JP2013143609A - Image processing device, coding method and decoding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To code or decode image data with the same method irrespective of a color space to which each pixel of the image data belongs.SOLUTION: An image processing device comprises: an aggregation processing unit for extracting a pixel from each of pieces of image data different in color space according to an arrangement position when the image data different in color space is aggregated, creating a pixel value plane for each color in which a pixel value of a color in a color space to which each extracted pixel belongs is mixed among the different color spaces, and creating an identification plane indicating the color space to which each pixel belongs; a coding unit for a gradation plane indicating a gradation of each color in the pixel value plane, and coding the pixel value according to a section of the gradation of each color to which the pixel value of each color in the pixel value plane belongs, and creating a code value plane indicating the code value; and decoding unit for specifying a color of each code value in the code value plane according to the color space indicated by the identification plane, and coding the code value of each specified color by using the gradation of each color indicated by the gradation plane.

Description

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

  Image data to be printed by a printing machine such as a copier or a printer is generally image data including four color spaces of C (cyan), M (magenta), Y (yellow), and K (black). . In order to support special printing, there is also a printing device that can process image data composed of another color space. On the other hand, image data displayed and edited by a PC (personal computer) is image data including three color spaces of R (red), G (green), and B (blue). When printing image data processed by the PC, the printing device converts the color space of the image data from RGB to CMYK.

  In recent years, the amount of image data to be processed has been increased due to improvements in image processing technology, but the capacity of a storage device that can be mounted on a printing device is limited. For this reason, the amount of data stored in the storage device is reduced by compressing the image data by encoding when storing the image data and expanding the image data by decoding when using the image data.

There are various methods for encoding and decoding, and an optimal method is adopted depending on the form of image data. For example, JPEG (Joint Photographic Experts Group) is known as a method suitable for multivalued image data, and JBIG (Joint Bi-level Image experts Group), run-length code, etc. are known as methods suitable for binary image data. It has been.
In addition, switching between a reversible type and an irreversible type is performed depending on an image attribute such as a character or a photographic image (see, for example, Patent Document 1).

Similarly, for image data having different color spaces, encoding and decoding methods suitable for the respective color spaces are required. However, one piece of image data may be created by aggregating image data with different color spaces. Although such image data has different color spaces to which each pixel belongs, at the time of encoding and decoding, it is difficult to switch between encoding and decoding methods according to different color spaces for each pixel. In particular, according to JPEG or run-length code using DCT (Discrete Cosine Transform), it is difficult to reproduce the position of a pixel having a different color space before encoding by decoding.
Therefore, conventionally, image data is separated for each color space, and encoding and decoding are performed by a method suitable for each color space.

JP 2006-120145 A

Originally, the process itself for encoding or decoding multi-valued image data is complicated, and a large number of memories and gates are required for processing by hardware. In addition, if the encoding and decoding processes are implemented in hardware for each different method, the scale of the hardware increases and the cost increases.
In addition, if image data encoded for each color space is stored in a storage device, use areas of the storage device are wasted. Address management is also necessary when reading out the image data of each color space from the storage device, which is complicated.

  An object of the present invention is to perform encoding or decoding in the same manner regardless of the color space to which each pixel of image data belongs.

According to the invention of claim 1,
An encoding unit that encodes image data by the BTC method;
A decoding unit that decodes the image data encoded by the encoding unit by a BTC method;
According to the arrangement position when the image data with different color spaces are aggregated, pixels are extracted from each of the image data with different color spaces, and the pixel values of the colors of the color spaces to which the extracted pixels belong are different color spaces An aggregation processing unit that creates a pixel value plane for each color mixed together and creates an identification plane that represents a color space to which each pixel belongs in the pixel value plane;
The encoding unit includes:
Create a gradation plane representing the gradation of each color in the pixel value plane,
The pixel value of each color in the pixel value plane is encoded according to which section of the gradation of each color belongs to create the code value plane representing the code value,
The gradation plane, the code value plane, and the identification plane are output as code data,
The decoding unit
Image processing for identifying the color of each code value of the code value plane by the color space represented by the identification plane, and decoding the code value of each identified color using the gradation of each color represented by the gradation plane An apparatus is provided.

According to invention of Claim 2,
The image processing apparatus according to claim 1, wherein the aggregation processing unit creates pixel value planes by the number of colors in a color space having a larger number of colors among different color spaces.

According to invention of Claim 3,
The pixel value plane is composed of planes corresponding to the number of bits of pixel value data, and one plane represents 1-bit data.
The image processing apparatus according to claim 1, wherein the aggregation processing unit replaces the identification plane with a least significant bit plane of a pixel value plane of any color.

