JP2008131125A - Image processing apparatus, image processing method and image processing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To execute color conversion corresponding to a color reproduceable region of an output device. <P>SOLUTION: A color conversion table creating section 104a creates a color conversion table for converting a color value in a color space of image data into a color value in a color space of an output device, smoothes the created color conversion table, and corrects a smoothed color value so that it comes within the color reproduceable region of the output device when the color value (smoothed color value) of the color space of the output device in the smoothed color conversion table is out of the color reproduceable region of the output device. A color conversion processing section 104b uses the color conversion table after correction to execute color conversion processing for the image data. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing apparatus for processing an image, an image processing method, and an image processing program for executing the method.

The following color conversion devices are known. This apparatus creates a color conversion table for user's favorite color conversion, combines this color conversion table and a color conversion table based on a color space based on the output device, and combines the combined table. By smoothing,
Color conversion characteristics for performing favorite color conversion are smoothed (for example, Patent Document 1).

Japanese Patent Laid-Open No. 2002-77659

  However, according to the conventional apparatus, since the color conversion table created by the user is combined with the color conversion table based on the color space based on the output device, the color based on the color space based on the output device in advance is combined. It was necessary to prepare a conversion table. For this reason, an output device that does not have a color conversion table may not be able to perform color conversion that matches the color reproducible area of the device.

The present invention is an image processing apparatus that performs color conversion processing on input image data in accordance with a color reproducible area of an output device, from the color value of the color space of the image data to the color space of the output device. When the color conversion table for conversion to color values is smoothed and the color value of the color space of the output device (color value after smoothing) in the color conversion table after smoothing is outside the color reproducible area of the output device Is characterized in that the color values after smoothing are corrected so that they fall within the color reproducible region of the output device, and color conversion processing is performed on the image data using the color conversion table after correction. And
At this time, a color conversion table may be created and the created color conversion table may be smoothed, or a color conversion table created in advance may be read and the read color conversion table may be smoothed.
Further, it is preferable to repeat the smoothing and correction until all the smoothed color values in the color conversion table fall within the color reproducible area of the output device, and the coordinate values in the color space are used as grid point information, and the image A lookup table in which the color value of the data color space is associated with the color value of the color space of the output device may be created as a color conversion table.
Then, the color value of the color conversion destination before smoothing and the color value of the color conversion destination after smoothing are displayed on the same color space and connected with arrows, and the direction and length of the arrows are changed. Correct the color values after smoothing to be within the color reproducible area of the output device, or change the grid point arrangement of the color conversion table so that the color values after smoothing can be reproduced by the output device. You may make it correct | amend so that it may be settled in an area | region.
Further, color conversion processing may be performed on the image data by interpolating the grid point information of the color conversion table after correction and calculating the color value after color conversion of the image data. .

  According to the present invention, color conversion suitable for the color reproducible region of the output device can be performed without preparing a color conversion table for each output device in advance.

  FIG. 1 is a block diagram showing a configuration of an embodiment of an image processing apparatus according to the present embodiment. For example, a personal computer (personal computer) is used as the image processing apparatus 100. The image processing apparatus 100 includes an input device 101, an image input I / F (image input interface) 102, a colorimeter 103, a control device 104, an HDD (hard disk drive) 105, and an output device connection I. / F (output device connection interface) 106.

  The input device 101 includes various input devices operated by a user such as a keyboard and a mouse.

  The image input I / F 102 is a connection interface for connecting an external image input device, for example, a digital camera or an image storage device, and is for capturing an image to be processed, which will be described later, from the image input device. As the image input I / F 102, for example, a USB interface or a wireless LAN interface is used.

  The colorimeter 103 reads an image printed on a print medium such as paper and measures the color. In the present embodiment, the colorimeter 103 outputs station value XYZ data to the control device 104 as a colorimetric result.

  The HDD 105 records various data such as image data captured via the image input I / F 102 and a program executed by the control device 104 as described later. In this embodiment, it is assumed that at least one image has already been taken in via the image input I / F 102 as an image to be processed, and that image data is stored in the HDD 105.

  The output device connection I / F 106 is a connection interface for connecting an external device as an output destination of image data, for example, an output device such as a monitor or a printer. For example, a USB interface or a wireless LAN interface is used as the output device connection I / F 106. The output devices connected to the output device connection I / F 106 generally have different color reproducible regions between the output devices. For this reason, the color conversion characteristics between the input / output devices also differ for each output device.

