according to a first color system in the first raster data is the upper pixel value. If there is, a first code insertion unit that incorporates a variable-length code assigned to the pixel value in the encoding table into the encoded data, and a pixel value by the first color system in the first raster data Is one of the plurality of other pixel values, the variable length code assigned to the plurality of other pixel values in the encoding table is used together with the pixel value according to the first color system as the code. It is also possible to provide a second code incorporation unit that incorporates into the data. According to the image processing system of the application example 3, by inserting a plurality of other pixel values different from the upper pixel having a high appearance frequency into the encoded data together with the variable length code, the first raster can be obtained without dropping the data. Data can be encoded.

  Application Example 4 In the image processing system of Application Example 3, when the decoding unit of the second image processing unit is a code in which a variable length code in the encoded data is assigned to the upper pixel value, A first pixel value incorporation unit that incorporates pixel values of the second color system assigned to the variable length code in the decoding table into the second raster data; and a variable length code in the encoded data. Is a code assigned to the plurality of other pixel values, the second color system obtained by color-converting the pixel values of the first color system incorporated into the encoded data together with the variable length code And a second pixel value insertion unit that incorporates the pixel values obtained by (1) into the second raster data. According to the image processing system of the application example 4, it is possible to decode a plurality of other pixel values to which a single variable length code is assigned as second raster data.

  Application Example 5 In the image processing system according to any one of Application Examples 1 to 4, the encoding unit of the first image processing device includes the first raster data of the previous time and the first raster data of the subsequent time. If the appearance frequency of the pixel value is the same or similar between the first raster data, the subsequent first raster data is encoded using the encoding table used for variable-length encoding the previous first raster data. Coded data obtained by variable-length coding data may be generated. According to the image processing system of the application example 5, since it is not necessary to generate encoded data at the time of subsequent variable length encoding, it is possible to reduce a processing load for variable length encoding of image data.

  In the image processing system according to any one of Application Examples 1 to 5, the encoding table generation unit of the first image processing device may include pixels in each of a plurality of divided raster data obtained by dividing the first raster data. A plurality of encoding tables in which variable length codes are assigned to pixel values in the first color system may be generated according to the appearance frequency of values. According to this image processing system, subsequent processing can be advanced for each divided raster data without waiting for the entire first raster data to be variable-length encoded, so that the start of subsequent processing is accelerated. be able to.

  Application Example 6 An image processing apparatus that processes image data, and based on an encoding table in which variable-length codes are assigned to pixel values in the first color system, pixel values in the encoding table are set to a second value. A decoding table generation unit that generates a decoding table that is color-converted into the color system, and encoded data obtained by variable-length encoding the first raster data according to the first color system using the encoding table. And a decoding unit that generates second raster data according to the second color system by decoding using the decoding table generated by the decoding table generation unit, To do. According to the image processing apparatus of Application Example 6, the second raster data can be directly generated from the encoded data using the decoding table obtained by color-converting the encoding table. As a result, it is possible to reduce the processing load for color conversion of variable length encoded image data.

  The form of the present invention is not limited to the image processing system and the image processing apparatus, but is applied to other forms such as a printing apparatus (printer) incorporating the image processing apparatus, an image processing method using a computer, a computer program, and the like. You can also. Further, the present invention is not limited to the above-described embodiments, and it is needless to say that the present invention can be implemented in various forms without departing from the spirit of the present invention.

  In order to further clarify the configuration and operation of the present invention described above, an image processing apparatus to which the present invention is applied will be described below. In the present embodiment, a printing system will be described as an example of an image processing apparatus.

A. First embodiment:
A1. Printing system configuration:
FIG. 1 is an explanatory diagram showing the configuration of the printing system 10. A printing system 10 as an image processing system includes a personal computer (hereinafter referred to as a personal computer) 20 as a first image processing apparatus and a printer 30 as a second image processing apparatus. In the printing system 10, printing by the printer 30 is performed based on a printing request from the personal computer 20.
In this embodiment, the personal computer 20 and the printer 30 are connected via a local area network (LAN) so that data can be exchanged. However, as another embodiment, a wireless LAN, Internet, USB (Universal Serial Bus), Bluetooth, etc. may be used.

  The personal computer 20 of the printing system 10 includes a central processing unit (hereinafter referred to as CPU) 210, a memory 220, a communication interface 280, and a user interface 290.