According to invention of Claim 4,
An encoding unit that encodes image data by the BTC method;
Pixels are extracted from each of the image data with different color spaces according to the arrangement position when the image data with different color spaces are aggregated, and the pixel values of the colors of the color space to which each pixel belongs are mixed in different color spaces An aggregation processing unit that creates a pixel value plane for each color and creates an identification plane representing a color space to which each pixel belongs in the pixel value plane,
The encoding unit includes:
Create a gradation plane representing the gradation of each color in the pixel value plane,
The pixel value of each color in the pixel value plane is encoded according to which section of the gradation of each color belongs to create the code value plane representing the code value,
An image processing apparatus is provided that outputs the gradation plane, the code value plane, and the identification plane as code data.

According to the invention of claim 5,
A gradation plane that represents the gradation of each color in a pixel value plane in which pixel values of colors in different color spaces are mixed, and encoding according to which division of the gradation of each color the pixel value of each color in the pixel value plane belongs to A decoding unit that decodes code data composed of a code value plane representing a code value of the pixel value obtained and an identification plane representing a color space to which each pixel belongs;
The decoding unit identifies a code value of each color of the code value plane by using a color space represented by the identification plane, and uses the gradation of each color represented by the gradation plane by using the code value of each identified color. An image processing apparatus for decoding is provided.

According to the invention of claim 6,
Pixels are extracted from each of the image data with different color spaces according to the arrangement position when the image data with different color spaces are aggregated, and the pixel values of the colors of the color space to which each pixel belongs are mixed in different color spaces Creating a pixel value plane for each color,
Creating an identification plane representing a color space to which each pixel belongs in the pixel value plane;
Creating a gradation plane representing the gradation of each color in the pixel value plane;
Encoding the pixel value according to which section of the gradation of each color the pixel value of each color in the pixel value plane, and creating a code value plane representing the code value;
Outputting the gradation plane, the code value plane, and the identification plane as code data;
Is provided.

According to the invention of claim 7,
A gradation plane that represents the gradation of each color in a pixel value plane in which pixel values of colors in different color spaces are mixed, and a code depending on which division of the gradation of each color the pixel value of each color in the pixel value plane belongs to A code value plane consisting of a code value plane representing a coded code value and an identification plane representing a color space to which each pixel belongs; and
Identifying the code value of each color of the code value plane by the color space represented by the identification plane, and decoding the code value of each identified color using the gradation of each color represented by the gradation plane;
Is provided.

According to the present invention, encoding or decoding can be performed by the same BTC method regardless of the color space to which each pixel of image data belongs. There is no need to provide a different encoding or decoding processing circuit for each color space, and an increase in hardware scale can be avoided. According to the BTC method, even after encoding and decoding, it is possible to maintain the relationship between pixel positions and pixel values in different color spaces, and excellent image data reproducibility.
In addition, the amount of code data can be reduced by consolidating image data having different color spaces and encoding the image data as one image data. This makes it possible to effectively use memory resources and to easily save and read code data.

2 is a functional block diagram of an MFP. FIG. It is a functional block diagram of the image processing apparatus which concerns on this Embodiment. It is a figure which shows the example of the pixel value plane showing the pixel value of 4x4 pixel which belongs to the color space of CMYK. It is a figure which shows the example of the pixel value plane showing the pixel value of 4x4 pixel which belongs to RGB color space. It is a figure which shows 4x4 pixel in 1 plane. It is a figure which shows the example of the code data obtained by encoding the image data which consists of a single color space. 6 is a flowchart of processing executed by an image processing apparatus when image data having different color spaces are aggregated to create one image data. It is a figure which shows the example of the pixel value plane showing the pixel value of each color mixed in the color spaces of CMYK and RGB, and an identification plane. It is a figure which shows the example by which the K pixel value plane of the 0th bit was replaced by the identification plane. It is a figure which shows the example of one image data produced by aggregating the image data from which a color space differs. It is a flowchart of the process of the encoding which an image processing apparatus performs. It is a figure which shows an example of the code data obtained by the encoding of the image data which consists of different color spaces. It is a flowchart of the process of the decoding which an image processing apparatus performs.

  Embodiments of the present invention will be described below with reference to the drawings.

[MFP]
FIG. 1 is a functional block diagram of an MFP (Multifunction Peripheral) 10 equipped with an image processing apparatus G according to the present embodiment.
As shown in FIG. 1, the MFP 10 includes a control unit 1, a scanner 2, a reading processing unit 3, a buffer 4, a communication unit 5, an image memory 6, a storage control unit 7a, a storage device 7, a printing unit 8, and an image processing device G. It is configured with.

  The control unit 1 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like. The control unit 1 reads out a program stored in the storage device 7 and controls each unit of the MFP 10 by executing the program. For example, the control unit 1 inputs image data to the image processing apparatus G and causes it to perform image processing. In addition, the control unit 1 outputs the image data written in the image memory 6 to the printing unit 8 for print processing.

  The scanner 2 includes a contact glass, a light source that irradiates light on a document on the contact glass, a mirror group that guides the reflected light, a condensing lens that forms an image of light guided by the mirror group, and a photoelectric conversion of the imaged light. And a photoelectric conversion element for generating an analog image signal for each reading line. The analog image signal generated by the scanner 2 is composed of R (red), G (green), and B (blue) color spaces, and is output to the reading processing unit 3.

