JP2001292332A - Color correction method, color correction device, and recording medium recording color correction control program - Google Patents

Abstract

(57) [Problem] It is an object of the present invention to provide a color correction method, a color correction device, and a recording medium in which a color correction control program is recorded, which can automatically and appropriately correct a color. A color correction device according to the present invention corrects color of color image data representing a color image by a plurality of component color components based on a color conversion table. First, the saturation calculation circuit 20
a, a value for each component color component of the color image data is calculated, and a predetermined value for each component color component is calculated by the gray histogram creation circuit 20b and the average value calculation circuit 20c based on the value for each component color component. Is calculated so as to eliminate the difference from the reference value. Then, the LUT creation / incorporation circuit 20d generates the color conversion table for each element color component based on the color correction amount, and incorporates the generated color conversion table into the color correction device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color correction method for creating a color conversion table for executing optimal color correction on real image data such as a digital photographic image and incorporating the same into an input / output device. The present invention relates to a color correction device incorporating the color conversion table and a recording medium recording a control program for creating the color conversion table and incorporating the color conversion table into an input / output device.

[0002]

2. Description of the Related Art As an image processing apparatus for handling high-quality image data using a computer or the like, light is converted into an electric signal by an image pickup process such as a CCD, and the electric signal is converted into digital data to convert the light into a digital data. 2. Description of the Related Art Digital cameras that record data on a recording medium are known. With a digital camera, image data can be stored and various processes can be easily performed by an individual using a personal computer or the like.
By outputting image data to a printer, a photograph can be printed without developing the film. 2. Description of the Related Art Improvements in the printing quality of printers have made it possible to print high-quality photographs that are almost indistinguishable from silver halide photographs.

[0003]

However, as described in Japanese Patent Application Laid-Open No. H11-120325, according to the object sampling method in the conventional input device, only the edge pixels of the image are subjected to the color correction processing. In the case where the subject is a person dressed in a high-saturated color pattern, there is a possibility that accurate color correction cannot be performed. Images obtained from such an input device such as a conventional digital camera often have a so-called color cast due to the influence of a light source characteristic and an automatic white balance characteristic of the camera. Especially in the case of red-colored clothes,
The color correction device determines that the red cast is strong, and the color correction device corrects the color in the cyan direction and cannot appropriately correct the skin color and the like. In the case of the conventional color correction device, it is very difficult to appropriately correct such a color cast by software.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a color correction method, a color correction device, and a recording medium on which a color correction control program is recorded which can automatically and appropriately correct a color. That is the task.

[0005]

SUMMARY OF THE INVENTION In view of the above problems, the invention according to claim 1 is a color correction apparatus for correcting a color image data representing a color image by a plurality of component color components based on a color conversion table. A correction method, comprising: an element color component value calculation step of calculating a value for each element color component of the color image data; and a value for each element color component calculated by the element color component value calculation step. A color correction amount calculating step of calculating a color correction amount that eliminates a difference from a predetermined reference value for each element color component; and a color correction amount calculated by the color correction amount calculating step. A color conversion table generating step of generating the color conversion table for each color component; and a color conversion table incorporating step of incorporating the color conversion table generated by the color conversion table generating step into the color correction device. It is made.

[0006] According to the color correction method in the color correction apparatus configured as described above, which corrects color image data representing a color image by a plurality of component color components based on a color conversion table, first, the component color component values are set. The calculation step calculates a value for each element color component of the color image data, and the color correction amount calculation step calculates a value for each element color component based on the value for each element color component calculated in the element color component value calculation step. A color correction amount that eliminates a difference from a predetermined reference value for each color component is calculated. Then, in the color conversion table generation step, the color conversion table is generated for each element color component based on the color correction amount calculated in the color correction amount calculation step, and the color conversion table is incorporated in the color conversion table. The color conversion table generated by the conversion table generation step is incorporated in the color correction device.

[0007] The invention described in claim 2 is the first invention.
Wherein the element color component value calculation step is configured to calculate a value for each element color component of the color image data for a pixel having an element color component close to a gray area. .

Further, according to a third aspect of the present invention, in the color correction method according to the second aspect, in the element color component value calculation step, the element color component value with respect to a minimum value of an element color component of a predetermined pixel is determined. When the ratio of the maximum values of the color components is smaller than the first threshold value, the pixel is determined to be a pixel having an element color component close to the gray area.

The invention described in claim 4 is the same as the invention described in claim 2.
Alternatively, in the color correction method described in 3, the element color component value calculation step is configured such that a pixel having a luminance larger than a second threshold is set as an element color component calculation target.

Further, according to a fifth aspect of the present invention, there is provided a color correcting step according to any one of the second to fourth aspects,
The color correction amount calculation step calculates an average value for each element color component of the color image data based on the value for each element color component calculated in the element color component value calculation step, and calculates the average value and It is configured to obtain a color correction amount that eliminates a difference from a predetermined reference value.

