JP2002290754A - Image processor, image processing method, program and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processor, an image processing method, a pro gram and a recording medium having small color shift and gradation collapse. SOLUTION: CMY data are generated on the basis of an image input signal by CMY data generation means (20a, 20b and 20c) according to the image processor performing desired color correction for the image input signal and generating CMYK data. The CMY data are converted into the CMYK data by using a continuously changing data conversion curve with a data conversion means (20d). Since data conversion is performed by using the continuously changing data conversion curve, the relation of a virtual CMY value and an Lu value output from a printer can have small non-linearity, and the color shift and gradation collapse can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus and an image processing method for performing desired color correction on an image input signal.
It relates to a program and a recording medium.

[0002]

2. Description of the Related Art When an image processing apparatus performs printing processing by a printer based on a monitor image signal, it is necessary to perform color conversion because the color system of the monitor is different from the color system of the printer. Normally, in a Luv space, a color reproduction process is performed by a printer by performing color matching using a target of RGB image input data as a color reproduction area of a monitor. Then, a corresponding virtual CMY value is obtained from the input Luv value using linear interpolation,
Based on this virtual CMY value and the K ink generation process, the C'M'Y'K 'values of the ink used in the printer are obtained.

[0003]

However, the virtual C
If the non-linearity of the relationship between the MY value and the Luv value output from the printer is large, color misregistration and loss of gradation will occur.

[0004] The present invention has been made to solve the above problems, and has as its object to provide an image processing apparatus, an image processing method, a program, and a recording medium with less color shift and gradation collapse.

[0005]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the invention according to claim 1 is an image processing apparatus for generating CMYK data by performing a desired color correction on an image input signal. The CMY data generating unit generates CMY data based on an input signal, and the data converting unit converts the CMY data into CMYK data using a continuously changing data conversion curve.

According to the image processing apparatus configured as described above and performing desired color correction on an image input signal to generate CMYK data, the CMY data generating means uses the CMY data based on the image input signal. Is generated, and the CMY data is converted into CMYK data by a data conversion unit using a continuously changing data conversion curve.

[0007] The invention described in claim 2 is the first invention.
3. The image processing device according to item 1, wherein the shape of the data conversion curve is variable.

Further, the invention according to claim 3 is the image processing apparatus according to claim 2, further comprising input means for inputting a value for determining the shape.

The invention described in claim 4 is the same as the invention described in claim 2.
The image processing apparatus according to any one of claims 1 to 3, further comprising a selection unit for selecting a value for determining the shape.

Further, the invention according to claim 5 is an image processing method for generating CMYK data by performing a desired color correction on an image input signal, wherein the CMY data is generated based on the image input signal. And a data conversion step of converting the CMY data into CMYK data using a continuously changing data conversion curve.

According to a sixth aspect of the present invention, there is provided a program for causing a computer to execute image processing for generating desired CMYK data by performing desired color correction on an image input signal. CMY data generation processing for generating CMY data based on the CMY data, and converting the CMY data into a CM using a continuously changing data conversion curve.
And a data conversion process of converting the data into YK data.

Further, the invention according to claim 7 is a medium recording the program according to claim 6.

[0013]

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 an image processing apparatus and a color correction table generation apparatus according to an embodiment of the present invention. FIG. 2 is a specific hardware configuration of the image processing apparatus and the color correction table generation apparatus. An example is shown by a schematic block diagram.

In FIG. 1, a color correction table (LUT)
The generation device 20A includes a color correction LUT generation unit 20h that generates a color correction table (LUT) based on an instruction from the instruction unit 20i and stores the color correction table (LUT) in the color correction LUT storage unit 20g. Details of the processing of each of these components will be described later.

The image processing device 20 performs desired image processing on the color image input signal (data), and outputs the color processed image data to the image output device 30. Here, the color image data represents the strength of each element color while separating the color image for each predetermined element color, and is represented by gray when it is a chromatic color and mixed at a predetermined ratio. Color and black. In the present embodiment, a case where the image output device 30 such as a printer performs a printing process based on CMYK data will be described.

