JP2012119968A - Image processing device and image processing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing device and an image processing program which color an achromatic image and execute color conversion processing while suppressing lowering of accuracy of color conversion of a chromatic image.SOLUTION: The image processing device comprises: color conversion means 100 and 101 which convert an input RGB signal Sof an image to plural signals written in the form of a uniform color space by using plural conversion matrixes respectively corresponding to plural degrees of saturation; saturation calculation means 102 which calculates the saturation of one of the plural color-converted signals; mixture ratio determination means 103 which determines a mixture ratio from the saturation calculated by the saturation calculation means 102; and signal mixture means 104 which mixes the plural signals color-converted by the color conversion means with the mixture ratio determined by the mixture ratio determination means 103.

Description

  The present invention relates to an image processing apparatus and an image processing program.

  A technique for executing color correction processing according to the type of image has been proposed.

  As a technology related to this, Patent Document 1 discloses an input color correction unit that corrects the signal intensity of a color component of an image input using a matrix coefficient, and a memory that stores a plurality of matrix coefficients corresponding to the type of image. An image processing apparatus is disclosed that includes a control unit that reads out a matrix coefficient corresponding to the type of an input image and sets the matrix coefficient in the input correction unit.

JP 2004-23401 A

  An object of the present invention is to provide an image processing apparatus and an image processing program for performing color conversion processing while coloring an achromatic image and suppressing deterioration in color conversion accuracy of a chromatic image. It is in.

[1] A color for converting an input signal of an image into a plurality of signals in a uniform color space using a plurality of conversion matrices respectively corresponding to a plurality of predetermined saturations for the saturation of the input signal of the image Conversion means;
Saturation calculating means for calculating the saturation of any of the plurality of signals after the color conversion;
Mixing ratio determining means for determining a mixing ratio based on the saturation calculated by the saturation calculating means;
An image processing apparatus comprising: a signal mixing unit that mixes the plurality of signals color-converted by the color conversion unit at the mixing ratio determined by the mixing ratio determination unit.

[2] The image processing device according to [1], wherein the saturation calculation unit calculates a saturation of the input signal.

[3]
Color conversion means for converting the input signal of the image into a plurality of signals in a uniform color space using a plurality of conversion matrices respectively corresponding to a plurality of predetermined saturations for the saturation of the input signal of the image; ,
Saturation calculating means for calculating the saturation of any of the plurality of signals after the color conversion;
Mixing ratio determining means for determining a mixing ratio based on the saturation calculated by the saturation calculating means;
An image processing program for functioning as a signal mixing unit that mixes the plurality of signals color-converted by the color conversion unit at the mixing ratio determined by the mixing ratio determination unit.

  According to the first or third aspect of the invention, it is possible to execute the color conversion process while suppressing the coloring of the achromatic image and the decrease in the color conversion accuracy of the chromatic image.

  According to the second aspect of the invention, the mixture ratio can be determined from the mixture ratio table based on the saturation.

FIG. 1 is a block diagram illustrating a configuration example of an image processing apparatus. FIG. 2 is a graph showing an example of the characteristics of the mixture ratio table 113. FIG. 3 is a flowchart illustrating an operation example of the image processing apparatus 1. FIG. 4 is a graph showing another example of the characteristics of the mixture ratio table 113.

(Configuration of image processing apparatus)
FIG. 1 is a block diagram illustrating a configuration example of an image processing apparatus.

The image processing apparatus 1 is provided in, for example, a printer function unit or a scanner function unit of a printer, a scanner, or a multifunction machine, and outputs an input RGB signal S _in input from an input unit 12 by a signal processing operation of the control unit 10. The signal is converted into a Lab signal S _out and output to the output unit 13. The input RGB signal S _in is a device-specific signal that depends on the characteristics of the input unit 12, and the output Lab signal S _out is a signal expressed in a uniform color space that does not depend on the device. Note that the Lab signal expressed in the uniform color space includes a parameter L indicating brightness, and parameters a and b indicating hue and provisional saturation.

  The control unit 10 is a CPU (Central Processing Unit) or the like having a function for processing information, and includes a first color conversion unit 100, a second color conversion unit 101, a saturation calculation unit 102, and a mixture ratio determination. It operates as the means 103 and the signal mixing means 104.