[0011] The invention described in claim 6 is the invention according to claim 2.
Wherein the element color component value calculating step calculates a value for each element color component of the color image data by dividing the color image data into two or more luminance areas, and the color correction amount calculating step includes: It is configured to calculate a color correction amount that eliminates a difference from a predetermined reference value for each element color component for each of the divided luminance regions.

Further, according to a seventh aspect of the present invention, in the color correction method according to the sixth aspect, the element color component calculation step includes the step of calculating the element color component with respect to a minimum value of the element color component of a predetermined pixel. When the ratio of the maximum values of the components is smaller than a predetermined threshold, the pixel is determined to have a component color component close to the gray area.

The invention described in claim 8 is the same as the claim 6.
Or the color correction step according to 7, wherein the color correction amount calculation step is based on the value for each element color component calculated in the element color component value calculation step and for each of the divided luminance areas, An average value for each element color component of the image data is calculated, and a color correction amount that eliminates a difference between the average value and a predetermined reference value is obtained.

[0014] In view of the above problem, an invention according to claim 9 is a color correction apparatus for correcting a color image data representing a color image by a plurality of component color components based on a color conversion table, Element color component value calculating means for calculating a value for each element color component, and a value for each element color component calculated by the element color component value calculating means.
A color correction amount calculating unit that calculates a color correction amount that eliminates a difference from a predetermined reference value for each element color component; and a color correction amount calculated by the color correction amount calculating unit. A color conversion table generating unit that generates the color conversion table for each color component; and a color conversion table incorporation unit that incorporates the color conversion table generated by the color conversion table generating unit into the color correction device. Is done.

According to the color correction apparatus configured as described above, which corrects color image data representing a color image by a plurality of element color components based on a color conversion table, first, the element color component value calculation means uses: A value for each element color component of the color image data is calculated, and a color correction amount calculation unit calculates a value for each element color component based on the value for each element color component calculated by the element color component value calculation unit. A color correction amount that eliminates a difference from a predetermined reference value is calculated. Then, based on the color correction amount calculated by the color correction amount calculating means, the color conversion table is generated for each of the component color components by the color conversion table generating means, and the color conversion table is incorporated by the color conversion table incorporating means. The color conversion table generated by the conversion table generating means is incorporated in the color correction device.

In view of the above-mentioned problem, the invention according to claim 10 executes, on a computer, a color correction process in a color correction apparatus that corrects color image data representing a color image by a plurality of component color components based on a color conversion table. A computer-readable recording medium having recorded thereon a program for causing the computer to execute a program for calculating a value for each element color component of the color image data, and calculating the element color component value by the element color component value calculation processing. A color correction amount calculation process of calculating a color correction amount that eliminates a difference from a predetermined reference value of each element color component based on the calculated value of each element color component, and a color correction amount calculation process. A color conversion table generation process for generating the color conversion table for each element color component based on the calculated color correction amount, and a color conversion table generation process Recorded readable constituted by a computer program for executing a color conversion table embedded process incorporating a color conversion table in the color correction device, to the computer.

On the recording medium readable by the computer constructed as described above, a color correction process in a color correction apparatus for correcting color image data representing a color image by a plurality of component color components based on a color conversion table. In a computer. Then, by executing the program, first, a value for each element color component of the color image data is calculated by element color component value calculation processing, and the color correction amount calculation processing
Based on the values for each element color component calculated by the element color component value calculation processing, a color correction amount that eliminates a difference from a predetermined reference value for each element color component is calculated. And
The color conversion table generation processing generates the color conversion table for each element color component based on the color correction amount calculated by the color correction amount calculation processing, and the color conversion table The color conversion table generated by the generation process is incorporated in the color correction device.

[0018]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

First Embodiment FIG. 1 is a diagram for explaining the structure of a digital camera 100 according to a first embodiment of the present invention, in which a color conversion table for executing optimal color correction on real image data is incorporated. It is a block diagram of. The digital camera 100
Is a control unit 111, a condenser lens 112, a CCD (Charge Coupled Device) 113 as an imaging process, and an A / D converter 1.
14. RAM (Random Access Memory) for temporarily storing image data and storing the color conversion table.
ory) 115, a flash memory 116 for recording image data, a liquid crystal display (LCD) 117 for displaying images,
VRAM (Video RAM) 118 for storing data for images displayed on the liquid crystal display device, flash memory 11
6 is provided with an interface 119 for outputting the content of No. 6 to an external device. The digital camera 1
Reference numeral 00 denotes an LUT creation / color correction control circuit 2 for creating a color conversion table for executing optimal color correction and performing optimal color correction using the color conversion table.
0 and a color correction selection circuit 120 for selecting whether or not to perform color correction by the LUT creation / color correction control circuit. When the color correction selection circuit 120 selects the color correction by the LUT generation / color correction control circuit 20, the color correction is performed by the LUT generation / color correction control circuit 20, which will be described in detail later, and the LUT generation / color correction is performed. If the color correction by the control circuit 20 is not selected, the A / D converter 11
4 is supplied directly to the RAM 115.