  Therefore, the control device 104, which will be described later, determines a color conversion characteristic suitable for each output device, applies the color conversion characteristic to the image data of the target image, and then performs color conversion processing on the output device. It is necessary to output image data. In the present embodiment, the control device 104 creates a color conversion table (lookup table) that represents the color conversion characteristics of each output device, and uses this color conversion table to perform color matching on the image data of the target image. Perform conversion processing.

  In order for the control device 104 to create a color conversion table for each output device, the user needs to make the following preparations in advance. In the following description, it is assumed that the output device connected to the output device connection I / F 106 is a printer, and a case where a color conversion table representing the color conversion characteristics of the connected printer is created will be described.

  First, the user creates patches (color patches) that can be represented by R, G, and B color components using data evenly carved in the Lab space using image processing software. The image processing software is installed in the image processing apparatus 100 and other information devices such as a personal computer, and the user creates an RGB patch by operating the device in which the image processing software is installed. The user saves the created RGB patch as image data in the HDD 105 and prints (prints) the RGB patch image data using an output device connected to the output device connection I / F 106.

  The user measures the color of each patch represented by the printed R, G, and B color components using the colorimeter 103. As a result, the colorimeter 103 obtains the RGB patch colorimetric value XYZ data and outputs them to the control device 104.

  The control device 104 includes a CPU, a memory, and other peripheral circuits, and functionally includes a color conversion table creation unit 104a, a color conversion processing execution unit 104b, and an image data output unit 104c.

  The color conversion table creation unit 104 a reads the colorimetric value XYZ data of each RGB patch input from the colorimeter 103. Further, as described above, the RGB patch image data created by the user is read from the HDD 105. Then, the color conversion table creation unit 104a, based on the RGB patch image data and the read colorimetric value data of the RGB patch, in the Lab space representing the color conversion characteristics of the printer (output device) that printed the RGB patch. A color conversion table (first color conversion table) is created. That is, L, a, and b in the Lab space are set as grid point information, and the color value of the color space of the image data is associated with the color value of the color space of the output device using the coordinate values on the color space. Create a lookup table.

  Specifically, the color conversion table creation unit 104a converts RGB patch colorimetric value data (XYZ data) into Lab data, converts RGB patch image data (RGB data) into XYZ data, and then converts the Lab data into Lab data. Convert to At this time, when converting the colorimetric value data of the RGB patch into Lab data and when converting the XYZ data into Lab data in the respective processes of converting the RGB patch image data into Lab data, conversion is performed. A common white reference value is used. Thereby, the colorimetric value data of the RGB patch and the image data of the RGB patch can be associated in the Lab space.

FIG. 2 is a diagram illustrating a specific example of the first color conversion table. In FIG. 2, the grid point information of the RGB patch image data is represented as L ^* , a ^* , b ^*, and the grid point information of the RGB patch colorimetric value data is L ^* ′, a ^* ′, b ^* ′. It expresses. That is, the first color conversion table shown in FIG. 2 uses a coordinate value in the color space as a grid point, and looks up by associating input data of a printer as an output device with colorimetric value data of an output image. It is a table. The more data contained in this table, the more accurate the color conversion characteristics are recorded.

  The color conversion table creation unit 104a optimizes the first color conversion table and newly creates a second color conversion table. This is because, in the first color conversion table shown in FIG. 2, the output value (colorimetric value) for the input data (image data) includes the colorimetric error of the colorimeter 103. The purpose of this is to correct the variation that occurs. For example, if the output values of the first color conversion table shown in FIG. 2 are expressed in the same color space with the vertical axis being L and the horizontal axis being b as shown in FIG. 3, the output values vary. I understand that. In addition, when color conversion is performed based on the first color conversion table, the color value after conversion may be outside the color reproducible area of the output device. Yes.

