JP4472594B2 - Image data color conversion apparatus, color conversion method, and color conversion program - Google Patents

Description

  The present invention, for example, converts input image data received from an input device such as an image scanner or a digital camera into a color space corresponding to the color gamut of an output device such as a color electrophotographic printer, a color copying apparatus, or an ink jet printer. The present invention relates to a color conversion device, a color conversion method, and a color conversion program for image data output to the output device.

  Input image data output from an input device such as an image scanner or a digital camera is converted into an R (red) G (green) B (blue) image format by a color conversion device for a display device, and then displayed on a display or the like. In addition, after being converted into a C (cyan), M (magenta), Y (yellow), and K (black) image format by a color conversion device for an output device, it is printed by a printer or the like.

  By the way, since the input image data is usually in the RGB image format, color conversion can be performed between the input device and the display device in a color space having substantially the same color gamut. Since it is necessary to convert the RGB image format to a color space having a different color gamut called CMYK image formation, the RGB color space is divided into grids, and the conversion values at the grid points are converted into color conversion tables. All colors are converted to CMYK image format.

Conventionally, as an apparatus for converting an RGB image format into CMYK image formation, for example, an apparatus for converting a specific color in input image data so that output image data is output in accordance with human sensitivity (for example, a patent) And a device that clips data outside the RGB color reproduction range to the outermost saturation of the CMKY color reproduction range (for example, see Patent Document 2).
JP-A-6-121159 JP 7-298073 A

  However, in each of Patent Document 1 and Patent Document 2, the saturation amount distribution of the RGB input image data is color-converted without being reflected in the CMYK output image data, and is printed by the output device. There is a problem that variations in saturation occur in photographs and the like.

  Further, in Patent Document 2, when clipping data outside the RGB color reproduction range to the outermost saturation of the CMKY color reproduction range, the high saturation portion where the clipping amount is large is crushed, and the high saturation portion is smooth. There is a problem that it is difficult to reproduce various gradations.

  The present invention has been made to eliminate such inconveniences, and can prevent variations in the saturation of output image data, and can prevent collapse in the high saturation portion of the color gamut of the output device. An object of the present invention is to provide a color conversion device, a color conversion method, and a color conversion program for image data that can reproduce a smooth gradation in a high saturation portion.

To achieve the above object, the color conversion device of the image data of the present invention, the input image data received from the input device, is converted into a color space corresponding to the color gamut of the output device, the output to the output device A color conversion device for image data, the saturation amount distribution information calculating means for calculating distribution information of the saturation amount for each hue in the color space of the input image data, and each hue based on the saturation amount distribution information Saturation ratio calculation means for calculating a saturation ratio, saturation range information calculation means for calculating and holding reproducible range area information for each hue in the color space of the color gamut of the output device, and Based on the saturation ratio and the range information, a modified saturation value calculation means for calculating a corrected saturation value for each hue so as to be within the saturation range while maintaining the saturation ratio; and Based on modified saturation value Create an output image data Te is the output image data as a configuration and an image data output means for outputting to the output device.

According to the above configuration, it is possible to obtain output image data by color-converting the input image data within the saturation range of the color gamut of the output device while maintaining the saturation ratio of all hues of the input image data. it can.
Thereby, color conversion can be performed so that the saturation amount distribution of the input image data is reflected in the output image data having a different color gamut, and as a result, variation in the saturation of the output image data can be prevented, It is possible to prevent the color reproduction area of the output device from being crushed in the high saturation portion and to reproduce a smooth gradation in the high saturation portion.

The color conversion device of the image data of the present invention, the saturation metric distribution information calculation means, by dividing the hue of the input image data color space into a plurality of angles, the segmented saturation metric for each hue distribution The information is calculated respectively.

Furthermore, the color conversion apparatus for image data according to the present invention is configured such that the saturation ratio calculation means calculates the saturation ratio of each hue by normalizing the saturation value for each hue category.

Furthermore, the color conversion device of the image data of the present invention, the saturation range information calculation means, by dividing the hue in the color space of the color gamut of the output device into a plurality of angles, segmented reproduction of each hue Each possible range information is calculated and held.