The control unit 111 includes a CPU and an image processing control program for the digital camera 100.
The digital camera 100 includes an OM and an input / output step, and controls other devices provided in the digital camera 100. One control unit 111
Instead of performing all the controls, a plurality of control units may be provided. The condenser lens 112 is provided with an aperture 121 for adjusting the amount of light input to the condenser lens 112.

As the RAM 115, a DRAM (Dynamic RAM) having a self-refresh function is used. The flash memory 116 is a rewritable recording medium capable of holding recorded contents without power supply, and is built in the digital camera 100 or is detachably attached to the digital camera 100. For example, by using a memory card conforming to the PCMCIA standard or a memory card attachable to a PCMCIA card adapter as the flash memory 116, a personal computer having a PCMCIA card slot can
6 can be read and written directly.

A control program for creating a color conversion table and incorporating it into a digital camera according to the present invention is usually recorded in a computer-readable form on a recording medium such as a floppy (registered trademark) disk or CD-ROM. And circulate. The program is read by the media reading device and written in the ROM in the control unit 111. The LUT creation / color correction control circuit 20 is configured to read a desired program from the ROM as appropriate and execute a desired process.

FIG. 2 shows an LU according to the first embodiment of the present invention.
FIG. 2 shows a functional block diagram of a T creation / color correction control circuit 20.

As shown in FIG. 2, the LUT creation / color correction control circuit 20 converts the input real image data (real image data represented as pixels in a dot matrix such as a photograph) according to an operation mode. A data input switching circuit 20f for supplying to the saturation calculation circuit 20a and the Y value calculation circuit 20g or the color correction circuit 20e; a saturation calculation circuit 20a, a gray histogram creation circuit 20b, and an average value calculation circuit 20c; LUT creation / embedding circuit 20d,
It comprises a color correction circuit 20e and a Y value calculation circuit 20g. Details of the data processing of each component will be described later.

Second Embodiment FIG. 3 is a specific hardware diagram of a color correction system according to a second embodiment of the present invention, in which a color conversion table for executing optimal color correction on real image data is incorporated. FIG. 3 is a schematic block diagram illustrating a configuration example. In the second embodiment, as an example, a case where the color conversion table is incorporated in a driver of each input / output device will be described.

FIG. 4 shows a second embodiment of the present invention.
FIG. 2 is a block diagram of a color correction system to which an LUT (color conversion table) creation / color correction control unit is applied. In FIG.
The image input device 10 outputs actual image data (original image data) represented as pixels in a dot matrix form such as a photograph to the LUT creation / color correction control unit 20. The LUT
The creation / color correction control unit 20 performs desired color correction on the input real image data, and then outputs the color-corrected image data (color-corrected image data) to the image output device 30. The image output device 30 outputs the color-corrected image using dot matrix pixels.

As in FIG. 2, the LUT creation / color correction control unit 20 in FIG. 4 includes a data input switching unit 20f, a saturation calculation unit 20a, a gray histogram creation unit 20b, an average value calculation unit 20c, An LUT creation / incorporation unit 20d, a color correction unit 20e, and a Y value calculation unit 20g are provided. Details of the data processing of each component will be described later.

A specific example of the image input device 10 corresponds to the digital still camera 12 or the video camera 14 in FIG. A specific example of the LUT creation / color correction control unit 20 corresponds to a computer system including a computer 21, a hard disk 22, a keyboard 23, a CD-ROM drive 24, a floppy disk drive 25, and a modem 26. . A specific example of the image output device 30 corresponds to the printer 31, the display 32, and the like. The modem 26 is connected to a public telephone line and connected to an external network via the public communication line, and can download software and data.

A control program for creating a color conversion table according to the present invention and incorporating it into a color correction system is usually recorded on a recording medium such as a floppy disk or CD-ROM in a form readable by the computer 21 and distributed. . The program is a media reader (CD-R
OM drive 24, floppy disk drive 25, etc.) and installed on hard disk 22. Then, the CPU is configured to appropriately read out a desired program from the hard disk 22 and execute a desired process.