  The color conversion table creation unit 104a optimizes the output values of the first color conversion table by performing a smoothing process and a correction process described below to create a second color conversion table. . First, the smoothing process will be described. The color conversion table creation unit 104a smoothes the first color conversion table by interpolating the grid point information of the output values of the first color conversion table. Specifically, the color conversion table creation unit 104a performs a weighted averaging process on the output value of the first color conversion table according to the distance to the grid point of the table for the color value in a specific color space. As a result, the grid point information of the first color conversion table is interpolated. Thereby, even if there is a variation in the data of the grid point of the output value of the first color conversion table, the variation of the data of the grid point of the output value can be corrected.

Here, the distance to the grid point corresponds to the color difference ΔE in the Lab space, and the color conversion table creation unit 104a performs weighted averaging only for data in which ΔE is within a predetermined threshold. Process. On the other hand, for data in which ΔE is outside a predetermined threshold, data of corresponding points closest to the target grid point is used. For example, the relationship between input data and output data in the first color conversion table is “L ^* _n , a ^* _n , b ^* _n → L ^* _n ′, a ^* _n ′, b ^* _n ′” ( _{where n} is a table). This is described as being expressed as In this case, the color conversion table creation unit 104a performs weighting according to the Gaussian distribution G (L ^* , a ^* , b ^* ) expressed by the following equation (1), and finally by the following equation (2). The interpolated conversion amount LUT (L ^* , a ^* , b ^* ) is calculated.

  FIG. 4 is a diagram illustrating a specific example when smoothing is performed on data in the region 4a where the color difference ΔE in the Lab space is ΔE ≦ 10. In FIG. 4, the color value of the color conversion destination before smoothing and the color value of the color conversion destination after smoothing are displayed on the same color space (Lab space). That is, the color value of the color conversion destination before smoothing is represented by a point (white point and black point), and the tip of the arrow extending from each point represents the color value of the color conversion destination after smoothing. In other words, the direction and the length of the arrow connecting the coordinate value indicating the color value of the color conversion destination before smoothing and the coordinate value indicating the color value of the color conversion destination after smoothing are as follows. The direction and the size of the color conversion when the color conversion is performed using the data are shown.

  In the example shown in FIG. 4, the points (white dots) 4b are used as a reference according to the formulas (1) and (2) to weight each point (black dot) other than the point 4b according to the Gaussian distribution, and the data of each black dot is obtained. Can be smoothed. Specifically, the weight value given to the black point close to the white point 4b is increased, and each black point is weighted and smoothed so that the weight value given to the black point decreases as the distance from the white point 4b increases. Yes. The first color conversion table can be smoothed by performing this process in the same manner with respect to points other than the white point 4b.

  Next, the correction process will be described. When the first color conversion table is smoothed by the smoothing process described above, the color value (output value) of the color conversion destination may be outside the color reproducible region of the output device. In this case, it is necessary to correct the first color conversion table after smoothing in consideration of gamut mapping. Specifically, the color conversion table creation unit 104a displays the color value of the color conversion destination before smoothing and the color value of the color conversion destination after smoothing shown in FIG. 4 in the same color space. It is necessary to change the direction and length of the arrow in this case so that the coordinate value of the color value of the color conversion destination after smoothing falls within the color reproducible region of the output device.

  For example, the coordinate value of the intersection of the straight line constituting each arrow and the boundary line of the color reproducible area of the output device is calculated as the color value of the color conversion destination after correction. Then, the corresponding color conversion destination color value in the first color conversion table after smoothing is updated with the corrected color conversion destination color value. Or you may correct | amend by changing arrangement | positioning of the grid point of the 1st color conversion table after smoothing. For example, the lattice point information may be corrected by replacing it with an interval of 5 increments, such as (0, 0, 0), (5, 0, 0).

  The table creation unit 104a performs the above-described smoothing process of the first color conversion table and the correction process of the first color conversion table, and the value outside the color reproducible region of the output device is set as the color value of the color conversion destination. The process is repeated until there is no more, and the finally obtained color conversion table is used as the second color conversion table. As a result, the second color conversion table that can optimize the first color conversion table and realize more natural color conversion can be obtained.

  The color conversion processing execution unit 104b performs color conversion processing on the image data (input data) of the target image using the second color conversion table created by the color conversion table creation unit 104a. That is, the color value of the input data is converted from the color value of the color conversion source in the corresponding second color conversion table to the color value of the conversion destination. At this time, the color conversion processing execution unit 104b calculates color value data to be output from the input color value data by interpolating the grid point information of the second color conversion table. Specifically, the color conversion process execution unit 104b performs the same process as the smoothing process by the table creation unit 104a described above on the second color conversion table, thereby obtaining the grid point information of the second color conversion table. Interpolate.