  The reading processing unit 3 A / D converts the analog image signal output from the scanner 2 into digital image data having a predetermined bit width. The reading processing unit 3 performs shading correction processing and MTFγ correction processing on the image data. The image data obtained by these correction processes is temporarily stored in the buffer 4 and then output to the image processing apparatus G.

  The buffer 4 is a memory that temporarily holds image data.

The communication unit 5 includes a communication interface, and communicates with the print controller 20 or the PC 30 via the network N. The network N is a LAN (Local Area Network) or the like.
The communication unit 5 receives PDL (Page Description Language) data from the PC 30 and outputs it to the image memory 6. Further, the print controller 20 rasterizes the PDL data transmitted from the PC 30, and the generated image data is received by the communication unit 5 and output to the buffer 4. This image data consists of C (cyan), M (magenta), Y (yellow), and K (black) color spaces.

  The image memory 6 is generated by the control unit 1 from code data obtained by encoding image data by the image processing apparatus G, image data obtained by decoding the code data, PDL data transmitted from the PC 30, or the PDL data. Temporarily store the intermediate language data. As the image memory 6, a DRAM (dynamic RAM) or the like can be used.

  The storage device 7 stores a program used for the control unit 1, data necessary for executing the program, and the like. As the storage device 7, a nonvolatile large-capacity memory such as a hard disk can be used.

The storage device 7 can store the code data of the image data by the image processing device G.
The storage control unit 7 a writes the code data held in the image memory 6 to the storage device 7. Further, the storage control unit 7 a reads the code data stored in the storage device 7 and writes it in the image memory 6.

  The print unit 8 is a buffer that temporarily holds the image data transferred from the storage device 7, a print control unit that performs PWM (Pulse Width Modulation) conversion on the image data held in the buffer, and controls printing by the printer engine. A printer engine or the like that forms a toner image on a sheet based on the PWM-converted image data is provided. The printer engine includes toners of C, M, Y, and K colors, and can form a color image.

  The image processing apparatus G performs various image processes on the image data. Examples of the image processing include color conversion processing, encoding processing, decoding processing, image processing such as image enlargement, reduction, rotation, page allocation, and screen processing. Further, the image processing apparatus G can collect image data having different color spaces and create one image data.

[Image processing device]
FIG. 2 is a functional block diagram of the image processing apparatus G. Note that FIG. 2 shows only main components related to encoding and decoding of image data.
As illustrated in FIG. 2, the image processing apparatus G includes a color conversion unit 11, an encoding unit 12, a decoding unit 13, and an aggregation processing unit 14.

  The color conversion unit 11 includes an LUT in which CMYK output values are determined for RGB input values, and converts the color space of the input image data from RGB to CMYK using the LUT.

  The encoding unit 12 encodes and compresses the input image data by a BTC (Block Truncation Coding) method. The encoding unit 12 writes the code data obtained by encoding into the image memory 6.

  The decoding unit 13 decodes the input code data by the BTC method and decompresses the code data. The decoding unit 13 writes the image data obtained by the decoding into the buffer 4.

  The aggregation processing unit 14 aggregates image data with different color spaces and creates one image data.

[Input image data]
A flow until the MFP 10 obtains image data and stores it in the storage device 7 will be described. Image data includes image data whose color space is CMYK and image data whose color space is RGB.

CMYK image data is obtained by the scanner 2 or the print controller 20.
In the case of the scanner 2, the image signal read by the scanner 2 is A / D converted into RGB image data by the reading processing unit 3 and held in the buffer 4. The control unit 1 reads the image data from the buffer 4 and transfers it to the image processing apparatus G. The image processing apparatus G performs color conversion on RGB image data to generate CMYK image data. The image processing apparatus G encodes CMYK image data and writes the encoded data in the image memory 6. The storage control unit 7 a reads the code data from the image memory 6 and stores it in the storage device 7.
On the other hand, the CMYK image data created and transmitted by the print controller 20 is similarly held in the buffer 4 and transferred to the image processing apparatus G. The image processing apparatus G encodes CMYK image data and writes the encoded data in the image memory 6. The storage control unit 7 a reads the code data from the image memory 6 and stores it in the storage device 7.

RGB image data is obtained by rasterizing the PDL data transmitted from the PC 30.
When PDL data is transmitted from the PC 30, the control unit 1 writes the PDL data in the image memory 6. The control unit 1 analyzes the PDL data, creates intermediate language data, and writes it in the image memory 6. Based on the intermediate language data, the control unit 1 draws RGB image data of the bitmap and writes it in the buffer 4. The control unit 1 reads RGB image data from the buffer 4 and transfers it to the image processing apparatus G. The image processing apparatus G encodes RGB image data and writes the encoded data in the image memory 6. The storage control unit 7 a reads the code data from the image memory 6 and stores it in the storage device 7.