In the embodiment, a scanner 11 or a digital still camera 12 as an image input device 10 is used.
Outputs RGB (green, blue, red) gradation data as image data, and the printer 31 as the image output device 30 outputs CMY (cyan, magenta, yellow) as gradation data or adds black to the CMY (cyan, magenta, yellow). CMYK binary data is required as input. Display 3
2 requires RGB tone data as input. On the other hand, in the computer 21, the printer driver 21b and the display driver 2 corresponding to the operating system 21a, the printer 31 and the display 32
1c. The color correction processing application 21d is controlled by the operating system 21a to execute processing, and performs a predetermined color correction processing in conjunction with a printer driver 21b or a display driver 21c in which a color conversion table is incorporated as necessary. Execute. Therefore, the specific role of the computer 21 as the LUT creation / color correction control unit 20 is to input RGB tone data, create RGB tone data with optimal color correction, and create a display driver 21c. Is displayed on the display 32 through the printer driver 21.
The data is converted into binary data of CMY (or CMYK) via b and printed by the printer 31.

As described above, in this embodiment,
A computer system is incorporated between image input / output devices, and color correction is performed by incorporating a color conversion table created in a driver of each input / output device installed in the computer. A system is not required, and any system that performs desired color correction on image data may be used. For example, as shown in FIG. 5, an LUT creation / color correction control unit 20 for performing desired color correction is incorporated in the scanner 11a, and the converted image data is used to display on the display 32a or print on the printer 31a. Such a system may be used. As shown in FIG. 6, in a printer 31b that inputs and prints image data without using a computer system, an LUT creation / color correction control unit 2 that performs desired color correction on a control unit of the printer 31b.
0 may be incorporated to automatically perform desired color correction from image data input via the scanner 11b, the digital still camera 12b, the modem 26b, or the like.

Hereinafter, a control program for creating a color conversion table (LUT) and performing color correction processing in the first embodiment or the second embodiment will be described.

First Embodiment Referring now to FIG. 7, an LUT creation / color correction control circuit 20 shown in FIGS. 1 and 2 or a computer 21 shown in FIG. A control program for color conversion table (LUT) creation and color correction processing executed by the color correction control unit 20 will be described.
In the first embodiment, as an example of color cast correction, high-precision color correction is performed by targeting only pixels close to a gray area of a predetermined image as data analysis targets.

LUT creation / color correction control circuit (or unit)
The 20 operation modes include an LUT creation mode and a color correction mode. In the LUT creation mode, the data input switching circuit (or unit) 20f supplies the input image data to the saturation calculation circuit (or unit) 20a and the Y value calculation circuit (or unit) 20g. Then, after processing the image data in the gray histogram creation circuit (or unit) 20b and the average value calculation circuit (or unit) 20c, the LU
After a desired color conversion table is created in the T creating / embedding circuit (or unit) 20d, the color conversion table is
It is incorporated in a color correction circuit (or unit) 20e that actually corrects the color of the input image data. On the other hand, in the color correction mode, the data input switching circuit (or unit) 20f supplies the input image data to the color correction circuit (or unit) 20e. The color correction circuit (or unit) 20e performs a desired color correction using a color conversion table created and incorporated by the LUT creation / incorporation circuit (or unit) 20d.

1) Processing in LUT creation mode First, the saturation calculation circuit (or section) 20a of the LUT creation / color correction control circuit (or section) 20 according to the present invention is supplied from the data input switching circuit (or section) 20f. The saturation Sat is obtained from the RGB values of each pixel of the image data to be processed (step 40). Sat is obtained by Sat = 256 × (I−i) / (I + i). Here, I is defined by I = max {R, G, B}, and is the maximum value among the RGB values of each pixel. I is defined as i = min {R, G, B}, and is the minimum value among the RGB values of each pixel.

Then, the Y value calculation circuit (or unit) 20g
Calculates the reference value Y from the RGB values of each pixel of the image data supplied from the data input switching circuit (or unit) 20f (step 41). The reference value Y is a value calculated by Y = (R + G + B) / 3. The definition of the reference value Y in this way means that the ideal gray image satisfies R = G = B, so that the reference value is based on a value obtained by adding the respective colors for the time being.

Next, in the gray histogram creation circuit (or unit) 20b of the LUT creation / color correction control circuit (or unit) 20 according to the present invention, Sat is smaller than thS and Y
Is greater than or equal to 128 (step 4).
2). Here, thS is a threshold value for determining whether or not the predetermined pixel is a pixel near gray, and when Sat is smaller than thS, it is determined that the predetermined pixel is a pixel near gray. Data analysis. The reason why Y> 128 is set in step 42 is to calculate the average value of the reference value Y only for an area having a high lightness that is sensitive to the gray component. If Sat is smaller than thS and Y is larger than 128 (Yes in step 42), the RGB value and the Y value of each pixel are added to the histogram (step 44).

