JP2003333353A - Color correction table generating method, image processing apparatus, image processing method, program, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color correction table generating method capable of enhancing the consecutiveness in color correction of image data, an image processing apparatus for using the color correction table, an image processing method, a program, and a recording medium. <P>SOLUTION: The image processing apparatus of this invention performs image processing by using a smoothing degree evaluation function for evaluating a degree of smoothing in each of grating point data after color conversion in a CMY space by the color correction table. The smoothing degree evaluation function includes: an evaluation function on the basis of a color distortion amount by CMY colors before and after the color conversion by the color correction table; an evaluation function on the basis of a degree of departure from the target CMY colors; an evaluation function on the basis of it that the CMY value exceeds 255; and an evaluation function on the basis of it that the CMY value takes a negative value. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of generating a color correction table capable of enhancing the continuity of color correction of image data, an image processing apparatus, method, program and recording medium using the color correction table.

[0002]

2. Description of the Related Art In a color reproduction device such as a scanner, a monitor, a printer or a projector, color reproduction characteristics differ depending on whether self-emission or reflection, difference in gradation expression method, difference in primary color used, etc. Value or CM
Even if the Y value or the CMYK value is input, the reproduced color is greatly different. Therefore, in order to reproduce the same color with different color reproduction devices, the color is expressed in a device-independent space that can be expressed independently of the characteristics of the device, and the actual color must be the same in that space. So-called color management that determines ink amount, monitor RGB values, etc. (Color Ma
nagement) is required.

For example, in the case of a color printer, the Lab value calculated according to the standard can be calculated and reproduced by the printer under the assumption that the RGB value of the scanner, printer, monitor, etc. is the sRGB value which is an international standard. Color conversion to an ink combination for reproducing a color having a value closest to the Lab value among the various colors. Then, this conversion is performed at a predetermined RGB grid interval, and RGB conversion is performed.
Color correction table (LU that performs color conversion of ink amount from values
Generally, T) is created in advance and mounted in a printer driver or the like so that a desired color can be reproduced.

[0004]

Generally, the color reproduction characteristics of a printer are determined by the characteristics of what kind of ink combination is used for input RGB values (hereinafter referred to as "color separation"). Since the color separation is designed to satisfy various conditions, in many cases, the ink amount changes discontinuously. Therefore, the color correction table created using the color separation characteristics as it is always has a portion where the ink amount changes discontinuously, which causes gradation. Further, when the grid has rattling, a large error occurs in the linear interpolation performed when the data in the grid is obtained, and in such a case, color distortion and the like also occur.

The present invention has been made in order to solve the above-mentioned problems, and by improving the continuity of the color correction table, color distortion of an output image and color correction capable of suppressing tone jump as much as possible. Table generation method,
An object is to provide an image processing device, method, program, and recording medium that use the color correction table.

[0006]

In view of the above problems, the invention described in claim 1 is a method for generating a color correction table, wherein each color correction table is used after color conversion in a color space such as CMY space. It is configured to generate the color correction table using a smoothing degree evaluation function for evaluating the degree of smoothing in the grid point data.

According to a second aspect of the present invention, there is provided an image processing device, wherein smoothing for evaluating the degree of smoothing in each grid point data after color conversion in a color space such as a CMY space by a color correction table. The color correction table generated using the degree evaluation function is used to perform image processing.

The invention described in claim 3 is the image processing apparatus according to claim 2, wherein the smoothing degree evaluation function is
It is configured to have an evaluation function based on the amount of twist in a color space such as a CMY space before and after color conversion by the color correction table.

According to a fourth aspect of the present invention, in the image processing apparatus according to the second or third aspect, the smoothing degree evaluation function has an evaluation function based on a degree of deviation from a target CMY value. Consists of

The invention according to claim 5 is the invention according to claims 2 to 4.
The image processing device according to any one of items 1 to 5, wherein the smoothing degree evaluation function includes an evaluation function that prevents a CMY value from exceeding 255.

The invention according to claim 6 is the invention according to claims 2 to 5.
The image processing device according to any one of items 1 to 3, wherein the smoothing degree evaluation function has an evaluation function that prevents a CMY value from becoming negative.

