JP2740436B2 - Color correction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color tone correcting apparatus for converting a RGB signal of each pixel of an original image read by a color scanner into a CMYK signal for plate making and then performing a desired color tone correction.

[0002]

2. Description of the Related Art Conventionally, many methods of RGB / CMYK conversion and subsequent color tone correction have been proposed for RGB signals of a color image displayed on a color monitor or the like.
Devices that are easy to operate and that provide sufficient image quality have not been put to practical use.

[0003] For example, a color scanner for plate making can provide sufficient image quality. In this color scanner for plate making, the RG of the original image is
After converting the B signal into a CMYK signal, the color tone is corrected using a color tone correction function called color correction.

In the masking process, for example, RGB signals (R _X, G _{X, and} B _X ) of each pixel of an original image are respectively converted into CMYK by an RGB / CMYK conversion equation as shown in the following equation.
The signal is converted into a signal (C _X, M _X, Y _X, K _X ). _{C X = α 11 R X -α} 12 G X -α 13 B X M X = -α 21 R X + α 22 G X -α 23 B X Y X = -α 31 R X -α 32 G X + α 33 B _X K _X = MAX (C _X, MX _, Y _X ) where α _ij (i = 1 to 3, j = 1 to 3) is a predetermined coefficient (positive value), and MAX (C _{X ,} M _X, Y _X) is, C _X,
A function for extracting the largest one of M _{X and} Y _X is shown.

[0005] Further, C _X,
M _X, Y _X, each portion of the K _X signal, C (cyan), M (magenta), Y (yellow), 6 of R (red), G (green), B (blue)
When the color signals of the system are separated into ΔC, ΔM, ΔY, ΔR, ΔG, and ΔB, they can be expressed by the following equation. _{C X = C X '± β} 11 ΔC ± β 12 ΔM ± β 13 ΔY ± β 14 ΔR ± β 15 ΔG ± β 16 ΔB M X = M X' ± β 21 ΔC ± β 22 ΔM ± β 23 ΔY ± β ₂₄ ΔR ± β ₂₅ ΔG ± β ₂₆ ΔB Y _X = Y _X '± β ₃₁ ΔC ± β ₃₂ ΔM ± β ₃₃ ΔY ± β ₃₄ ΔR ± β ₃₅ ΔG ± β ₃₆ ΔB K _X = K _X ' ± β ₄₁ ΔC ± β ₄₂ ΔM ± β ₄₃ ΔY ± β ₄₄ ΔR ± β ₄₅ ΔG ± β ₄₆ ΔB Here, β _ij (i = 1 to 4, j = 1 to 6) indicate variable coefficients. By adjusting the coefficient β _ij , the color tone of the C _X, M _X, Y _{X, and} K _X signals is corrected.

In order to execute the color correction according to the above equation, an operation panel of a circuit which performs the operation of the above equation includes:
There are provided 24 knobs for adjusting the above-mentioned coefficient β _ij , and the operator changes the coefficient β _ij by adjusting each knob to perform a desired color tone correction.

[0007]

First, the operation of color correction is difficult, and in order to perform desired color correction,
The operator must be quite skilled, and the operator wants to modify the color tone with six hues (C, M, Y, R,
In the case of the boundary portion of (G, B), for example, since the hues overlap each other in a complicated manner, there is a problem that the color tone correction requires considerable skill.

[0008] Further, since color correction by color correction does not include an element for judging lightness or saturation, for example, it is necessary to correct only a bright red portion of an output signal in the operation. There is also the problem that it cannot be done.

The present invention has been made in view of such circumstances, and it is possible to easily perform color correction.
Moreover, it is an object of the present invention to provide a color tone correcting device in which the intention of the operator is reliably reflected.

[0010]

The present invention has the following configuration to achieve the above object. That is, according to the first aspect of the present invention, the three primary color signals (RGB signals) of the additive color mixture of each pixel of the original image are converted into predetermined RGB / CM signals for each pixel.
Three primary colors (CMY signals) of subtractive color mixing by YK conversion processing
And a black (K signal), and a color tone correction device for correcting the color tone of these CMYK signals, comprising: original image data storage means for storing RGB signals of respective pixels of the original image; RGB / CMYK conversion means for converting a signal into the CMYK signal, an image data conversion table for converting the RGB signal into three perceived color attribute values (hue, saturation, lightness: HSL value), and storing the original image data A target signal to be subjected to color correction processing from the RGB signals stored in the means; a target signal to be obtained after the color correction of the corrected signal; and a color correction based on the corrected signal. A processing condition designating unit for designating the effective range of the process with the HSL value, and a signal to be corrected designated by the processing condition designating unit being converted into CMYK by the RGB / CMYK conversion unit. Parameter calculation means for calculating a parameter for color tone correction based on the corrected conversion signal converted into a signal and the target signal specified by the processing condition specification means, and an original image data stored in the original image data storage means. An HSL value obtained by giving the RGB signal of each pixel to the image data conversion table, and an HSL indicating an effective range of a color tone correction process designated by the processing condition designation means.
A processing target determining unit that determines a pixel to be subjected to a color tone correction process by comparing the RGB signal of each pixel of the original image stored in the original image data storing unit with the RGB / C.
CMY obtained by sequentially giving to MYK conversion means
Correction processing means for performing a color tone correction processing by applying a parameter calculated by the parameter calculation means to a CMYK signal of a pixel within an effective range determined by the processing target determination means among the K signals. It is provided.