  The CPU 210 of the personal computer 20 executes various arithmetic processes based on the program stored in the memory 220. The CPU 210 includes a RIP (Raster Image Processor) unit 212, a coding table generation unit 214, a coding unit 216, and a data delivery unit 218 as functional elements realized based on a program. The RIP unit 212 of the CPU 210 generates RGB raster data 222 that is raster data based on the RGB color system by rasterizing image data printed by the printer 30. Raster data refers to data that represents an image by listing a plurality of pixel values having color information of pixels (pixels). In the RGB color system, various colors are reproduced by mixing three colors of red, green, and blue. The RGB raster data 222 generated by the RIP unit 212 is stored in the memory 220.

  The encoding table generation unit 214 of the CPU 210 detects the appearance frequency of the pixel value in the RGB raster data 222 and generates an encoding table 224 in which a Huffman code is assigned to the RGB value according to the appearance frequency. The encoding table 224 generated by the encoding table generation unit 214 is stored in the memory 220. Details of the encoding table 224 will be described later. The encoding unit 216 of the CPU 210 uses the encoding table 224 generated by the encoding table generation unit 214 to generate encoded data 226 obtained by Huffman encoding the RGB raster data 222 generated by the RIP unit 212. Details of the encoded data 226 will be described later. The data delivery unit 218 of the CPU 210 delivers the encoding table 224 and the encoded data 226 to the printer 30 through the communication interface 280.

  In the present embodiment, the memory 220 of the personal computer 20 includes a read only memory (hereinafter referred to as “ROM”) and a random access memory (hereinafter referred to as “RAM”). (Hard Disk Drive, hereinafter referred to as HDD) may be virtually used as part of the memory 220. A communication interface 280 of the personal computer 20 exchanges data with the printer 30. The user interface 290 of the personal computer 20 includes a display, a keyboard, and a mouse, and exchanges information with the user of the personal computer 20. Details of the operation of the personal computer 20 will be described later.

  The printer 30 of the printing system 10 is an ink jet printer that prints data such as characters and images by ejecting ink droplets onto a print medium such as paper or a label. In the present embodiment, the printer 30 has various functions such as a scanner and a copy as a so-called multifunction machine. The printer 30 includes a CPU 310, a memory 320, a printing mechanism unit 330, a scanner 340, a communication interface 380, and a user interface 390.

  The CPU 310 of the printer 30 executes various arithmetic processes based on programs stored in the memory 320. The CPU 310 includes an image acquisition unit 312, a decoding table generation unit 314, a decoding unit 316, and a print instruction unit 318 as functional elements realized based on the program. The image acquisition unit 312 of the CPU 310 acquires the encoding table 224 and the encoded data 226 from the personal computer 20 through the communication interface 380. The encoding table 224 and the encoded data 226 acquired by the image acquisition unit 312 are stored in the memory 320.

  The decoding table generation unit 314 of the CPU 310 generates a decoding table 325 in which pixel values in the encoding table 224 acquired from the personal computer 20 are color-converted from the RGB color system to the CMYK color system. In the CMYK color system, various colors are reproduced by mixing four colors of cyan, magenta, yellow, and black. The decoding table 325 generated by the decoding table generation unit 314 is stored in the memory 320. Details of the decoding table 325 will be described later. The decoding unit 316 of the CPU 310 decodes the encoded data 226 acquired from the personal computer 20 by using the decoding table 325 generated by the decoding table generation unit 314, thereby converting the encoded data 226 into raster data using the CMYK color system. Some CMYK raster data 328 is generated. The CMYK raster data 328 generated by the decoding unit 316 is stored in the memory 320. The print instruction unit 318 of the CPU 310 instructs the print mechanism unit 330 to print the CMYK raster data 328 generated by the decryption unit 316. In this embodiment, the CMYK raster data 328 that is instructed to be printed by the printing mechanism unit 330 is subjected to halftone processing by the print instruction unit 318.

  In this embodiment, the memory 320 of the printer 30 includes a ROM and a RAM, and as another embodiment, an HDD may be used virtually as a part of the memory 320. The printing mechanism unit 330 of the printer 30 performs printing by ejecting four color inks of cyan, magenta, yellow, and black onto the printing medium based on an instruction from the CPU 310. Execute. The scanner 340 of the printer 30 reads a document placed on a document table (not shown) and converts it into digital data (scan). A communication interface 380 of the printer 30 exchanges data with the personal computer 20. The user interface 390 of the printer 30 includes a display and an operation panel, and exchanges information with the user of the printer 30. Details of the operation of the printer 30 will be described later.

