JP6044347B2 - Image processing apparatus, encoding method, and decoding method - Google Patents

Description

  The present invention relates to an image processing device, an encoding method, and a decoding method.

Devices that handle image data, such as image forming apparatuses, generally have a function for performing encoding processing on image data (see, for example, Patent Document 1). The encoding process here is a process of reducing the data amount of the image data by quantizing the pixel value of one or a plurality of pixels constituting the image data with a predetermined number of quantization bits. The image forming apparatus reduces the amount of storage capacity of the storage unit for storing image data by reducing the amount of image data by encoding processing.
In addition, a device that handles image data performs a decoding process on the image data that has been subjected to the encoding process at the time of image formation, and acquires image data that is the same as that before encoding or approximated before the encoding. Here, the encoding method in the encoding process and the decoding method in the decoding process are paired. Therefore, a device that handles such image data includes an image processing unit having a function of performing both the encoding process and the decoding process as a pair.

JP 2006-120145 A

By the way, the color space to which each of a plurality of image data input to a device that handles image data belongs may be different. For example, image data belonging to the CMYK color space and image data belonging to the RGB color space may be input. In some cases, it is necessary to handle image data in which image data of different color spaces are aggregated. For example, when the image forming apparatus requests formation of an image in which a plurality of image data is combined.
Conventionally, when encoding processing is performed on image data in which different color spaces are mixed as described above, encoding processing dedicated to each color space is performed, or one color space is unified among the mixed color spaces. As described above, the color conversion processing is performed on the image data of another color space, and then the encoding processing for the one color space is performed. However, the former method requires an image processing unit corresponding to the encoding method for each color space, and also consumes a storage capacity for individually storing image data that has been individually encoded. There was a problem that increased. Further, the latter method has a problem that the original color information of another color space subjected to the color conversion process is lost.

In addition, a suitable encoding method may differ depending on the gradation width of the image data. Specifically, an encoding method suitable for a halftone region in which the width indicated by the gradation difference between adjacent pixels is relatively small, and a high resolution in which the width indicated by the gradation difference between adjacent pixels is relatively large It is different from the encoding method suitable for the region.
Therefore, the encoding process needs to correspond to a plurality of color spaces and gradation widths to which the image data belongs, and the decoding process needs to correspond to the encoding process. there were. However, the conventional encoding process and decoding process have a problem that they cannot cope with them.

  An object of the present invention is to provide an image processing apparatus, an encoding method, and a decoding method capable of performing encoding or decoding corresponding to a plurality of color spaces and gradation widths to which image data belongs.

  According to the first aspect of the present invention, an encoding unit that encodes image data in units of a predetermined pixel region, and decoding that decodes the image data encoded by the encoding unit in units of the predetermined pixel region In the image processing apparatus comprising: an encoding unit, the encoding unit includes information indicating each color space of the predetermined pixel region when pixel regions having different color spaces are mixed in the image data When the first generation unit that generates the first information and the image data include pixel regions having different color spaces, the image data includes information indicating the maximum value and the minimum value of the pixel values of each color constituting each color space. A second generator for generating second information; a third generator for generating third information including information indicating a gradation width of each color included in each predetermined pixel region; the first information; and the second information. And the predetermined pixel based on the third information A fourth generation unit for generating fourth information indicating a code value obtained by encoding pixel values of a plurality of pixels constituting a region by an encoding method according to the gradation width for each color; the first information; 2, an output unit that outputs the data including the third information and the fourth information as the encoded image data, and the decoding unit is configured to output the predetermined pixel based on the first information. A specifying unit that specifies each color space of the region, an acquisition unit that acquires the maximum value and the minimum value of the pixel values of each color constituting each color space based on the second information, and the color specified by the specifying unit A fifth generation unit that generates a decoded value obtained by decoding a code value for each color based on the space, the maximum and minimum values of the pixel values of each color acquired by the acquisition unit, the third information, and the fourth information And.

  According to a second aspect of the present invention, in the image processing apparatus according to the first aspect, the third generation unit is configured such that the gradation width of each color included in each predetermined pixel region is a halftone region or a high resolution region. The fourth processing unit generates information indicating whether it belongs as a third information, and the fourth generation unit encodes a pixel value of a color belonging to the halftone region among the colors included in the predetermined pixel region. And a second processing unit that encodes a pixel value of a color belonging to the high-resolution region among the colors included in the predetermined pixel region by an encoding method different from the encoding by the first processing unit. The fifth generation unit, based on the third information, whether each color included in the predetermined pixel region encoded by the fourth generation unit belongs to the halftone region or the high resolution region And a determination unit for determining A third processing unit that decodes a code value of a color determined to be a halftone region, and a decoding method different from that of the third processing unit that converts a code value of a color determined to be the high-resolution region by the determination unit. And a fourth processing unit for decoding.

  According to a third aspect of the present invention, in the image processing apparatus according to the second aspect, the first processing unit is based on an average value obtained by averaging pixel values of a plurality of pixels constituting the predetermined pixel region. A code value is obtained.

  According to a fourth aspect of the present invention, in the image processing apparatus according to the third aspect, for the color determined to belong to the halftone area, the first processing unit has the maximum value and the minimum value of the color. The gradation range corresponding to the difference is divided into a predetermined number of sections, code values corresponding to the respective sections are set, code values corresponding to the sections including the average values are specified, and the average value is calculated. The third processing unit sets an individual decoded value for each color that can be taken by the code value and belongs to the halftone area. For the determined color, a decoded value corresponding to a code value of the color corresponding to the predetermined pixel area for which the average value is calculated is specified.

  According to a fifth aspect of the present invention, in the image processing device according to any one of the second to fourth aspects, the second processing unit includes a pixel value of each of a plurality of pixels constituting the predetermined pixel region. The code value corresponding to the density pattern obtained by binarizing the pixel values of the colors belonging to the high resolution region is obtained, and the fourth processing unit obtains the code value obtained by the second processing unit and the code value. The decoded value corresponding to the code value is obtained based on the reference data for obtaining the density pattern corresponding to.

  According to a sixth aspect of the present invention, in the image processing apparatus according to any one of the first to fifth aspects, the output unit includes a number of color plates corresponding to the number of colors in the color space having the largest number of colors. And the color-specific plate and another additional plate are generated, and the second information, the third information, and the fourth information of the color space having the largest number of colors are set for each color in each of the color-specific plates. In addition, the third information and the fourth information of the other color space are set for each color in a part or all of the color-specific plates, and the first information and the second information of the other color spaces are set in the additional plate. Information is set, and data constituted by the color-specific plate and the additional plate is output as the encoded image data.

  According to a seventh aspect of the present invention, in the image processing apparatus according to any one of the first to sixth aspects, the image data in which pixel regions having different color spaces are mixed is in the color space having the largest number of colors. Each of the partial data of the number corresponding to the number of colors includes the pixel value of the color space for each color, and the partial or all of the partial data of the number includes the pixel value of the other color space for each color. Features.

  According to an eighth aspect of the present invention, in the image processing apparatus according to the seventh aspect, the image data in which the pixel areas having different color spaces are mixed is information indicating the color space of the pixel value included in each partial data. Including additional data including.

  According to a ninth aspect of the present invention, in the image processing apparatus according to the eighth aspect, the additional data is the other color among the number of partial data corresponding to the number of colors in the color space having the largest number of colors. It is characterized in that it is included in the partial data that does not include the pixel value of the space.

  According to a tenth aspect of the present invention, in the encoding method for encoding image data in units of a predetermined pixel area, when the pixel area having different color spaces is mixed in the image data, the predetermined pixel area Generating first information including information indicating each color space; and when the image data includes pixel regions having different color spaces, the maximum and minimum pixel values of each color constituting each color space Generating second information including information indicating a value; generating third information including information indicating a gradation width of each color included in each predetermined pixel region; and the first information and the second information. Then, based on the third information, fourth information indicating a code value obtained by encoding pixel values of a plurality of pixels constituting the predetermined pixel region for each color by an encoding method corresponding to the gradation width is generated. Step and the first information Said second information, and having the steps of: outputting the data including the third information and the fourth information as the image data encoded.

  The invention described in claim 11 is a decoding method for decoding the image data encoded by the encoding method according to claim 10 in units of the predetermined pixel area, based on the first information. Identifying each color space of a predetermined pixel area; obtaining a maximum value and a minimum value of pixel values of each color constituting each color space based on the second information; and identifying the specified color space. Generating a decoded value obtained by decoding the code value for each color based on the maximum value and the minimum value of the pixel values of each color, the third information, and the fourth information.

  According to the present invention, encoding or decoding corresponding to the color space and gradation width to which each pixel of image data belongs can be performed.

1 is a functional block diagram illustrating an example of an image forming apparatus including an image processing unit that functions as an image processing apparatus of the present invention and a configuration connected to the image forming apparatus. It is a block diagram which shows an example of a structure of an image process part. It is explanatory drawing which concerns on the production | generation of the mixed data by an aggregation part. FIG. 3A is a schematic diagram showing a configuration of image data in the CMYK color space before the aggregation process. FIG. 3B is a schematic diagram illustrating a configuration of image data in the RGB color space before the aggregation process. FIG. 3C is a schematic diagram showing the configuration of mixed data. It is explanatory drawing which shows an example of the correspondence of the pixel of image data, and the block of code | cord | chord data. It is a figure which shows an example of the structure of the code data produced | generated by encoding of mixed data. It is a figure which shows an example of the detailed structure of the plate classified by color of code data. It is explanatory drawing which shows an example of the relationship between the division | segmentation which concerns on a halftone area | region, the maximum value, the minimum value, and the division value, and the code value and decoding value of each division. It is a figure which shows an example of the density pattern which concerns on encoding of a high resolution area | region. It is a figure which shows an example of the 1st template group corresponding to the code value of "00" of a high resolution area | region. It is a figure which shows an example of the 2nd template group corresponding to the code value of "01" of a high resolution area | region. It is a figure which shows an example of the 3rd template group corresponding to the code value of "10" of a high resolution area | region. It is a figure which shows an example of the 4th template group corresponding to the code value of "11" of a high resolution area | region. It is a flowchart which shows an example of the flow of an encoding process. It is a flowchart which shows an example of the flow of an encoding process. It is a flowchart which shows an example of the flow of a 1st encoding process. It is a flowchart which shows an example of the flow of a 2nd encoding process. It is a flowchart which shows an example of the flow of a decoding process. It is a flowchart which shows an example of the flow of a 1st decoding process. It is a flowchart which shows an example of the flow of a 2nd decoding process. It is a flowchart which shows an example of the flow of pattern matching. It is a schematic diagram which shows another example of a structure of mixed data.

  Embodiments of an image processing apparatus according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a functional block diagram illustrating an example of an image forming apparatus 1 including an image processing unit 20 that functions as an image processing apparatus of the present invention and a configuration connected to the image forming apparatus 1.

The image forming apparatus 1 includes a communication control unit 11, a reading control unit 12, an image memory 13, an image processing unit 20, an input / output control unit 14, a storage control unit 15, a storage unit 16, an image forming unit 17, a central control unit 18, and the like. Is provided.
The image forming apparatus 1 is connected to the PC 2 and the print controller 3 via the communication network N, for example. The communication network N is, for example, a communication network constructed using a dedicated line or an existing general public line, and various line forms such as a LAN and a WAN can be applied. The communication network N includes, for example, various communication line networks such as a telephone line network, an ISDN line network, a dedicated line, a mobile communication network, a communication satellite line, a cable TV line network, and an Internet service provider that connects them. Is included.

The PC 2 outputs data to the image forming apparatus 1 via the communication network N. Here, the data output from the PC 2 is image data described in a page description language such as PostScript (registered trademark), for example. Here, the color space of the image data is, for example, an RGB color space.
The print controller 3 outputs image data in the CMYK color space via the communication network N. Specifically, the print controller 3 is interposed between a device (not shown) that outputs image data and the image forming apparatus 1, and converts the image data output from the device into image data in the CMYK color space. Output to the image forming apparatus 1.