[Image data output]
The MFP 10 can print the code data stored in the storage device 7 by the printing unit 8 or transfer it to the PC 30.
When the print process is performed, the storage control unit 7 a reads the code data from the storage device 7 and writes it in the image memory 6. The control unit 1 reads the code data from the image memory 6 and transfers it to the image processing apparatus G. The image processing device G decodes the code data and writes the image data obtained by the decoding into the buffer 4. The control unit 1 reads the image data from the buffer 4 and stores it in the image memory 6. The control unit 1 reads out image data from the image memory 6 in units of pages and transfers it to the printing unit 8. The print unit 8 prints the transferred image data.

  When transferring to the PC 30, the storage control unit 7 a reads the code data from the storage device 7 and writes it in the image memory 6. The communication unit 5 reads the code data from the image memory 6 and transmits it to the PC 30. The code data is decoded by the PC 30, and the image data obtained by the decoding is used for display, editing, storage, and the like.

[Encoding and decoding of image data consisting of a single color space]
The image processing apparatus G can perform encoding or decoding by the same BTC method regardless of whether each pixel of image data is a single color space or a different color space.
Hereinafter, processing contents of the image processing apparatus G when encoding and decoding image data in which each pixel has a single color space will be described.

The encoding unit 12 inputs image data to be encoded in units of 4 × 4 pixels. The pixel value of each pixel is 8-bit data.
In the CMYK image data, each pixel has a pixel value of each color of C, M, Y, and K. If the pixel values of each pixel are classified by color, CMYK 4 × 4 pixel image data can be represented by pixel value planes 101 to 104 of C, M, Y, and K colors as shown in FIG. The pixel value plane is composed of planes for the number of bits of pixel value data. One plane is a data layer composed of 4 × 4 pixels, and one pixel represents 1-bit data. Since the pixel value is 8-bit data, the pixel value plane of each color is composed of eight planes.
The same applies to RGB image data. As shown in FIG. 4, RGB image data having a color space of RGB can be represented by pixel value planes 201 to 203 of three colors of R, G, and B.

  The encoding unit 12 pays attention to any one of the colors if the color space of the image data is CMYK, and pays attention to any one of the colors if the color space of the image data is RGB. The encoding unit 12 obtains the maximum value and the minimum value of the pixel values of 4 × 4 pixels in the pixel value plane of the target color among the pixel value planes of each color of 4 × 4 pixels. The maximum value and the minimum value represent the gradation of 4 × 4 pixels.

As shown in FIG. 5, each pixel of 4 × 4 pixels is set to ij depending on the position in the main scanning direction i (i is an integer of 0 to 3) and the sub scanning direction j (j is an integer of 0 to 3). When the pixel value of each pixel ij is expressed as Pij, the maximum value Max and the minimum value min are obtained by the following equations.
Max = MAX {P00, P10, P20, P30, P01, P11, P21, P31, P02, P12, P22, P32, P03, P13, P23, P33}
min = MIN {P00, P10, P20, P30, P01, P11, P21, P31, P02, P12, P22, P32, P03, P13, P23, P33}
In the above expression, MAX {} represents a function that outputs an element having the maximum value among elements in {}. MIN {} represents a function that outputs an element having the minimum value among the elements in {}.

The encoding unit 12 calculates a threshold value THn from the obtained maximum value Max and minimum value min. Here, an example is shown in which nine threshold values TH0 to TH8 are calculated in order to convert an 8-bit pixel value into a 3-bit code value. The calculation formula of the thresholds TH0 to TH8 is as follows.
TH8 = Max
TH7 = TH6 + (Max-min) / 8
TH6 = TH5 + (Max-min) / 8
TH5 = TH4 + (Max-min) / 8
TH4 = TH3 + (Max-min) / 8
TH3 = TH2 + (Max-min) / 8
TH2 = TH1 + (Max-min) / 8
TH1 = TH0 + (Max-min) / 8
TH0 = min

The encoding unit 12 determines which section of the gradation of the target color the pixel value Pij of the target color belongs to the threshold THn, and encodes the pixel value Pij according to the section to which the target color pixel value Pij belongs, and converts the pixel value Pij into a code value φij To do. The code value φij is obtained as follows from the magnitude relationship between the threshold value THn and the pixel value Pij.
When TH7 <Pij ≦ TH8, φij = 111
When TH6 <Pij ≦ TH7, φij = 110
When TH5 <Pij ≦ TH6, φij = 101
When TH4 <Pij ≦ TH5, φij = 100
When TH3 <Pij ≦ TH4, φij = 011
When TH2 <Pij ≦ TH3, φij = 010
When TH1 <Pij ≦ TH2, φij = 001
When TH0 ≦ Pij ≦ TH1, φij = 000

  The encoding unit 12 switches the target color and repeats the above encoding process, converts the pixel value Pij into the code value φij for the pixel value planes of all colors, and represents the code value φij of 4 × 4 pixels. Create a code value plane.