The above steps 40 and 4 are performed for all the pixels.
The processes of steps 40, 41, 42 and 44 are repeated until the processes of 1, 42 and 44 are completed. When the processing of steps 40, 41, 42 and 44 is completed for all the pixels (step 46, Yes), the gray histogram is completed, and the processing by the gray histogram creation circuit (or unit) 20b ends. In addition,
In performing the addition, totaling is performed on all pixels while moving the target pixel as shown in FIG. Next, the gray histogram creation circuit (or section)
When the processing by 20b is completed, the average value calculation circuit (or unit) 20c calculates R
The average value of the GB values and the average value of the Y values are obtained (step 50), and the characteristics of the RGB distribution of the image can be known. For example, the average value of R

[0039]

(Equation 1) Is given by j _Rg

[0040]

(Equation 2) Is required. Similarly,

[0041]

(Equation 3)

(Equation 4) And so on. In addition, the average of the reference values

[0042]

(Equation 5) Can also be requested.

When the processing by the average value calculation circuit (or unit) 20c is completed, the LUT creation / embedding circuit (or unit)
20d is the RGB average value obtained in step 50;
A correction LUT (lookup table) is created based on the difference between the reference value Y and the average value (step 52). For example, the difference for Red is

[0044]

(Equation 6) Required by As shown in FIG.
Is created by shifting the control point by the difference value and smoothly interpolating with a spline curve passing through the three points of the gradation “0”, the gradation “255”, and the shifted control point. Similarly, the difference ΔGg between green and blue
And ΔBg are also determined.

As described above, when the creation of the correction LUT (look-up table) by the LUT creation / embedding circuit (or unit) 20d (step 52) is completed, the LUT
The creation / incorporation circuit (or unit) 20d incorporates the created correction LUT into the color correction circuit (or unit) 20e (step 53), and ends the processing in the LUT creation mode.

2) Processing in the Color Correction Mode In the color correction mode, the image data supplied from the data input switching circuit (or unit) 20f is processed by the color correction circuit (or unit) 20e (step in FIG. 9). 5
4 and 56) are performed. That is, the color correction circuit (or unit) 20e is an LUT creation / incorporation circuit (or unit).
An RGB value after correction (after color correction) is obtained based on the correction LUT created and incorporated by 20d (step 54). When step 54 is completed for all the pixels (step 56, Yes), the processing in the color correction mode for the color image data is completed.

Next, the processing of FIG. 7 will be described by applying it to a specific example.

FIG. 11 shows an example of the gray histogram created after the processing in steps 40 to 46 of FIG. In the specific example, the threshold value thS of Sat for determining a pixel in the vicinity of gray in step 42 is thS = 32. The value of ThS is obtained by back calculation from the degree of color cast to be corrected. In other words, a pixel having a saturation of thS = 32 or more is less affected by color cast and is determined to be substantially the original color. In the case of the gray histogram shown in FIG. 11, the green histogram (Gg) is shifted to the right and G
Fog is detected.

Then, in step 42, Sat <3
When a histogram is created only for the area of 2 and Y> 128, and each average value is calculated,

[0050]

(Equation 7) Becomes

The tone curve of the correction LUT shown in FIG. 10 passes through three points of gray scale "0", gray scale "255", and the control point when the control point is 3/4 tone (gray scale "192"). It is obtained by smooth interpolation with a spline curve.

The tone curve control amounts are respectively

[0053]

(Equation 8) Becomes The corrected RGB tone curve (LUT) is shown in FIG.
It becomes as shown in. By the RGB correction tone curve, green is weakened, and green cast in the original image is reduced in the output image. As described above, according to the first embodiment, aggregation is performed on pixels having element color components close to the gray region having high brightness, and the color image is calculated according to the color correction amount calculated based on the aggregated pixels. Color correction circuit (or unit) for LUT for color correction of data
Since the built-in color correction is performed on the image 20e, it is possible to reduce the influence of unnecessary image portions such as a background of high chroma colors and clothes, and to automatically perform appropriate color correction with high accuracy.

Second Embodiment Referring now to FIG. 13, the LUT creation / color correction control circuit 20 of FIG. 1 and FIG. 2 or FIG.
A control program for color conversion table (LUT) creation and color correction processing executed by the LUT creation / color correction control unit 20 constituted by the computer 21 will be described. In the second embodiment, as a second example of the color cast correction, the correction amount is determined for each of the divided luminance areas and the correction R is determined.
A more detailed color correction is performed by generating a GB tone curve. In the present embodiment, the brightness area is represented by a gray level, and a shadow area (shadow: 0 to 64 gray levels), a midtone area (mid: 64 to 128 gray levels), and a highlight area (highli
ght: 128 to 255 gradations) and divides into three luminance areas to obtain an average value.