According to a seventh aspect of the present invention, which is an image processing method, a smoothing for evaluating the degree of smoothing in each grid point data after color conversion in a color space such as a CMY space by a color correction table. The color correction table generated using the degree evaluation function is used to perform image processing.

According to an eighth aspect of the present invention, there is provided a program for causing a computer to execute image processing, the degree of smoothing in each grid point data after color conversion in a color space such as CMY space by a color correction table. Is configured to cause the computer to execute image processing using the color correction table generated using the smoothing degree evaluation function for evaluating.

The invention described in claim 9 is a computer-readable recording medium in which the program according to claim 8 is recorded.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a functional block diagram of a color correction table generating apparatus according to an embodiment of the present invention, and FIG. 3 is a functional block diagram of an image processing apparatus.

Hardware Configuration FIG. 2 is a schematic block diagram showing an example of a concrete hardware configuration of the color correction table generating device and the image processing device.

In this embodiment, a computer system is adopted as an example of hardware for realizing the color correction table generating device and the image processing device. Figure 2
Shows a block diagram of the same computer system. The computer system includes a scanner 11a, a digital still camera 11b, and a video camera 11c as image input devices, and is connected to the computer main body 12. Each input device is capable of generating image data in which an image is represented by pixels in a dot matrix and outputting the image data to the computer main body 12.
Here, the same image data can represent approximately 16.7 million colors by displaying 256 gradations in each of the three primary colors of RGB.

A floppy (registered trademark) disk drive 13a, a hard disk 13b and a CD-ROM drive 13c as an external auxiliary storage device are connected to the computer main body 12, and a main system-related program is recorded on the hard disk 13b. It is possible to read necessary programs and the like from a floppy disk or a CD-ROM. Also, a modem 14a is connected as a communication device for connecting the computer main body 12 to an external network or the like, and the modem 14a can be connected to the external network through the same public communication line to download and install software and data. Has become. In this example, the modem 14a is used to access the outside via the telephone line, but it is also possible to have a configuration for accessing the network via the LAN adapter. Besides this, the computer main body 1
A keyboard 15a and a mouse 15b are also connected for the operation of 2.

Further, a display 17a, a color printer 17b and a projector 17c are provided as image output devices. The display 17a has a display area of 800 pixels in the horizontal direction and 600 pixels in the vertical direction, and each pixel can display the above-mentioned 16.7 million colors. This resolution is just an example,
The number of pixels can be appropriately changed to 640 × 480 pixels or 1024 × 768 pixels.

The color printer 17b is an ink jet printer, and is C (cyan) M (magenta) Y.
It is possible to print an image by using dots of six colors of ink (yellow) K (black) c (light cyan) m (light magenta) on a printing paper as a medium. Image density is 360 x 360 dpi or 720 x 720 dpi
Although high density printing is possible, the gradation expression is expressed in two gradations such as whether or not color ink is applied. On the other hand, since an image is input using such an image input device and displayed or output on the image output device, a predetermined program is executed in the computer main body 12. Of these, the operating system (OS) 12a operates as a basic program, and the operating system 12a has a display driver (DSP DRV) 12b for displaying on the display 17a and a print output to the color printer 17b. A printer driver (PRT DRV) 12c for performing the above and a projector driver 12d (not shown) for performing the display on the projector 17c are incorporated. These drivers 12b, 1
2c and 12d depend on the model of the display 17a, the color printer 17b, and the projector 17c, and can be additionally changed to the operating system 12a according to each model. Also, depending on the model, it is possible to realize additional functions beyond the standard processing. That is, it is possible to realize various additional processes within an allowable range while maintaining a common processing system on the standard system called the operating system 12a.

As a premise for executing such a program, the computer main body 12 has a CPU 12e and a RAM 1
2f, ROM 12g, I / O 12h, etc., and the CPU 12e that executes arithmetic processing appropriately executes the basic program written in the ROM 12g while using the RAM 12f as a temporary work area or setting storage area or as a program area. However, it controls external devices and internal devices connected via the I / O 12h.