Furthermore, the color conversion device of the image data of the present invention, the modified saturation value calculating means, for each hue, by multiplying the said saturation ratio the range gamut information, the hue a product obtained by the multiplication In the configuration, the corrected saturation value in FIG.

The color conversion method of the image data of the present invention, the input image data received from the input device, is converted into a color space corresponding to the color gamut of the output device, the color conversion process of the image data to be output to the output device A saturation amount distribution information calculating process for calculating saturation amount distribution information for each hue in the color space of the input image data, and a saturation ratio for calculating a saturation ratio of each hue based on the saturation amount distribution information. A saturation ratio calculation process, a saturation range information calculation process for calculating and holding reproducible range information for each hue in the color space of the color gamut of the output device, and the saturation ratio and the range information A corrected saturation value calculation process for calculating a corrected saturation value for each hue that falls within the saturation range while maintaining the saturation ratio, and an output based on the corrected saturation value Create image data A configuration equipped with the image data output process of outputting the output image data to the output device.

A color conversion program according to the present invention converts input image data received from an input device into a color space corresponding to a color gamut of the output device, and performs color conversion processing of the image data output to the output device. A color conversion program to be executed, wherein the hue of the color space of the input image data is divided into a plurality of angles, and saturation amount distribution information calculation processing for calculating saturation amount distribution information for each of the divided hues; The saturation ratio calculation process for calculating the saturation ratio of each hue based on the saturation amount distribution information and the hue in the color space of the color gamut of the output device are divided into a plurality of angles, Based on the saturation range information calculation process for calculating and holding reproducible saturation range information for each hue, and the saturation ratio and the saturation range information, the saturation ratio is maintained and the saturation ratio is maintained. Within the range of degrees A corrected saturation value calculation process for calculating a corrected saturation value for each hue, and output image data based on the corrected saturation value and outputting the output image data to the output device And the processing is executed by the color conversion device.

  According to the present invention, the color conversion can be performed so that the saturation amount distribution of the input image data is reflected in the output image data having a different color gamut, so that variations in the saturation of the output image data can be prevented. Thus, it is possible to prevent the color reproduction range of the output device from being crushed in the high saturation portion and to reproduce a smooth gradation in the high saturation portion.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a color image processing system including an image data color conversion apparatus as an example of an embodiment of the present invention, and FIG. 2 is an image data color conversion apparatus as an example of an embodiment of the present invention. FIG. 3 is a block diagram, FIG. 3 is a diagram showing a state in which input image data in all hues is divided by a plurality of hue angles, FIG. 4 is a graph showing distribution of saturation values in one hue angle, and FIG. FIG. 6 is a chart showing CMY100% combination color samples, FIG. 7 is a chart showing the colorimetric results of the color samples shown in FIG. 6, and FIG. 8 is an example of an embodiment of the present invention. It is a flowchart for demonstrating operation | movement of a color converter.

In FIG. 1, reference numeral 1 denotes an input device such as an image scanner or a digital camera, and RGB input image data output from the input device 1 is color conversion device 2 and color conversion which is an example of an embodiment of the present invention. Received by device 4.
Based on the received data received by the color conversion device 2, the image is converted into an RGB image format corresponding to the display color reproduction range, and then displayed on the display device 3 such as a display, and received by the color conversion device 4. Based on the received data, the data is converted into a CMYK image format corresponding to the output color gamut and then printed by the output device 5 such as a printer.

  The color conversion device 4 for image data, which is an example of an embodiment of the present invention, is composed of, for example, a digital image processing computer or the like. As shown in FIG. Calculation means 7, saturation range information calculation means 8, modified saturation value calculation means 9, and image data output means 10 are provided. Each processing of these means is executed by the CPU after the color conversion program stored in the storage means (ROM, hard disk, etc.) of the color conversion device 4 is loaded into the RAM.

  As shown in FIG. 3, the saturation amount distribution information calculation unit 6 divides the hue of the color space of the RGB input image data into a plurality of angles (in this embodiment, six divisions), and the hue angle ( Hue) LCh (L: lightness, C: saturation, h: hue) value is calculated, and a saturation amount distribution Xi is calculated based on the LCh value. Here, it is preferable to classify the hue so that there are at least three image data.