The image processing device 20 converts the RGB image data into image data of a Luv coordinate system, and converts the image data of the display Luv coordinate system into image data of the printer Luv coordinate system. Correction unit 20b for the image processing and the virtual CMY
(Cyan, magenta, yellow) Second to convert to data
The color correction table selected based on the instruction from the color conversion unit 20c and the instruction unit 20f is read from the color correction LUT storage unit 20g, and the virtual CMY (cyan, magenta, A third color conversion unit 20d that converts yellow) data into CMYK (cyan, magenta, yellow, black) data;
Binarization unit 20e that converts YK data into binary data
And

On a display, a color image is displayed in gray scale in three primary colors of red, green and blue (R, G, B) for each pixel arranged vertically and horizontally. In the printer of this embodiment, cyan, magenta and yellow are displayed. , Four colors of black (C,
(M, Y, K) is printed without gradation display. Therefore,
To perform color printing, color conversion work from the display of the three primary colors of red, green, and blue (R, G, B) to the display of four colors (C, M, Y, K) of cyan, magenta, yellow, and black, and gradation An operation of gradation conversion from display to display without gradation is required.

Hardware Configuration In the present embodiment, a computer system is adopted as an example of hardware for realizing the color correction table generation device 20A and the image processing device 20.
FIG. 2 is a block diagram showing the computer system. The computer system includes a scanner 11a and a digital still camera 11 as image input devices.
b and a video camera 11c, and are connected to the computer main body 12. Each input device is capable of generating image data expressing an image by dot matrix pixels and outputting the image data to the computer main unit 12. Here, the image data is displayed in 256 gradations in three primary colors of RGB. , About 16.7 million colors can be expressed.

The computer main body 12 is connected to a floppy (registered trademark) disk drive 13a, a hard disk 13b, and a CD-ROM drive 13c as external auxiliary storage devices, and the hard disk 13b stores main system-related programs. The necessary programs can be read from a floppy disk or a CD-ROM as needed. Also, a modem 14a is connected as a communication device for connecting the computer main body 12 to an external network or the like. The modem 14a is connected to the external network via the same public communication line, and software and data can be downloaded and introduced. Has become. In this example, the modem 14a accesses the outside through a telephone line. However, a configuration in which a network is accessed through a LAN adapter is also possible. In addition, the computer body 1
The keyboard 15a and the mouse 15b are also connected for the operation of Step 2.

Further, a display 17a and a color printer 17b 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-described 16.7 million colors. This resolution is merely an example, and can be changed as appropriate, such as 640 × 480 pixels or 1024 × 768 pixels.

The color printer 17b is an ink jet printer, and is capable of printing an image by attaching dots to printing paper as a medium using four color inks of CMYK. Image density is 360 × 360dpi or 7
High-density printing such as 20 × 720 dpi is possible, but the gradation expression is a two-tone expression such as whether or not to apply color ink. On the other hand, while the image is input using such an image input device, the image is displayed or output on an image output device.
A predetermined program is to be executed inside. Of these, an operating system (OS) 12a is operating as a basic program, and the operating system 12a has a display driver (DSP DRV) for performing display on a display 17a.
A printer driver (PRT DRV) 12c that causes the printer 12b and the color printer 17b to perform print output is incorporated. These drivers 12b and 12c depend on the models of the display 17a and the color printer 17b, and can be additionally changed to the operating system 12a according to each model. Further, depending on the model, additional functions beyond the standard processing can be realized. That is, it is possible to realize various additional processes within an allowable range while maintaining a common processing system on the standard system of the operating system 12a.