Here, the application 12d is executed on the operating system 12a as the basic program. The processing contents of the application 12d are various, and the operation of the keyboard 15a or the mouse 15b as an operation device is monitored, and when operated, various external devices are appropriately controlled to execute corresponding arithmetic processing, Further, the processing result is displayed on the display 17a or output to the color printer 17b.

In such a computer system, image data is acquired by the scanner 11a, which is an image input device, and predetermined image processing is executed by the application 12d, and then the display 1 as an image output device.
7a, the color printer 17b, and the projector 17c can display and output.

In this embodiment, the image processing apparatus is realized as a computer system, but such a computer system is not always necessary.
Any system that requires image processing according to the present invention for similar image data may be used. For example, there may be a system in which an image processing apparatus for performing image processing according to the present invention is incorporated in a digital still camera and a color printer is used to print using image data subjected to image processing. Also,
In a color printer that inputs and prints image data without using a computer system, image data input through a scanner, digital still camera, modem or the like is automatically subjected to image processing according to the present invention for printing. It can also be configured to process.

In addition to the above, the present invention is naturally applicable to various devices such as a color facsimile device, a color copying device, and a projector that handle image data.

Image Processing Control Program The image processing control program according to the present invention is usually in a form readable by the computer 12, such as a floppy disk or C.
It is recorded on a recording medium such as a D-ROM and distributed. The program is read by a media reading device (CD-ROM drive 13c, floppy disk drive 13a, etc.) and installed in the hard disk 13b. Then, the CPU is configured to read a desired program from the hard disk 13b as appropriate and execute a desired process. The image processing control program itself according to the present invention also constitutes a part of the present invention.

Color correction table generation device 20A shown in FIG.
Is C ′ that matches the CMY data represented as the complement of RGB (sRGB) image data to the color space of the image output device.
A color correction table for converting into M'Y 'image data is generated. In the color correction table, CMY image data is converted into C ′.
When converting into M'Y 'image data, a color correction table capable of enhancing continuity of color correction of image data is generated. In the embodiment, a case of color conversion in the CMY space will be described as an example of color conversion.

In FIG. 1, a color correction table generating device 2
0A is the cost calculation unit 20d and the color correction table (LU
T) smoothing unit 20e and color correction table (LU
The T) generation unit 20f and the color correction table (LUT) storage unit 20b are included. Details of the processing of each of these components will be described later.

The color correction table generation processing program executed by the color correction table generation device 20A shown in FIG. 1 will be described below with reference to FIGS.

FIG. 4 shows a flowchart for explaining the color correction table generation processing by the color correction table generation device 20A.

Calculation Process of Each Cost (S22) As shown in FIG. 4, first, the color correction table generating device 20A
The cost calculation unit 20d calculates the cost of each function E for evaluating the degree of smoothing in the data of each grid point (grid) after color conversion by the color correction table (hereinafter referred to as “evaluation function”) E. Processing is performed (S22). Less than,
The evaluation function E will be described in detail. (1) The evaluation function E is for a certain grid in the LUT,
Design so that a smaller value can be obtained by satisfying each condition. When smoothing processing (hereinafter referred to as “smoothing processing”) is applied to CMY vectors, the evaluation function E is expressed as the sum of cost terms designed under each condition, as in the following equation.

E = E _vt + E _v + E _d + E _n (1) where E _vt is the cost of the amount of twist due to CMY, and E _v is
E is the cost of leaving the target CMY, E
_d is the cost of CMY values is generated by more than 255, E _n is the cost incurred by the CMY value is negative.

E _vt is a cost related to the twist between adjacent grids, and by reducing E _vt , C
The twist between adjacent grids when converting from MY to C'M'Y 'can be reduced to improve continuity of image data by color correction. Further, E _v is a cost generated from the difference between the CMY vectors before and after smoothing, and is a cost related to the difference between the CMY vectors due to the temporal change of the same grid. E _d and E _n are costs incurred when the CMY values are standardized to 0 to 255 and do not fall within that range.

Each item will be described in detail below. Equation (1) is an example in which smoothing is performed on CMY vectors, and other vectors (eg, XYZ, La) are used.
b, other space vectors) can be similarly applied. (2) General form of each term of the evaluation function E The cost term E _c of the evaluation function for a certain vector X is generally expressed by the following equation.