The saturation ratio calculation unit 7 normalizes all data of the saturation amount distribution Xi obtained by the saturation amount distribution information calculation unit 6 for each section, and normalizes all the RGB input image data used in each section. The calculated value Uoi (see FIG. 4) is calculated using the following equation (1).
Uoi = (Xi−Xave) / s (1)
However,
Xave: Average value of saturation X in the hue s: Standard deviation Generally, it is known that this normalized value Uoi takes a value of 0 on average and 1 on standard deviation.

Next, since the normalized saturation ratio takes a negative value of −3Σ to + 3Σ in the 99% confidence interval (see FIG. 4), the saturation ratio ratio ( Uoi) is calculated by the following equation (2).
ratio (Uoi) = (Uoi−Min (Uoi)) / Max (Uoi) −Min (Uoi) (2)
From the above equation (2), this saturation ratio ratio (Uoi) takes a value from 0 to 1.

  Then, the RGB input image data, the hue angle Hue, the normalized value Uoi, and the saturation ratio ratio (Uoi) of each section no (i) obtained by the saturation amount distribution information calculation means 6 and the saturation ratio calculation means 7. ) Is stored in the storage means as a list as shown in FIG. Note that the hue in the color space of the RGB input image data is calculated as a chroma distribution ratio ratio (Uoi) in the hue section after the movement when conversion / movement is required for sensory inspection or the like.

The saturation range information calculation unit 8 divides the hue in the CMYK color space of the color gamut of the output device 5 into a plurality of angles, and obtains the outermost saturation that can reproduce the hue angle Hue for each section.
Specifically, the color sample of CMY100% combined which becomes the outermost saturation of the printer is color-measured, and the outermost saturation for each hue (Hue) is calculated from the colorimetric value.
As shown in FIG. 6, the CMY100% combination color sample refers to a sample composed of M100% → MY100% → Y100% → CY100% → C100% → CM100% → M100%.
When the color of the sample of FIG. 6 is measured, it is as shown in FIG. Each is divided into hues, and the outermost saturation is calculated. Then, the calculated outermost saturation is stored in the storage means as correspondence table information.

  The Hue information and outermost saturation information on the output device 5 side are also shown in the table shown in FIG. It should be noted that the manner of dividing the hue in the CMYK color space may not match the hue division of the RGB color space in the saturation amount distribution information calculation means 6.

The corrected saturation value calculation means 9 is based on the saturation ratio ratio (Uoi) obtained by the saturation ratio calculation means 7 and the outermost saturation obtained by the saturation range information calculation means 8. A corrected saturation value (C ′) for each hue that is within the range of saturation 0 to the outermost saturation is calculated while maintaining (Uoi). In this embodiment, the product value of the saturation ratio ratio (Uoi) and the outermost saturation of the output device 5 is used as the corrected saturation value (C ′), and is calculated using the following equation (3).
Corrected saturation value (C ′) = ratio (Uoi) × outermost saturation (3)

  The image data output means 10 sets the RGB → CMYK color conversion table by using the CMYK value that can reproduce the corrected saturation value (C ′) obtained by the corrected saturation value calculation means 9 as the value of the color conversion table. It is created and output to the output device 5 as output image data.

  Next, the operation of the color conversion apparatus 4 configured as described above will be described with reference to FIG. Here, step S1 is saturation amount distribution information calculation means 6, steps S2 and S3 are saturation ratio calculation means 7, step S4 is saturation range information calculation means 8, step S5 is corrected saturation value calculation means 9, step Steps S6 and S7 correspond to the image data output means 10, respectively.

First, in step S1, the hue of the color space of the RGB input image data received from the input device 1 is divided into six angles, the LCh value of the hue angle for each section is calculated, and the saturation amount is calculated based on the LCh value. Calculate distribution information.
Next, in step S2, all data of the saturation amount distribution are normalized for each section, and normalized values Uoi in all the RGB input image data used in each section are calculated using Expression (1). Then, the process proceeds to step S3, and in step S3, a saturation ratio ratio (Uoi) between 0 and 1 in the normalized value Uoi is calculated using equation (2).