A2. PC behavior in the printing system:
FIG. 2 is a flowchart showing print request processing executed by the CPU 210 of the personal computer 20 in the printing system 10. The print request process in FIG. 2 is a process for transmitting the encoded print data from the personal computer 20 to the printer 30. In the present embodiment, when a print request for printing image data by the printer 30 is received from the user of the personal computer 20 via the user interface 290, the CPU 210 of the personal computer 20 performs the print request processing of FIG. To start. In the present embodiment, the print request process of FIG. 2 is realized by the CPU 210 of the personal computer 20 operating based on software. As another embodiment, the electronic circuit of the personal computer 20 has a physical circuit configuration. It may be realized by operating based on this.

  When the CPU 210 of the personal computer 20 starts the print request process of FIG. 2, the rasterization process is performed by operating as the RIP unit 212 (step S220). In the present embodiment, in the rasterizing process (step S220), the image data designated by the user of the personal computer 20 via the user interface 290 is rasterized into the RGB raster data 222. Stored in the memory 220. An example of the RGB raster data 222 described in this embodiment is shown in the following formula 1.

  Here, X1 is RGB raster data 222, and C1, C2, C3... Are data representing RGB values indicating component values of the RGB color system in 24 bits (for example, C1 = (0, 0, 225)).

  After the rasterization process (step S220), the CPU 210 executes the encoding table generation process by operating as the encoding table generation unit 214 (step S240). In the encoding table generation process (step S240), the CPU 210 generates the appearance frequency (histogram) of the RGB values in the RGB raster data 222 (step S242). In this embodiment, the CPU 210 aggregates the appearance frequencies of the RGB values in the RGB raster data 222 from the higher appearance frequency using the “n” RGB values as the upper pixel values, and these “n” upper values. The RGB values other than the pixel values are summed up to a single appearance frequency as the lower pixel values. In this embodiment, “7” RGB values from the highest appearance frequency are tabulated as upper pixel values, but as other embodiments, the processing capacity of the CPU 210 in the personal computer 20, the storage capacity of the memory 220, The number of upper pixel values may be increased or decreased according to the communication speed with the printer 30, the processing capacity of the CPU 310 in the printer 30, the storage capacity of the memory 320, and the like.

  An example of the appearance frequency described in this embodiment is as follows. The upper pixel values are C1, C2, C3, C4, C5, C6, and C7, and their appearance frequencies are 50% for C1, 20% for C2, 15% for C3, 5% for C4, and 3 for C5. %, C6 is 2%, C7 is 1%, and the appearance frequency of the lower pixel is 4%.

  After the appearance frequency (histogram) of the RGB values in the RGB raster data 222 is generated (step S242), the CPU 210 generates an encoding table 224 in which Huffman codes are assigned to the RGB values according to the appearance frequencies (step S244). ). In the present embodiment, “n + 1” pixel values, which are obtained by adding “n” upper pixel values to lower pixel values obtained by combining other pixel values into one, according to their appearance frequencies. “N + 1” Huffman codes are assigned.

  FIG. 3 is an explanatory diagram schematically illustrating an example of the encoding table 224. The encoding table 224 includes an RGB data string 2242 indicating RGB values and a Huffman code string 2244 indicating Huffman codes assigned to the RGB values of the RGB data string 2242, respectively. In the present embodiment, eight Huffman values corresponding to the appearance frequency are obtained for a total of eight pixel values obtained by adding the lower pixel values obtained by combining the other upper pixel values to the seven upper pixel values. A code is assigned. In the present embodiment, the shortest Huffman code “F1 = 0” is assigned to the highest pixel C1 having the highest appearance frequency, and subsequently “F2 = 10” in C2 and “F3 in C3 in order of appearance frequency. = 110 ", and" F4 = 11100 "is assigned to C4. In the present embodiment, the appearance frequency of the lower pixel is 4%, which is higher than the appearance frequency of 3% of the upper pixel C5. Therefore, the Huffman code “G = G = 11101 "is assigned. In this embodiment, “F5 = 11110” is assigned to C5, “F6 = 111110” is assigned to C6, and “F7 = 111111” is assigned to C7 following the lower pixel.

