JP2005117220A - Image processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus for relieving a load on image processing in an RGB color space whose components include more bits than 8-bits in components of another RGB color space. <P>SOLUTION: An image processing section 102 in an input color space processes input image data and thereafter a color gamut discrimination section 103 discriminates whether the image data are included in the 8-bit RGB color space, when the image data are included in the 8-bit RGB color space, an 8-bit RGB conversion section 104 converts the color space of the image data into the 8-bit RGB color space and an image processing section 105 in the 8-bit RGB color space processes the converted image data. When the image data are not included in the 8-bit RGB color space, an image processing section 16 in a 16-bit RGB color space processes the image data, and finally an image processing section 107 in an output color space processes the image data to obtain output data in both the cases. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to data processing of image data.

  Currently, an RGB color space that expresses each color of R, G, and B by 8 bits is widely used in many image processing apparatuses. In particular, the standardized sRGB color space is representative, but in addition to this, an 8-bit color space that represents device-specific RGB values is also generally used. For convenience of explanation, an RGB color space in which each color of R, G, and B is expressed by 8 bits is referred to as an “8-bit RGB color space”.

  While the sRGB color space is widely used, there is also a request to handle colors outside the range that can be expressed by sRGB and a request to obtain gradation (bit) accuracy of 8 bits or more. In order to satisfy these requirements, the sRGB color space is used. Several new color spaces such as the scRGB color space have been proposed as an extended color space in which the color gamut is expanded and the bit accuracy is increased. FIG. 2 is a conceptual diagram showing an extended color space such as the scRGB color space. In the figure, an extended color space 201 (for example, scRGB) having an expanded color gamut including an 8-bit RGB color space 202 (for example, sRGB) is shown. ) Is defined. In the case of the scRGB color space, each color of R, G, and B is expressed by 16 bits, and the increase in the number of bits relative to sRGB is used for both the expansion of the color gamut and the improvement of the gradation (bit) accuracy. . In the following, for convenience of explanation, the RGB color space that expresses each of the R, G, and B colors with 16 bits is referred to as a “16-bit RGB color space”.

  Here, a printer with a direct printing function is taken as an example of the image processing apparatus, and its configuration will be described with reference to FIG. The printer 303 is connected to an image input device 301 such as a digital camera via a wired or wireless communication path and a printer communication unit 304. An input image to be printed by the printer is transmitted from the image input device 301 to the printer communication. Sent to the unit 304. Alternatively, the recording medium reading unit 305 reads an input image recorded on the recording medium 302 by connecting a recording medium 302 such as a nonvolatile memory in which an image is recorded to the recording medium reading unit 305 of the printer. The input image input to the printer 303 by either method is converted into data suitable for printing by the printer engine 307 by the printer image processing unit 306, and the processed print data is sent to the printer engine 307. It is done. The printer engine 307 actually prints on the paper 308 according to the input print data, and a final printer output is obtained. Next, the inside of the printer image processing unit 306 will be described.

  FIG. 4 is a diagram showing an outline of a printer image processing unit that is generally used at present. An input image is an image processing unit 402 in the color space (input color space) of the input image first. Is then converted to an 8-bit RGB color space (for example, sRGB) and then transferred to the image processing unit 403 in the 8-bit RGB color space. The image processed in the 8-bit RGB color space is converted into an output color space (CMYK or the like in the case of a printer), and then transferred to the image processing unit 404 in the next output color space to be sent to the printer engine. It is converted into data to be sent. The specific contents of each processing unit may vary depending on factors such as the type of input image and the print mode. As a representative example, when the input image is JPEG and the input color space is YCbCr, the input color space The image processing unit 402 performs processing such as JPEG compression, color correction in the YCbCr color space, image size scaling, and conversion to an 8-bit RGB color space. Next, the image processing unit 403 in the 8-bit RGB color space performs processing such as color correction / color conversion in the RGB space, scaling of the image size, conversion to the output color space, etc. Finally, the output color In the image processing unit 404 in space, processing such as gradation correction and halftone processing is performed.

  FIG. 5 is a diagram showing an overview of the printer image processing unit when the input image corresponds to the extended color space. Instead of the image processing 403 in the 8-bit RGB color space of FIG. 4, a 16-bit RGB color is shown. Image processing 503 in space is performed.