  The communication control unit 11 includes a communication device such as a network interface card, and performs communication according to a predetermined standard such as TCP / IP with devices such as the PC 2 and the print controller 3 connected via the communication network N. For example, the communication control unit 11 acquires image data output from the PC 2 or the print controller 3.

The reading control unit 12 is connected to the reading device 4.
The reading device 4 includes a contact glass on which an original is placed, a light source that irradiates light on the original through the contact glass, a mirror group for guiding reflected light reflected by the original, and a mirror group. An image sensor such as a CCD that generates an analog image signal for each reading line by photoelectrically converting reflected light from the original image formed by the condensing lens; And the like, and outputs an analog image signal to the reading control unit 12.
The reading control unit 12 converts an analog image signal generated by the image sensor of the reading device 4 into digital image data having a predetermined bit width, shading correction and MTFγ for the image data. A correction unit that performs various correction processes such as correction is provided, and the corrected image data is output.

  The image memory 13 is a volatile storage device including, for example, a DRAM and stores image data acquired through the communication control unit 11 and the reading control unit 12.

The image processing unit 20 includes a color conversion unit 21 that performs color conversion processing on the image data output from the reading control unit 12 and the like, an encoding unit 30 that encodes image data stored in the image memory 13, and an encoding unit. 30 includes a decoding unit 40 that decodes the image data encoded by 30, an aggregation unit 22 that uses a plurality of pieces of image data as one image data, and the like. Details of the image processing unit 20 will be described later.
The input / output control unit 14 controls input / output of various data. The input / output control unit 14 controls, for example, data transfer among the communication control unit 11, the reading control unit 12, the image memory 13, the storage control unit 15, the image forming unit 17, the image processing unit 20, and the like.

The storage control unit 15 is a controller that controls input / output of data stored in the storage unit 16.
The storage unit 16 has an auxiliary storage device such as an HDD, and stores various data under the control of the storage control unit 15.

The image forming unit 17 forms an image on a sheet based on the image data.
Specifically, the image forming unit 17 responds to, for example, a conveyance unit that conveys paper, a buffer that temporarily stores image data processed by the image processing unit 20, and the image data stored in the buffer. A developing unit that develops the developed toner image, a first transfer unit that transfers the developed toner image to the photoconductor, a second transfer unit that transfers the toner image transferred to the photoconductor to the conveyed paper, and a second transfer A fixing unit that fixes the toner image transferred by the unit to the paper, a discharge unit that discharges the paper processed by the fixing unit, and the like. The configuration of the image forming unit 17 is an example of a configuration for performing image formation by an electrophotographic method, and is not limited thereto. For example, the image forming unit 17 may perform image formation using another method such as image formation using an inkjet recording method.

The central control unit 18 includes a CPU, a RAM, a ROM, and the like. The CPU reads out and executes various programs, data, and the like stored in the ROM, and controls the operation of each unit of the image forming apparatus 1 in accordance with the contents of the executed processing. In addition to various programs executed by the CPU, the RAM stores parameters and data necessary for processing.
For example, when the central control unit 18 acquires image data described in the page description language output from the PC 2 via the communication control unit 11, the central control unit 18 performs analysis processing on the image data to convert it into intermediate language data, Bitmap data corresponding to the intermediate language data is generated and stored in the image memory 13.

Next, the image processing unit 20 will be described with reference to FIG.
As described above, the image processing unit 20 includes the color conversion unit 21, the encoding unit 30, the decoding unit 40, the aggregation unit 22, and the like. The image processing unit 20 includes, for example, an integrated circuit such as an FPGA or an ASIC, or a system LSI provided with a plurality of these integrated circuits. Each component included in the image processing unit 20 and wiring between each component are mounted on an integrated circuit. Note that FPGA is a field programmable gate array, ASIC is an application specific integrated circuit, and LSI is an acronym for Large Scale Integration.

The color conversion unit 21 performs various color conversion processes on the image data. Examples of the color conversion processing by the color conversion unit 21 include color conversion processing related to a change in the color space of image data. Specifically, the color conversion unit 21 converts image data in the RGB color space output from the reading control unit 12 into image data in the CMYK color space. Since the specific contents of the processing relating to the conversion are well known, detailed description thereof will be omitted.
The color conversion process performed by the color conversion unit 21 is not limited to the color conversion process related to the change of the color space. For example, color conversion processing related to subtractive color such as gray scale processing, individual color conversion processing for each color for the purpose of changing the visual influence, such as emphasis on a specific color, etc. can be mentioned. It is not something that can be done.

The encoding unit 30 performs an encoding process for encoding image data.
Specifically, the encoding unit 30 encodes, for example, image data in the CMYK color space that has been subjected to color conversion by the color conversion unit 21. The image data encoded by the encoding unit 30 is stored in the storage unit 16 via the storage control unit 15. Hereinafter, the image data encoded by the encoding unit 30 is referred to as code data.
For example, the encoding unit 30 encodes the CMYK color space image data output from the color conversion unit 21. The encoding unit 30 encodes image data in the CMYK color space output from the print controller 3 via the communication control unit 11.

The decoding unit 40 performs a decoding process for decoding the code data.
Specifically, for example, the decoding unit 40 decodes code data read from the storage unit 16 via the storage control unit 15 and acquires decoded image data. Hereinafter, the code data decoded by the decoding unit 40 is referred to as decoded data.

The aggregation unit 22 performs an aggregation process in which a plurality of pieces of image data having different color spaces are used as one image data.
For example, based on the image data in the CMYK color space and the image data in the RGB color space, the aggregating unit 22 generates one image data in which data corresponding to these color spaces are mixed. Hereinafter, image data generated by the aggregating unit 22 and including data corresponding to a plurality of color spaces is referred to as mixed data.

The generation of mixed data by the aggregation unit 22 will be described with reference to FIGS. 3 (a), (b), and (c). FIG. 3A is a schematic diagram showing a configuration of image data in the CMYK color space before the aggregation process. FIG. 3B is a schematic diagram illustrating a configuration of image data in the RGB color space before the aggregation process. FIG. 3C is a schematic diagram showing the configuration of mixed data. In FIGS. 3A, 3B, and 3C, each plate is schematically shown as a 4 × 4 cell. However, the illustration is only for convenience and does not indicate the exact number of pixels. .
Each image data before the aggregation processing has partial data corresponding to the number of colors constituting each color space. Here, each partial data is data in which information indicating pixel values of each color set for each pixel constituting image data is collected. Specifically, for example, as shown in FIG. 3A, the image data in the CMYK color space before the aggregation processing includes four partial data such as a C plate, an M plate, a Y plate, and a K plate. . Further, as shown in FIG. 3B, the image data in the RGB color space before the aggregation processing has three partial data such as an R plate, a G plate, and a B plate.

The aggregating unit 22 mixes mixed data so that partial data of other image data is aggregated into partial data of image data in the color space having the largest number of colors constituting the color space among a plurality of image data having different color spaces. Is generated. Specifically, as shown in FIG. 3 (c), the consolidating unit 22 uses the same C / R plate for C and R, the same M / G plate for M and G, and the same for Y and B. The Y / B plate is generated as each aggregated partial data. Further, the data corresponding to the RGB color space can be aggregated into the data corresponding to the CMYK color space by using these aggregated partial data, so that the K plate is generated independently without mixing the color spaces.
As described above, the mixed data includes the pixel values of the color space in each of the partial data corresponding to the number of colors in the color space having the largest number of colors, and a part or all of the partial data of the number. Each pixel includes a pixel value in another color space for each color.

  In addition to the four partial data of the C / R plate, M / G plate, Y / B plate, and K plate, the aggregation unit 22 newly provides a 1-bit color system plate as additional data. The color system plate includes information indicating a color space of pixel values included in each partial data. Specifically, the aggregating unit 22 colors data indicating a matrix format corresponding to the pixel value of each pixel included in the four partial data of the C / R plate, the M / G plate, the Y / B plate, and the K plate. Generate as a system plate. Then, the aggregation unit 22 includes pixels corresponding to the CMYK color space in the four partial data of the C / R plate, the M / G plate, the Y / B plate, and the K plate among the positions of the pixels indicated by the matrix. A sign of “0” is set at a position where the value is included, and a sign of “1” is set at a position where the pixel value corresponding to the RGB color space is included. The bit patterns “0” and “1” corresponding to each color space are merely examples, and the present invention is not limited thereto.

Next, a flow of processing related to image data handled by the image forming apparatus 1 will be described.
For example, when image data is output from the reading control unit 12, the color conversion unit 21 performs color conversion processing on the image data to obtain image data in the CMYK color space, and the encoding unit 30 outputs image data in the CMYK color space. Is encoded data. Further, when the CMYK color space image data output from the print controller 3 via the communication control unit 11 is acquired, the encoding unit 30 encodes the CMYK color space image data into code data. Further, when the RGB color space image data output from the PC 2 is acquired via the communication control unit 11, the encoding unit 30 encodes the RGB color space image data into code data. These code data are stored in the storage unit 16 via the storage control unit 15.

  When the image is formed by the image forming unit 17, the code data stored in the storage unit 16 is read out via the storage control unit 15 and decoded by the decoding unit 40 of the image processing unit 20. The decoded data generated through the decoding by the decoding unit 40 is output to the image forming unit 17 via the image memory 13. The image forming unit 17 forms an image based on the decoded data.

Here, the outline of the encoding by the encoding unit 30 and the decoding by the decoding unit 40 will be described with reference to the example of FIG.
For example, as illustrated in FIG. 4, the encoding unit 30 sequentially encodes a plurality of pixels arranged in directions orthogonal to each other in image data in units of 8 × 8 pixels. In the encoding process, the encoding unit 30 sets 8 × 8 pixels as 4 × 4 block code data. That is, the encoding unit 30 performs encoding processing so that 2 × 2 pixels are included in one block.
An 8-bit pixel value is set for each pixel constituting the image data before the encoding process. The encoding unit 30 generates a 4-bit code value based on four pixels of 2 × 2 pixels each having an 8-bit pixel value set, and a code value of a block corresponding to the 2 × 2 pixels And

The decoding unit 40 decodes the code data generated by the encoding unit 30 in units of 4 × 4 blocks to generate decoded data. In the decoding process, the decoding unit 40 generates 8 × 8 pixel decoded data corresponding to 4 × 4 blocks.
In the description with reference to FIG. 4, for the purpose of simply showing the correspondence between the pixel area and the block, the relationship in which the pixel a _ij is restored from the b _IJ block in the illustration of the restoration arrow is illustrated. In the case of lossy compression, the pixel value before restoration may be different from the pixel value after restoration. Hereinafter, in the description of the present embodiment, in order to distinguish between a pixel value before encoding and a decoded pixel value, the pixel value before encoding is referred to as a _ij, and the pixel value after decoding is referred to as A _ij. It describes.

In the present embodiment, it is possible to perform encoding of the mixed data generated by the aggregation unit 22 and decoding of the code data generated by the encoding. Details will be described below.
FIG. 5 is a diagram illustrating an example of the structure of code data generated by encoding mixed data.
FIG. 6 is a diagram illustrating an example of a detailed configuration of the color-specific plate of the code data.
The encoding unit 30 includes a plate for each color corresponding to each partial data of the mixed data, and an additional plate for setting various types of information that are not set in the plate for each color among the information related to encoding generated by the encoding process. And generate. The encoding unit 30, for example, encodes the mixed data shown in FIG. 3 (c), so that four colors of C / R plate, M / G plate, Y / B plate, and K plate are used as shown in FIG. 5. A separate plate and a TAG plate as an additional plate are generated. Here, the number of plates for each color is a number corresponding to the number of colors in the color space having the largest number of colors among the color spaces included in the mixed data. Each color plate is data that can include code values of different colors. For example, among the colors constituting the CMYK color space, the code value of cyan (C) is included in the C / R plate, the code value of magenta (M) is included in the M / G plate, and the code value of yellow (Y) The value is included in the Y / B plate, and the sign value of black (K) is included in the K plate. Among the colors constituting the RGB color space, the code value of red (R) is included in the C / R plate, the code value of green (G) is included in the M / G plate, and the color of blue (B) The sign value is included in the Y / B plate.
Although the structure of the code data shown in FIG. 5 is a 4 × 4 block corresponding to 8 × 8 pixels, the code data finally generated as encoded data of the image data constitutes the image data. The data is a combination of a plurality of 4 × 4 blocks shown in FIG.