  Returning to the description of FIG. 2, after the encoding table generation process (step S240), the CPU 210 of the personal computer 20 reads out and prepares the first RGB value of the RGB raster data 222 from the memory 220 (step S261). Thereafter, the CPU 210 checks the prepared RGB values against the encoding table 224 (step S264).

  When the RGB value is an upper pixel value (in this embodiment, the RGB value is any one of C1 to C7) (step S265), the CPU 210 changes the Huffman code of the encoding table 224 corresponding to the RGB value. The encoded data 226 is incorporated (step S266). On the other hand, when the RGB value is a lower pixel value (in this embodiment, the RGB value is other than C1 to C7) (step S265), the CPU 210 encodes a coding table corresponding to another pixel value that is a lower pixel. Together with the Huffman code 224, the RGB values are incorporated into the encoded data 226 (step S267). After the Huffman code corresponding to the RGB value is incorporated into the encoded data 226 (steps S266 and S267), the CPU 210 Huffman-encodes all the RGB values included in the RGB raster data 222 into the encoded data 226. Until the process is repeated (steps S264, S268, S269).

  An example in which the RGB raster data 222 shown in Equation 1 is Huffman encoded into the encoded data 226 is shown below. In this embodiment, the first RGB value in the RGB raster data 222 of Equation 1 is C1. According to the encoding table 224 of FIG. 3, since the pixel value C1 is associated with the Huffman code “F1 = 0”, the Huffman code “F1 = 0” is stored in the encoded data 226 ( Step S266). An example of the encoded data 226 in this state is shown in the following Equation 2.

  Here, X2 is the encoded data 226.

  In the present embodiment, the second RGB value in the RGB raster data 222 of Formula 1 is C3. According to the encoding table 224 of FIG. 3, since the pixel value C3 is associated with the Huffman code “F3 = 110”, the Huffman code “F3 = 110” is stored in the encoded data 226 ( Step S266). An example of the encoded data 226 in this state is shown in Equation 3 below.

  In the present embodiment, the third RGB value in the RGB raster data 222 of Formula 1 is C9. According to the encoding table 224 of FIG. 3, the pixel value C9 is another pixel value that is a lower pixel value, and the Huffman code “G = 11101” is associated with the other pixel value. The RGB value “C9” is stored in the encoded data 226 together with the Huffman code “G = 11101” (step S267). An example of the encoded data 226 in this state is shown in the following Expression 4.

  By repeating the processing as described above, the RGB raster data 222 of Equation 1 is Huffman-encoded into the encoded data 226 expressed by Equation 5 below (Step S260).

  Returning to the description of FIG. 2, after the encoding process (step S260), the CPU 210 of the personal computer 20 performs the data delivery process by operating as the data delivery unit 218 (step S280). In the data delivery process (step S280), the CPU 210 combines the encoded data 226 generated in the encoding process (step S260) with the encoding table 224 generated in the encoding table generation process (step S240). The data is transmitted to the printer 30 through the communication interface 280 (step S280). After the data delivery process (step S280), the CPU 210 ends the print request process of FIG.

A3. Printer behavior in the printing system:
FIG. 4 is a flowchart showing image printing processing executed by the CPU 310 of the printer 30 in the printing system 10. The image printing process of FIG. 4 is a process for decoding and printing the encoded print data received from the personal computer 20. In this embodiment, when the communication interface 380 of the printer 30 receives the encoding table 224 and the encoded data 226 from the personal computer 20, the CPU 310 of the printer 30 starts the image printing process of FIG. In the present embodiment, the image printing process of FIG. 4 is realized by the CPU 310 of the printer 30 operating based on software. However, as another embodiment, the electronic circuit of the printer 30 has a physical circuit configuration. It may be realized by operating based on this.

  When the image printing process of FIG. 4 is started, the CPU 310 of the printer 30 executes the image acquisition process by operating as the image acquisition unit 312 (step S320). In the image acquisition process (step S320), in this embodiment, the CPU 310 acquires the encoding table 224 from the personal computer 20 through the communication interface 380 (step S322). Thereafter, the CPU 310 acquires the encoded data 226 from the personal computer 20 through the communication interface 380 (step S324). In this embodiment, the encoding table 224 and the encoded data 226 acquired from the personal computer 20 are stored in the memory 320 of the printer 30.