As in the first embodiment, the operation modes of the LUT creation / color correction control circuit (or unit) 20 include an LUT creation mode and a color correction mode. In the LUT creation mode, the data input switching circuit (or unit) 20f supplies the input image data to the saturation calculation circuit (or unit) 20a and the Y value calculation circuit (or unit) 20g. Then, through the processing of the image data in the gray histogram creation circuit (or section) 20b and the average value calculation circuit (or section) 20c, the LUT creation / embedding circuit (or section)
After a desired color conversion table is created in 20d,
The color conversion table is incorporated in a color correction circuit (or unit) 20e that actually corrects the color of the input image data.
On the other hand, in the color correction mode, the data input switching circuit (or unit) 20f supplies the input image data to the color correction circuit (or unit) 20e. The color correction circuit (or unit) 20e is an LUT creation / embedding circuit (or unit) 2
A desired color correction is performed using the color conversion table created and incorporated according to Od.

1) Processing in LUT Creation Mode First, the saturation calculation circuit (or section) 20a of the LUT creation / color correction control circuit (or section) 20 according to the present invention is supplied from the data input switching circuit (or section) 20f. The saturation Sat is obtained from the RGB values of each pixel of the image data to be processed (step 60). Sat is obtained by Sat = 256 × (I−i) / (I + i). Here, I is defined by I = max {R, G, B}, and is the maximum value among the RGB values of each pixel. I is defined as i = min {R, G, B}, and is the minimum value among the RGB values of each pixel.

Then, the Y value calculation circuit (or unit) 20g
Calculates the reference value Y from the RGB values of each pixel of the image data supplied from the data input switching circuit (or unit) 20f (step 61). The reference value Y is a value calculated by Y = (R + G + B) / 3. The definition of the reference value Y in this way means that the ideal gray image satisfies R = G = B, so that the reference value is based on a value obtained by adding the respective colors for the time being.

Next, the gray histogram creation circuit (or unit) 20b of the LUT creation / color correction control circuit (or unit) 20 according to the present invention determines whether or not Sat is smaller than thS (step 62). Here, thS is a threshold value for determining whether or not the predetermined pixel is a pixel near gray, and when Sat is smaller than thS, it is determined that the predetermined pixel is a pixel near gray. Data analysis. If Sat is smaller than thS (step 62, Yes), the RGB value and the Y value of each pixel are added to the histogram (step 64). In the gray histogram creation circuit (or unit) 20b, for pixels satisfying Sat <thS, R, G,
Nine (3 × 3) histograms of B and one histogram of Y are created, for a total of ten histograms.

Steps 60 and 6 for all pixels
The processes of steps 60, 61, 62 and 64 are repeated until the processes of 1, 62 and 64 are completed. When the processing of steps 60, 61, 62 and 64 is completed for all pixels (step 66, Yes), the gray histogram is completed (step 68), and the processing by the gray histogram creation circuit (or unit) 20b is completed. . In addition, when performing the addition, as in the first embodiment, as shown in FIG. 8, all the pixels are counted while moving the target pixel.

Next, when the processing by the gray histogram creation circuit (or unit) 20b is completed, the average value calculation circuit (or unit) 20c outputs the luminance values obtained by dividing the average value of RGB values from the created gray histogram. It is obtained for each area (step 70), and the characteristics of the RGB distribution of the image can be known for each of the divided luminance areas. In the present embodiment, for each of R, G, and B, the brightness region is represented by a gradation, and a shadow region (shadow: 0 to 64 gradations)
An average value is obtained by dividing the image into three luminance areas of a midtone area (mid: 64 to 128 gradations) and a highlight area (highlight: 128 to 255 gradations). For example, the average value of the shadow area of R

[0061]

(Equation 9) , Average value in the midtone area

[0062]

(Equation 10) , And the average value of the highlight area

[0063]

[Equation 11] Is given by j _Rg

[0064]

(Equation 12) Is required. Similarly, G and B can be obtained for each luminance area. Furthermore, the average of the reference values for each luminance area

[0065]

(Equation 13) (Shadow area),

[0066]

[Equation 14] (Midtone area),

[0067]

(Equation 15) (Highlight area) can also be obtained.

When the processing by the average value calculation circuit (or unit) 20c is completed, the LUT creation circuit (or unit) 20d
Creates a correction LUT (lookup table) based on the difference between the RGB average value obtained in step 70 and the average value of the reference value Y (step 72). For example, the difference for Red is

[0069]

(Equation 16) (Shadow area)

[0070]

[Equation 17] (Midtone area)

[0071]

(Equation 18) (Highlight area). As shown in FIG. 14, the tone curve of the correction LUT is obtained by shifting three control points by the difference value to obtain a gradation “0” and a gradation “25”.
5 "and a spline curve that passes through a total of five shifted three control points. Similarly, green

[0072]

[Equation 19] (Shadow area)

[0073]

(Equation 20) (Midtone area)

[0074]

(Equation 21) (Highlighted area) and blue difference

[0075]

(Equation 22) (Shadow area)

[0076]

(Equation 23) (Midtone area)

[0077]

(Equation 24) (Highlight area) is also required.

