JP2006081209A - Image processing apparatus and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that a data size of a conversion table for color conversion becomes larger when using inks of seven colors adding three colors of cmy of low density to four colors of CMYK in a color ink jet printer. <P>SOLUTION: A compressed data buffer 100 stores compressed conversion table data compressing lattice point data of a conversion table arrayed for each of color components constituting image data. A data restoration unit 101 extends the compressed conversion table data, and a color conversion process unit 103 applies a color conversion process to input image data by an interpolation operation process based on the extended conversion table data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus and method, and a recording medium, and more particularly to an image processing apparatus and method for performing conversion processing on image data by interpolation processing based on a conversion table, and a recording medium.

  When image output is performed using a color printer or the like, color conversion is necessary. For example, when RGB image data representing an image displayed on a computer monitor is printed by a color ink jet printer, it is necessary to perform color conversion to a CMYK signal representing the ink color of the color ink jet printer. One of the color conversion methods is a matrix operation that has been used for a long time.

  However, as is well known, color conversion using matrix calculation has drawbacks such as insufficient color reproducibility. For example, when matching the hue of an image displayed on a monitor and a printed image, it is required to simulate the color conversion characteristics with high accuracy. The demand cannot be satisfied.

  Therefore, there is a lookup table interpolation method in which a conversion table for color conversion is prepared in advance, and converted image data is obtained by interpolation calculation based on the conversion table. For example, “Display and Imaging” SCI, Volume 2, Number 1 (1993), pages 17 to 25. According to this, a method of performing cubic interpolation by referring to the data of the neighboring eight points, a method of performing the prism interpolation by referring to the data of the six nearby points, and a four-surface by referring to the data of the four neighboring points A method for performing body interpolation is described.

  When interpolation processing using such a lookup table (LUT) is performed, there is a disadvantage that the data size of the LUT becomes large. For example, when the output image data is CMYK four-color interpolation processing, if the conversion table is divided into 16 parts and the color component of each grid point is 8 bits of data, 4 × 17 × 17 × 17 = 19652 bytes of data is obtained. I need.

  Further, in a color ink jet printer that realizes further high definition image quality, seven colors of ink are used, in which the conventional CMYK four colors are added with lighter CMY three colors. For this reason, the data size of the LUT for color conversion increases more and more.

  The present invention is intended to solve the above-described problems, and provides an image processing apparatus and method, and a recording medium that can reduce the storage capacity of a conversion table used for image data conversion processing. For the purpose.

  The present invention has the following configuration as one means for achieving the above object.

An image processing apparatus according to the present invention is an image processing apparatus that converts input color data into a plurality of color component data including cyan, magenta, yellow, and black by color conversion processing using interpolation calculation processing using a conversion table. And
Storage means for storing the compression conversion table data obtained by compressing the conversion table in the first arrangement order in which the color component data of each color component is collected for each identical color component and arranged in the order of the grid point number;
Decompression means for decompressing the compression conversion table data;
For the expanded conversion table in the first arrangement order, a plurality of color component data related to the same grid point number are collected as grid point data, and the grid point data is rearranged in the order of the grid point number to form a second sequence. Reordering means for converting the conversion table in order;
Conversion means for performing color conversion processing by interpolation processing using the conversion table of the second arrangement order to generate the output image data,
The grid point number is a plurality of color component data of the input color data from a grid point in which the plurality of color component data of the input color data are all 0 for each of a plurality of grid points constituting the conversion table. Up to the grid point where
The input color data corresponding to the grid points of the conversion table are sequentially added according to the size of each of the plurality of color component data.

  Further, the plurality of color component data includes, for example, light cyan, light magenta, and light yellow in addition to cyan, magenta, yellow, and black.

Furthermore, the image processing apparatus according to the present invention has means for reading out the compression conversion table data corresponding to the conditions in printing from the storage means,
The decompressing means decompresses the read compression conversion table data.