Each of the color-specific plate and the additional plate includes a plurality of pieces of information.
The color plate includes information represented by 4 bits in each 4 × 4 block. The first 1 bit counted from the upper side of the 4 bits functions as an identification plane, the subsequent 2 bits function as a BTC plane, and the last 1 bit functions as a first difference plane.

The identification plane includes information indicating the gradation width of each color included in the pixel region of 2 × 2 pixels before encoding corresponding to each block.
Specifically, the identification plane indicates whether the gradation width corresponding to the pixel value difference of each pixel included in the 2 × 2 pixel area before encoding belongs to the halftone area or the high resolution area Contains information in each block. Here, the halftone area and the high resolution area are distinguished from each other by a predetermined value indicating that the value indicating the gradation width calculated based on the difference between the pixel values of each pixel included in the 2 × 2 pixel area is the halftone area. This is in accordance with whether or not this condition is met. The predetermined condition will be described later.
For example, Flag ₀₀ of the identification plane in the color-specific plane shown in FIG. 6 includes a color among the pixel values of each pixel in a 2 × 2 pixel region composed of pixels a ₀₀ , a ₀₁ , a ₁₀ , and a _11. A value indicating whether the gradation width corresponding to the difference between the pixel values of the colors corresponding to the different plates belongs to the halftone area or the high resolution area is set. As the value, for example, “0” is set in the case of the halftone area and “1” is set in the case of the high resolution area, but this is an example and is not limited thereto. The same applies to the other Flag _IJs .

The BTC plane includes code values obtained by encoding pixel values of a plurality of pixels constituting a pixel region of 2 × 2 pixels by an encoding method corresponding to the gradation width.
Specifically, the BTC plane is encoded by a coding method selected based on information set as an identification plane, that is, information indicating whether the pixel area belongs to a halftone area or a high resolution area. A code value of 2 bits of any one of “00”, “01”, “10” or “11” generated by encoding the pixel values of a plurality of pixels constituting a pixel area of × 2 pixels. Include in each block.

For example, the pixel values of the pixels a ₀₀ , a ₀₁ , a ₁₀ , and a ₁₁ shown in FIG. 3C are encoded, and the code value BTC ₀₀ of the block b ₀₀ shown in FIG. 6 is generated. Also, the pixel values of the pixels a ₀₂ , a ₀₃ , a ₁₂ , and a ₁₃ are encoded to generate the code value BTC ₀₁ of the block b ₀₁ . Further, the pixel values of the pixels a ₀₄ , a ₀₅ , a ₁₄ , and a ₁₅ are encoded to generate the code value BTC ₀₂ of the block b ₀₂ . Further, the pixel values of the pixels a ₀₆ , a ₀₇ , a ₁₆ , and a ₁₇ are encoded to generate the code value BTC ₀₃ of the block of b ₀₃ . Further, the pixel values of the pixels a ₂₀ , a ₂₁ , a ₃₀ , and a ₃₁ are encoded to generate the code value BTC ₁₀ of the block b ₁₀ . Other 4 pixels similarly be encoded, code values BTC _IJ of the corresponding block b _IJ is generated.

The BTC plane is in a state where code data corresponding to pixel values having different color spaces are mixed when image data includes pixel regions having different color spaces, such as mixed data.
Referring to the example of FIG. 4, the pixels in the CMYK color space are a _{00 to} a ₀₇ , a _{10 to} a ₁₇ , a _{20 to} a ₂₇ , a _{30 to} a ₃₇ , a _{40 to} a ₄₃ , a _{50 to} a. _53, located in _{a 60 ~a 63, a 70 ~a} 73, the pixel of the RGB color _space, a case in _{a 44 ~a 47, a 54 ~a} 57, a 64 ~a 67, a 74 ~a 77 Take an example. In the case of this example, as shown in FIG. 5, the pixels represented by the image data in the CMYK color space and the pixels represented by the image data in the RGB color space are encoded independently. Among the blocks included in the code data, the blocks b ₀₀ , b ₀₁ , b ₀₂ , b ₀₃ , b ₁₀ , b ₁₁ , b ₁₂ , b ₁₃ , b ₂₀ , b ₂₁ , b ₃₀ , b ₃₁ are CMYK colors. The blocks b ₂₂ , b ₂₃ , b ₃₂ , and b ₃₃ correspond to the RGB color space.

The first difference plane is the maximum pixel value of each color constituting one color space among the different color spaces mixed in the image data when the pixel areas having different color spaces are mixed in the image data. Contains information indicating the value and the minimum value.
Specifically, the first difference plane includes information indicating the maximum value and the minimum value of the pixel values of each color constituting each of the CMYK color spaces.
Since the pixel value is 8 bits, a 16-bit information amount is required to indicate the two pixel values of the maximum value and the minimum value. Further, since the first difference plane has an information amount of 1 bit for each of a total of 16 blocks of 4 × 4, the total information amount is 16 bits. Therefore, as shown in FIGS. 5 and 6, half of the 8 bits of the total information amount of the first difference plane is assigned as information indicating the maximum value, and the remaining half of 8 bits is the information indicating the minimum value. Assigned.

  In the first difference plane included in the C / R plate shown in FIG. 5, the maximum value CMax and the minimum value CMin of the cyan (C) pixel value are set. In the first difference plane included in the M / G plate, the maximum value MMax and the minimum value MMin of the magenta (M) pixel value are set. Further, the maximum value YMax and the minimum value YMin of the yellow (Y) pixel value are set in the first difference plane included in the Y / B plate. In the first difference plane included in the K plate, the maximum value KMax and the minimum value KMin of the black (K) pixel value are set. As described above, the first difference plane that is the difference plane of the color-specific plate is the color space corresponding to the number of color-specific planes, that is, the color space having the largest number of colors among the color spaces included in the mixed data. It includes information indicating the maximum and minimum pixel values of each color.

  The additional plate also includes information represented by 4 bits in each 4 × 4 block, similarly to the color-specific plate. The first 1 bit counted from the upper side of the 4 bits functions as a color plane, and the remaining 3 bits function as a second difference plane for each bit.

The color plane includes information indicating each color space of a predetermined pixel region when pixel regions having different color spaces are mixed in the image data.
Specifically, the color system plane has four parts of C / R plate, M / G plate, Y / B plate, and K plate included in the image data before encoding, out of a total of 16 blocks of 4 × 4. In the data, a code of “0” is set for the block of the pixel area corresponding to the CMYK color space, and a code of “1” is set for the block of the pixel area corresponding to the RGB color space.

The second difference plane is different from the color space corresponding to the first difference plane among the different color spaces mixed in the image data when pixel regions having different color spaces are mixed in the image data. It includes information indicating the maximum value and the minimum value of the pixel values of each color constituting one color space.
Specifically, the second difference plane includes information indicating the maximum value and the minimum value of the pixel values of each color constituting each of the RGB color spaces. More specifically, the maximum value BMax and the minimum value Bmin of the blue (B) pixel value are set in 16 blocks of the second bit counted from the high-order side of the 4-bit constituting the TAG plate. Also, the maximum value GMax and the minimum value GMin of the pixel value of green (G) are set in 16 blocks of the third bit. Further, the maximum value RMax and the minimum value Rmin of the pixel value of red (R) are set in 16 blocks of the fourth bit. The correspondence between the information amount of the maximum and minimum pixel values of each color in the second difference plane and the information setting method using 16 blocks is the same as that of the first difference plane.

Here, the information indicating the color space of each 2 × 2 pixel area of the image data before encoding is the first information, and the maximum value and the minimum pixel value of each color constituting each color space related to the image data The information indicating the value is the second information, the information indicating the gradation width of each color included in each pixel area of 2 × 2 pixels is the third information, and pixels of a plurality of pixels constituting the pixel area of 2 × 2 pixels A code value obtained by encoding the value with an encoding method corresponding to the gradation width for each color is set as fourth information.
The code data has a number of color plates corresponding to the number of colors in the color space with the largest number of colors, a color plate and another additional plate, and each color plate has the largest number of colors. The second information, the third information, and the fourth information of the space are included for each color, and the third information and the fourth information of the other color space are included for each color except for the K plate, and the additional plate includes the second information. Data including one information and second information of another color space.

Next, generation of code data will be described.
As shown in FIG. 2, the encoding unit 30 includes a first generation unit 31, a second generation unit 32, a third generation unit 33, a fourth generation unit 34, an output unit 35, and the like.
Hereinafter, as an example, encoding according to pixel values included in the C / R plate in the mixed data before encoding will be described.

The first generation unit 31 generates first information, that is, information indicating each color space of a pixel region of 2 × 2 pixels of image data before encoding.
Specifically, the first generation unit 31 determines the color space to which each pixel belongs in accordance with the code “0” or “1” set in the additional data of the mixed data, so that the unit of the encoding process The color space to which each pixel included in the pixel region of 2 × 2 pixels becomes is determined. Then, the first generation unit 31 sets information for setting a code indicating each color space in each block according to the determination result, the second generation unit 32, the third generation unit 33, the fourth generation unit 34, and Output to the output unit 35.

For example, as above, a _{00 to} a ₀₇ , a _{10 to} a ₁₇ , a _{20 to} a ₂₇ , a _{30 to} a ₃₇ , a _{40 to} a ₄₃ , a _{50 to} a ₅₃ , a _{60 to} a ₆₃ , a A code of “0”, that is, a code indicating the CMYK color space is set in _{70 to} a ₇₃ , and a code of a _{44 to} a ₄₇ , a _{54 to} a ₅₇ , a _{64 to} a ₆₇ , and a _{74 to} a ₇₇ is set. , “1”, that is, mixed data in which a code indicating an RGB color space is set as an example. In the case of the example, as illustrated in FIG. 5, the first generation unit 31 includes b ₀₀ , b ₀₁ , b ₀₂ , b ₀₃ , b ₁₀ , b ₁₁ , b ₁₂ , b ₁₃ , b ₂₀ , b ₂₁ , b ₃₀ , b ₃₁ are set to “0” indicating the CMYK color space, and b ₂₂ , b ₂₃ , b ₃₂ , b ₃₃ are set to “1” indicating the RGB color space. Set the sign.

The second generation unit 32 generates second information, that is, information indicating the maximum value and the minimum value of the pixel values of each color constituting each color space related to the image data before encoding.
Specifically, the second generation unit 32 specifies the maximum value and the minimum value of the pixel values of each color included in the C / R plate of the mixed data before encoding. That is, the second generation unit 32 specifies the maximum value CMax and the minimum value CMin of the cyan (C) pixel value and the maximum value RMax and the minimum value Rmin of the red (R) pixel value. Then, the second generation unit 32 outputs information indicating the maximum value and the minimum value of each specified color to the third generation unit 33, the fourth generation unit 34, and the output unit 35. Note that the determination of whether each pixel value included in the C / R plate is a cyan (C) or red (R) pixel value is based on the determination result of the color space by the first generation unit 31.