The encoding unit 12 creates a gradation plane that represents the gradation of each color in the pixel value plane. Here, an example of a gradation plane representing the maximum value Max and the minimum value min obtained for each color is given as the gradation plane representing the gradation. However, if the gradation can be represented, each pixel value plane Other values such as an average value or an intermediate value of pixel values may be adopted.
The gradation plane has the same structure as the pixel value plane and the like. One plane is composed of 4 × 4 pixels, and one pixel represents 1-bit data. Therefore, 16-bit data can be represented by one plane. The encoding unit 12 assigns 8-bit data of the maximum value Max one bit at a time to eight pixels having ij of 00 to 03 and 10 to 13, and ij has eight pixels of 20 to 23 and 30 to 33, A gradation plane is created by allocating 8-bit data of the minimum value min bit by bit.

The encoding unit 12 writes the generated code value plane and gradation plane in the image memory 6 as 4 × 4 pixel code data.
The encoding unit 12 newly inputs 4 × 4 pixel image data, and repeats the above-described encoding process to encode all the pixels of the image data.

FIG. 6 shows an example of code value planes 111 to 114 and gradation planes 121 to 124 for each color of CMYK.
As shown in FIG. 6, the code data consists of a total of 16 planes of 4 colors × 4 bits of CMYK. Among the planes, the 0th bit gradation planes 121 to 124 each represent 8-bit data of the maximum value Max and the minimum value min of each color. The 1st to 3rd bit code value planes 111 to 114 represent data of a 3 bit code value φij.
FIG. 6 shows an example of code data in the CMYK color space. In the case of the RGB color space, the code value plane is for three colors of RGB, and the code data is composed of a total of 12 planes of 3 colors × 4 bits.

When decoding the code data composed of such code value planes and gradation planes, the decoding unit 13 inputs the code data in units of 4 × 4 pixels. The decoding unit 13 pays attention to any color in each color space of CMYK or RGB, and obtains data of the maximum value Max and the minimum value min representing the gradation from the gradation plane of the attention color. Using the obtained maximum value Max and minimum value min, the decoding unit 13 decodes the code value φij of the code value plane of the target color to obtain 8-bit pixel value data.
When the pixel value obtained from the code value φij by decoding is represented by Dij, the formula for calculating the pixel value Dij is as follows.
Dij = ΔT × φij + ΔT / 2 + min
ΔT = (Max−min) / 8

The decoding unit 13 switches the target color and repeats the above decoding process, converts the code value φij to the pixel value Dij for the pixel value planes of all colors, and represents the pixel value Dij of 4 × 4 pixels. Create a pixel value plane. As shown in FIG. 3 or FIG. 4, the pixel value plane is composed of eight planes that hold the data of the pixel value Dij of 4 × 4 pixels bit by bit.
The decoding unit 13 newly inputs 4 × 4 pixel code data, and repeats the decoding process described above to decode all the pixels of the image data.

[Create image data with mixed pixels in different color spaces]
The image processing apparatus G can create one image data in which image data of RGB color space and image data of CMYK are mixed. For example, the image processing apparatus G may create image data in which RGB image data created by the PC 30 is arranged in a part of CMYK image data obtained by color conversion after reading by the scanner 2. it can. Hereinafter, the code data composed of the CMYK color space that has already been encoded and stored in the storage device 7 and the image data composed of the RGB color space created and input by the PC 30 are aggregated to obtain one image data. An example of creating is described.

The storage control unit 7 a reads out code data composed of a single color space of CMYK from the storage device 7 and writes it into the image memory 6. The control unit 1 reads this code data from the image memory 6 and transfers it to the image processing apparatus G. The image processing apparatus G decodes the transferred code data and writes the obtained image data in the buffer 4.
On the other hand, the control unit 1 converts the PDL data transmitted from the PC 30 via the communication unit 5 and held in the image memory 6 into intermediate language data and writes the intermediate language data in the image memory 6. The control unit 1 draws bitmap image data in the RGB color space based on the intermediate language data, and writes it in the buffer 4.
The image processing apparatus G aggregates CMYK image data and RGB image data held in the buffer 4 and creates one image data in which pixels having different color spaces are mixed.

FIG. 7 shows a flow of processing executed by the image processing apparatus G when creating one image data in which pixels having different color spaces are mixed.
As shown in FIG. 7, the aggregation processing unit 14 of the image processing apparatus G inputs the CMYK image data and the RGB image data held in the buffer 4 in units of 4 × 4 pixels (step S11). The pixel value of one pixel is 8-bit data.

  The aggregation processing unit 14 extracts pixels from each of the CMYK 4 × 4 pixels and the RGB 4 × 4 pixels according to the arrangement positions of the image data when the CMYK image data and the RGB image data are aggregated. . For example, out of 4 × 4 pixels, when the pixels having ij of 22, 32, 23, and 33 are in the arrangement positions of the RGB image data, the aggregation processing unit 14 uses the pixel value plane of 4 × 4 pixels of RGB, Pixels having ij of 22, 32, 23, and 33 are extracted. Further, the aggregation processing unit 14 extracts pixels having ij of 00 to 03, 10 to 13, 20, 21, 30, and 31 from the CMYK 4 × 4 pixel value plane.