  After the image acquisition process (step S320), the CPU 310 performs a decoding table generation process by operating as the decoding table generation unit 314 (step S340). In the decoding table generation process (step S340), the CPU 310 performs color conversion by converting the RGB values in the encoding table 224 acquired from the personal computer 20 in the image acquisition process (step S320) into CMYK values (step S342). A decoding table 325 in which the CMYK values are associated with the Huffman codes in the table 224 is generated (step S344).

  FIG. 5 is an explanatory diagram schematically showing an example of the decoding table 325. The decoding table 325 includes a CMYK data string 3252 indicating CMYK values and a Huffman code string 3254 indicating Huffman codes respectively assigned to the CMYK values of the CMYK data string 3252. The CMYK values D1 to D7 indicating the component values of the CMYK color system are data obtained by color-converting the RGB values C1 to C7 into CMYK values, respectively.

  Returning to the description of FIG. 4, after the decoding table generation process (step S340), the CPU 310 of the printer 30 performs the decoding process by operating as the decoding unit 316 (step S360). In the decoding process (step S360), the CPU 310 uses the decoding table 325 generated by the decoding table generation process (step S340) for the encoded data 226 acquired from the personal computer 20 by the image acquisition process (step S320). By decoding, CMYK raster data 328 is generated. Details of the decoding process (step S360) will be described later.

  After the decryption process (step S360), the CPU 310 performs the print instruction process by operating as the print instruction unit 318 (step S380). In the print instruction process (step S380), the CPU 310 controls the print mechanism unit 330 to print the CMYK raster data 328 generated in the decryption process (step S360). After the print instruction process (step S380), the CPU 310 of the printer 30 ends the image print process of FIG.

  FIG. 6 is a flowchart showing details of the decoding process (step S360) in the image printing process of FIG. When the decoding process (step S360) in FIG. 6 is started, the CPU 310 of the printer 30 reads out the first Huffman code of the encoded data 226 acquired from the personal computer 20 in the image acquisition process (step S320) and prepares it. (Step S361). Thereafter, the CPU 310 checks the prepared Huffman code against the decoding table 325 generated by the decoding table generation process (step S340) (step S362).

  When the Huffman code is a code associated with the upper pixel value (in this embodiment, the Huffman code is any one of F1 to F7) (step S364), the CPU 310 decodes the Huffman code. The CMYK values in the table 325 are incorporated into the CMYK raster data 328 (step S366). On the other hand, when the Huffman code is a code associated with the lower pixel value (in this embodiment, the Huffman code is G) (step S364), the CPU 310 incorporates the Huffman code G into the encoded data 226. The specified RGB value is specified (step S372). Thereafter, the CPU 310 color-converts the RGB value specified from the encoded data 226 into a CMYK value (step S374), and incorporates the CMYK value color-converted from this RGB value into the CMYK raster data 328 (step S376). After the CMYK values corresponding to the Huffman codes are incorporated into the CMYK raster data 328 (steps S366 and S376), the CPU 310 until all of the Huffman codes included in the encoded data 226 are decoded into the CMYK raster data 328. The process is repeated (steps S362, S368, S369).

  An example of decoding the encoded data 226 shown in Equation 5 into CMYK raster data 328 is shown below. In the present embodiment, the first Huffman code in the encoded data 226 of Equation 5 is “F1 = 0”. According to the decoding table 325 of FIG. 5, since the CMYK value “D1” is associated with the Huffman code F1, the CMYK value “D1” is stored in the CMYK raster data 328 (step S366). An example of the CMYK raster data 328 in this state is shown in the following Expression 6.

  Here, X3 is CMYK raster data 328.

  In the present embodiment, the second Huffman code in the encoded data 226 of Equation 5 is “F3 = 110”. According to the decoding table 325 of FIG. 5, since the CMYK value “D3” is associated with the Huffman code F3, the CMYK value “D3” is stored in the CMYK raster data 328 (step S366). An example of the CMYK raster data 328 in this state is shown in the following Expression 7.