[0036]

[Equation 1] Here, E _c is a cost (scalar value), X is a column vector having the number of elements X, M is a Y × X matrix, and
The vector X is the vector Y = M
Y _T is a column vector with the number of elements Y, W ₁ is a column vector with the number of elements Y, and weights for the cost to each element of the vector Y−Y _T are W ₂ is a vector representing Y, a diagonal matrix of Y × Y, and a vector Y−
Is a matrix that represents the weight for the cost to each element of Y _T ,
t represents transposition.

In the following description, the first expression of the expression (2) is changed to 1
The following formula form and the second formula are called quadratic formula forms. (3) Cost of twist amount of CMY vector E _vt (CMY vector space) Let a grid adjacent to a certain grid p be pr (hereinafter referred to as “reference grid”). Further, a grid adjacent to the grid p and different from the grid pr is set as pt (hereinafter referred to as “transition grid”), and a grid having the same positional relationship as the positional relationship between the grids p and pr is pt is set as ptr. . Here, the CMY vectors held by the respective grids p, pr, pt, and ptr are defined as V _p , V _pr , V _pt , and V _ptr , respectively.

FIG. 6 shows the positional relationship between these grids and the CMY vectors held by each grid. In FIG. 6, _assuming that the difference vector between V _pr and V _p transits to the difference vector between V _ptr and V _pt , the “displacement amount of the difference vector before and after the transition” can be expressed as a difference vector between the two difference vectors. Also, considering the transition distance as the magnitude of the difference vector between V _pt and V _p , by dividing the “displacement amount of the difference vector before and after the transition” by the transition distance, “per unit transition distance,
The displacement amount of the difference vector before and after the transition can be obtained. By adding the square of the magnitude of this “displacement amount of difference vector before and after transition per unit transition distance” with respect to all grids pr and pt adjacent to the grid p,
It is defined as the twist amount of the CMY vector in the grid p. However, pr and pt may be in the same grid as long as they are adjacent to p.

The twist amount of this CMY vector is taken as the cost and is shown in equation (3).

[0040]

[Equation 2] In equation (3), t is some pt, T is the number of pt, r is some pr, R is the number of pr, and D _vt is
is the transition distance at t.

The smaller the cost E _vt , the smaller the amount of twist in CMY.

Here, the formula (3) is compared with the quadratic form of the formula (2).
Put together, the CMY vector becomes a vector in another space
Omitted because it is a unit vector because it does not need to be converted
it can. Also, since each element is not weighted, W₂Also
It is a unit vector and can be omitted. X is V_pAnd Y_TIs V
_ptr−V_pr−V_ptIs. 1 / D_vt ²Is a constant at some t
Therefore, the quadratic form of formula (2) and the formula (3) have the same form.
It (4) Cost E of moving away from the target CMY_v CMY vector V on grid p_pIs CMY vector
Le V_TLet V be the ideal (desired) vector, then V
_pAnd V_TThe larger the difference vector of, the more costly
Considered to be large. This cost is E_VAs shown in equation (4)
You However, W_VIs a 3 × 3 diagonal matrix of CMY vectors
It is a weight matrix for each element.

[0043]

[Equation 3] It can be confirmed that the expression (4) has the same form as the quadratic expression of the expression (2).

It is impossible to know the ideal CMY vector V _T in advance, and a CMY vector closer to the ideal state or a CMY vector as another target will be considered. Here, the CMY vector before smoothing is used as the CMY vector closer to the ideal state. As smoothing progresses, CMY of the grid
This is because the vector is expected to approach the ideal value, and the smoothing time constraint is also taken into consideration. (5) Cost for CMY values over 255 If the CMY values are standardized from 0 to 255, grid p
It is considered that the cost increases as the number of elements of the CMY vector V _{p in} the above exceeds 255 and the excess amount increases. This cost is set as E _d and is shown in Expression (5). Here, V _L is a column vector with 3 elements, whose limit value is 255, and W _d1
Is a weight column vector with three elements, and W _d2 is a 3 × 3 weight diagonal matrix. Each weight element of W _d1 and W _d2 is 0 when V _P −V _L is 0 or less, and takes a positive value when it is positive.