FIG. 6 is a diagram showing an outline when a conventional color conversion method is used. The 16-bit RGB color space data output from the image processing unit 602 in the input color space is a partial color space mapping unit. By 603, mapping is performed in a partial color space narrower than the 16-bit RGB color space (wider than the 8-bit RGB color space). The data mapped in the partial color space is then converted into the output color space by table reference and interpolation operation in the partial color space / output color space conversion unit 604, and then the image processing unit in the output color space. 605.
JP 2002-223367 A

  As shown in FIG. 5, when image processing in the 16-bit RGB color space is performed on an image in the extended color space, the processing load is greatly increased as compared with the processing in the current general 8-bit RGB color space. Resulting in. Due to the expansion of bit accuracy and color gamut, the data size increases and the calculation accuracy must be increased. In the case of processing using table reference, the size of the table to be held increases due to the expansion of the color gamut, and the processing load increases in terms of both processing resources and processing speed.

  On the other hand, in the case of the method of FIG. 6, by performing mapping to a partial color space smaller than the 16-bit RGB color space, it is possible to limit the color gamut and reduce the processing load compared to the case of FIG. Become. However, the partial color space is larger than the 8-bit RGB color space, and there is also an overhead of mapping to the partial color space and an overhead of the partial color space / output color space conversion unit. Become heavier.

  Therefore, according to the present invention, most of input data actually input from an image input device such as a digital camera falls within the range of the 8-bit RGB color space, and the frequency of occurrence of data outside the 8-bit RGB color space is low. By utilizing this tendency, although there is an overhead for processing in the 8-bit RGB color space of FIG. 4, an image processing apparatus with a lighter processing load than the method of FIG. 5 or FIG. 6 is realized. .

  In order to solve the above problems, the image processing apparatus of the present invention has the following configuration.

  An image processing apparatus that processes image data in a color space in which each color element is represented by a number of bits larger than 8 bits, and the input image data is included in a color space range in which each color element is represented by 8 bits. A color gamut determining unit that determines whether or not the image data is included in the range of a color space in which each color element is represented by 8 bits. Color space conversion means for converting into data of a color space represented by bits, and each color element for the image data converted into a color space represented by 8 bits by the 8-bit color space conversion means. An image processing means for performing image processing for a color space represented by 8 bits, and when the color gamut judging means determines that each color element is out of the range of the color space represented by 8 bits The image data Each color element is characterized by having an image processing means for performing image processing for a color space represented by the larger number of bits than 8 bits.

  Alternatively, an image processing method for processing image data in a color space in which each color element is represented by a number of bits greater than 8 bits, wherein the input image data is within a color space range in which each color element is represented by 8 bits. A color gamut determining step for determining whether or not the image data is included; and, when the color gamut determining means determines that the image data is included in a color space range represented by 8 bits, A color space converting step for converting the data into data of a color space represented by 8 bits, and each color of the image data converted into a color space represented by 8 bits by the 8-bit color space conversion means An image processing step for performing image processing for a color space in which elements are represented by 8 bits, and the color gamut determining means determine that the image data is outside the color space range in which each color element is represented by 8 bits. In case It characterized by having an image processing step of performing image processing for color space of each color component is represented by a large number of bits than 8 bits image data.

  According to the present invention, it is possible to realize an image processing apparatus capable of executing image processing in a 16-bit RGB color space with a small increase in processing load as compared with the case of performing image processing in an 8-bit RGB color space.

  An embodiment of an image processing apparatus according to the present invention will be described with reference to FIGS.

  FIG. 1 is a diagram illustrating a configuration of a printer image processing unit 101 of a printer having a direct printing function as an example of the image processing apparatus of the present invention. In the figure, input image data is first input to the image processing unit 102 in the input color space, and after being subjected to image processing performed in the input color space, it is converted into a 16-bit RGB color space (for example, scRGB). Is output. When the input color space is a 16-bit RGB color space, there may be a case where the image processing unit in the input color space does not need to perform any particular processing. The image data converted to the 16-bit RGB color space is then input to the color gamut determination unit 103, where it is determined whether or not the image data is in the range of an 8-bit RGB color space (for example, sRGB). . If the image data is included in the 8-bit RGB color space according to the determination result, the image data is input to the 8-bit RGB conversion unit 104. If not, the image data is an image processing unit in the 16-bit RGB color space. 106 is input. When the image data is input to the 8-bit RGB conversion unit 104, the image data in the 16-bit RGB color space is converted into image data in the 8-bit RGB color space by simple conversion, and then in the 8-bit RGB color space. Input to the image processing unit 105. The image processing unit 105 in the 8-bit RGB color space is efficient because it can make use of the currently general implementation of image processing for the 8-bit RGB color space (cooperation of hardware, software, or hardware / software). High-speed image processing can be realized.