For example, in the case of mixed data according to the above example, the maximum values CMax and CMin of cyan (C) are specified by the following equations (1) and (2).
_{CMax = MAX (a 00, a} 01, a 02, a 03, a 04, a 05, a 06, a 07,
_{a 10, a 11, a 12} , a 13, a 14, a 15, a 16, a 17,
_{a 20, a 21, a 22} , a 23, a 24, a 25, a 26, a 27,
a ₃₀ , a ₃₁ , a ₃₂ , a ₃₃ , a ₃₄ , a ₃₅ , a ₃₆ , a ₃₇ ,
a ₄₀ , a ₄₁ , a ₄₂ , a ₄₃ ,
a ₅₀ , a ₅₁ , a ₅₂ , a ₅₃ ,
a ₆₀ , a ₆₁ , a ₆₂ , a ₆₃ ,
a ₇₀ , a ₇₁ , a ₇₂ , a ₇₃ ) (1)
_{CMin = MIN (a 00, a} 01, a 02, a 03, a 04, a 05, a 06, a 07,
_{a 10, a 11, a 12} , a 13, a 14, a 15, a 16, a 17,
_{a 20, a 21, a 22} , a 23, a 24, a 25, a 26, a 27,
a ₃₀ , a ₃₁ , a ₃₂ , a ₃₃ , a ₃₄ , a ₃₅ , a ₃₆ , a ₃₇ ,
a ₄₀ , a ₄₁ , a ₄₂ , a ₄₃ ,
a ₅₀ , a ₅₁ , a ₅₂ , a ₅₃ ,
a ₆₀ , a ₆₁ , a ₆₂ , a ₆₃ ,
a ₇₀ , a ₇₁ , a ₇₂ , a ₇₃ ) (2)
Further, the maximum values RMax and RMin of red (R) are specified by the following formulas (3) and (4).
RMax = MAX (a ₄₄ , a ₄₅ , a ₄₆ , a ₄₇ ,
a ₅₄ , a ₅₅ , a ₅₆ , a ₅₇ ,
a ₆₄ , a ₆₅ , a ₆₆ , a ₆₇ ,
a ₇₄ , a ₇₅ , a ₇₆ , a ₇₇ ) (3)
Rmin = MIN (a ₄₄ , a ₄₅ , a ₄₆ , a ₄₇ ,
a ₅₄ , a ₅₅ , a ₅₆ , a ₅₇ ,
a ₆₄ , a ₆₅ , a ₆₆ , a ₆₇ ,
a ₇₄ , a ₇₅ , a ₇₆ , a ₇₇ ) (4)
The description of MAX () in Expressions (1) and (3) indicates that the maximum pixel value is extracted from the corresponding color pixel values in (). The description of MIN () in Expressions (2) and (4) indicates that the minimum pixel value is extracted from the corresponding color pixel values in ().

The third generation unit 33 generates third information, that is, information indicating the gradation width of each color included in each pixel region of 2 × 2 pixels.
Specifically, the third generation unit 33 uses the maximum value and the minimum value of each color obtained by the second generation unit 32 to determine whether each 2 × 2 pixel region belongs to a halftone region. A partition value used for determination is calculated. More specifically, the third generation unit 33 calculates cyan (C) segment values CTh1, CTh2, and CTh3 by the following equations (5) to (7). The third generation unit 33 calculates the red (R) segment values RTh1, RTh2, and RTh3 according to the following equations (8) to (10). Considering the correspondence described in FIG. 7 and FIG. 13 described later, among the three segment values of each color, the minimum segment value of each color corresponding to CTh1, RTh1, etc. is denoted as Th1, and CTh2, RTh2 The intermediate segment value of each color corresponding to etc. is described as Th2, and the maximum segment value of each color corresponding to CTh3, RTh3, etc. is described as Th3.
CTh1 = CMin + (CMax−CMin) × 1/6 (5)
CTh2 = CMin + (CMax−CMin) × 3/6 (6)
CTh3 = CMin + (CMax−CMin) × 5/6 (7)
RTh1 = RMin + (RMax−RMin) × 1/6 (8)
RTh2 = RMin + (RMax−RMin) × 3/6 (9)
RTh3 = RMin + (RMax−RMin) × 5/6 (10)

  Next, the 3rd production | generation part 33 performs the determination which concerns on the characteristic of the pixel area which belongs to the halftone area | region described below.

As the determination related to the characteristics of the pixel area belonging to the halftone area, the third generation unit 33 determines whether the difference between the maximum value and the minimum value is less than the reference value for each color. Here, when it is determined that the difference between the maximum value and the minimum value is less than the reference value, the third generation unit 33 sets the color of the color included in the 8 × 8 pixel corresponding to the maximum value and the minimum value. It is determined that all the pixel areas are halftone areas.
For example, the third generation unit 33 determines whether or not the following expression (11) is satisfied with respect to the maximum value CMax and the minimum value CMin of the cyan (C), and when it is determined that they are satisfied, FIG. Of the mixed data of (c), all the pixel areas including the cyan (C) pixel value are determined as pixel areas belonging to the halftone area.
CMax-CMin <CT (11)
Here, CT is a threshold value set to determine the displacement width of the cyan (C) tone value among the colors of the color space constituting the 8 × 8 pixel image block. In consideration of the correspondence relationship described in FIG. 13 and the like to be described later, the threshold value of each color set in order to determine the displacement width of the gradation value is described with the symbol T. CT is a threshold value T of cyan (C). CT is determined from an empirical rule within the range of 0 ≦ CT ≦ 255.
Similarly, the third generation unit 33 determines whether or not the following expression (12) is satisfied with respect to the maximum value RMax and the minimum value Rmin of the red (R), and when it is determined that the expression is satisfied, Of the mixed data of 3 (c), all the pixel areas including the red (R) pixel value are determined as halftone areas.
RMax-RMin <RT (12)
Here, RT is a threshold value T of red (R). RT is determined from empirical rules within the range of 0 ≦ RT ≦ 255.

In addition, as a determination related to the characteristics of the pixel area belonging to the halftone area, the third generation unit 33 calculates the following expression (13) among the four pixels included in the 2 × 2 pixel area of cyan (C). It is determined for each pixel area whether one or more pixels are satisfied. The third generation unit 33 determines a 2 × 2 pixel area of cyan (C) including pixels determined to satisfy Expression (13) as a pixel area belonging to the halftone area.
CTh1 <a _ij ≦ CTh3 (13)
Further, as a determination related to the characteristics of the pixel area belonging to the halftone area, the third generation unit 33 includes the following expression (14) among the total of four pixels included in the red (R) 2 × 2 pixel area: It is determined for each pixel area whether or not there is one or more pixels satisfying the above condition. The third generation unit 33 determines a pixel region of 2 × 2 pixels of red (R) that includes a pixel determined to satisfy Expression (14) as a pixel region belonging to the halftone region.
RTh1 <a _ij ≦ RTh3 (14)

Further, as a determination related to the characteristics of the pixel area belonging to the halftone area, the third generation unit 33 satisfies all of the following Expression (15) for all four pixels included in the pixel area of 2 × 2 pixels of cyan (C). Is determined for each pixel region. The third generation unit 33 determines a pixel area of 2 × 2 pixels of cyan (C) that is determined that all four pixels satisfy Expression (15) as a pixel area belonging to the halftone area.
a _ij ≦ CTh1 (15)
In addition, as a determination relating to the characteristics of the pixel area belonging to the halftone area, the third generation unit 33 satisfies all of the following Expression (16) for all four pixels included in the red (R) 2 × 2 pixel area. Is determined for each pixel region. The third generation unit 33 determines that the pixel area of 2 × 2 pixels of red (R), in which it is determined that all four pixels satisfy Expression (16), as the pixel area belonging to the halftone area.
a _ij ≦ RTh1 (16)

Further, as a determination related to the characteristics of the pixel area belonging to the halftone area, the third generation unit 33 satisfies all of the four pixels included in the pixel area of 2 × 2 pixels of cyan (C) satisfying the following expression (17). Is determined for each pixel region. The third generation unit 33 determines a pixel area of 2 × 2 pixels of cyan (C) that is determined that all four pixels satisfy Expression (17) as a pixel area belonging to the halftone area.
CTh3 <a _ij (17)
Further, as a determination relating to the characteristics of the pixel area belonging to the halftone area, the third generation unit 33 satisfies all of the following Expression (18) for all four pixels included in the red (R) 2 × 2 pixel area. Is determined for each pixel region. The third generation unit 33 determines that the pixel area of 2 × 2 pixels of red (R), in which it is determined that all four pixels satisfy Expression (18), as the pixel area belonging to the halftone area.
RTh3 <a _ij (18)

In addition, the third generation unit 33 determines, as a high-resolution area, a 2 × 2 pixel area that has not been determined as a halftone area in any of the determinations after determining the characteristics of the pixel areas belonging to these halftone areas. The pixel area is determined to belong.
The third generation unit 33 outputs, to the fourth generation unit 34 and the output unit 35, information indicating whether the pixel area corresponding to each block belongs to the halftone area or the high resolution area according to the determination result. .

Based on the first information, the second information, and the third information, the fourth generation unit 34 converts the fourth information, that is, the pixel values of a plurality of pixels constituting the pixel region of 2 × 2 pixels for each color to the gradation width. A code value encoded by an encoding method according to the above is generated. Further, the fourth generation unit 34 outputs information indicating the code value of each block corresponding to each pixel region to the output unit 35.
As illustrated in FIG. 2, the fourth generation unit 34 includes a first processing unit 34a and a second processing unit 34b.

The first processing unit 34a encodes pixel values of colors belonging to the halftone area. Hereinafter, the encoding by the first processing unit 34a may be referred to as a first encoding process.
Specifically, the first processing unit 34a first calculates an average value of pixel values of four pixels included in a 2 × 2 pixel region belonging to the halftone region for each pixel region. Then, the first processing unit 34 a calculates the calculated average value, the maximum and minimum pixel values of each color output from the second generation unit 32, and the division value of each color output from the third generation unit 33. Based on the above, the code value of the block corresponding to each pixel region is determined.

また、第１処理部３４ａは、シアン（Ｃ）の２×２画素の画素領域について、以下の関係式（２０）〜（２３）により、平均値ａｖｒ_ｉｊを最小値ＣＭｉｎ、３つの区分値ＣＴｈ１、ＣＴｈ２、ＣＴｈ３、最大値ＣＭａｘと比較することによって量子化してＢＴＣ符号の符号値ＢＴＣ_ＩＪを割り当てる。
ＣＭｉｎ≦ａｖｒ_ｉｊ＜ＣＴｈ１の場合、ＢＴＣ_ＩＪ＝００…（２０）
ＣＴｈ１≦ａｖｒ_ｉｊ＜ＣＴｈ２の場合、ＢＴＣ_ＩＪ＝０１…（２１）
ＣＴｈ２≦ａｖｒ_ｉｊ＜ＣＴｈ３の場合、ＢＴＣ_ＩＪ＝１０…（２２）
ＣＴｈ３≦ａｖｒ_ｉｊ≦ＣＭａｘの場合、ＢＴＣ_ＩＪ＝１１…（２３）
また、第１処理部３４ａは、レッド（Ｒ）の２×２画素の画素領域について、以下の関係式（２４）〜（２７）により、平均値ａｖｒ_ｉｊを最小値ＲＭｉｎ、３つの区分値ＲＴｈ１、ＲＴｈ２、ＲＴｈ３、最大値ＲＭａｘと比較することによって量子化してＢＴＣ符号の符号値ＢＴＣ_ＩＪを割り当てる。
ＲＭｉｎ≦ａｖｒ_ｉｊ＜ＲＴｈ１の場合、ＢＴＣ_ＩＪ＝００…（２４）
ＲＴｈ１≦ａｖｒ_ｉｊ＜ＲＴｈ２の場合、ＢＴＣ_ＩＪ＝０１…（２５）
ＲＴｈ２≦ａｖｒ_ｉｊ＜ＲＴｈ３の場合、ＢＴＣ_ＩＪ＝１０…（２６）
ＲＴｈ３≦ａｖｒ_ｉｊ≦ＲＭａｘの場合、ＢＴＣ_ＩＪ＝１１…（２７） For example, the first processing unit 34a calculates the average value avr _ij of the pixel values of four pixels included in the pixel region of 2 × 2 pixels of the color belonging to the halftone region by the following equation (19).