As described above, when the creation of the correction LUT (look-up table) by the LUT creation / embedding circuit (or unit) 20d (step 72) is completed, the LUT
The creation / incorporation circuit (or unit) 20d incorporates the created correction LUT into the color correction circuit (or unit) 20e (step 73), and ends the processing in the LUT creation mode.

2) Processing in Color Correction Mode Processing in the color correction mode is the same as in the first embodiment. That is, in the color correction mode, the processing (steps 54 and 56 in FIG. 9) by the color correction circuit (or unit) 20e is performed on the image data supplied from the data input switching circuit (or unit) 20f. That is,
The color correction circuit (or unit) 20e obtains corrected (color corrected) RGB values based on the correction LUT created and incorporated by the LUT creation / incorporation circuit (or unit) 20d (step 54). Step 5 for all pixels
When Step 4 is completed (Step 56, Yes), the processing in the color correction mode for the color image data ends.

Next, the processing of FIG. 13 will be described by applying it to a specific example.

In this specific example, the gray scale chart (original image data) shown in FIG.
It is assumed that the data is supplied from 0 to the LUT creation / color correction control circuit (or unit) 20. Furthermore, in the specific example, the threshold value thS of Sat for determining that the pixel is a pixel near gray in step 62 is set to thS = 32. The value of thS is obtained by back calculation from the degree of color fog to be corrected. In other words, a pixel having a saturation of thS = 32 or more is less affected by color cast and is determined to be substantially the original color. When the grayscale chart shown in FIG. 15 is the original image data, each average value in each luminance area is

[0082]

(Equation 25) Becomes

The tone curve of the correction LUT shown in FIG. 14 has five control points of gradation "0", gradation "255", and three control points, where the control points are 32 gradations, 96 gradations, and 192 gradations. By smoothly interpolating with a spline curve passing through.

The tone curve control amounts are respectively

[0085]

(Equation 26) Becomes FIG. 16 shows the tone curve output correction amount. A corrected RGB tone curve (LUT) is generated based on the tone curve output correction amount. As described above, the LUT that determines the correction amount for each of the divided luminance areas and generates the corrected RGB tone curve is converted to the color correction circuit (or unit) 20e.
Since the built-in color correction is performed, more precise color balance correction can be performed.

[0086]

According to the present invention, the color conversion table for each element color component is determined based on the amount of color correction that eliminates the difference from a predetermined reference value for each element color component of the image data. Since the generated color conversion table is incorporated in the color correction device, appropriate color correction can be automatically performed.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining a structure of a digital camera 100 according to a first embodiment of the present invention, in which a color conversion table for executing optimal color correction on real image data is incorporated. .

FIG. 2 is a diagram showing an example of LUT creation and operation according to the first embodiment of the present invention.
FIG. 3 is a functional block diagram of a color correction control circuit 20.

FIG. 3 is a schematic block diagram showing a specific hardware configuration example of a color correction system according to a second embodiment of the present invention, in which a color conversion table for executing optimal color correction on real image data is incorporated. It is.

FIG. 4 is a diagram showing an example of LUT creation and operation according to a second embodiment of the present invention.
FIG. 3 is a block diagram of a color correction control unit 20.

FIG. 5 is a schematic block diagram showing another application example of the LUT creation / color correction control unit according to the second embodiment of the present invention.

FIG. 6 is a schematic block diagram showing still another application example of the LUT creation / color correction control unit according to the second embodiment of the present invention.

FIG. 7 is a flowchart for explaining processing in an LUT creation mode of the LUT creation / color correction control circuit (or unit) according to the first embodiment of the present invention.

FIG. 8 is a diagram illustrating a state in which a processing target pixel is moved.

FIG. 9 is a flowchart for explaining processing in a color correction mode of the LUT creation / color correction control circuit (or unit) according to the first embodiment of the present invention.

FIG. 10 is a diagram showing a tone curve of a correction LUT according to the first embodiment of the present invention.

FIG. 11 is an example of a gray histogram created for RGB and a reference value Y according to the first embodiment of the present invention.

FIG. 12 is a graph showing an example of a correction LUT according to the first embodiment of the present invention.

FIG. 13 is a flowchart illustrating a process in an LUT creation mode of an LUT creation / color correction control circuit (or unit) according to a second embodiment of the present invention.

FIG. 14 is a diagram showing a tone curve of a correction LUT according to a second embodiment of the present invention.

FIG. 15 shows an image input device 10 according to a second embodiment of the present invention.
3 is an example of a grayscale chart (original image data) supplied to the color correction device 20 from FIG.