The first color conversion means 100 executes a color conversion process suitable for the low saturation RGB signal on the input RGB signal S _in using the low saturation color conversion matrix 111 described later, and the first Lab signal S ₁ is output. The color conversion process suitable for RGB signals with low saturation is a process that suppresses a chromatic color due to color conversion when the RGB signal is an achromatic color.

The second color conversion means 101 executes a color conversion process suitable for the high-saturation RGB signal on the input RGB signal S _in using a high-saturation color conversion matrix 112 described later, and outputs a _second Lab signal S ₂ . . The color conversion process suitable for RGB signals with high saturation is a process in which the color conversion accuracy is suppressed from decreasing for high saturation colors. In general, when a process that suppresses a chromatic color due to color conversion is executed as in the case where the RGB signal described above is an achromatic color, the color conversion accuracy decreases. For this reason, color conversion processing suitable for RGB signals with high saturation and color conversion processing suitable for RGB signals with low saturation are processing in which the results of color conversion do not match.

Chroma calculation unit 102 calculates the provisional saturation c from the second Lab signal _{S 2.}

  The mixture ratio determining means 103 determines the mixture ratio r from the mixture ratio table 113 described later based on the provisional saturation c.

Signal mixing means 104 mixes the first Lab signal _{S 1} and the second Lab signal _{S 2} on the basis of the mixing ratio r.

  The storage unit 11 is a storage medium such as an HDD (Hard Disk Drive) or a flash memory, and an image processing program 110 that causes the control unit 10 to operate as the above-described means 100 to 104 and a color suitable for RGB signals with low saturation. A low saturation color conversion matrix 111 used for conversion processing, a high saturation color conversion matrix 112 used for color conversion processing suitable for high saturation RGB signals, and a mixing ratio table 113 that associates provisional saturation c and mixing ratio r. And store.

The input unit 12 is, for example, an image sensor such as a charge coupled device (CCD), and outputs an input RGB signal S _in as a result of imaging.

The output unit 13 is, for example, a printer, a scanner, or a printer function unit of a multifunction peripheral or an image processing module of the scanner function unit, and executes image processing on the output Lab signal S _out .

(Operation of image processing device)
Hereinafter, the operation example of the image processing apparatus 1 will be described by dividing into (1) color conversion operation, (2) mixing ratio determination operation, and (3) mixing operation, with reference to FIGS.

  FIG. 3 is a flowchart illustrating an operation example of the image processing apparatus 1.

(1) Color Conversion Operation First, the first color conversion unit 100 of the image processing apparatus 1 receives the input RGB signal S _in input from the input unit 12, and the color conversion matrix 111 for low saturation in the storage unit 11. As a matrix K, a color conversion process is executed on the input RGB signal S _in to output a _first Lab signal S ₁ (S1).

The second color conversion unit 101 receives the input RGB signal S _in input from the input unit 12 and uses the matrix K ′ as the high-saturation color conversion matrix 112 of the storage unit 11 to convert the input RGB signal S _in to the input RGB signal S _in . run the color conversion processing, and outputs a second Lab signal _{S 2} (S2).

The first and second color conversion processes are executed by, for example, the following formulas (1) and (2).

S _offset and S ′ _offset are offset values.

(2) Mixing Ratio Determination Operation Next, the saturation calculation unit 102 calculates the temporary saturation c by the following formula (3) based on the _second Lab signal S2 (S3).

  Next, the mixture ratio determining means 103 determines the mixture ratio r from the mixture ratio table 113 described later based on the provisional saturation c (S4).

  FIG. 2 is a graph showing an example of the characteristics of the mixture ratio table 113.

Mixing ratio r, as described in Equation (4) described later, which defines a first Lab signal _{S 1} and the second Lab signal ratio of mixing of _{S 2,} the first Lab signal as r is greater the ratio of the second Lab signal _{S 2} becomes larger than the S _1. That is, the second fraction of the Lab signal S ₂ is increased when the provisional saturation c is large, the first fraction of the Lab signals S ₁ is increased when the provisional saturation c is small.

(3) mixing operation signal mixing means 104, first Lab signal _{S 1} and the second Lab signal _{S 2} are mixed outputs the output Lab signal _{S out} on the basis of the mixing ratio r (S5). The output Lab signal S _out is determined by the following equation (4).

By mixing the first Lab signal S ₁ and the second Lab signal S ₂ according to Equation (4) described above, the color conversion processing which suppresses placing a color for low saturation image is performed It was first to increase the weighting of the Lab signal S _1, also with respect to the high saturation image second color conversion processing which suppresses reducing the color conversion accuracy is performed in the Lab signal S ₂ Increase the weight.