Further, the first processing unit 34a calculates the average value avr _ij as the minimum value CMin and the three segment values CTh1 according to the following relational expressions (20) to (23) for the pixel region of 2 × 2 pixels of cyan (C). , CTh2, CTh3, and the maximum value CMmax are quantized and assigned with a code value BTC _IJ of the BTC code.
When CMin ≦ avr _ij <CTh1, BTC _IJ = 00 (20)
In the case of CTh1 ≦ avr _ij <CTh2, BTC _IJ = 01 (21)
If CTh2 ≦ avr _ij <CTh3, BTC _IJ = 10 (22)
If CTh3 ≦ avr _ij ≦ CMax, BTC _IJ = 11 (23)
Further, the first processing unit 34a sets the average value avr _ij to the minimum value RMin and the three segment values RTh1 according to the following relational expressions (24) to (27) for the pixel region of 2 × 2 pixels of red (R). , RTh2, RTh3 and the maximum value RMax are quantized and assigned a code value BTC _IJ of the BTC code.
When RMin ≦ avr _ij <RTh1, BTC _IJ = 00 (24)
When RTh1 ≦ avr _ij <RTh2, BTC _IJ = 01 (25)
When RTh2 ≦ avr _ij <RTh3, BTC _IJ = 10 (26)
When RTh3 ≦ avr _ij ≦ RMax, BTC _IJ = 11 (27)

  As described above, the first processing unit 34a obtains the code value of the one color based on the average value obtained by averaging the pixel values of a plurality of pixels constituting the 2 × 2 pixel region. In addition, the first processing unit 34a has four gradation values corresponding to the difference between the maximum value and the minimum value of the color for the color belonging to the halftone area with three division values such as CTh1, CTh2, and CTh3. The code values of “00”, “01”, “10”, “11” are set as the code values corresponding to each of the sections divided into the sections, the code values corresponding to the sections including the average value are specified, The code value of the color of the pixel region of 2 × 2 pixels for which the average value is calculated is used.

The second processing unit 34b encodes the pixel value of the color belonging to the high resolution region by an encoding method different from the encoding by the first processing unit 34a. Hereinafter, the encoding by the second processing unit 34b may be referred to as a second encoding process.
Specifically, the second processing unit 34b first binarizes the pixel values of the four pixels constituting the pixel region of 2 × 2 pixels belonging to the high resolution region, and density patterns corresponding to 2 × 2 pixels. Is generated. Then, the second processing unit 34b obtains a code value corresponding to the generated density pattern in accordance with a correspondence relationship between a predetermined density pattern and a code value.

For example, the second processing unit 34b uses the following relational expressions (28) and (29) to calculate the pixel values of the four pixels constituting the 2 × 2 pixel area of cyan (C) belonging to the high resolution area. A binarization process is performed to replace the value with either “0” or “1”.
When a _ij > CTh3, a _ij = 1 (28)
When a _ij ≦ CTh1, a _ij = 0 (29)
Then, as shown in FIG. 8, the second processing unit 34b refers to the density pattern data indicating the correspondence between the predetermined density pattern and the code value, and the relational expressions (28) and (29) described above. Thus, the code value corresponding to the density pattern of 2 × 2 pixels replaced with the combination of the values “0” and “1” is specified. The density pattern data is stored in, for example, a density pattern data storage unit 34c connected to the second processing unit 34b.
For example, in the case of a density pattern in which four pixels included in a pixel area of 2 × 2 pixels have three pixels replaced with “0” and one pixel replaced with “1”, The two processing unit 34b sets the code of the pixel area to “00”. In the case of a density pattern in which one pixel replaced with “0” and three pixels replaced with “1” among the four pixels included in the 2 × 2 pixel region are The two processing unit 34b sets the code of the pixel area to “11”. In the case of a density pattern in which two pixels replaced with “0” and two pixels replaced with “1” are included in the four pixels included in the pixel region of 2 × 2 pixels, The two processing unit 34b sets the code of the pixel area to “01” or “10” according to the positional relationship between “0” and “1”.
In addition, the second processing unit 34b calculates the pixel values of the four pixels constituting the red (R) 2 × 2 pixel area belonging to the high resolution area according to the following relational expressions (30) and (31). A binarization process is performed to replace the value with either “0” or “1”.
When a _ij > RTh3, a _ij = 1 (30)
When a _ij ≦ RTh1, a _ij = 0 (31)
Then, as shown in FIG. 8, the second processing unit 34b refers to the density pattern data indicating the correspondence relationship between the predetermined density pattern and the code value, and the relational expressions (30) and (31) described above. Thus, the code value corresponding to the density pattern of 2 × 2 pixels replaced with the combination of the values “0” and “1” is specified.

As described above, the second processing unit 34b divides the density pattern into four patterns, quantizes the 2 × 2 pixel area belonging to the high resolution area according to the code value assigned to each group, and performs BTC. A code value BTC _IJ of the code is assigned.

In the above, encoding of pixel values included in the C / R plate among the partial data included in the mixed data has been described. However, encoding related to other partial data is performed in the same flow.
For example, the encoding process of the pixel values included in the M / G plate is a process in which the above cyan (C) is replaced with magenta (M) and the above red (R) is replaced with green (G). Similarly, the encoding process of the pixel values included in the Y / B plate is a process in which the above cyan (C) is replaced with yellow (Y) and the above red (R) is replaced with blue (B). Further, the encoding process of the pixel values included in the K plate is a process in which the above cyan (C) is replaced with magenta (K).

The output unit 35 outputs data including first information, second information, third information, and fourth information as code data.
Specifically, the output unit 35 generates a number of color-specific plates corresponding to the number of colors in the color space with the largest number of colors, a color-specific plate, and another additional plate, and each color-specific plate The second information, the third information, and the fourth information of the color space having the largest number of colors are set for each color, and the third information and the fourth information of the other color space are set on each of the color-specific plates. Setting is performed for each color, the first information and the second information of another color space are set on the additional plate, and data constituted by the color-specific plate and the additional plate is output as code data.
More specifically, the output unit 35 outputs code data in the format described with reference to FIGS. 5 and 6, for example.

  As described above, the encoding unit 30 encodes a plurality of pixels constituting the mixed data for each color in units of 8 × 8 pixels, and repeats the process of generating the code data, whereby all the pixels and all the colors of the mixed data are generated. Is encoded.

Next, decoding of code data will be described.
As illustrated in FIG. 2, the decoding unit 40 includes a specifying unit 41, an acquisition unit 42, a fifth generation unit 43, and the like.

The specifying unit 41 specifies the color space of each 2 × 2 pixel area based on the first information.
Specifically, the specifying unit 41 reads the color system plane set to the first bit counted from the upper side of the TAG plate, which is an additional plate of code data, and determines the color space of each 4 × 4 block. Identify. The specifying unit 41 outputs the result of specifying the color space of each block to the fifth generation unit 43.

For example, in the case of the example shown in FIG. 5, b ₀₀ , b ₀₁ , b ₀₂ , b ₀₃ , b ₁₀ , b ₁₁ , b ₁₂ , b ₁₃ , b ₂₀ , b ₂₁ , b ₃₀ , b ₃₁ are in the CMYK color space. A code “0” indicating the RGB color space is set in b ₂₂ , b ₂₃ , b ₃₂ , and b ₃₃ . In this case, the specifying unit 41 is a block corresponding to each block of b ₀₀ , b ₀₁ , b ₀₂ , b ₀₃ , b ₁₀ , b ₁₁ , b ₁₂ , b ₁₃ , b ₂₀ , b ₂₁ , b ₃₀ , b _31. The 2 × 2 pixel area corresponding to each block of b ₂₂ , b ₂₃ , b ₃₂ , and b ₃₃ is identified as a pixel area including a pixel value of the CMYK color space before encoding. It is specified that the pixel region includes a pixel value in the RGB color space before encoding.

The acquisition unit 42 acquires the maximum value and the minimum value of the pixel values of each color constituting each color space based on the second information.
Specifically, the acquisition unit 42 reads the first difference plane set to the fourth bit, that is, the last one bit from the upper side of each color-coded plate of the code data, and obtains the CMYK color space. The maximum value and the minimum value of the pixel values of each color are acquired.
In addition, the acquisition unit 42 reads the second difference plane set in the 2nd to 4th bits from the upper side of the TAG plate, which is an additional plate of code data, and calculates the maximum pixel value of each color in the RGB color space. Get value and minimum value.
The acquisition unit 42 outputs the acquired maximum value and minimum value of the pixel values of each color to the fifth generation unit 43.

The fifth generation unit 43 sets the code value for each color based on the color space specified by the specifying unit 41, the maximum and minimum pixel values of each color specified by the acquisition unit 42, the third information, and the fourth information. A decrypted value is generated by decrypting the data. Hereinafter, as an example of the generation of the decoded value by the fifth generation unit 43, generation of a decoded value corresponding to the code value included in the C / R plate among the color-specific plates of the code data will be described.
As illustrated in FIG. 2, the fifth generation unit 43 includes a determination unit 43a, a third processing unit 43b, and a fourth processing unit 43c.

The determination unit 43a determines, based on the third information, whether each color included in the predetermined pixel region encoded by the fourth generation unit 34 of the encoding unit 30 belongs to the halftone region or the high resolution region. To do.
Specifically, the determination unit 43a reads the identification plane set to the first 1 bit counted from the upper side of the C / R plate of the code data, and the pixel area of 2 × 2 pixels corresponding to each block is obtained. Before encoding, it is determined whether the pixel area belongs to the halftone area or the high resolution area.

The third processing unit 43b decodes the code value of the color determined as the halftone area by the determination unit 43a. Hereinafter, the decoding by the third processing unit 43b may be referred to as a first decoding process.
Specifically, the third processing unit 43b uses the information output from the specifying unit 41, for example, among the blocks of the C / R plate, the color of the block determined as the halftone area by the determination unit 43a Identify the space. Next, the third processing unit 43b reads the code value set in the second and third bits from the upper side of the block identified as the CMYK color space. Here, since the code value of the CMYK color space read from the C / R plate is the code value of cyan (C), that is, the third processing unit 43b reads the code value of cyan (C). Then, the third processing unit 43b decodes the read cyan (C) code value using the information output from the acquisition unit 42.
In addition, the third processing unit 43b reads the code value set in the second and third bits from the upper side of the block specified as the RGB color space, for example, and reads the code value of red (R). And the 3rd process part 43b decodes the read code value of red (R) using the information output from the acquisition part 42. FIG.

For example, as shown in FIG. 7, the third processing unit 43b decodes the code value of cyan (C) according to the following relational expressions (32) to (35), and sets the code value to the block. A pixel value A _ij of four pixels in the corresponding 2 × 2 pixel pixel region is calculated. All the 2 × 2 pixel values of cyan (C) corresponding to the block determined to be a halftone area are decoded into the same calculated pixel value A _ij .
When BTC _IJ = 00, A _ij = CMin (32)
When BTC _IJ = 01, A _ij = CMin + (CMax−CMin) × 1/3 (33)
When BTC _IJ = 10, A _ij = CMin + (CMax−CMin) × 2/3 (34)
When BTC _IJ = 11, A _ij = CMax (35)
Further, as shown in FIG. 7, the third processing unit 43b decodes the code value of red (R) according to the following relational expressions (36) to (39) and sets the code value to the block set with the code value. A pixel value A _ij of four pixels in the corresponding 2 × 2 pixel pixel region is calculated. The red (R) pixel value of 2 × 2 pixels corresponding to the block determined to be a halftone area is decoded to the same pixel value A _ij for all four pixels.
When BTC _IJ = 00, A _ij = RMin (36)
When BTC _IJ = 01, A _ij = RMin + (RMax−RMin) × 1/3 (37)
When BTC _IJ = 10, A _ij = RMin + (RMax−RMin) × 2/3 (38)
When BTC _IJ = 11, A _ij = RMax (39)

In this way, the third processing unit 43b individually sets the decoded value for each color for each of “00”, “01”, “10”, and “11” that can be taken by the code value, Among the code values of each block, for a color block determined to belong to the halftone area, a decoded value corresponding to the code value of the color is specified.
In the above equations (32) to (39), the pixel value A _ij is an 8-bit pixel value. That is, the third processing unit 43b decodes the code value into an 8-bit pixel value by performing case classification according to the read code value.

The fourth processing unit 43c decodes the code value of the color determined as the high resolution region by the determination unit 43a by a decoding method different from that of the third processing unit 43b. Hereinafter, the decoding by the fourth processing unit 43c may be referred to as a second decoding process.
Specifically, the fourth processing unit 43c, based on the code value obtained by the second processing unit 34b of the encoding unit 30 and the reference data for obtaining the density pattern corresponding to the code value, A decoded value corresponding to the value is obtained.