An image processing method for converting input color data into a plurality of color component data including cyan, magenta, yellow, and black by color conversion processing using interpolation calculation processing using a conversion table,
Storing the compression conversion table data obtained by compressing the conversion table of the first arrangement order in which the color component data of each color component is collected for each identical color component and arranged in the order of the grid point number;
Decompressing the compression conversion table data;
For the expanded conversion table in the first arrangement order, a plurality of color component data related to the same grid point number are collected as grid point data, and the grid point data is rearranged in the order of the grid point number to form a second sequence. A step of converting to a sequential conversion table;
Performing color conversion processing by interpolation processing using the conversion table of the second arrangement order and generating the output image data,
The grid point number is a plurality of color component data of the input color data from a grid point in which the plurality of color component data of the input color data are all 0 for each of a plurality of grid points constituting the conversion table. Up to the grid point where
The input color data corresponding to the grid points of the conversion table are sequentially added according to the size of each of the plurality of color component data.

The recording medium according to the present invention has an image processing program code for converting input color data into a plurality of color component data including cyan, magenta, yellow, and black by color conversion processing using interpolation calculation processing using a conversion table. A recorded recording medium,
The code of the step of storing the compression conversion table data obtained by compressing the conversion table in the first arrangement order in which the color component data of each color component is collected for each identical color component and arranged in the order of the grid point number;
A code for decompressing the compression conversion table data;
For the expanded conversion table in the first arrangement order, a plurality of color component data related to the same grid point number are collected as grid point data, and the grid point data is rearranged in the order of the grid point number to form a second sequence. The code of the step to be the order conversion table,
A code of a step of performing color conversion processing by interpolation processing using the conversion table of the second arrangement order to generate the output image data;
The grid point number is a plurality of color component data of the input color data from a grid point in which the plurality of color component data of the input color data are all 0 for each of a plurality of grid points constituting the conversion table. Up to the grid point where
The input color data corresponding to the grid points of the conversion table are sequentially added according to the size of each of the plurality of color component data.

  As described above, according to the present invention, it is possible to provide an image processing apparatus and method, and a recording medium that can reduce the storage capacity of a conversion table used for image data conversion processing.

Hereinafter, an image processing apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.
[First Embodiment]
FIG. 1 is a schematic diagram showing a configuration example of an image processing apparatus according to the present invention.

  A compressed data buffer 100 stores compressed LUT data. A data restoration unit 101 decompresses (restores) the compressed LUT data. Reference numeral 102 denotes an LUT data buffer in which restored LUT data is stored. Reference numeral 103 denotes a color conversion processing unit that generates CMYK output image data by performing an interpolation operation on RGB input image data based on the LUT data stored in the LUT data buffer 102.

  FIG. 6 is a flowchart illustrating an example of image processing executed by the color conversion processing unit 103. In step S11, based on the input RGB image data, it is determined which interpolation solid (small cube) shown in FIG. 2A belongs, and based on the determination result, eight grid points necessary for the interpolation processing That is, the grid point number corresponding to the vertex of the interpolation solid is determined. In step S 12, a plurality of grid point data (CMYK data) corresponding to the determined grid point numbers are read from the LUT data buffer 102. Subsequently, in step S13, cube interpolation processing is performed for each color component of CMYK using the read plurality of grid point data and input image data, and CMYK output image data is generated.

  As shown in FIG. 4, the LUT data buffer 102 stores a set of CMYK data corresponding to the same grid point in the order of grid point numbers. By arranging the data as shown in FIG. 4, the grid point data necessary for the interpolation calculation process can be easily read out. In the present embodiment, one grid point data consists of 4 bytes. Therefore, for the lattice point data of lattice point number i, 4 bytes from the 4i-th byte counted from the head address of the LUT data buffer 102 are read from the LUT data buffer 102. Thereby, lattice point data of lattice point number i can be obtained. That is, 4-byte CMYK data corresponding to one grid point number can be obtained by one reading operation.