[0045]

[Equation 4] The formula (5) has a linear formula form and a quadratic formula form, which can be appropriately selected and used. Comparing expression (5) with expression (2), it can be confirmed that both the primary expression form and the secondary expression form have the same shape. (6) As in the case of the cost E _d when the CMY value is smaller than 0, in the case of the CMY value normalized to 0 to 255, the element of the CMY vector V _P takes a negative value and the negative value thereof It is considered that the larger the excess amount, the higher the cost. This cost is defined as E _n and is shown in equation (6). Here, W _n1 is a weight column vector with three elements, and W _n2 is a 3 × 3 weight diagonal matrix. Each weight element of W _n1 and W _n2 has a negative value when V _P is negative, and 0 when it is 0 or more.

[0046]

[Equation 5] The formula (6) also has a linear formula form and a quadratic formula form, and can be appropriately selected and used. Comparing expression (6) with expression (2), it can be confirmed that both the primary expression form and the secondary expression form have the same shape.

After the costs are calculated in the above (1) and (3), (4), (5), and (6), the following smoothing processing is performed.

Smoothing Process (S24) Next, as shown in FIG.
The color correction LUT smoothing unit 20e of A performs smoothing processing (minimizes the evaluation function E) described in detail below.
Performing calculation processing) of V _p (S24). (1) Outline of LUT Smoothing in Grid p Smoothing (smoothing) of the LUT in the grid p is performed by minimizing the evaluation function E of the equation (1). Although any method that minimizes the evaluation function E of Expression (1) can be used, the following method is used in this embodiment.

Each term in the equation (1) is represented by the sum of the equations (3) to (6). That is, all the terms of the evaluation function E include each element of V _p , and are represented by the maximum quadratic for those elements. Further, in the case of the quadratic, it can be seen that it is a square of the first order and is always a convex function. That is, the function of partial differentiation of E with respect to each element of V _p is made equal to the zero vector.
The evaluation function E can take the minimum value due to V _p .

As described above, the expressions (3) to (6) are all expressions
It has the same shape as (2). Here, using the formula (2), the evaluation function E
Here is the general form for partial differentiation of each term in V _p (X in equation (2)). Equation (7) shows a case where Equation (2) is partially differentiated with respect to each term of X.

[0051]

[Equation 6] Here, A is a column vector having the number of elements X, and each element is a partial differentiation of E _c with each element X _x of X. However, x is the element number of the vector X, and x = 1, 2, ..., X. (2) Partial differentiation of Eqs. (3) to (6) with each element of V _{p in} the same way as the partial differentiation expression (7) of V _p of the evaluation function E is as follows. Where A _vt , A _v , A _d , A _n are
A column vector having three elements obtained by partially differentiating E _vt , E _v , E _d , and E _n with each element C _p , M _p, and Y _p of V _p is shown.

[0052]

[Equation 7] The sum of Expressions (8) to (11) is a vector obtained by partially differentiating the evaluation function E with each element of V _p . Solving for V _p as the vector is zero vector, it is possible to obtain the V _p that minimizes E. That is,

[0053]

[Equation 8] Means to solve for V _p . However, f is E to V _p
The vector obtained by partial differentiation with each element of is expressed in the form of a function, and 0 represents a zero vector.

As described above, the color correction LUT smoothing unit 20f obtains V _p that minimizes the evaluation function E,
The smoothing process is ended.

Smoothing Processing for Entire LUT (S25) As shown in FIG.
The A color correction LUT smoothing unit 20e performs a smoothing process for the entire color correction LUT described in detail below (S25).

In order to perform the smoothing process for the entire LUT, the C held in the grids other than the grid p
If without changing the MY vector may be only a correction V _p, it is possible to obtain an optimum V _p by the method described above.
However, in actuality, in order to perform the smoothing process for the entire color correction LUT, it is necessary to correct the CMY vectors held in grids other than the grid p. Therefore, by sequentially correcting the CMY vectors of each grid, the entire color correction LUT is smoothed.