  More specifically, for example, the fourth processing unit 43c decodes a block determined as a high-resolution area among the code values of each block of the code data using, for example, the template group illustrated in FIGS. 9 to 12 as reference data. Performs processing to obtain a value for each color. The template group illustrated in FIGS. 9 to 12 is a template group for performing pattern matching on the relationship between the block of interest P and its surrounding blocks, with the block to which the code value to be processed is set as the block of interest P. . The reference data is stored in, for example, a reference data storage unit 43d connected to the fourth processing unit 43c.

Hereinafter, as an example, decoding of a code value of cyan (C) determined to be a high resolution region will be described.
When the code value of cyan (C) determined to be the high resolution region is “00”, the fourth processing unit 43c refers to the first template group shown in FIG. Here, in FIG. 9 and the like, the block to which the symbol V is attached is a block determined as a halftone area, and satisfies the following expression (40).
_{| V den -b IJMax | <T} C ... (40)
Here, V _den is a decoded value of the block of V decoded by the third processing unit 43b. B _IJMax is the maximum value CMax of cyan (C) in the 4 × 4 block of the code data including the _target block P. _TC is a predetermined value set as a threshold value for determining the magnitude of the density difference between the decoded value of the halftone area and b _IJMax .
In addition, in FIG. 9 and the like, a block to which a symbol W is attached is a block that is determined to be a high-resolution area and satisfies the following expression (41).
| W _Max −b _IJMax | <T _M (41)
Here, W _Max is the maximum value of cyan (C) in a 4 × 4 block of code data including W. Further, b _IJMax is the maximum value CMax of cyan (C) in the 4 × 4 block of the code data including the _target block P, as described above. Here, if the block with the symbol W and the _target block P are included in the same 4 × 4 block, | W _Max −b _IJMax | is 0. When the relationship between the block to which the sign of W is attached and the target block P is an adjacent block across the boundary between 4 × 4 blocks to be encoded, | W _Max −b _IJMax | does not become 0. There may be cases. Further, _TM is a predetermined value set as a threshold for determining the magnitude of the density difference between blocks in the high resolution area.
In addition, when the area | region to which the code | symbol is attached | subjected in the template is a color space different from the color space of the block of attention P, it is handled as what is not satisfy | filled. For example, the condition is not satisfied when the color of a block to which a symbol of V or W is attached is red (R), which is a color in the RGB color space, for the target block P of cyan (C).

Note that T _C and T _M are thresholds for determining whether the density difference is small, and can be set as appropriate. For example, T _C = 30, T _M = 35, and the like can be set. it can. Thus, T _C and T _M may be different values or the same value. By comparing with T _C and T _M , a density pattern is predicted in which the density difference is small, that is, the pixel at the V or W position and the target block P have the same density.

As shown in FIG. 9 and the like, each template is associated with information indicating a decoding pattern and a priority order.
The decoding pattern is a density pattern used when decoding the code value of the block of interest P. For each template, the fourth processing unit 43c determines whether or not a condition related to a block with a symbol such as V or W is satisfied, and specifies a template that most closely matches the condition. And the 4th process part 43c calculates the decoding value according to the decoding pattern matched with the identified template. Here, among the numerical values assigned to the 2 × 2 pixels described as the decoding pattern, the pixel at the position corresponding to “1” includes cyan (C) in the 4 × 4 block of the code data including the target block P. Is set as the decoded value. Of the numerical values assigned to the 2 × 2 pixels described as the decoding pattern, the pixel at the position corresponding to “0” has cyan (C) in the 4 × 4 block of the code data including the block of interest P. The minimum value CMin is set as the decoded value. Here, CMax and CMin to be set as decoded values are both 8-bit values. That is, the fourth processing unit 43c decodes the code value into an 8-bit pixel value.

The information indicating the priority order indicates the priority order of templates used when the fourth processing unit 43c performs pattern matching using a plurality of templates included in each template group.
Specifically, as shown in FIG. 9 and the like, templates are classified into three priority orders Q1, Q2, and Q3, and information indicating each priority order is associated with each template. The priority level Q1 indicates that the priority level is higher than the priority levels Q2 and Q3, and the priority level Q2 indicates that the priority level is higher than the priority level Q3.
First, the fourth processing unit 43c performs pattern matching using a template with the priority order Q1. If none of the templates with the priority order Q1 satisfies the “condition for calculating the decoded value”, the fourth processing unit 43c performs pattern matching using the template with the priority order Q2. If neither of the templates of the priority orders Q1 and Q2 satisfies the “condition for calculating the decoded value”, the fourth processing unit 43c performs pattern matching using the template of the priority order Q3.

Here, a template selection criterion satisfying the “condition for calculating the decoded value” can be arbitrarily determined.
For example, in the pattern matching using the template of the priority order Q1, the fourth processing unit 43c decodes the template in which all the conditions are satisfied for the blocks with the codes such as V and W. In the pattern matching using the template of the priority order Q2, the fourth processing unit 43c quantifies the number of blocks that satisfy the condition for the blocks with the signs such as V and W, and performs the quantification. In the pattern matching using a template having a numerical value equal to or greater than the first reference value and indicating the maximum numerical value for decoding and using a template with the priority order Q3, the fourth processing unit 43c uses codes such as V and W. The number of blocks for which the condition is satisfied is quantified for the blocks marked with, and the quantified numerical value is equal to or lower than a second reference value lower than the first reference value. In, and may be used to decrypt the template indicating the maximum value. The said example is an example, Comprising: It is not restricted to this, It can change suitably.

In addition, even when all the pattern matching using the templates of the priority order Q3 is completed, if there is no template that satisfies the “condition for calculating the decoded value”, the fourth processing unit 43c uses the average pattern. Decode the code value.
For example, pattern matching is performed using the template shown in FIG. 9 for the code value “00” of cyan (C) determined to be a high resolution area, and there is no template that satisfies the “condition for calculating the decoded value”. When the result is obtained, the fourth processing unit 43c calculates a pixel value A _ij averaged by the following equation (42) and decodes the code value.
When BTC _IJ = 00, A _ij = CMax × 1/4 (42)
When the code value is decoded using the average pattern, the fourth processing unit 43c averages all four pixels included in the 2 × 2 pixel pixel area corresponding to the block in which the code value is set. Decode with pixel value A _ij .

The decoding of the code value “00” of cyan (C) determined to be the high resolution region has been described above, but the fourth processing unit 43 c performs decoding in the same flow for other code values.
For example, for the code value “01” of cyan (C) determined to be a high resolution region, the fourth processing unit 43c performs pattern matching using the second template group shown in FIG. For the code value “10” of cyan (C) determined to be the high resolution region, the fourth processing unit 43c performs pattern matching using the third template group shown in FIG. Further, the fourth processing unit 43c performs pattern matching on the code value “11” of cyan (C) determined to be the high resolution region, using the fourth template group shown in FIG.
When the result of the pattern matching is that there is no template that satisfies the “condition for calculating the decoded value”, the fourth processing unit 43c decodes among the expressions (43) to (45). The averaged pixel value is calculated by an expression corresponding to the code value, and the code value is decoded. As shown in equations (42) to (45), the pixel value A _ij is an 8-bit pixel value calculated using CMax. That is, the fourth processing unit 43c decodes the code value into an 8-bit pixel value.
When BTC _IJ = 01, A _ij = CMax × 2/4 (43)
When BTC _IJ = 10, A _ij = CMax × 2/4 (44)
When BTC _IJ = 11, A _ij = CMax × 3/4 (45)

In addition, in the template shown in FIG. 10 and the like, the block to which the code of X is attached is conditional on the code value of the block being “01” in addition to the condition relating to the code of W described above.
Further, in addition to the condition relating to the above W code, the block to which the Y code is attached is conditional on the code value of the block being “10”.
Moreover, the block to which the code | symbol of Z was attached | subjected is on condition that it is a block which does not satisfy | fill all the conditions of said V, W, X, and Y.

  The decoding of the code value of cyan (C) determined to be the high resolution region has been described above. However, the decoding of code values of other colors determined to be the high resolution region is performed in the same flow. Is called. For example, when decoding a red (R) code value determined to be a high-resolution area, the fourth processing unit 43c performs pattern matching using the template group of FIGS. 9 to 12, and according to the result of pattern matching. Thus, decoding is performed using the maximum value RMax and the minimum value Rmin of red (R) output from the acquisition unit 42.

The decoding of the code values included in the C / R plate among the color-specific plates of the code data has been described above. However, the decoding of the code values of the other color-specific plates is performed in the same flow. .
For example, the decoding process of the code value included in the M / G plate is a process in which the above cyan (C) is replaced with magenta (M) and the above red (R) is replaced with green (G). Similarly, the decoding process of the code value included in the Y / B plate is a process in which the above cyan (C) is replaced with yellow (Y) and the above red (R) is replaced with blue (B). The decoding process of the code value included in the K plate is a process in which the above cyan (C) is replaced with magenta (K).

  The decoding unit 40 decodes all the blocks and all the colors by repeating the process of decoding the encoded data, which is the encoded image data, for each color in units of 4 × 4 blocks and generating decoded data, As a result, the image data encoded by the encoding unit 30 is decoded.

Hereinafter, the flow of the encoding process will be described with reference to the flowcharts of FIGS.
During the encoding process, image data is input to the encoding unit 30 in units of 8 × 8 pixels (step S1).
When 8 × 8 pixels are input, the first generation unit 31 acquires information indicating the color space of each pixel, and a block unit corresponding to a pixel region of 2 × 2 pixels, which is an encoding processing unit The color space is specified by and information indicating the specified color space is generated and output (step S2). That is, the 1st production | generation part 31 outputs 1st information.
Further, the second generation unit 32 specifies the maximum value and the minimum value of the pixel values of each color constituting each color space, and outputs information indicating the specified maximum value and minimum value (step S3). In other words, the second generation unit 32 outputs the second information.

  Next, the third generation unit 33 determines whether the difference between the maximum value and the minimum value of the color that is not yet encoded is less than the threshold T (step S4). Here, when it is determined that the difference between the maximum value and the minimum value of the color is less than the threshold value T (step S4: YES), the third generation unit 33 includes 8 × 8 pixels for the one color. It is determined that all 2 × 2 pixel areas are halftone areas, and information indicating the determination result is generated and output. In this case, the encoding process of the halftone area, that is, the first encoding process is performed on all the 2 × 2 pixel areas included in the 8 × 8 pixels for the one color (step S5). ).

Here, the flow of the first encoding process will be described with reference to FIG.
First, the first processing unit 34a of the fourth generation unit 34 first calculates an average value avr _ij of the pixel values of four pixels included in the pixel region of 2 × 2 pixels that is an encoding processing unit among the 8 × 8 pixels. Calculate (step S21).
Further, as illustrated in FIG. 7, the third generation unit 33 calculates three segment values Th1, Th2, and Th3 using the maximum and minimum values of the color determined in step S4 (step S22).
Thereafter, as shown in the examples of the above formulas (20) to (23) and (24) to (27), the fourth generation unit 34 calculates the average value avr _ij calculated in step S21 and the step S4. In step S21, the code value BTC _IJ of the pixel area in which the average value avr _ij is calculated is determined according to the comparison result of the maximum and minimum values of the color determined in this way and the segment values Th1, Th2, and Th3. (Step S23), information indicating the determined code value BTC _IJ is output.

Returning to FIG. 13, the first processing unit 34a completes encoding for all 2 × 2 pixel pixel areas included in 8 × 8 pixels for one color determined in step S4. The process of step S5 is repeated (step S6: NO).
When the encoding for all the 2 × 2 pixel areas is completed for one color determined in step S4 (step S6: YES), the fourth generation unit 34 includes the 8 × 8 pixels. It is determined whether or not encoding has been completed for all colors constituting each of all the included color spaces (step S7). Here, when it is determined that encoding has not been completed for all the colors constituting each of all the color spaces (step S7: NO), the process proceeds to step S4.
On the other hand, when it is determined in step S7 that encoding has been completed for all the colors constituting each of all the color spaces (step S7: YES), the output unit 35 configures each of all the color spaces. Code data of 4 × 4 blocks corresponding to 8 × 8 pixels for which encoding has been completed for all colors to be performed is output (step S8). Thereafter, when encoding of all the pixels constituting the image data has not been completed (step S9: NO), the process proceeds to step S1 again. That is, encoding is performed in units of 8 × 8 pixels until encoding of all pixels constituting the image data is completed. When encoding of all the pixels constituting the image data is completed (step S9: YES), the encoding unit 30 ends the encoding process.