In step S4, the hue in the CMYK color space in the color gamut of the output device 5 is divided into a plurality of angles, and the reproducible outermost saturation of the hue angle Hue for each section is obtained.
In step S5, a hue that maintains the saturation ratio ratio (Uoi) based on the saturation ratio ratio (Uoi) and the outermost contour saturation and that falls within the range from saturation 0 to the outermost saturation. The corrected saturation value (C ′) for each is calculated using equation (3).

In step S6, an RGB → CMYK color conversion table is created using CMYK values that can reproduce the corrected saturation value (C ′) as values in the color conversion table, and this is used as output image data.
Next, in step S7, the output image data is output to the output device 5, whereby a printing process or the like by the output device 5 is performed.

As is apparent from the above description, in this embodiment, the input image data is kept within the saturation range of the CMYK color gamut of the output device 5 while maintaining the saturation ratio of all the hues of the RGB input image data. The output image data can be obtained by color conversion.
Thereby, color conversion can be performed so that the saturation amount distribution of the RGB input image data is reflected in the CMYK output image data having different color gamuts. As a result, the variation in the saturation of the CMYK output image data is prevented, All hue saturations can be arranged in a well-balanced manner, and collapse of the output device 5 in the color reproduction range in the high saturation portion can be prevented, and a smooth gradation in the high saturation portion can be reproduced.

Further, by calculating each design value without increasing the saturation more than necessary, it is possible to prevent occurrence of distortion of the hue line near the solid.
Furthermore, by matching specific colors without destroying the algorithm of the color conversion table, all colors can be faithfully reproduced as desired.

Next, a color conversion program will be described.
The color conversion function of the computer (color conversion device or the like) in the above embodiment is realized by a color conversion program stored in storage means (for example, ROM, HDD, or the like).
The color conversion program is read by a computer control means (CPU or the like) to send commands to each component of the computer and perform color conversion processing, for example, saturation amount distribution calculation processing by the saturation amount distribution information calculation means 6, The saturation ratio ratio (Uoi) calculation process by the saturation ratio calculation means 7, the outermost saturation calculation process by the saturation range information calculation means 8, and the corrected saturation value (C ′) by the correction saturation value calculation means 9. Calculation processing, color conversion table creation and output processing by the image data output means 10 are performed.
These color conversion processes are realized by the cooperation of a color conversion program that is software and each component of a computer (such as a color conversion apparatus) that is a hardware resource.

The color conversion program for realizing the color conversion processing of the present invention is stored in a computer ROM, hard disk, or the like, or stored in a computer-readable recording medium such as an external storage device or a portable recording medium. can do.
Examples of the external storage device include a memory expansion device that incorporates a storage medium such as a CD-ROM and is externally connected to a color conversion device or the like. On the other hand, the portable recording medium is a recording medium that can be mounted on a recording medium driving device (drive device) and is portable, and examples thereof include a flexible disk, a memory card, and a magneto-optical disk. .

Then, the program recorded on the recording medium is loaded into the RAM of the computer and executed by the CPU. By this execution, the above-described color conversion processing function of the present embodiment is realized.
Furthermore, when the color conversion program of the present invention is loaded by a computer, the color conversion program held by another computer can be downloaded to a RAM or an external storage device of its own computer using a communication line. The downloaded color conversion program is also executed by the CPU to realize the color conversion processing function of the present embodiment.

  The configurations of the input device, output device, saturation amount distribution information calculation means, saturation ratio calculation means, saturation range information calculation means, modified saturation value calculation means, image data output means, etc. of the present invention are as described above. It is not limited to what was illustrated to the form, In the range which does not deviate from the summary of this invention, it can change suitably.

  For example, in the above embodiment, the case where the color conversion device 4 is configured by a single digital image processing computer or the like has been exemplified. Alternatively, the color conversion device 4 may be mounted on an image forming apparatus such as a composite device (MFP (multifunction peripheral)) in which the output device 5, the input device 1, and the like are integrated.