  The data restoration unit 101 and the color conversion processing unit 103 can be realized, for example, by supplying a program stored in the ROM to the CPU. Alternatively, the image processing of this embodiment can be realized as a driver by supplying a program to a personal computer or the like. In these cases, the LUT data buffer 102 may be allocated on a RAM or the like used as a work memory for the CPU. The compressed data buffer 100 may be stored in a nonvolatile memory such as a ROM or a hard disk.

  Note that input image data is input to the color conversion processing unit 103 from an image input device such as an image reader, a film reader, a digital still camera, or a digital video camera via a predetermined interface. Alternatively, input image data is input from a storage device including a storage medium such as a magnetic disk or an optical disk. The color conversion processing unit 103 outputs output image data to an image output device such as a CRT or LCD monitor, printer, or film recorder via a predetermined interface. Alternatively, the output image data is output to a storage device including a storage medium such as a magnetic disk or an optical disk. It is also possible to exchange image data via a network interface card (NIC) with a computer device to which the image input / output device or storage device is connected. Examples of such a network include a network using Ethernet (registered trademark) and FDDI (Fiber Distributed Data Interface). In addition, there are a serial bus defined by IEEE 1394, a USB (Universal Serial Bus), and the like.

Hereinafter, a method of creating a conversion table in which each color component is divided as shown in equations (1) to (4) will be described. This is used to perform complementary color inversion processing for color conversion from the color space RGB of the input image data to the color space CMYK of the output image data, and 100% under color removal (UCR) processing. Note that the data of each color component is expressed by 8 bits (0 to 255).
K = 255−MAX (R, G, B) (1)
C = (255−R) −K (2)
M = (255−G) −K (3)
Y = (255−B) −K (4)
However, the function MAX () outputs the maximum value.

  FIG. 2A shows an example of coordinate setting of the conversion table, and FIG. 2B shows an example of input data of each grid point of the conversion table. When the output data corresponding to the data of each grid point shown in FIG. 2B on a one-to-one basis is obtained based on the equations (1) to (4), it is as shown in FIG. 2C. The compressed data buffer 100 stores the compressed LUT data representing the correspondence between the grid point numbers and the output data (C, M, Y, K) shown in FIG. 2C.

  The compressed LUT data stored in the compressed data buffer 100 is restored to LUT data as shown in FIG. 4 by the data restoration unit 101 and stored in the LUT data buffer 102 as necessary.

  FIG. 5 is a flowchart illustrating an example of processing executed by the data restoration unit 101. In step S1, compressed LUT data arranged as shown in FIG. 3 for efficient compression is read from the compressed data buffer 100 and decompressed. The expanded LUT data is arranged in the order of the grid point number for each color component. In step S2, this data arrangement is rearranged as shown in FIG. 4, and in step S3, the rearranged data is changed. Stored in the LUT data buffer 102. Note that the LUT data compression method may be a compression method that increases the compression rate when the same data continues, such as the commonly used Pack bit method.

  Here, the LUT data stored in the compressed data buffer 100 is arranged and compressed in the order of the number of grid points for each color component, as shown in FIG. Note that FIG. 3 shows that the grid point data for each color of CMYK of 125 bytes is compressed to i, j, k, and m bytes, respectively. That is, i <125, j <125, k <125, and m <125.

  The advantage of arranging the LUT data in the order of the grid points for each color component is as follows. For example, when attention is paid to the grid point numbers 120 to 124, as shown in FIG. 2C, this portion is changed from Y single color yellow (C, M, Y, K) = (0, 0, 255, 0) to white (C , M, Y, K) = (0, 0, 0, 0). Therefore, only the Y color has data other than zero, and the C, M, and K colors are zero. Therefore, zero continues in the C, M, and K color data arranged in the order of the grid points, and the compression efficiency can be improved.

  In general, in the portion where the output image data is expressed by primary colors (cyan, magenta and yellow) and secondary colors (red, green and blue), the black component K does not exist. Zero continues. For example, the transition portion from red (C, M, Y, K) = (0,255,255,0) to magenta (C, M, Y, K) = (0,255,0,0) is M Since it is expressed by the Y and Y color data, zero continues for the C and K colors. Such a tendency appears not only in the color conversion processing of complementary color inversion and 100% UCR processing but also in appearance.