If the correction of the CMY vector in a certain state n of the grid p to the next state (solving the equation (12) with respect to V _p ) is represented by g, the correction is generally performed in the equation (13). Is represented as

[0058]

[Equation 9] When the state n is corrected to the state n + 1 in all the grids, the cost E is not always small in each grid. This is because the CMY vector of the state n + 1 is obtained for each grid based on the cost E in the state n as in the equation (13).
This is because the cost E of the state n + 1 is not taken into consideration when obtaining the equation (13). That is, since the goal is to keep costs low, most grids are expected to cost less in state n + 1 than in state n, but this is not absolute.

Therefore, all corrections are made by the equation (13) (S4
0), the cost is not corrected (S54), or the annealing method (S56) is used to allow the cost to increase to some extent.

Next, the smoothing process of the entire color correction LUT shown in S25 of FIG. 4 will be described in more detail with reference to the flow chart shown in FIG.

As shown in FIG. 5, when the smoothing process of the entire color correction LUT in S25 is started, the equation (13)
N of 0 is set to 0 (S30), and the CMY vector:

[0062]

[Equation 10] (P = 0, 1, ..., P-1) is input (S32). Here, P represents the number of grids.

Next, it is judged whether or not n <N (S3
4), if n <N (S34, Y), cost for grid p in state n:

[0064]

[Equation 11] (P = 0, 1, ..., P-1) is calculated (S36), and the CMY vector in the state n where the grid p (p = 0, 1, ..., P-1) is present is given by the equation (13). The variable Count is set to P (S38).

Here, N represents the number of smoothing times, and indicates that the maximum value of the state n is N-1.

Then, under the condition that "all grids are not corrected" (S40, N), p is 0 (zero).
(S42), and it is determined whether or not p <P (S44).

Then, "correct all grids"
If the condition is (S40, Y) or p <P is not satisfied (S44, N) and Count is not 0 (S46, N), then n + 1 is set to n for the annealing method. The random variable parameter of is reduced (S48), S3
Return to 4.

On the other hand, when p <P (S44, Y), state n +
Cost for grid p in 1:

[0069]

[Equation 12] Is calculated (S50),

[0070]

[Equation 13] Is determined (S52). And state n +
When the cost for grid p in 1 is greater than or equal to the cost for grid p in state n (S52, N)
Is determined whether or not the condition is "correction is not performed if cost is not small" (S54). It is determined whether or not the condition "permit correction using" is performed (S5
6).

When the condition "correction is not performed unless the cost is small" is satisfied (S54, Y) or the condition "correction using the annealing method is not permitted" (S56, N), the grid in state n is used. CMY vector for p:

[0072]

[Equation 14] Is the CMY vector for grid p in state n + 1:

[0073]

[Equation 15] And the variable (Count-1) is set to Count (S60).

Then, after S60, or when the cost for the grid p in the state n + 1 is smaller than the cost for the grid p in the state n (S52,
Y) or the condition of “permitting correction using the annealing method” (S56, Y), (p + 1) is set to p (S58), and the process returns to S44.

On the other hand, when n <N is not satisfied in S34 (S
34, N) or S46 when Count is 0 (S
46, Y) contains the CMY vector:

[0076]

[Equation 16] (P = 0, 1, ..., P-1) is output (S62), and the process ends.

After the smoothing process for the entire LUT (S25), the process returns to S26 in FIG. 4 to generate a color correction table (S26), and the generated color correction table is stored in the color correction LUT storage section 20b. (S28).

As described above, the color correction table capable of enhancing the continuity of the color correction of the image data can be generated.

Image Processing Device In FIG. 3, the image processing device 20B performs desired image processing on the RGB image data and outputs the image-processed image data to the image output device 30.

Here, the image data expresses the strength and weakness for each element color while separating the color image for each predetermined element color. When the color data is chromatic and mixed at a predetermined ratio, it becomes gray. It consists of representative achromatic colors and black.

In this embodiment, the image output device is C (cyan) M (magenta) Y (yellow) K (black) c.
A case will be described in which a color printer using six colors (light cyan) m (light magenta) performs color reproduction based on RGB data.