FIG. 16 is a graph showing an example of a tone curve output correction amount according to the second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10 Image input device 11 Scanner 12 Digital still camera 14 Video camera 20 LUT creation / color correction control circuit (part) 20a Saturation calculation circuit (part) 20b Gray histogram creation circuit (part) 20c Average value calculation circuit (part) 20d LUT Creation / embedding circuit (part) 20e Color correction circuit (part) 20f Data input switching circuit (part) 20g Y value calculation circuit (part) 21 Computer 23 Keyboard 24 CD-ROM drive 25 Floppy disk drive 26 Modem 30 Image output device 31 Printer 32 Display 100 Digital camera 111 Control unit 112 Condenser lens 113 CCD 114 A / D converter 115 RAM 116 Flash memory 117 LCD 118 VRAM 119 Interface 120 Color correction selection circuit

Continued on the front page F term (reference) 5B057 AA11 CA01 CA08 CB01 CB07 CE16 5C066 AA01 EA05 GA01 GB03 HA03 JA03 KE09 KE17 KE19 KM02 5C077 MP01 MP08 PP15 PP32 PP33 PP35 PP37 PP46 PQ18 PQ19 PQ23 5C079 HB01 MA02 NA02 MA02

Claims (10)

[Claims] 1. A color correction method for a color correction apparatus for correcting a color image data representing a color image by a plurality of component color components based on a color conversion table, wherein a value for each component color component of the color image data is provided. And calculating, based on the values for each element color component calculated in the element color component value calculation step, a difference between a predetermined reference value for each element color component. A color correction amount calculating step of calculating a color correction amount, and a color conversion table generating step of generating the color conversion table for each element color component based on the color correction amount calculated by the color correction amount calculating step. A color conversion table incorporation step of incorporating the color conversion table generated in the color conversion table generation step into the color correction device. 2. The color correction method according to claim 1, wherein:
A color correction method, wherein the element color component value calculation step calculates a value for each element color component of color image data for a pixel having an element color component close to a gray area. 3. The color correction method according to claim 2, wherein
In the element color component value calculation step, when the ratio of the maximum value of the element color component to the minimum value of the element color component of the predetermined pixel is smaller than the first threshold value, the pixel having the element color component close to the gray area Color correction method to determine. 4. The color correction method according to claim 2, wherein said element color component value calculation step includes setting a pixel having a luminance larger than a second threshold as a target of calculation of an element color component. Method. 5. The color correction step according to claim 2, wherein the color correction amount calculation step includes calculating a value for each element color component calculated by the element color component value calculation step. A color correction method for calculating an average value for each element color component of the color image data and obtaining a color correction amount that eliminates a difference between the average value and a predetermined reference value. 6. The color correction method according to claim 2, wherein
The element color component value calculation step calculates a value for each element color component of the color image data by dividing into two or more luminance areas,
A color correction method in which a color correction amount calculating step calculates a color correction amount for each of the divided luminance regions so as to eliminate a difference from a predetermined reference value for each element color component. 7. The color correction method according to claim 6, wherein:
The element color component calculation step, when the ratio of the maximum value of the element color component to the minimum value of the element color component of a predetermined pixel is smaller than a predetermined threshold, a pixel having an element color component close to the gray region Judgment color correction method. 8. The color correction step according to claim 6, wherein the color correction amount calculation step is based on the value for each element color component calculated in the element color component value calculation step. A color correction method for calculating an average value for each of the component color components of the color image data for each of the obtained luminance areas, and obtaining a color correction amount that eliminates a difference between the average value and a predetermined reference value. 9. A color correction device for correcting a color image data representing a color image by a plurality of component color components based on a color conversion table, wherein a component for calculating a value for each component color component of the color image data is provided. A color correction value for eliminating a difference between a predetermined reference value for each element color component based on the value for each element color component calculated by the color component value calculation means; A color correction amount calculating means for calculating; a color conversion table generating means for generating the color conversion table for each element color component based on the color correction amount calculated by the color correction amount calculating means; A color conversion table incorporating means for incorporating the color conversion table generated by the generation means into the color correction apparatus. 10. A computer readable recording medium storing a program for causing a computer to execute a color correction process in a color correction device for correcting a color image data representing a color image by a plurality of component color components based on a color conversion table. A recording medium, based on an element color component value calculation process for calculating a value for each element color component of the color image data, and a value for each element color component calculated by the element color component value calculation process, A color correction amount calculation process for calculating a color correction amount that eliminates a difference from a predetermined reference value for each element color component; and a color correction amount calculated by the color correction amount calculation process. A color conversion table generating process for generating the color conversion table for each color component, and assembling the color conversion table generated by the color conversion table generating process into the color correction device. Recording medium readable by the recording a computer program for executing a color conversion table embedded process, to the computer that writes.