  On the other hand, when image data is input to the image processing unit 106 in the 16-bit RGB color space, the load is heavy compared to the image processing in the 8-bit RGB color space. However, since image data input from a general image input device such as a digital camera is not frequently included in the 8-bit RGB color space, the image processing unit 106 in the 16-bit RGB color space has a low frequency. Even if the processing is heavy and slow, a large amount of image data is processed by the image processing unit 105 in the 8-bit RGB color space, so that the overall processing load is compared to the processing in the 8-bit RGB color space. , There will be a small overhead. Compared to the case of FIG. 6, in FIG. 6, all input image data must pass through a partial color space / output color space conversion unit that is heavier than the processing of the 8-bit RGB color space. Since the conventional image processing in the 8-bit RGB color space can be applied, the relative processing load is reduced. Note that the image data input to the image processing unit 106 in the 16-bit RGB color space is known in advance to be out of the range of the 8-bit RGB color space. It is also possible to reduce the load of image processing in the 16-bit RGB color space, such as excluding table data corresponding to the space or simplifying the processing.

  Finally, in both cases of the image processing unit 105 in the 8-bit RGB color space and the image processing unit 106 in the 16-bit RGB color space, the output is image data in the output color space (for example, CMYK in the case of a printer). The image data is converted and processed by the image processing unit 107 in the output color space, and becomes final output data.

  Note that these processing units may be implemented in various ways such as dedicated hardware, software, or a combination of hardware and software.

  Next, the processing of the color gamut determination unit 103 will be described with reference to FIG. In FIG. 7, R, G, and B indicate the values of R, G, and B components of the input 16-bit RGB color space image data. Rw, Gw, and Bw are values of R, G, and B components in the 16-bit RGB color space corresponding to white in the 8-bit RGB color space. Rk, Gk, and Bk are values in the 8-bit RGB color space. R, G, and B component values in the 16-bit RGB color space corresponding to black. First, in step 701, the input data is compared with the values of R and Rw and Rk. If the value of R is in the range between Rw and Rk, the process proceeds to the next step 702. If not, it is determined that the image is not included in the 8-bit RGB color space, so the determination process is terminated and the process proceeds to image processing in the 16-bit RGB color space. When the process proceeds to step 702, the value of G is compared with the values of Gw and Gk. When the value of G is in the range between Gw and Gk, the process proceeds to the next step 703. If not, it is determined that the image is not included in the 8-bit RGB color space, so the determination process is terminated and the process proceeds to image processing in the 16-bit RGB color space. When the process proceeds to step 703, the value of B is compared with the values of Bw and Bk. If the value of B is in the range between Bw and Bk, the image data may be included in the 8-bit RGB color space. Prove. If not, it is determined that it is not included in the 8-bit RGB color space, and the process proceeds to image processing in the 16-bit RGB color space. Note that the order of steps 701, 702, and 703 is not important, and can be performed in different orders or simultaneously depending on the implementation.

  Further, the processing of the 8-bit RGB conversion unit 104 will be described with reference to FIG. In FIG. 8, since the input 16-bit RGB color space image data is image data that has been previously determined to be included in the 8-bit RGB color space by the color gamut determination unit 103, the values of R, G, and B Is known to be within a certain range. Therefore, the color gamut restriction unit 802 extracts values within the range. Next, in order to match the bit precision expanded for the 16-bit RGB color space to the 8-bit RGB color space, the bit precision conversion unit 803 reduces the bit precision by a technique such as bit cutting (rounding down) or rounding. . Here, if the bit accuracy is completely aligned with the 8-bit RGB color space, the calculation accuracy of the next nonlinear characteristic conversion unit 804 will drop, so once between the 16-bit RGB color space and the 8-bit RGB color space. It is also possible to process with reduced bit precision. Finally, the nonlinear characteristic conversion unit 804 converts the difference between the nonlinear characteristics of the 16-bit RGB color space and the 8-bit RGB color space, and finally outputs image data in the 8-bit RGB color space.