The image processing apparatus 20B includes a first color conversion section 20h for converting RGB image data into CMY image data,
The color correction LUT storage unit 20b that stores at least the color correction table generated by the color correction table generation device 20A, and the color correction LUT storage unit 2 that stores the color correction table (LUT) selected by the color correction LUT selection unit 20c.
0b, the color correction unit 20a that converts the CMY image data into C′M′Y ′ image data by referring to the read color correction LUT, and the C′M′Y ′ image data by C
The second color conversion unit 20g for converting into MYKcm image data is provided.

Next, referring to FIG. 7, the image processing device 20
The operation of B will be described.

As shown in FIG. 7, the user instructs the image output start (S70) and the color correction LUT
When the predetermined color correction LUT is selected via the selection unit 20c (S72, Yes), the predetermined color correction LUT is read from the color correction LUT storage unit 20b and read into the RAM (S74). Then, the color correction LUT is incorporated in the color correction unit 20a (S76), and the three-dimensional color correction LUT is used.
, The image processing is performed by the interpolation calculation, and the image output processing is performed (S78).

According to the image processing apparatus 20B of the present embodiment, the color correction table generating apparatus 20A in S72.
When a color correction table that can improve the continuity of color correction of the image data generated by is selected, the color correction is performed using the color correction table, and therefore gradation may be fluctuated after the color correction. Can be prevented.

[Brief description of drawings]

FIG. 1 is a functional block diagram of a color correction table generation device according to an embodiment of the present invention.

FIG. 2 is a schematic block diagram showing a hardware configuration of a color correction table generating device and an image processing device.

FIG. 3 is a functional block diagram of an image processing apparatus according to an embodiment of the present invention.

FIG. 4 is a flowchart illustrating a color correction table generation process by the color correction table generation device.

FIG. 5 is a flowchart for explaining a smoothing process for the entire LUT by the color correction table generating device.

FIG. 6 is a diagram for explaining the definition of CMY vectors.

FIG. 7 is a flowchart illustrating a process performed by the image processing apparatus.

[Explanation of symbols]

11a scanner 11b digital still camera 11c video camera 12 computer body 12a operating system 12b display driver 12c printer driver 12d application 13a floppy disk drive 13b hard disk 13c CD-ROM drive 14a modem 15a keyboard 15b mouse 17a display 17b color printer 17c projector 20A color correction table generation device 20B image processing device 20a color correction unit 20b Color correction LUT storage unit 20c Color correction LUT selection section 20d cost calculator 20e Color correction LUT smoothing section 20f color correction LUT generator 20g Second color converter 20h First color conversion unit

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Claims (9)

[Claims] 1. A method of generating a color correction table using a smoothing degree evaluation function for evaluating the degree of smoothing in each grid point data after color conversion in a color space such as a CMY space using a color correction table. 2. A color correction table generated using a smoothing degree evaluation function for evaluating the degree of smoothing in each grid point data after color conversion in a color space such as a CMY space by a color correction table is used. An image processing device that performs image processing. 3. The image processing apparatus according to claim 2, wherein the smoothing degree evaluation function has an evaluation function based on a twist amount in a color space such as CMY space before and after color conversion by a color correction table. Image processing device. 4. The image processing apparatus according to claim 2, wherein the smoothing degree evaluation function has an evaluation function based on a degree of deviation from a target CMY value. 5. The image processing apparatus according to claim 2, wherein the smoothing degree evaluation function has an evaluation function that prevents a CMY value from exceeding 255. Image processing device. 6. The image processing apparatus according to claim 2, wherein the smoothing degree evaluation function has an evaluation function for preventing a CMY value from becoming negative. Processing equipment. 7. A color correction table generated by using a smoothing degree evaluation function for evaluating the degree of smoothing in each grid point data after color conversion in a color space such as a CMY space using the color correction table is used. An image processing method that performs image processing by using. 8. A program for causing a computer to execute image processing, the smoothing for evaluating the degree of smoothing in each grid point data after color conversion in a color space such as a CMY space by a color correction table. A program for causing a computer to execute image processing using a color correction table generated using a degree evaluation function. 9. A computer-readable recording medium in which the program according to claim 8 is recorded.