Further, when it is determined in step S4 that the difference between the maximum value and the minimum value of the color is not less than the threshold value T (step S4: NO), as illustrated in FIG. 14, the third generation unit 33 performs step S4. The three segment values Th1, Th2, and Th3 are calculated using the maximum value and the minimum value of one color that has been determined in step S10 (step S10).
In addition, the third generation unit 33 sets a pixel region of 2 × 2 pixels that is not yet encoded for one color determined in step S4 out of 8 × 8 pixels as a processing target ( Step S11) Unless the pixel area is determined to be a halftone area, the determinations in steps S12 to S14 using the segment values are sequentially performed. The order of determination in steps S12 to S14 is merely an example, and is not limited to this, and the order is not limited.

The third generation unit 33 determines whether or not a pixel having a pixel value greater than Th1 and equal to or less than Th3 is included in the pixel region (step S12). Here, when it is determined that a pixel having a pixel value greater than Th1 and equal to or less than Th3 is included in the pixel area (step S12: YES), the third generation unit 33 determines that the pixel area is a halftone area. It is determined that there is, and information indicating the determination result is generated and output. In this case, the halftone area encoding process, that is, the first encoding process is performed on the pixel area (step S15).
On the other hand, when it is determined in step S12 that the pixel area has a pixel value greater than Th1 and less than or equal to Th3 (step S12: NO), the third generation unit 33 sets the pixel area in the pixel area. It is determined whether or not all of the four pixel values included are equal to or less than Th1 (step S13). Here, when it is determined that all the pixel values of the four pixels included in the pixel area are equal to or less than Th1 (step S13: YES), the third generation unit 33 determines that the pixel area is a halftone area. Then, information indicating the determination result is generated and output. In this case, the process proceeds to step S15.
On the other hand, when it is determined in step S13 that all the pixel values of the four pixels included in the pixel region are not equal to or less than Th1 (step S13: NO), the third generation unit 33 includes the four pixels included in the pixel region. It is determined whether or not all the pixel values of are larger than Th3 (step S14). Here, when it is determined that all the pixel values of the four pixels included in the pixel area are larger than Th3 (step S14: YES), the third generation unit 33 determines that the pixel area is a halftone area. Then, information indicating the determination result is generated and output. In this case, the process proceeds to step S15.
On the other hand, when it is determined in step S14 that all the pixel values of the four pixels included in the pixel area are not greater than Th3 (step S14: NO), the third generation unit 33 determines that the pixel area is a high-resolution area. And information indicating the determination result is output. In this case, the high-resolution area encoding process, that is, the second encoding process is performed on the pixel area (step S16).
Thus, the 3rd production | generation part 33 produces | generates 3rd information based on the determination result of step S4 or step S12-S14.

  Since the flow of the first encoding process in step S15 is the same as the flow of the first encoding process in step S5, description thereof is omitted. In the first encoding process in step S15, the process in step S22 may be omitted.

The flow of the second encoding process will be described with reference to FIG.
First, the second processing unit 34b of the fourth generation unit 34 binarizes the pixel values of the four pixels included in the pixel region of 2 × 2 pixels, which is an encoding processing unit (step S31). Then, the second processing unit 34b specifies the code value BTC _IJ corresponding to the binarized 2 × 2 pixel density pattern with reference to the density pattern data (step S32).
Thus, the 4th production | generation part 34 produces | generates 4th information according to the processing content of step S5, step S15, or step S16.

  After the processing of step S15 or step S16, the fourth generation unit 34 encodes all the 2 × 2 pixel pixel regions included in the 8 × 8 pixels with respect to one color determined in step S4. It is determined whether or not has been completed (step S17). Here, when it is determined that the encoding for all the pixel regions of 2 × 2 pixels included in the 8 × 8 pixels is not completed for one color that is the determination target in Step S4 (Step S17). : NO), the process proceeds to step S11. On the other hand, when it is determined that the encoding of all the 2 × 2 pixel pixel areas included in the 8 × 8 pixels has been completed for one color that has been determined in step S4 (step S17: YES). The process proceeds to step S7.

Hereinafter, the flow of the decoding process will be described with reference to the flowcharts of FIGS.
In the encoding process, code data is input to the decoding unit 40 in units of 4 × 4 blocks (step S41).
When the 4 × 4 block is input, the specifying unit 41 specifies the color space of each pixel region of 2 × 2 pixels corresponding to each block based on the first information (step S42).
Further, the acquisition unit 42 acquires the maximum value and the minimum value of the pixel values of each color constituting each color space based on the second information (step S43).

  Next, the fifth generation unit 43 sets one color that has not been decoded yet as a color to be processed (step S44). In addition, the fifth generation unit 43 sets one block that has not been decoded yet as a processing target among the color-specific plates corresponding to the one color to be processed in step S44 (step S45). .

  Based on the third information, the determination unit 43a of the fifth generation unit 43 determines that the 2 × 2 pixel region before encoding corresponding to the block is intermediate based on the third information. It is determined whether it belongs to a tone area or a high resolution area. If it is determined that the image belongs to the halftone area (step S46: YES), the decoding process of the halftone area, that is, the first decoding process is performed on the block (step S47). On the other hand, if it is determined that the block belongs to the high resolution area (step S46: NO), the high resolution area decoding process, that is, the second decoding process is performed on the block (step S48).

Hereinafter, the flow of the first decoding process and the second decoding process will be sequentially described.
FIG. 18 is a flowchart illustrating an example of the flow of the first decoding process.
The third processing unit 43b of the fifth generation unit 43 obtains the maximum value acquired in step S43 as shown in the examples of the relational expressions (32) to (35) and the relational expressions (36) to (39). And, using the maximum value and the minimum value of one color that is the processing target in step S44 among the minimum values, the decoding value corresponding to the code value BTC _IJ of the block that is the processing target is calculated in step S45. (Step S61). Then, the third processing unit 43b sets the decoded value calculated in step S61 as the pixel values of all four pixels in the pixel region of 2 × 2 pixels corresponding to the block (step S62), and outputs decoded data.

FIG. 19 is a flowchart illustrating an example of the flow of the second decoding process.
The fourth processing unit 43c of the fifth generation unit 43 first performs processing related to the identification of reference data corresponding to the code value BTC _IJ of the block to be processed in step S45.
Specifically, for example, the fourth processing unit 43c determines whether or not the code value BTC _{IJ of the} block is “00” (step S71), and when it is “00” (step S71: YES). Reference is made to the first template group shown in FIG. 9 (step S74).
In step S71, if the code value BTC _{IJ of the} block is not “00” (step S71: NO), the fourth processing unit 43c determines whether the code value BTC _{IJ of the} block is “01”. If it is determined (step S72) and it is “01” (step S72: YES), the second template group shown in FIG. 10 is referred to (step S75).
In step S72, if the code value BTC _{IJ of the} block is not “01” (step S72: NO), the fourth processing unit 43c determines whether the code value BTC _{IJ of the} block is “10”. If it is determined (step S73) and is “10” (step S73: YES), the third template group shown in FIG. 11 is referred to (step S76). If not, that is, the code value BTC _{IJ of the} block. Is “11” (step S73: NO), the fourth template group shown in FIG. 12 is referred to (step S77).
Note that the determination order of steps S71 to S73 and the code value BTC _IJ to be determined are merely examples, and the present invention is not limited to this, and it is sufficient that the reference data corresponding to the code value BTC _IJ can be specified.

The fourth processing unit 43c performs pattern matching using the template group referred to through any of the processes in steps S74 to S77 (step S78).
FIG. 20 is a flowchart illustrating an example of the flow of pattern matching.
First, the fourth processing unit 43c performs collation using the template with the priority order Q1 (step S81). Here, when there is a template that satisfies all the conditions (step S82: YES), the fourth processing unit 43c calculates a decoded value according to the decoding pattern associated with the template, The decoded data is output as a pixel value of 2 × 2 pixels corresponding to the block (step S83).
On the other hand, if there is no template that satisfies all the conditions in step S82 (step S82: NO), the fourth processing unit 43c performs collation using the template of the priority order Q2 (step S84). Here, when the number of blocks that satisfy the conditions set in each of the templates of the priority order Q2 is quantified, there is a template in which the quantified numerical value is equal to or greater than the first reference value ( (Step S85: YES), the fourth processing unit 43c specifies the template having the maximum value (Step S86), calculates a decoded value according to the decoding pattern associated with the specified template, and performs processing. The decoded data is output as the pixel value of 2 × 2 pixels corresponding to the determined block (step S83).
On the other hand, in step S85, when there is no template whose numerical value is equal to or greater than the first reference value (step S85: NO), the fourth processing unit 43c performs collation using the template of the priority order Q3 (step S87). ). Here, when the number of blocks satisfying the conditions set in each of the templates of the priority order Q3 is digitized, there is a template in which the numeric value is equal to or greater than the second reference value ( Step S88: YES), the process proceeds to Step S86. On the other hand, when there is no template whose numerical value is equal to or larger than the second reference value (step S88: NO), the fourth processing unit 43c calculates a decoded value using the average pattern, and sets the block to be processed. The decoded data is output as the corresponding 2 × 2 pixel value (step S89).

Returning to FIG. 17, after the processing in step S47 or step S48, the fifth generation unit 43 performs the code values BTC of all the blocks included in the 4 × 4 block for one color determined in step S44. _It is determined whether or not _IJ decoding has been completed (step S49). Here, when it is determined that the decoding of the code values BTC _IJ of all the blocks included in the 4 × 4 block has not been completed for one color to be determined in step S44 (step S49: NO), the process proceeds to step S45.
On the other hand, when it is determined that the decoding of the code values BTC _IJ of all the blocks included in the 4 × 4 block has been completed for one color that has been determined in step S44 (step S49: YES), It is determined whether or not the decoding has been completed for all the colors constituting each of all the color spaces specified in step S42 (step S50). Here, when it is determined that decoding has not been completed for all the colors constituting each of all the color spaces (step S50: NO), the process proceeds to step S44.
On the other hand, if it is determined in step S50 that the decoding has been completed for all the colors constituting each of all the color spaces (step S50: YES), all the pixels of the image data before encoding are processed. When the corresponding decoding is not completed (step S51: NO), the process proceeds to step S41 again. In other words, decoding is performed in units of 4 × 4 blocks until decoding of all blocks of the code data is completed. When encoding of all blocks is completed (step S51: YES), the decoding unit 40 ends the decoding process.

As described above, according to the image forming apparatus 1 of the present embodiment, the first information including information indicating each color space of the pixel area of 2 × 2 pixels is generated in the encoding process, and thus each color space is indicated. Information can be retained and encoded. Therefore, even image data in which pixel areas having different color spaces are mixed, such as mixed data, can be encoded by one image processing apparatus. Further, based on the third information including information indicating the gradation width of each color included in each pixel area of 2 × 2 pixels, the pixel values of the four pixels constituting the pixel area of 2 × 2 pixels are set for each color. Since the fourth information indicating the code value encoded by the encoding method corresponding to the gradation width is generated, encoding according to the gradation width of each pixel region can be performed. In this way, encoding corresponding to the color space and gradation width to which each pixel of image data belongs can be performed. Since the data including the first information, the second information, the third information, and the fourth information is output as code data, information necessary for decoding can be output as a single code data. The storage area of the converted image data can be managed more easily.
Further, in the decoding process, the specification of each color space of the pixel area of 2 × 2 pixels before encoding based on the first information, and the maximum pixel value of each color constituting each color space based on the second information Decoding that performs code value decoding for each color based on the specified color space, the maximum and minimum values of the acquired pixel values of each color, the third information, and the fourth information. Since the value is generated, it is possible to perform decoding corresponding to the specified color space and the gradation width indicated by the third information.