[Other embodiments]
The present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the present invention. For example, the number of color conversion means is not limited to two, and a plurality of color conversion means may be prepared according to the saturation of the signal. In that case, the above formula (4) is replaced with the following formula (5).

Additional _r 1 ~r _n are defined as in FIG. 4 in the following by the mixing ratio table 113.

  FIG. 4 is a graph showing another example of the characteristics of the mixture ratio table 113.

The mixing ratio _r 1 ~r _n is for determining the ratio of mixing of the first Lab signals ~ Lab signal of the n, to increase the percentage of optimized Lab signal provisional saturation c.

  Further, the saturation calculation means 102 calculates the provisional saturation c by applying the formula (3) again to (L, a, b) obtained by the formula (4), and again by the formula (4) ( Saturation calculation may be repeated until c converges to a certain value, such as obtaining L, a, b).

The saturation calculation unit 102 is arranged immediately after the input unit 12 and before the first color conversion unit 100 and the second color conversion unit 101, and inputs the output to the mixture ratio determination unit 103. It may be a thing. In this case, the saturation calculation unit 102 is obtained from the difference between the maximum value and the minimum value of the R signal, the G signal, and the B signal by using the following formula (6). This is because the difference between the maximum value and the minimum value is close to 0 in the case of an achromatic color.

  The calculation using the formula (6) has a smaller processing load than the formula (3). The difference in processing load is calculated by software (image processing program 110) as in the present embodiment, compared to the case where the saturation calculation unit 102 is configured by hardware and executed. The effect is great in some cases.

  Further, as described above, the saturation calculation unit 102 is provided immediately after the input unit 12 and before the color conversion units 100 and 101 and after the color conversion units 100 and 101. The calculation means performs the saturation calculation by the above equation (6), and then the Lab signal subjected to the color conversion processing suitable for the saturation determined by the previous saturation calculation means, that is, the color conversion means 100 or The saturation calculation accuracy may be improved by calculating the provisional saturation according to Equation (3) by the subsequent saturation calculation means for the signal output from any one of 101.

  In this embodiment, attention is paid to the saturation of the signal, but the mixing ratio of the color conversion means may be changed according to the type of color.

  The image processing program 110 can be provided by being stored in a storage medium such as a CD-ROM, and can be downloaded from a server device connected to a network such as the Internet to a storage unit in the device. Good. Further, some or all of the first color conversion unit 100, the second color conversion unit 101, the saturation calculation unit 102, the mixing ratio determination unit 103, and the signal mixing unit 104 may be realized by hardware such as an ASIC. Good. Note that each step shown in the operation description of the above embodiment can be changed in order, omitted or added.

DESCRIPTION OF SYMBOLS 1 Image processing apparatus 10 Control part 11 Storage part 12 Input part 13 Output part 100 1st color conversion means 101 2nd color conversion means 102 Saturation calculation means 103 Mixing ratio determination means 104 Signal mixing means 110 Image processing program 111 Low Saturation color conversion matrix 112 High saturation color conversion matrix 113 Mixing ratio table

Claims (3)

Color conversion means for converting the input signal of the image into a plurality of signals in a uniform color space using a plurality of conversion matrices respectively corresponding to a plurality of predetermined saturations for the saturation of the input signal of the image; ,
Saturation calculating means for calculating the saturation of any of the plurality of signals after the color conversion;
Mixing ratio determining means for determining a mixing ratio based on the saturation calculated by the saturation calculating means;
An image processing apparatus comprising: a signal mixing unit that mixes the plurality of signals color-converted by the color conversion unit at the mixing ratio determined by the mixing ratio determination unit.   The image processing apparatus according to claim 1, wherein the saturation calculation unit calculates a saturation of the input signal. Computer
Color conversion means for converting the input signal of the image into a plurality of signals in a uniform color space using a plurality of conversion matrices respectively corresponding to a plurality of predetermined saturations for the saturation of the input signal of the image; ,
Saturation calculating means for calculating the saturation of any of the plurality of signals after the color conversion;
Mixing ratio determining means for determining a mixing ratio based on the saturation calculated by the saturation calculating means;
An image processing program for functioning as a signal mixing unit that mixes the plurality of signals color-converted by the color conversion unit at the mixing ratio determined by the mixing ratio determination unit.

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