  The aggregation processing unit 14 creates a pixel value plane for each color in which pixel values of colors in the color space to which each extracted pixel belongs are mixed in different color spaces (step S12). At this time, it is preferable that the aggregation processing unit 14 creates pixel value planes by the number of colors in the color space having the larger number of colors among the different color spaces. Thereby, pixel values of colors in different color spaces can be mixed efficiently. In the case of CMYK and RGB color spaces, the aggregation processing unit 14 creates four pixel value planes 301 to 304 as shown in FIG. 8 according to the four colors of CMYK having a large number of colors. Of the four pixel value planes 301 to 304, Y and B share M and G, C and R share the same pixel value plane, and K occupies the other one.

  FIG. 8 shows pixel values of 4 × 4 pixels in which the lower right 2 × 2 pixels (pixels having ij of 22, 32, 23, and 33) belong to the RGB color space and the other pixels belong to the CMYK color space. An example of a plane is shown. As shown in FIG. 8, in the Y / G pixel value plane 302 shared by Y and B, the lower right 2 × 2 pixels represent B pixel values, and the others represent Y pixel values. Similarly, in the M / G pixel value plane 303 shared by M and G, the lower right 2 × 2 pixels represent G pixel values, and the others represent M pixel values. In the C / R pixel value plane 304 shared by C and R, the lower right 2 × 2 pixel represents the R pixel value, and the others represent the C pixel value. Since the K pixel value plane 301 has no color in the RGB color space to be mixed, the lower right 2 × 2 pixels are vacant areas, and the others represent the K pixel values.

  The aggregation processing unit 14 creates an identification plane indicating which color space each pixel of the pixel value plane belongs to, CMYK or RGB (step S13). For example, as illustrated in FIG. 8, the aggregation processing unit 14 creates an identification plane 400 that holds 0 data for pixels belonging to the CMYK color space and 1 data for pixels belonging to the RGB color space in the pixel value plane. To do. The binary data of 0 and 1 can identify whether the color space of each pixel is CMYK or RGB.

  The aggregation processing unit 14 can create the identification plane separately from the pixel value planes 301 to 304 of K, Y / B, M / G, and C / R as shown in FIG. As shown in FIG. 8, the least significant bit plane of the 8-bit K pixel value plane 301 can be replaced with the identification plane 400. By the replacement, the data amount of the image data can be reduced by 16 bits of the identification plane 400. The pixel value of the K color lacks the data of the least significant bit, but since it is the least significant bit of the 8 bits, it hardly affects the reproducibility of the pixel value. As long as the plane is replaced with the least significant bit plane, the color is not limited to K, and any color may be used.

When the above process has not been completed for all pixels (step S14; N), the process returns to step S11. The aggregation processing unit 14 newly inputs 4 × 4 pixel CMYK and RGB pixel value planes, and repeats the processes of steps S11 to S13.
When the above process is completed for all pixels (step S14; Y), this process ends, and as shown in FIG. 10, a part of the CMYK image data is replaced with RGB image data, and the CMYK and RGB are different. Image data in which pixels in the color space are mixed is obtained. The obtained image data is output from the aggregation processing unit 14 to the encoding unit 12.

〔Coding〕
The image processing apparatus G can encode and decode image data in which pixels belonging to different color spaces are mixed by the BTC method in the same manner as image data consisting of only a single color space.
FIG. 11 shows a flow of processing executed by the image processing apparatus G when encoding image data in which pixels belonging to different color spaces are mixed.

As shown in FIG. 11, the encoding unit 12 of the image processing apparatus G inputs image data to be encoded in units of 4 × 4 pixels (step S21). As shown in FIG. 8, the image data includes an identification plane 400 and pixel value planes 301 to 304 for each color. The encoding unit 12 pays attention to one of CMYK and RGB colors, and identifies a pixel of the target color from 4 × 4 pixels of the pixel value plane of the target color by the color space represented by the identification plane. The encoding unit 12 obtains the gradation of the pixel of the specified target color, that is, the maximum value Max and the minimum value min (step S22).
For example, when the target color is B, the encoding unit 12 specifies that the B pixel in the Y / B pixel value plane is the lower right 2 × 2 pixels by the identification plane. The encoding unit 12 obtains the maximum value Max and the minimum value min of the specified 2 × 2 pixel values.

The encoding unit 12 calculates a threshold value THn from the obtained maximum value Max and minimum value min of the target color (step S23).
The encoding unit 12 determines, based on the threshold value THn, to which division of the gradation composed of the maximum value Max and the minimum value min of the target color the pixel value Pij of the target color belongs. The encoding unit 12 encodes the pixel value Pij according to the section to which it belongs, and creates a code value plane representing the code value φij (step S24).
Further, the encoding unit 12 creates a gradation plane representing the gradation of the target color in the pixel value plane of the target color (step S25).