In the encoding process, information indicating whether the gradation width of each color included in each pixel area of 2 × 2 pixels belongs to a halftone area or a high resolution area is set as third information and belongs to the halftone area Since the pixel value of the color and the pixel value of the color belonging to the high resolution area are encoded by separate processing, encoding corresponding to both the halftone area and the high resolution area can be performed.
In the decoding process, based on the third information, it is determined whether each color included in the encoded pixel region of 2 × 2 pixels belongs to the halftone region or the high resolution region, Since the code value of the determined color and the code value of the color determined to be the high resolution area are decoded by separate processing, decoding corresponding to both the halftone area and the high resolution area can be performed.

  Further, when encoding the halftone area, the code value is obtained based on the average value obtained by averaging the pixel values of the four pixels constituting the pixel area of 2 × 2 pixels. Therefore, it is possible to more easily encode a small halftone area.

In addition, for a color determined to belong to the halftone area, a range of gradation corresponding to the difference between the maximum value and the minimum value of the color is divided into a predetermined number of sections, and a code value corresponding to each section is set. Since the code value corresponding to the section including the average value is identified and the average value is calculated as the code value of the color of the image area of 2 × 2 pixels, the halftone area is set according to the gradation range. Can be encoded.
In the decoding of the encoded halftone area, an individual decoded value is set for each color for each possible value of the code value, and the average value is calculated in the pixel area of 2 × 2 pixels. Since the decoding value corresponding to the corresponding code value of the color is specified, it is possible to decode with the individual decoding value set according to the number of code value categories obtained according to the gradation range.

Also, in the encoding process, a code value corresponding to a density pattern obtained by binarizing the pixel values of colors belonging to the high resolution region among the pixel values of the four pixels constituting the pixel region of 2 × 2 pixels is obtained. Therefore, it is possible to encode a high-resolution region having a relatively large pixel value difference between pixels by pattern matching using a density pattern, and to perform encoding more easily.
Further, in the decoding process of the encoded high-resolution area, the decoded value corresponding to the code value is obtained based on the code value and the reference data for obtaining the density pattern corresponding to the code value. By pattern matching using data, it is possible to decode a code value in a high resolution region where the difference in pixel value between pixels is relatively large, and encoding can be performed more easily.

  Also, in the encoding process, a number of color plates corresponding to the number of colors in the color space with the largest number of colors, a color plate and another additional plate are generated, and each color plate has the number of colors. The second information, the third information, and the fourth information in the most color space are set for each color, and the third information and the fourth information for the other color space are set for each color in some or all of the color plates. Since the first information and the second information of the other color space are set in the additional plate and the data constituted by the color-specific plate and the additional plate is output as the code data, the encoded image data is in a predetermined format. Therefore, by using the format as a premise for encoding and decoding, information necessary for data management and decoding of encoded image data can be made easier. so That.

  Further, the image data in which pixel regions having different color spaces are mixed includes the pixel values of the color space in each of the partial data corresponding to the number of colors of the color space having the largest number of colors, and Since the pixel values of other color spaces are included for each color in part or all of the partial data, it is not necessary to provide partial data for each color space, so that more compact image data can be obtained. It is possible to reduce the memory capacity consumed in the processing of image data.

  In addition, image data in which pixel areas having different color spaces are mixed includes additional data including information indicating the color space of the pixel value included in each partial data. Therefore, by referring to the additional data, each partial data It is possible to determine which color space the pixel value included in the color value belongs to, and encoding processing for each color space can be performed more easily.

  The embodiment of the present invention should be considered that the embodiment disclosed this time is illustrative and not restrictive in all respects. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

For example, as shown in FIG. 21, image data in which pixel areas having different color spaces are mixed does not include information indicating the color space of the pixel value included in each partial data. It may be included in the partial data.
In the example shown in FIG. 21, the least significant bit of the K plate that does not include the color of the RGB color space is assigned as the color system plate among the partial data. Since the least significant bit corresponds to only one gradation of 8-bit color values that maximize 256 gradations from 0 to 255, the influence of black (K) pixel values on color reproduction is slight. It is believed that there is.
In this way, by including information indicating the color space of the pixel value included in each partial data in the partial data not including the pixel value of the other color space, the image data can be made more compact.

In the above embodiment, the image data in the CMYK color space is encoded before the mixed data is generated. However, this is an example, and the present invention is not limited to this. For example, encoding and decoding of image data in the CMYK color space performed before the mixed data generation is omitted, and image data in the CMYK color space and image data in the RGB color space that have not been encoded are aggregated. Good.
It is also possible to encode and decode image data only in the RGB color space.

  In the above-described embodiment, the gradation range is divided into four by the three segment values Th1 to Th3. Since the code value is represented by 2 bits, “00”, “ This corresponds to a total of four patterns of code values of “01”, “10”, and “11”, and is an example and is not limited thereto. The number of bits of the code value can be changed as appropriate, and the number of partition values, that is, the number of sections of the gradation range set for encoding is also changed according to the number of bits of the code value.

  Further, in the above embodiment, various processes such as the generation of the first information to the fourth information and the output of the code data in the encoding process are individually performed by each unit of the encoding unit 30. It is not limited to this. For example, a processing unit having two or more functions among the functions of the units included in the encoding unit 30 may be provided. The same applies to various processes in the decryption process.

In the decoding process, information indicating a color space to which a pixel at the same position before encoding may be added to each pixel included in the decoded data.
In the above embodiment, the 2 × 2 pixel area is a predetermined pixel area. However, this is only an example, and the present invention is not limited to this, and can be changed as appropriate. In the above embodiment, the image data is encoded into 4 × 4 block code data in units of 8 × 8 pixels. However, this is an example, and the present invention is not limited to this, and can be changed as appropriate. Similarly, decoding can be changed as appropriate according to changes in encoding.

  In the above embodiment, the image forming apparatus 1 and other devices are connected via the communication network N, but this is an example and the present invention is not limited to this. For example, the image forming apparatus 1 may be connected to another device via a dedicated interface or bus.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 4 Reading apparatus 11 Communication control part 12 Reading control part 13 Image memory 14 Input / output control part 15 Storage control part 16 Storage part 17 Image forming part 18 Central control part 20 Image processing part 21 Color conversion part 22 Aggregation part 30 Encoding unit 31 First generation unit 32 Second generation unit 33 Third generation unit 34 Fourth generation unit 34a First processing unit 34b Second processing unit 34c Density pattern data storage unit 35 Output unit 40 Decoding unit 41 Identification unit 42 Acquisition unit 43 Fifth generation unit 43a Determination unit 43b Third processing unit 43c Fourth processing unit 43d Reference data storage unit

Claims (11)

An image processing apparatus comprising: an encoding unit that encodes image data in units of a predetermined pixel region; and a decoding unit that decodes the image data encoded by the encoding unit in units of the predetermined pixel region. In
The encoding unit includes:
A first generation unit configured to generate first information including information indicating each color space of the predetermined pixel region when pixel regions having different color spaces are mixed in the image data;
A second generation unit that generates second information including information indicating a maximum value and a minimum value of a pixel value of each color constituting each color space when pixel regions having different color spaces are mixed in the image data;
A third generation unit that generates third information including information indicating a gradation width of each color included in each predetermined pixel region;
Based on the first information, the second information, and the third information, a code obtained by encoding pixel values of a plurality of pixels constituting the predetermined pixel region for each color by an encoding method corresponding to the gradation width A fourth generation unit for generating fourth information indicating a value;
An output unit that outputs the data including the first information, the second information, the third information, and the fourth information as the encoded image data;
The decoding unit
A specifying unit that specifies each color space of the predetermined pixel area based on the first information;
An acquisition unit for acquiring a maximum value and a minimum value of pixel values of each color constituting each color space based on the second information;
Decoding by decoding the code value for each color based on the color space specified by the specifying unit, the maximum and minimum pixel values of each color acquired by the acquiring unit, the third information, and the fourth information A fifth generation unit for generating a value;
An image processing apparatus comprising: The third generation unit generates, as third information, information indicating whether the gradation width of each color included in each predetermined pixel region belongs to a halftone region or a high resolution region,
The fourth generation unit includes:
A first processing unit that encodes pixel values of colors belonging to the halftone area among the colors included in the predetermined pixel area;
A second processing unit that encodes a pixel value of a color belonging to the high-resolution region among the colors included in the predetermined pixel region by an encoding method different from the encoding by the first processing unit;
The fifth generator is
A determination unit that determines, based on the third information, whether each color included in the predetermined pixel region encoded by the fourth generation unit belongs to the halftone region or the high-resolution region;
A third processing unit for decoding the code value of the color determined as the halftone region by the determination unit;
A fourth processing unit that decodes the code value of the color determined as the high-resolution area by the determination unit by a decoding method different from that of the third processing unit;
The image processing apparatus according to claim 1, further comprising:   The image processing apparatus according to claim 2, wherein the first processing unit obtains a code value based on an average value obtained by averaging pixel values of a plurality of pixels constituting the predetermined pixel region. For each color determined to belong to the halftone area, the first processing unit divides a gradation range corresponding to a difference between the maximum value and the minimum value of the color into a predetermined number of sections. Set the code value corresponding to the above, specify the code value corresponding to the section including the average value, and the code value of the color of the predetermined image area where the average value is calculated,
The third processing unit sets a separate decoded value for each color that can be taken by the code value for each color, and the average value is calculated for the color determined to belong to the halftone area. The image processing apparatus according to claim 3, wherein a decoded value corresponding to a code value of the color corresponding to the pixel region is specified. The second processing unit obtains a code value corresponding to a density pattern obtained by binarizing pixel values of colors belonging to the high resolution region among pixel values of a plurality of pixels constituting the predetermined pixel region. ,
The fourth processing unit obtains a decoded value corresponding to the code value based on the code value obtained by the second processing unit and reference data for obtaining a density pattern corresponding to the code value. The image processing apparatus according to claim 2, wherein the image processing apparatus is characterized.   The output unit generates a number of color-specific plates corresponding to the number of colors in the color space having the largest number of colors, the color-specific plate, and another additional plate, and each of the color-specific plates has a number of colors. The second information, the third information, and the fourth information of the most color space are set for each color, and the third information and the fourth of the other color space are set on each of all or some of the color plates. Information is set for each color, the first information and the second information of another color space are set in an additional plate, and the data composed of the color-specific plate and the additional plate is encoded as the image data The image processing apparatus according to claim 1, wherein the image processing apparatus outputs the image.   The image data in which pixel areas having different color spaces are mixed includes the pixel values of the color space in each of the partial data corresponding to the number of colors in the color space having the largest number of colors, The image processing apparatus according to any one of claims 1 to 6, wherein a pixel value of another color space is included for each color in part or all of the partial data.   The image processing apparatus according to claim 7, wherein the image data in which pixel areas having different color spaces are mixed includes additional data including information indicating a color space of a pixel value included in each partial data. .   The additional data is included in partial data that does not include pixel values in the other color space, out of the number of partial data corresponding to the number of colors in the color space having the largest number of colors. The image processing apparatus according to 8. In an encoding method for encoding image data in a predetermined pixel area unit,
When pixel regions having different color spaces are mixed in the image data, generating first information including information indicating each color space of the predetermined pixel region;
Generating second information including information indicating a maximum value and a minimum value of pixel values of each color constituting each color space when pixel regions having different color spaces are mixed in the image data;
Generating third information including information indicating a gradation width of each color included in each predetermined pixel region;
Based on the first information, the second information, and the third information, a code obtained by encoding pixel values of a plurality of pixels constituting the predetermined pixel region for each color by an encoding method corresponding to the gradation width Generating fourth information indicating a value;
And outputting the data including the first information, the second information, the third information, and the fourth information as the encoded image data. The decoding method for decoding the image data encoded by the encoding method according to claim 10 in units of the predetermined pixel area,
Identifying each color space of the predetermined pixel area based on the first information;
Obtaining a maximum value and a minimum value of pixel values of each color constituting each color space based on the second information;
Generating a decoded value obtained by decoding a code value for each color based on the specified color space, the maximum value and minimum value of the acquired pixel values of each color, the third information, and the fourth information; A decoding method characterized by comprising:

Images