As a prerequisite for executing such a program, the computer main unit 12 includes a CPU 12e, a RAM 1
2f, a ROM 12g, an I / O 12h, and the like, and a CPU 12e that executes arithmetic processing appropriately executes a basic program written in the ROM 12g while using the RAM 12f as a temporary work area, a setting storage area, or a program area. 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 a basic program. The processing contents of the application 12d are various, monitor operations of the keyboard 15a and the mouse 15b as operation devices, and when operated, appropriately control various external devices to execute corresponding arithmetic processing and the like. Further, the processing result is displayed on the display 17a or output to the color printer 17b.

In this computer system, image data is acquired by a scanner 11a or the like, which is an image input device, and a predetermined image processing is executed by an application 12d.
7a and a color printer 17b.

Image processing control program Printer driver 12 as image processing control program
c and the display driver 12b are usually provided in a form readable by the computer 12, such as a floppy disk, a CD-
It is recorded on a recording medium such as a ROM and distributed. The program is stored in a media reader (CD-ROM drive 1).
3c, floppy disk drive 13a) and installed on the hard disk 13b. The CPU is configured to read a desired program from the hard disk 13b and execute a desired process. Therefore, these media constitute a medium on which the image processing control program is recorded. Note that the image processing control program itself is also included in the scope of the present invention.

Other Configuration Examples In the present embodiment, the image processing apparatus is realized as a computer system. However, such a computer system is not necessarily required. Any system may be used if necessary. For example, 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 prints using the image data subjected to image processing may be used. Also, in a color printer that inputs and prints image data without passing through a computer system, image processing according to the present invention is automatically performed on image data input via a scanner, a digital still camera, a modem, or the like. It is also possible to configure so as to perform the printing process.

In addition, the present invention can naturally be applied to various apparatuses that handle image data, such as a color facsimile apparatus and a color copying apparatus.

Color Correction Table Generation Processing Control Program A color correction table generation processing control program executed by the color correction table generation apparatus 20A shown in FIG. 1 will be described below with reference to FIGS. The color correction table generated by the program converts virtual CMY data into CMYK data using a continuously changing data conversion curve (color correction curve). That is, the color correction table realizes a K generation process that enables highly accurate ink amount prediction using a data conversion curve (color correction curve) that changes continuously.

The basic formula of the K ink generation process is as follows: C ′ = C−α · min (C, M, Y) (1) M ′ = M−α · min (C, M, Y) (2) Y ′ = Y−α · min (C, M, Y) (3) K ′ = α · min (C, M, Y) (4) Here, α satisfies the condition of 0.0 ≦ α ≦ 1.0.
Also, as shown in FIG. 5, min (C, M, Y) is CMY
Indicates the minimum amount of ink among the amounts of ink.

In the virtual CMY space, min (C, M,
Y) changes discontinuously locally. For example, in FIG.
The change of min (C, M, Y) when the M gradation value is increased under the condition of Y = 145 and C ≧ 145 is shown. Since the change amount of min (C, M, Y) is discontinuous at M = 145 with respect to the M gradation value, C′M′Y′K ′ is expressed by M ′ from equations (1) to (4). = 145, the Luv output from the printer also changes discontinuously.

In this embodiment, in the equations (1) to (4),
Instead of min (C, M, Y), by using a continuous function F taking a value close to it, the local value of the C′M′Y′K ′, and thus the Luv value output by the printer in the virtual CMY space can be obtained. Avoid discontinuities.

First Embodiment FIG. 6 is a flowchart for explaining a first embodiment of a color correction table generation control program executed by the color correction table generation device 20A.

As shown in FIG. 6, the color correction table generator 20h of the color correction table generator 20A first obtains a continuously changing data conversion function F (step 4).
0).

Processing in Step 40 The processing in Step 40 will be described with reference to FIG. As shown in FIG. 7, the color correction table generation unit 2
0h first sets a function F (step 50). FIG. 4 shows an example of a curve indicating the function F. The point (x0, y0) on the function shown in FIG. 4 satisfies the following condition.