  Therefore, by arranging the LUT data for each color component in the order of the grid point numbers and compressing the data, the case where data having zero values continues increases. That is, compared with the case where the LUT data is arranged and compressed in the order of the grid points like C0, M0, Y0, K0, C1, M1, Y1, K1, C2,. The way of arranging the data can dramatically improve the compression rate. Therefore, the storage capacity of the compressed data buffer 101 that stores the compressed LUT data can be saved.

  In the above description, the input color space is the RGB color space, and the output color space is the CMYK color space. However, the present embodiment can also be applied to the CMYK cmy color space of a color inkjet printer for the purpose of high-definition printing that employs CMYK four-color dark ink and light Cmy three-color ink. For example, when an image is formed in the CMYKcmy color space, the high density portion of the image is expressed by dark CMYK ink, and the low density portion is expressed by thin cmy ink. Therefore, the output image data corresponding to the high density region often has zero cmy color data, and conversely, the output image data corresponding to the low density region often has zero CMYK color data. As a result, in the LUT data in the CMYKcmy color space, there are more portions where zeros continue than in the CMYK color space, and the compression efficiency of the LUT data is further improved. According to the present embodiment, not only the CMYKcmy color space but also color conversion to a color space with a large number of color components can be performed, the compression efficiency of the LUT data can be improved.

  In order to simplify the description, the conversion from the RGB color space to the CMYK color space is described as an example in which complementary color conversion (inversion) processing and 100% UCR processing are performed. However, the color conversion method, that is, any relationship between the input image data and the output image data at each grid point may be used.

  Furthermore, the conversion table interpolation method for color conversion is not limited to cubic interpolation. For example, the triangular prism interpolation and the oblique triangular prism interpolation shown in pages 347 to 350 of the 1993 24th Image Engineering Conference Papers may be used. Also, an interpolation method using an interpolation body of another shape such as tetrahedral interpolation disclosed in Japanese Patent Laid-Open No. 2-87192 may be used.

  Further, the number of LUT data stored in the compressed data buffer 100 is not limited to one, and a plurality of compressed LUT data can be stored by making the compressed data buffer 100 into a database format. The color space of the input / output image data is not limited to RGB and CMYK, and may be a color space such as YIQ, Lab, and XYZ.

When the output image data corresponding to the input image data at each grid point is stored for each grid point, the LUT data becomes a list of data of different color components, and the continuity of data of the same value is reduced, so the compression efficiency of the LUT data is extremely high. Lower. Furthermore, when storing a plurality of LUT data as an LUT database, there is a disadvantage that the storage capacity of the storage unit becomes enormous. On the other hand, according to the present embodiment, the output image data corresponding to the input image data at each grid point is stored for each color component, so that data of the same value can be continued. Accordingly, when image data conversion processing is performed using LUT interpolation calculation processing, it is possible to improve the compression efficiency of LUT data and save the storage capacity for storing LUT data.
[Second Embodiment]
The image processing apparatus according to the second embodiment of the present invention will be described below. Note that in the present embodiment, the same reference numerals are given to substantially the same configurations as those in the first embodiment, and the detailed description thereof is omitted.

  In the second embodiment, processing when the image processing shown in the first embodiment is applied to a printer driver will be described.

  In recent printers, it is necessary to consider that an image is formed on a recording medium having various characteristics such as plain paper, glossy paper, and glossy film. In order to realize good color reproduction on recording media having different characteristics, it is necessary to prepare an LUT having conversion characteristics corresponding to the characteristics of the recording medium.

  Furthermore, an image formed by a printer may include a plurality of objects having different preferable color reproduction methods such as photographs and graphics. For example, gradation and color continuity are important for photographs, and vivid colors tend to be used favorably for graphics, so it is important to reproduce colors vividly.