  In the present embodiment, the third Huffman code in the encoded data 226 of Equation 5 is “G = 11101”. According to the decoding table 325 in FIG. 5, since the Huffman code G is associated with other pixel values that are lower pixel values, RGB stored in the encoded data 226 next to the Huffman code G “D9” obtained by color-converting the value “C9” into a CMYK value is stored in the CMYK raster data 328 (step S376). An example of the CMYK raster data 328 in this state is shown in the following Expression 8.

  By repeating the process as described above, the encoded data 226 of Expression 5 is decoded into CMYK raster data 328 expressed by Expression 9 below (step S360).

A4. effect:
According to the printing system 10 described above, the CMYK raster data 328 can be directly generated from the encoded data 226 using the decoding table 325 obtained by color-converting the encoding table 224. As a result, it is possible to reduce the processing load for color-converting RGB raster data that has been subjected to Huffman coding into CMYK raster data.

  In addition, since a single Huffman code can be assigned to a plurality of other pixel values different from the upper pixel having a high appearance frequency (step S244), it is compared with a case where a Huffman code is assigned to each of these other pixel values. Thus, the data amount of the encoding table 224 can be suppressed. Also, RGB raster data 222 is encoded without dropping data by incorporating a plurality of other pixel values different from the high-appearance upper pixel together with Huffman code into encoded data 226 (step S267). Can do.

B. Other embodiments:
As mentioned above, although embodiment of this invention was described, this invention is not limited to such embodiment at all, Of course, it can implement with various forms within the range which does not deviate from the meaning of this invention. is there. For example, in the present embodiment, the RGB color system and the CMYK color system are shown as an example of the color system, but the data code when color conversion is required between other color systems such as RGBA and YCbCr. The present invention may be applied to the conversion. In the present embodiment, Huffman coding is shown, but the present invention may be applied to other variable length coding such as Shannon coding.

  In the above-described embodiment, the example in which the present invention is applied to the printing system 10 including the personal computer 20 and the printer 30 has been described. However, as another embodiment, for example, a digital still camera or a digital An image processing apparatus that can process image data such as a camera or a mobile phone may be connected to the printer 30. In the printer 30, the RGB raster data generated by the scanner 340 is Huffman-encoded in the memory 320 and temporarily stored, and then the RGB raster data is printed by the printing mechanism unit 330. May be.

  Further, the CPU 310 of the personal computer 20 in the printing system 10 converts the previous RGB raster data into Huffman data when the frequency of appearance of pixel values is the same or similar between the previous RGB raster data and the subsequent RGB raster data. Using the encoding table used for encoding, encoded data obtained by Huffman encoding subsequent RGB raster data may be generated. Accordingly, it is not necessary to generate encoded data in subsequent Huffman encoding, so that the processing load for Huffman encoding of image data can be reduced.

  Further, the CPU 310 of the personal computer 20 in the printing system 10 generates a plurality of encoding tables in which Huffman codes are assigned to the RGB values according to the appearance frequency of the pixel values in each of the plurality of divided raster data obtained by dividing the RGB raster data. You may do that. Accordingly, the subsequent process can be advanced for each divided raster data without waiting for the entire RGB raster data to be Huffman-encoded, so that the start of the subsequent process can be accelerated.

1 is an explanatory diagram showing a configuration of a printing system 10. FIG. 4 is a flowchart illustrating print request processing executed by a CPU 210 of the personal computer 20 in the printing system 10. 5 is an explanatory diagram schematically showing an example of an encoding table 224. FIG. 3 is a flowchart illustrating image printing processing executed by a CPU 310 of a printer 30 in the printing system 10. It is explanatory drawing which shows an example of the decoding table 325 typically. 6 is a flowchart showing details of a decoding process (step S360) in the image printing process of FIG.

Explanation of symbols

10 ... Printing system 20 ... Personal computer 30 ... Printer 210 ... CPU
212 ... RIP section 214 ... coding table generation section 216 ... coding section 218 ... data delivery section 220 ... memory 222 ... RGB raster data 224 ... coding table 226. .. Encoded data 280 ... Communication interface 290 ... User interface 310 ... CPU
312 ... Image acquisition unit 314 ... Decoding table generation unit 316 ... Decoding unit 318 ... Print instruction unit 320 ... Memory 325 ... Decoding table 328 ... CMYK raster data 330 ... Printing mechanism 340 ... Scanner 380 ... Communication interface 390 ... User interface 2242 ... RGB data string 2244 ... Huffman code string 3252 ... CMYK data string 3254 ... Huffman code Column