  The image data output unit 104c outputs the image data after the color conversion processing to an output device, for example, a printer, connected via the output device connection I / F 106.

  FIG. 5 is a flowchart showing processing of the image processing apparatus 100 in the present embodiment. The processing shown in FIG. 5 is executed by the control device 104 as a program that is activated when the user operates the input device 101 to instruct the output of the target image to the output device. Here, it is assumed that a printer is connected to the output device connection I / F 106, and a case where color conversion processing suitable for the color reproducible area of the printer is performed will be described. Further, it is assumed that the target image is selected in advance by the user, and the creation of the RGB patch and the color measurement of the RGB patch are performed in advance.

  In step S <b> 10, the color conversion table creation unit 104 a reads R, G, and B colorimetric values XYZ data input from the colorimeter 103. Also, the RGB patch image data created by the user is read from the HDD 105. Then, the color conversion table creation unit 104a, based on the RGB patch image data and the read colorimetric value data of the RGB patch, displays a color conversion table in the Lab space that represents the color conversion characteristics of the printer that printed the RGB patch ( A first color conversion table is created. Then, it progresses to step S20.

  In step S20, the color conversion table creation unit 104a optimizes the first color conversion table by performing the above-described smoothing process and correction process, and creates a second color conversion table. Then, it progresses to step S30. In step S30, the color conversion processing execution unit 104b performs color conversion processing on the image data (input data) of the target image using the second color conversion table created by the color conversion table creation unit 104a. At this time, color value data to be output is calculated from the input color value data by interpolating the grid point information of the second color conversion table.

  Thereafter, the process proceeds to step S40, where the image data output unit 104c outputs the image data after the color conversion process to the printer connected via the output device connection I / F 106, and ends the process.

According to the present embodiment described above, the following operational effects can be obtained.
(1) A first color conversion table for converting the color value of the color space of the image data to the color value of the color space of the output device is created, the first color conversion table is smoothed, and the smoothed color The second color conversion table was created by performing correction so that the value was within the color reproducible region of the output device. Then, color conversion processing is performed on the image data using the second color conversion table. This makes it possible to perform color conversion processing that fits in the color reproducible area of the output device.

(2) The smoothing and correction are repeated until all the converted color values in the first color conversion table after smoothing fall within the color reproducible region of the output device. As a result, it is possible to perform color conversion processing that completely fits in the color reproducible region of the output device.

(3) The first and second color conversion tables use coordinate values in the color space as grid point information,
The color value of the color space of the image data is associated with the color value of the color space of the output device. As a result, the color value in the color space of the input image data can be converted into a color value within the color reproducible range of the output device.

(4) Displaying the color value of the color conversion destination before smoothing and the color value of the color conversion destination after smoothing in the same color space, connecting them with arrows, and changing the direction and length of the arrows Thus, the smoothed color value is corrected so as to be within the color reproducible region of the output device. Further, by changing the arrangement of the grid points in the color conversion table, the color values after smoothing are corrected so as to be within the color reproducible area of the output device. Accordingly, it is possible to correct so that the color value after smoothing is surely contained within the color reproducible region of the output device.

(5) When performing color conversion processing on image data, the grid point information of the second color conversion table is interpolated to calculate the color value after color conversion of the image data. Thereby, more natural color conversion can be performed.

-Modification-
The image processing apparatus according to the above-described embodiment can be modified as follows.
(1) In the above-described embodiment, the color conversion table creation unit 104a optimizes the first color conversion table by performing a smoothing process and a correction process, thereby obtaining the second color conversion table. The example to create was demonstrated. However, the color conversion table creation unit 104a may perform only the smoothing process on the first color conversion table to create the second color conversion table.

(2) In the above-described embodiment, the example in which the second color conversion table is created as the lookup table (LUT) according to the color reproducible region of the output device has been described. However, the present invention can also be applied to a case where a lookup table relating to color creation for converting a certain color into another color according to a predetermined tendency is created.