That is, the distance between the point (x0, y0) and the straight line y = x is Y0, and the point (x0, y0) is y = t (t is a constant of 255 or less)
If you want to and the distance between the X0, the following relationship between the X0 and ^{Y0: α · X0 n + β} · Y0 n = L ... (5) it is assumed that is true. Here, n and L are constants having any positive values.

From the above definitions of X0 and Y0, X0 = t−y0 Y0 = [{(x0−y0) / 2} ² + {(y0−x0) / 2} ² ] ^1/2 = (x0−y0) / 2 ^1/2 at because, when rewriting equation (5) becomes ^{α · (t-y0) n} + β · {(x0-y0) / 2 1/2} n = L ... (6).

Next, the values of α and β are obtained (step 52). The values of α and β are determined from the boundary conditions of x = 0 and x = 255. The functions satisfying equation (6) are x = 0, y = 0
Α = L / t ⁿ (7) A function satisfying the equation (6) is x = 255, y = t
Since it passes through the point of (t255255), β = L · {2 ^1/2 / (255−t)} ⁿ (8)

From the above, the function F of the curve shown in FIG. 4 is given by the following equation.

[0040] (1) t When ≠ 255 {(x0-y0) / (255-t)} n + {(t-y0) / t} n = 1 ... (9) where, y0 ≦ x0, y0 ≦ t (2) When t = 255, y0 = x0 (10) In Equation (9), if n = 1, the curve shown in FIG.
= 0, y = 0, and a line passing through the points x = 255, y = t. As the value of n approaches 0, the curve in FIG. 4 becomes a straight line y = x and y = t. Get as close as you can.

In the virtual CMY space, when the C ink gradation value is increased from 0 to 255, min (C, M, Y) becomes
In FIG. 4, instead of the horizontal axis x, the C ink gradation value and the vertical axis y
, Instead of min (C, M, Y), the line connecting the coordinate O (0,0) and the coordinate A (t, t), and the coordinate A (t, t) and the coordinate B (255, Change on the line connecting t). Therefore, assuming that a continuous variable represented by a curve is f, f is x0 in equation (9).
Is given as a function that satisfies the equation with C and y0 as f.

Here, the value of t is a gradation value at which the min (C, M, Y) value becomes constant when the gradation value of the C ink is increased. It can be seen that the value is a value that is no longer a C ink gradation value, that is, a min (M, Y) value. Here, t is not min (M, Y) but a continuous variable indicating a value close to it. M ink gradation value from 0 to 2
As the value is increased to 55, min (M, Y) becomes the M ink gradation value instead of the horizontal axis x and the min ink value instead of the vertical axis y in FIG.
When (M, Y) is set, it changes on the line segment OA and the line segment AB. Assuming that a continuous variable represented by a curve is t, t
Is given as a function that satisfies the equation where x0 is M and y0 is t in equation (9). Here, the t value of the constant, not the continuous variable, becomes min (M, M,
Y) Since the tone value is constant, the value of min (M,
It can be seen that the Y) value is no longer the M ink gradation value, that is, the Y ink gradation value.

Using the above method, the t value is obtained from the M and Y ink gradation values, and min (C, M,
A continuous variable f having a value close to Y) can be obtained.

However, the variable f obtained from this method is
Since the input CMY space has different change characteristics in the respective directions of C, M, and Y, it is not suitable for use as a substitute for min (C, M, Y). Therefore, the average value F of f obtained from the six possible combinations of the input CMY is defined as min (C,
M, Y).

In summary, the variable F is given by the following equation (step 54).

F = ｛f (C, M, Y) + f (C, Y, M) + f (M, Y, C) + f (M, C, Y) + f (Y, M, C) + f (Y, C, M)} / 6 ... (11) where, f (x, y, z ) following equation: {(z-f) / (255-t)} n2 + {(t-f) / t } ⁿ² = 1 (12) {(y−t) / (255−x)} ⁿ¹ + {(x−t) / x} ⁿ¹ = 1 (13) A function satisfying f ≦ z, f ≦ t, t ≦ y, t ≦ x
It is.