Claims (8)

An image processing system for color-converting image data,
A first image processing device for processing first raster data using a first color system;
A second image processing device for processing second raster data obtained by color-converting the first raster data into a second color system;
The first image processing apparatus includes:
An encoding table generating unit that generates an encoding table in which variable length codes are assigned to the pixel values of the first color system in accordance with the appearance frequency of the pixel values in the first raster data;
An encoding unit that generates encoded data obtained by variable-length encoding the first raster data using the encoding table generated by the encoding table generation unit;
A data delivery unit that delivers the coded table and the coded data to the second image processing device;
The second image processing apparatus includes:
A decoding table generation unit that generates a decoding table obtained by color-converting pixel values in the encoding table delivered from the first image processing apparatus from the first color system to the second color system;
A decoding unit that generates the second raster data by decoding the encoded data delivered from the first image processing apparatus using the decoding table generated by the decoding table generation unit. An image processing system comprising: The image processing system according to claim 1,
The encoding table generation unit of the first image processing device includes:
An upper color specifying unit that specifies a predetermined number of pixel values as higher pixel values from the higher frequency among the pixel values of the first color system in the first raster data;
A lower color specifying unit for specifying a plurality of other pixel values different from the upper pixel value among the pixel values of the first color system in the first raster data;
The predetermined number of variable length codes are assigned to a predetermined number of upper pixel values specified by the upper color specifying unit, and a single variable length code is assigned to a plurality of other pixel values specified by the lower color specifying unit. An image processing system comprising: a code allocating unit that generates the coding table by allocating. The image processing system according to claim 2,
The encoding unit of the first image processing apparatus includes:
When the pixel value of the first color system in the first raster data is the upper pixel value, the first variable length code assigned to the pixel value in the encoding table is incorporated into the encoded data. The code incorporation part of
If the pixel value of the first color system in the first raster data is one of the plurality of other pixel values, the variable length code assigned to the plurality of other pixel values in the encoding table And a second code incorporation unit that incorporates the pixel values of the first color system into the encoded data. The image processing system according to claim 3,
The decoding unit of the second image processing unit includes:
When the variable length code in the encoded data is a code assigned to the upper pixel value, the pixel value of the second color system assigned to the variable length code in the decoding table is set to the second color system code. A first pixel value transfer unit for transfer to raster data;
When the variable length code in the encoded data is a code assigned to the plurality of other pixel values, the pixel value of the first color system that is incorporated into the encoded data together with the variable length code An image processing system comprising: a second pixel value incorporation unit that incorporates the converted pixel values of the second color system into the second raster data.   The encoding unit of the first image processing apparatus, when the appearance frequency of pixel values is the same or similar between the previous first raster data and the subsequent first raster data, 5. The encoded data obtained by variable-length encoding the subsequent first raster data is generated using an encoding table used for variable-length encoding the first raster data of the first time. Any one of the image processing systems. An image processing apparatus for processing image data,
A decoding table that generates a decoding table in which pixel values in the encoding table are color-converted to the second color system based on an encoding table in which variable-length codes are assigned to the pixel values of the first color system A generator,
Decoding encoded data obtained by variable-length encoding the first color system raster data using the encoding table, using the decoding table generated by the decoding table generating unit, An image processing apparatus comprising: a decoding unit that generates raster data of the second color system. An image processing method for processing image data using a computer,
Decoding table generation means provided in the computer performs color conversion of pixel values in the encoding table to the second color system based on an encoding table in which variable length codes are assigned to the pixel values of the first color system Generating a decoded table,
Decoding means included in the computer uses the decoding table generated by the decoding table generation means to generate encoded data obtained by variable-length encoding the first color system raster data based on the encoding table. And a step of generating raster data of the second color system by decoding. A program for causing a computer to execute a function of processing image data,
A decoding table that generates a decoding table in which pixel values in the encoding table are color-converted to the second color system based on an encoding table in which variable-length codes are assigned to the pixel values of the first color system Generation function,
By decoding the encoded data obtained by variable-length encoding the first color system raster data using the encoding table, using the decoding table generated by the decoding table generation function, A program for causing a computer to realize a decoding function for generating raster data of the second color system.

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