After that, if encoding has not been completed for all colors (step S26; N), the encoding unit 12 switches the target color to an unprocessed color (step S27), and steps S22 to S25 for the switched target color. Repeat the process.
When encoding is completed for all colors (step S26; Y), the encoding unit 12 uses, as code data, an identification plane that is input together with a 4 × 4 pixel code value plane, a gradation plane, and a pixel value plane. Writing to the image memory 6 (step S28).

FIG. 12 shows an example of 4 × 4 pixel code data.
As shown in FIG. 12, the code data consists of 20 planes hierarchized from the 0th bit to the 3rd bit. 1st to 3rd bits, a K code value plane 311, a Y / B code value plane 312 in which Y and B code values are mixed, an M / G code value plane 313 in which M and G code values are mixed, C The C / R code value plane 314 in which the code values of R and R are mixed is located. In addition, gradation planes 321 to 324 for each color of CMYK are located at the 0th bit of the code value planes 311 to 314 for each color. The identification plane 400 is located at the third bit, and the gradation planes 331 to 333 of each color of RGB are located below it.

After that, when encoding has not been completed for all the pixels of the image data (step S29; N), the process returns to step S21, and the encoding unit 12 inputs the next 4 × 4 pixels and performs the processing of steps S22 to S28. repeat. When encoding of all the pixels is completed (step S29; Y), this process ends.
Code data written to the image memory 6 for all pixels is stored in the storage device 7 by the storage control unit 7a.

〔Decryption〕
FIG. 13 shows a flow of processing executed by the image processing apparatus G when decoding code data of image data having different color spaces.
As illustrated in FIG. 13, the decoding unit 13 of the image processing apparatus G inputs code data in units of 4 × 4 pixels (step S31). The decoding unit 13 pays attention to any color in the color space of CMYK or RGB, and acquires the gradation plane of the target color from the code data. The decoding unit 13 obtains data of the maximum value Max and the minimum value min representing the gradation of the target color from the acquired gradation plane (step S32).

  The decoding unit 13 specifies the code value φij of the target color in the code value plane of the target color based on the color space represented by the identification plane. The encoding unit 12 decodes the identified code value φij of the target color using the maximum value Max and the minimum value min of the target color to obtain a pixel value Dij. The decoding unit 13 creates a pixel value plane representing the obtained pixel value Dij (step S33). Similarly to the pixel value plane shown in FIG. 9, the pixel value plane of each color is composed of eight planes that hold the data of the pixel value Dij of 4 × 4 pixels one bit at a time.

Thereafter, if the decoding has not been completed for all colors (step S34; N), the decoding unit 13 switches the target color to an unprocessed color (step S35), and steps S32 to S33 for the switched target color. Repeat the process.
When decoding has been completed for all colors used in 4 × 4 pixels (step S34; Y), the decoding unit 13 uses the pixel value plane and identification plane made up of the pixel values Dij as image data in the buffer 4 (Step S36).

  When decoding has been completed for all the colors of 4 × 4 pixels, but decoding has not been completed for all the pixels of the encoded data (step S37; N), the process returns to step S31, and the decoding unit 13 X4 pixels are input, and the processing of steps S31 to S36 is repeated. When the decoding of all the pixels is completed (step S37; Y), this process ends.

  The image data written in the buffer 4 by decoding is subjected to color conversion processing only for pixels having RGB pixel values by the color conversion unit 11 and output to the printing unit 8.

  As described above, the image processing apparatus G includes an encoding unit 12 that encodes image data using the BTC method, and a decoding unit 13 that decodes image data encoded using the encoding unit 12 using the BTC method. In addition, pixels are extracted from each of the image data with different color spaces according to the arrangement position when the image data with different color spaces are aggregated, and the pixel values of the colors of the color spaces to which the extracted pixels belong are different. An aggregation processing unit for creating a pixel value plane for each color mixed in the color spaces and creating an identification plane representing the color space to which each pixel belongs in the pixel value plane. The encoding unit 12 creates a gradation plane that represents the gradation of each color in the pixel value plane, and determines the pixel value according to which division of the gradation of each color the pixel value of each color in the pixel value plane belongs to. Encoding is performed to generate a code value plane representing the code value, and a gradation plane, a code value plane, and an identification plane are output as code data. The decoding unit 13 identifies the color of each code value of the code value plane using the color space represented by the identification plane, and decodes the code value of each identified color using the gradation of each color represented by the gradation plane. To do.

Thus, encoding and decoding can be performed in the same manner regardless of the color space to which each pixel of the image data belongs. There is no need to provide a different encoding or decoding processing circuit for each color space, and an increase in hardware scale can be avoided.
Since the encoding and decoding are based on the BTC method, the relationship between the pixel position and the pixel value in different color spaces can be maintained even after the encoding and decoding, and the reproducibility of the image data is excellent.
Also, by collecting image data with different color spaces and encoding them as one image data, it is possible to reduce the amount of code data compared to the case of individually encoding image data with different color spaces, Effective use of memory resources. The allocation of the code data storage area is also less wasteful, and the address management of the individually encoded code data is unnecessary, so that the code data can be easily stored and read.