  Therefore, in order to obtain a high-quality output image, it is necessary to prepare an LUT having conversion characteristics suitable for each object included in the input image. That is, in order to obtain a high-quality output image from a printer, it is necessary to prepare a very large number of LUTs corresponding to various conditions. It is also necessary to use a plurality of LUTs in one printing operation.

  Accordingly, the storage capacity of the memory required to store a plurality of LUTs is reduced by using the LUT data compression method described in the first embodiment. Further, the LUT can be switched at high speed by expanding a plurality of LUTs selected based on the image forming conditions manually designated by the user based on the print instruction.

  FIG. 7 is a flowchart illustrating an example of processing according to the second embodiment. In step S21, a print command is input. For example, when a user issues a print instruction to application software, a print command is input to the printer driver.

  Next, in step S22, recording medium information indicating the type of recording medium on which an image is formed is input. The recording medium information is information corresponding to the type of the recording medium selected by the user or the default setting on the setting dialog which is one of the user interfaces of the printer driver displayed when the user issues a print instruction. is there. If the printer has a function for identifying the type of the recording medium, information indicating the identification result obtained by this function can be used as the recording medium information.

  In step S23, a plurality of compressed LUT data corresponding to the input recording medium information is read from the compressed data buffer 100. The plurality of compressed LUT data to be read corresponds to the recording medium information and each of a plurality of object types, for example. In step S 24, the compressed LUT data is subjected to the processing shown in FIG. 5 and the processed data is stored in the LUT data buffer 102.

  Next, in step S25, color conversion processing using an LUT is performed on the image data input following the print command. The color conversion processing unit 103 determines the type of object belonging to the input image data by analyzing the input image data, and performs color conversion processing on the input image data using an LUT corresponding to the determination result.

As described above, according to the second embodiment, a plurality of LUTs corresponding to the conditions in the print input together with the print command are restored. The restored data is stored in the LUT data buffer 102. Therefore, even if the LUT is compressed and stored, complex color reproduction processing suitable for the input image can be performed efficiently.
[Third Embodiment]
The image processing apparatus according to the third embodiment of the present invention will be described below. Note that in the present embodiment, the same reference numerals are given to substantially the same configurations as those in the first embodiment, and the detailed description thereof is omitted.

  In the third embodiment, an LUT changing process will be described. For example, since the printer characteristics are converted according to the environment and time, when the image processing described in the first embodiment is applied to the printer driver to always obtain a high-quality output image, the printer characteristics are changed according to changes in the printer characteristics. Therefore, it is necessary to change the LUT data.

  There is calibration as a technique for changing LUT data. The LUT data is created by calibration by forming a plurality of color patches on the printer, measuring the color patches obtained, and generating LUT data based on the color measurement results.

  In the third embodiment, the LUT data created by calibration is stored in the compressed data buffer 100 using a process corresponding to the reverse process of the process shown in FIG. That is, the LUT data as shown in FIG. 4 created by the calibration is rearranged in order of the grid point number for each color component and compressed to create the compressed LUT data as shown in FIG. Store in the compressed data buffer 100.

Note that the third embodiment can be applied not only to the process of changing the LUT data but also to the addition of LUT data.
[Other embodiments]
Note that the present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, and a printer), and a device (for example, a copying machine and a facsimile device) including a single device. You may apply to.

  In addition, a storage medium storing software program codes for realizing the functions of the above-described embodiments is supplied to the system or apparatus. The computer (or CPU or MPU) of the system or apparatus reads and executes the program code stored in the storage medium. It goes without saying that the object of the present invention is also achieved by this. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment. The storage medium storing the program code constitutes the present invention. Further, the functions of the above-described embodiment are realized by executing the program code read by the computer. In addition, based on the instruction of the program code, an OS (operating system) running on the computer performs part or all of the actual processing. Needless to say, the process includes the case where the functions of the above-described embodiments are realized.

  Further, the program code read from the storage medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer. Thereafter, based on the instruction of the program code, the CPU or the like provided in the function expansion card or function expansion unit performs part or all of the actual processing. Needless to say, the process includes the case where the functions of the above-described embodiments are realized.