Next, the values of n1 and n2 are defined as 0 <n1 ≦ 1, 0 <n
It is set as a constant value in the range of 2 ≦ 1 (step 42).

In the formulas (12) and (13), n1 and n2
When the value of is close to 0, the function F changes its shape and mi
When n (C, M, Y) approaches as much as possible and n1 = n2 = 1, the function F changes linearly with respect to x, y, z, and the effect of continuity is maximized. Here, F ≦ min (C, M, Y)
Therefore, in equations (1) to (4), the amount of K generation and CM
The amount removed from Y is reduced, thus reducing the color gamut. As the values of n1 and n2 approach 1, the effect of continuity increases, but the color reproduction range narrows.

Next, as described above, a desired color correction table is obtained based on the function F (color correction curve) composed of continuously changing data conversion curves defined by the equations (11) to (13). Generated (step 44). Since data conversion is performed using a continuously changing data conversion curve,
Non-linearity in the relationship between the virtual CMY value and the Luv value output from the printer can be reduced, and color shift and gradation loss can be reduced.

Then, the generated color correction table is n1
The values are stored in the color correction table storage unit 20g together with the values of n and n2 (step 46).

Second Embodiment In the first embodiment, the color reproduction range is narrowed for the above reason. For this reason, in the second embodiment, by performing continuity only inside the input CMY space, the color shift and the loss of gradation are reduced without narrowing the color reproduction range. However, since continuation is not performed on the side of the input CMY space,
The reduction effect is smaller than that of the first embodiment, particularly near the side surface.

FIG. 8 is a flowchart for explaining a second embodiment of the color correction table generation processing control program executed by the color correction table generation device 20A.
6 and 8, the same processes are denoted by the same reference numerals.

In the second embodiment shown in FIG. 8, instead of setting the values of n1 and n2 in step 42 of the first embodiment shown in FIG.
The difference is that the value of _nim is set.
The processing at 0, 44 and 46 is identical.

As shown in FIG. 8, the color correction table generator 20h of the color correction table generator 20A first obtains a continuously changing data conversion function F (step 4).
0). The processing in step 40 is the same as in the first embodiment, and a description thereof will be omitted.

Next, the values of n_min and gam_min are set to 0 <n_m
It is set as a constant value in the range of in ≦ 1, 0 <gam_min (step 43). Based on the set values of n_min and gam_min, the following equation n1 = n_min · ｛1− (z / 255)} ^gam_min (14) n2 = n_min · [{1− (x / 255)} · {1− (y / 255)}] ^{gam_min / 2} ... (15), the values of n1 and n2 are given. Equation (14) and Equation (15)
From n1 and n2 within the input CMY space are 0 ≦ n1 ≦ 1,
0 ≦ n2 ≦ 1, n = n2 = 0 on the plane of C = 255, M = 255, Y = 255
Becomes By adjusting n_min and gam_min in Expressions (14) and (15), the characteristics of continuity in the input CMY space can be determined. The effect of continuity increases as the value of n_min approaches 1. Also, the effect of continuity decreases as the value of gam_min increases, and as the value approaches
The change of F becomes sharp near the side of the Y space. As an example, in this embodiment, n_min = 0.5, gam_min = 0.4
And

Next, a desired color correction table is generated based on a function F (color correction curve) composed of a continuously changing data conversion curve defined by the equations (11) to (15) (step). 44). Since data conversion is performed using a continuously changing data conversion curve, the non-linearity of the relationship between the virtual CMY value and the Luv value output from the printer can be reduced, and color misregistration and gradation collapse can be achieved. Can be reduced.

Then, the generated color correction table is represented by n_
The values of min and gam_min are stored in the color correction table storage unit 20g (step 46).