  As an example, the conversion algorithm when the 16-bit RGB color space is sRGB64 and the 8-bit RGB color space is sRGB is shown in Embodiment / Modification 7 of Japanese Patent Application Laid-Open No. 2001-292331, and FIG. Such an algorithm can be implemented by configuration.

  In the above, printer image processing has been taken up for the sake of specific description. However, the content of the image processing is not limited to printer image processing.

1 is a configuration diagram of a printer image processing unit to which the present invention is applied. FIG. The figure explaining 8-bit RGB color space and extended RGB color space. 1 is a configuration diagram of a printer that supports direct printing. A conventional printer image processing unit that performs image processing in an 8-bit RGB color space. A printer image processing unit that performs image processing in a 16-bit RGB color space. A printer image processing unit that uses a partial color space. The figure which shows the processing flow of a color gamut determination process. An example of the configuration of an 8-bit RGB converter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Printer image processing part 102 Image processing part in input color space 103 Color gamut determination part 104 8-bit RGB conversion part 105 Image processing part in 8-bit RGB color space 106 Image processing part in 16-bit RGB color space 107 Output color Image processing unit in space 201 Extended RGB color space range 202 8-bit RGB color space range 301 Image input device 302 Recording medium 303 Printer 304 Communication unit 305 Recording medium reading unit 306 Printer image processing unit 307 Printer engine 308 Paper 401 Printer Image Processing Unit 402 Image Processing Unit in Input Color Space 403 Image Processing Unit in 8-Bit RGB Color Space 404 Image Processing Unit in Output Color Space 501 Printer Image Processing Unit 502 Image Processing Unit in Input Color Space 503 16 Image processing unit in bit RGB color space 504 Image processing unit in force color space 601 Printer image processing unit 602 Image processing unit in input color space 603 Partial color space mapping unit 604 Partial color space / output color space conversion unit 605 Image processing unit in output color space 701 R Determination processing 702 Determination processing related to G 703 Determination processing related to B 801 8-bit RGB conversion unit 802 Color gamut restriction unit 803 Bit precision conversion unit 804 Non-linear characteristic conversion unit

Claims (8)

  An image processing apparatus that processes image data in a color space in which each color element is represented by a number of bits larger than 8 bits, and the input image data is included in a color space range in which each color element is represented by 8 bits. A color gamut determining unit that determines whether or not the image data is included in the range of a color space in which each color element is represented by 8 bits. Color space conversion means for converting into data of a color space represented by bits, and each color element for the image data converted into a color space represented by 8 bits by the 8-bit color space conversion means. An image processing means for performing image processing for a color space represented by 8 bits, and when the color gamut judging means determines that each color element is out of the range of the color space represented by 8 bits The image data Having an image processing means for performing image processing for color space of each color component is represented by a large number of bits than the 8-bit image processing apparatus according to claim.   2. The image processing apparatus according to claim 1, wherein the number of bits of each color element is 16 bits in a color space in which each color element is expressed by a number of bits larger than 8 bits.   2. The image processing apparatus according to claim 1, wherein the color space in which each color element is represented by a bit number larger than 8 bits is an scRGB color space.   4. The image processing apparatus according to claim 3, wherein the color space in which each color element is represented by 8 bits is an sRGB color space.   An image processing method for processing image data in a color space in which each color element is represented by a number of bits larger than 8 bits, and the input image data is included in a color space range in which each color element is represented by 8 bits. A color gamut determining step for determining whether or not the image data is included in the range of a color space in which each color element is represented by 8 bits by the color gamut determining means. A color space conversion step for converting the data into a color space represented by bits, and each color element for the image data converted into a color space represented by 8 bits by the 8-bit color space conversion means. An image processing step for performing image processing for a color space represented by 8 bits, and when the color gamut determining means determines that the image data is outside the color space range represented by 8 bits. The image data Image processing method characterized by having an image processing step of performing image processing for color space of each color component is represented by a large number of bits than 8 bits.   6. The image processing method according to claim 5, wherein the number of bits of each color element is 16 bits in a color space in which each color element is represented by a number of bits larger than 8 bits.   6. The image processing method according to claim 5, wherein the color space in which each color element is represented by a bit number larger than 8 bits is an scRGB color space. 8. The image processing method according to claim 7, wherein the color space in which each color element is represented by 8 bits is an sRGB color space.

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