1 is a block diagram showing an example of an image processing apparatus according to an embodiment of the present invention; The figure which shows an example of the coordinate setting of a conversion table, The figure which shows an example of the input data of each grid point of a conversion table, The figure which shows an example of the output data of each grid point of a conversion table, The figure which shows how to arrange the data of the conversion table data which is compressed, The figure which shows the example of a form of the data stored in a LUT data buffer, A flowchart showing an example of processing executed by the data restoration unit, A flowchart showing an example of image processing executed by the color conversion processing unit; It is a flowchart which shows an example of the process of 2nd Embodiment.

Claims (5)

An image processing apparatus that converts input color data into a plurality of color component data including cyan, magenta, yellow, and black by color conversion processing using interpolation calculation processing using a conversion table,
Storage means for storing the compression conversion table data obtained by compressing the conversion table in the first arrangement order in which the color component data of each color component is collected for each identical color component and arranged in the order of the grid point number;
Decompression means for decompressing the compression conversion table data;
For the expanded conversion table in the first arrangement order, a plurality of color component data related to the same grid point number are collected as grid point data, and the grid point data is rearranged in the order of the grid point number to form a second sequence. Reordering means for converting the conversion table in order;
Conversion means for performing color conversion processing by interpolation processing using the conversion table of the second arrangement order to generate the output image data,
The grid point number is a plurality of color component data of the input color data from a grid point in which the plurality of color component data of the input color data are all 0 for each of a plurality of grid points constituting the conversion table. Are sequentially added according to the size of each of the plurality of color component data of the input color data corresponding to the grid points of the conversion table, up to the grid points where all are maximum values. .   2. The image processing apparatus according to claim 1, wherein the plurality of color component data includes light cyan, light magenta, and light yellow in addition to cyan, magenta, yellow, and black. Furthermore, it has means for reading the compression conversion table data corresponding to the conditions in printing from the storage means,
The image processing apparatus according to claim 1, wherein the decompressing unit decompresses the read compression conversion table data. An image processing method for converting input color data into a plurality of color component data including cyan, magenta, yellow, and black by color conversion processing using interpolation calculation processing using a conversion table,
Storing the compression conversion table data obtained by compressing the conversion table of the first arrangement order in which the color component data of each color component is collected for each identical color component and arranged in the order of the grid point number;
Decompressing the compression conversion table data;
For the expanded conversion table in the first arrangement order, a plurality of color component data related to the same grid point number are collected as grid point data, and the grid point data is rearranged in the order of the grid point number to form a second sequence. A step of converting to a sequential conversion table;
Performing color conversion processing by interpolation processing using the conversion table of the second arrangement order and generating the output image data,
The grid point number is a plurality of color component data of the input color data from a grid point in which the plurality of color component data of the input color data are all 0 for each of a plurality of grid points constituting the conversion table. Are sequentially added according to the size of each of the plurality of color component data of the input color data corresponding to the grid points of the conversion table, up to the grid points where all are maximum values. . A recording medium recording a program code for image processing for converting input color data into a plurality of color component data including cyan, magenta, yellow, and black by color conversion processing using interpolation calculation processing using a conversion table. ,
The code of the step of storing the compression conversion table data obtained by compressing the conversion table in the first arrangement order in which the color component data of each color component is collected for each identical color component and arranged in the order of the grid point number;
A code for decompressing the compression conversion table data;
For the expanded conversion table in the first arrangement order, a plurality of color component data related to the same grid point number are collected as grid point data, and the grid point data is rearranged in the order of the grid point number to form a second sequence. The code of the step to be the order conversion table,
A code of a step of performing color conversion processing by interpolation processing using the conversion table of the second arrangement order to generate the output image data;
The grid point number is a plurality of color component data of the input color data from a grid point in which the plurality of color component data of the input color data are all 0 for each of a plurality of grid points constituting the conversion table. The recording medium is characterized in that, up to a grid point where all the values are the maximum value, the input color data corresponding to the grid points of the conversion table are sequentially added according to the size of each of the plurality of color component data.

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