Next, an image processing control program executed by the image processing apparatus 20 will be described with reference to FIG. In this embodiment, it is assumed that the color correction table generated by the above-described color correction table generation method is stored in the color correction LUT storage unit 20g in advance.

As shown in FIG. 8, the color correction unit 20a allows the user to instruct the start of printing with the instruction unit 20f, and the color correction table generated by the first embodiment of the color correction table generation processing program performs color correction. When stored in the LUT storage unit 20g, by inputting or selecting the values of n1 and n2, the color correction table generated by the second embodiment of the color correction table generation processing program stores the color correction LUT. If the desired color correction table is selected by inputting or selecting the values of n_min and gam_min in the case of being stored in the unit 20g (step S80, Yes), the color corresponding to the input or selected value is selected. The correction table is a color correction LUT storage unit 20g
And read into the RAM (step S
84). Then, the color correction table is stored in the third color conversion unit 2.
0d (Step S86), and a printing process is performed (Step S90).

[Brief description of the drawings]

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

FIG. 2 is a schematic block diagram illustrating a specific hardware configuration example of an image processing device and a color correction table generation device according to an embodiment of the present invention.

FIG. 3 is a graph showing a change in min (C, M, Y) when the gradation value of M is increased under the conditions of Y = 145 and C ≧ 145.

FIG. 4 is a diagram illustrating an example of a curve indicated by a function F;

FIG. 5 is a diagram for explaining the definition of min (C, M, Y).

FIG. 6 is a flowchart for explaining a first embodiment of a color correction table generation processing control program executed by the color correction table generation device 20A.

FIG. 7 is a flowchart illustrating a process in step 40 of FIG. 6;

FIG. 8 is a flowchart for explaining a second embodiment of the color correction table generation processing control program executed by the color correction table generation device 20A.

FIG. 9 is a flowchart for explaining an image processing control program executed by the image processing apparatus 20.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image input device 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 20 Image processing device 20a First color conversion unit 20b Color correction unit 20c Second color conversion unit 20d Third color conversion unit 20e Binarization unit 20f Instruction unit 20g Color correction LUT storage unit 20h Color correction LUT generation unit 20i Instruction unit 30 Image Output device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C262 AA24 AA26 AA27 AB13 AC02 BA02 BA07 BA09 BC03 BC11 5B057 AA11 CA01 CA08 CA12 CA16 CB01 CB07 CB12 CB16 CC01 CE13 CE17 CH11 5C077 LL19 MP08 PP33 PP36 PP37 PP38 PP39 PQ08 PQ08 TT02 5C079 HB01 HB02 HB03 HB09 HB11 HB12 LA31 LB02 MA05 MA11 NA03 NA05 PA03 PA05

Claims (7)

[Claims] 1. An image processing apparatus for generating CMYK data by performing a desired color correction on an image input signal, wherein the CMYK data is generated based on the image input signal.
An image processing apparatus comprising: MY data generation means; and data conversion means for converting the CMY data into CMYK data using a continuously changing data conversion curve. 2. The image processing apparatus according to claim 1, wherein the shape of the data conversion curve is variable. 3. The image processing apparatus according to claim 2, further comprising an input unit for inputting a value for determining the shape. 4. The image processing apparatus according to claim 2, further comprising a selection unit for selecting a value for determining the shape. 5. An image processing method for generating CMYK data by performing a desired color correction on an image input signal, the method comprising generating CMY data based on the image input signal.
An image processing method, comprising: a MY data generation step; and a data conversion step of converting the CMY data into CMYK data using a continuously changing data conversion curve. 6. A program for causing a computer to execute image processing for generating CMYK data by performing desired color correction on an image input signal, the program comprising: C for generating CMY data based on the image input signal.
A program for causing a computer to execute: MY data generation processing; and data conversion processing for converting the CMY data into CMYK data using a continuously changing data conversion curve. 7. A medium on which the program according to claim 6 is recorded.