(3) In the above-described embodiment, the color conversion table creation unit 104a creates the first color conversion table based on the input value from the colorimeter 103 and the RGB patch image data, and creates the first color conversion table. An example of optimizing one color conversion table has been described. However, the first color conversion table created in advance may be used. In this case, the color conversion table creation unit 104a reads and reads the first color conversion table created in advance. The first color conversion table may be optimized.

(4) The present invention is not limited to the image processing apparatus, and may be an image processing program executed by a general-purpose computer based on the flowchart shown in FIG.

  Note that the present invention is not limited to the configurations in the above-described embodiments as long as the characteristic functions of the present invention are not impaired.

It is a block diagram which shows the structure of one Embodiment of an image processing apparatus. It is a figure which shows the specific example of a 1st color conversion table. It is a figure which shows the dispersion | variation in the output value of a 1st color conversion table. It is a figure which shows the specific example at the time of smoothing for the data in the area | region 4a of (DELTA) E <= 10. 3 is a flowchart showing processing of the image processing apparatus 100. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image processing apparatus, 101 Operation member, 102 Image input I / F, 104 Control apparatus, 104a Color conversion table preparation part, 104b Color conversion process execution part, 104c Image data output part, 105 HDD, 106 Output device connection I / F

Claims (9)

An image processing apparatus that performs color conversion processing on input image data according to a color reproducible area of an output device,
Smoothing means for smoothing a color conversion table for converting the color value of the color space of the image data to the color value of the color space of the output device;
When the color value (color value after smoothing) of the output device in the color conversion table after smoothing by the smoothing means is outside the color reproducible region of the output device, the smoothing Correction means for correcting the rear color value to be within the color reproducible region of the output device;
An image processing apparatus comprising: a color conversion unit that performs the color conversion process on the image data using the color conversion table after the correction by the correction unit. The image processing apparatus according to claim 1.
Further comprising a creating means for creating the color conversion table,
The image processing apparatus characterized in that the smoothing means smoothes the color conversion table created by the creating means. The image processing apparatus according to claim 1.
It further comprises reading means for reading the color conversion table created in advance,
The image processing apparatus characterized in that the smoothing means smoothes the color conversion table read by the reading means. In the image processing device according to any one of claims 1 to 3,
The smoothing means and the correction means repeat the smoothing and correction until all the smoothed color values in the color conversion table fall within the color reproducible region of the output device. Image processing device. In the image processing device according to any one of claims 1 to 4,
The color conversion table is a lookup table that uses coordinate values in a color space as grid point information and associates color values in the color space of the image data with color values in the color space of the output device. An image processing apparatus. The image processing apparatus according to claim 5.
The correction means displays the color value of the color conversion destination before smoothing and the color value of the color conversion destination after smoothing in the same color space and connects them with arrows, and changes the direction and length of the arrows The post-smoothing color value is corrected so as to be within the color reproducible region of the output device, or the arrangement of the grid points in the color conversion table is changed, thereby An image processing apparatus, wherein a value is corrected so as to be within a color reproducible region of the output device. The image processing apparatus according to claim 5 or 6,
The color conversion unit interpolates the lattice point information of the color conversion table after correction by the correction unit, and calculates a color value after color conversion of the image data, thereby obtaining the image data. An image processing apparatus that performs the color conversion process on the image processing apparatus. An image processing method for performing color conversion processing according to a color reproducible area of an output device for input image data,
Smoothing a color conversion table for converting from a color value of the color space of the image data to a color value of the color space of the output device;
When the color value (smoothed color value) of the output device in the color conversion table after smoothing is outside the color reproducible region of the output device, the smoothed color value is Correct it to be within the color reproducible area of the output device,
An image processing method, wherein the color conversion process is performed on the image data using the color conversion table after correction. An image processing program for performing color conversion processing according to the color reproducible area of the output device for input image data,
On the computer,
A smoothing procedure for smoothing a color conversion table for converting from a color value of the color space of the image data to a color value of the color space of the output device;
When the color value (color value after smoothing) of the output device in the color conversion table after smoothing by the smoothing procedure is outside the color reproducible region of the output device, the smoothing A correction procedure for correcting the rear color value so as to be within the color reproducible region of the output device;
An image processing program for executing a color conversion procedure for performing the color conversion processing on the image data using the color conversion table after correction is performed in the correction procedure.

Images