1 is a block diagram of a color image processing system provided with a color conversion device for image data, which is an example of an embodiment of the present invention. 1 is a block diagram of a color conversion apparatus for image data, which is an example of an embodiment of the present invention. It is a figure which shows the state which divided the input image data in all the hues by several hue angles. It is a graph which shows distribution of the saturation value in one hue angle. It is a chart which shows each value of correspondence table information. It is a figure which shows a CMY100% combination color sample. It is a figure which shows the result of having measured color of the color sample shown in FIG. It is a flowchart for demonstrating operation | movement of the color conversion apparatus which is an example of embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input device 4 Color converter 5 Output device 6 Saturation amount distribution information calculation means 7 Saturation ratio calculation means 8 Saturation range information calculation means 9 Modified saturation value calculation means 10 Image data output means

Claims (5)

Input image data received from an input device is converted into a color space corresponding to the color gamut of the output device, and is a color conversion device for image data to be output to the output device,
Saturation amount distribution information calculating means for calculating distribution information of saturation amounts for each hue in the color space of the input image data;
Saturation ratio calculation means for calculating the saturation ratio of each hue based on the saturation amount distribution information,
Saturation range information calculating means for calculating and holding outermost saturation as reproducible range area information for each hue in the color space of the color gamut of the output device,
Based on the saturation ratio and the range information, a corrected saturation value calculation means for calculating a corrected saturation value for each hue that falls within the saturation range while maintaining the saturation ratio;
Image data output means for creating output image data based on the corrected saturation value and outputting the output image data to the output device;
Equipped with a,
The saturation ratio calculation means performs saturation value normalization for each hue category, and calculates a saturation ratio for each hue,
The modified saturation value calculating means multiplies the saturation ratio and the outermost saturation for each hue, and uses the product obtained by the multiplication as the modified saturation value in the hue. A color conversion device for image data. 2. The saturation amount distribution information calculation unit divides a hue of a color space of the input image data into a plurality of angles, and calculates saturation amount distribution information for each of the divided hues. A color conversion apparatus for image data as described. The saturation range information calculation unit divides the hue in the color space of the color gamut of the output device into a plurality of angles, and calculates and holds reproducible range information for each divided hue. The color conversion apparatus for image data according to claim 1 or 2 . A method for converting the input image data received from the input device into a color space corresponding to the color gamut of the output device and outputting the image data to the output device,
Saturation amount distribution information calculation processing for calculating saturation amount distribution information for each hue in the color space of the input image data,
Saturation ratio calculation processing for calculating the saturation ratio of each hue based on the saturation amount distribution information,
Saturation range information calculation processing for calculating and holding the outermost saturation as reproducible range area information for each hue in the color space of the color gamut of the output device,
Based on the saturation ratio and the range information, a corrected saturation value calculation process for calculating a corrected saturation value for each hue so as to be within the saturation range while maintaining the saturation ratio;
Creating output image data based on the corrected saturation value, and outputting the output image data to the output device; and
Equipped with a,
In the saturation ratio calculation process, the saturation value is normalized for each hue category, and the saturation ratio of each hue is calculated.
In the modified saturation value calculation process, for each hue, the saturation ratio and the outermost saturation are multiplied, and a product obtained by the multiplication is used as the modified saturation value in the hue. Color conversion method for image data. A color conversion program that converts input image data received from an input device into a color space corresponding to the color gamut of the output device, and causes the color conversion device to execute color conversion processing of the image data output to the output device. And
Saturation amount distribution information calculation processing for calculating saturation amount distribution information for each hue in the color space of the input image data,
Saturation ratio calculation processing for calculating the saturation ratio of each hue based on the saturation amount distribution information,
Saturation range information calculation processing for calculating and holding the outermost saturation as reproducible range area information for each hue in the color space of the color gamut of the output device,
Based on the saturation ratio and the range information, a corrected saturation value calculation process for calculating a corrected saturation value for each hue so as to be within the saturation range while maintaining the saturation ratio;
Creating output image data based on the corrected saturation value, and outputting the output image data to the output device; and
To the color conversion device ,
In the saturation ratio calculation process, the saturation value is normalized for each hue category, and the saturation ratio of each hue is calculated respectively.
In the modified saturation value calculation process, for each hue, the saturation ratio and the outermost saturation are multiplied, and a product obtained by the multiplication is used as the modified saturation value in the hue. A color conversion program for image data.

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