The above embodiment is a preferred example of the present invention, and the present invention is not limited to this. Modifications can be made as appropriate without departing from the spirit of the present invention.
For example, the image processing apparatus G may be mounted on the PC 30 and the code data transmitted from the MFP 10 may be decoded by the image processing apparatus G of the PC 30.

Further, although an example in which image data of RGB color space and CMYK image data are mixed as one image data has been shown, according to the image processing apparatus G, other color spaces such as L ^* a ^* b ^* , sRGB, etc. Similarly, it can be mixed in one image data and can be encoded and decoded by one method.

10 MFP
DESCRIPTION OF SYMBOLS 1 Control part 2 Scanner 3 Reading process part 4 Buffer 5 Communication part 6 Image memory 7 Storage device 7a Storage control part 8 Print part 20 Print controller 30 PC
G Image processing apparatus 11 Color conversion unit 12 Encoding unit 13 Decoding unit 14 Aggregation processing unit

Claims (7)

An encoding unit that encodes image data by the BTC method;
A decoding unit that decodes the image data encoded by the encoding unit by a BTC method;
According to the arrangement position when the image data with different color spaces are aggregated, pixels are extracted from each of the image data with different color spaces, and the pixel values of the colors of the color spaces to which the extracted pixels belong are different color spaces An aggregation processing unit that creates a pixel value plane for each color mixed together and creates an identification plane that represents a color space to which each pixel belongs in the pixel value plane;
The encoding unit includes:
Create a gradation plane representing the gradation of each color in the pixel value plane,
The pixel value of each color in the pixel value plane is encoded according to which section of the gradation of each color belongs to create the code value plane representing the code value,
The gradation plane, the code value plane, and the identification plane are output as code data,
The decoding unit
An image processing device that identifies the code value of each color of the code value plane by the color space represented by the identification plane and decodes the code value of each identified color using the gradation of each color represented by the gradation plane .   The image processing apparatus according to claim 1, wherein the aggregation processing unit creates pixel value planes by the number of colors in a color space having a larger number of colors among different color spaces. The pixel value plane is composed of planes corresponding to the number of bits of pixel value data, and one plane represents 1-bit data.
The image processing apparatus according to claim 1, wherein the aggregation processing unit replaces the identification plane with a least significant bit plane of a pixel value plane of any color. An encoding unit that encodes image data by the BTC method;
Pixels are extracted from each of the image data with different color spaces according to the arrangement position when the image data with different color spaces are aggregated, and the pixel values of the colors of the color space to which each pixel belongs are mixed in different color spaces An aggregation processing unit that creates a pixel value plane for each color and creates an identification plane representing a color space to which each pixel belongs in the pixel value plane,
The encoding unit includes:
Create a gradation plane representing the gradation of each color in the pixel value plane,
The pixel value of each color in the pixel value plane is encoded according to which section of the gradation of each color belongs to create the code value plane representing the code value,
An image processing apparatus that outputs the gradation plane, the code value plane, and the identification plane as code data. A gradation plane that represents the gradation of each color in a pixel value plane in which pixel values of colors in different color spaces are mixed, and encoding according to which division of the gradation of each color the pixel value of each color in the pixel value plane belongs to A decoding unit that decodes code data composed of a code value plane representing a code value of the pixel value obtained and an identification plane representing a color space to which each pixel belongs;
The decoding unit identifies a code value of each color of the code value plane by using a color space represented by the identification plane, and uses the gradation of each color represented by the gradation plane by using the code value of each identified color. An image processing apparatus for decoding. Pixels are extracted from each of the image data with different color spaces according to the arrangement position when the image data with different color spaces are aggregated, and the pixel values of the colors of the color space to which each pixel belongs are mixed in different color spaces Creating a pixel value plane for each color,
Creating an identification plane representing a color space to which each pixel belongs in the pixel value plane;
Creating a gradation plane representing the gradation of each color in the pixel value plane;
Encoding the pixel value according to which section of the gradation of each color the pixel value of each color in the pixel value plane, and creating a code value plane representing the code value;
Outputting the gradation plane, the code value plane, and the identification plane as code data;
An encoding method including: A gradation plane that represents the gradation of each color in a pixel value plane in which pixel values of colors in different color spaces are mixed, and a code depending on which division of the gradation of each color the pixel value of each color in the pixel value plane belongs to A code value plane consisting of a code value plane representing a coded code value and an identification plane representing a color space to which each pixel belongs; and
Identifying the code value of each color of the code value plane by the color space represented by the identification plane, and decoding the code value of each identified color using the gradation of each color represented by the gradation plane;
A decoding method including:

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