The invention described in claim 2 is the first invention.
In the color tone correction device described in the above, a difference value between the HSL value of the pixel corresponding to the signal to be corrected and the HSL value of the pixel determined to be a color tone correction processing target by the processing target determination means is calculated, and the difference value is calculated. The color correction process as the size increases
And a parameter correcting means for correcting the parameter so as to reduce the effect of (1).

[0012]

The operation according to the first aspect of the present invention is as follows. The processing target determination means includes an HSL value indicating an effective range of the color tone correction processing specified by the processing condition specification means,
An RGB signal of each pixel of the original image is given to the image data conversion table and compared with an HSL value obtained to determine whether or not the pixel is a target of color tone correction. Then, in the correction processing means, of the CMYK signals obtained by sequentially providing the RGB signals of the respective pixels of the original image to the RGB / CMYK conversion means, the CMYK signals of the pixels determined to be subjected to the color tone correction processing are processed. Then, based on the signal to be corrected (designated by RGB) and the target signal (designated by CMYK) designated by the processing condition designating means, the color tone is corrected by applying the parameters for the color tone correction calculated by the parameter calculating means.

That is, the processing target of the color tone correction is determined based on the HSL color space in which the hue H, the saturation S, and the lightness L, which are the three attribute values of the human perceived color, are three-dimensional coordinates. The operator can also specify the effective range, such as to correct only the bright red part, so that the operator can correct the color tone as desired. In addition, the operator can perform desired color correction only by specifying the signal to be corrected, the target signal, and the effective range of the color correction processing, so that the operation is extremely easy.

The operation according to the second aspect of the present invention is as follows. In the color tone correction according to claim 1, the HSL value (hsl) of the pixel determined to be a color tone correction target by the processing target determination means is a value determined to be within an effective range based on the signal to be corrected. Therefore, the difference between this value and the HSL value (HSL) of the pixel corresponding to the signal to be corrected is defined as the minimum value when (HSL) = (hsl).
(Hsl) increases as it approaches the limit value of the effective range, that is, the boundary value between the target pixel and the non-target pixel of the color tone correction process in the color space.

[0015] The parameter correcting means is adapted to reduce the effect of the color tone correction processing as the difference value increases.
Since the parameter is corrected, the intensity of the color tone correction processing in the correction processing means using this parameter is minimized at the boundary between the target pixel and the non-target pixel, and as the target pixel approaches the pixel corresponding to the signal to be corrected. growing. Therefore, in the image after the color tone correction processing, the color does not suddenly change at the boundary between the target pixel and the non-target pixel.

[0016]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an external perspective view of the color tone correcting device. An image monitor 3 for displaying an original image or the like to be subjected to color correction (hereinafter simply referred to as color correction), a data input device 4, and a magneto-optical disk drive 1 for storing image data (a magneto-optical disk driver 1) The main components are a frame memory unit 2 having a built-in frame memory for storing an RGB signal of each pixel of an original image, and a computer main unit 8 having a main function of color correction processing.

The data input device 4 comprises an operation monitor 5, keyboard, and mouse 7 for inputting data from an operator of the present device.

FIG. 2 shows a system block diagram of the present apparatus, and the configuration and operation of the present apparatus will be described with reference to the block diagram together with the operation of the operator. However, FIG. 2 independently shows, as a block diagram, functions relating to color correction processing among the processing functions of the computer main body 8, and other processing such as processing for outputting and displaying data on the operation monitor 5 and the like. Is included in the data input device 4.

The magneto-optical disk driver 1 is for taking the digitized image signal of the original image into the present apparatus. It is assumed that the original image signal is stored on a magneto-optical disk, but it may be stored on a magnetic tape or on a hard disk. In such a case, the drive device that accesses each storage medium replaces the magneto-optical disk driver 1.

The first frame memory 10 stores R for one frame of the original image read by the magneto-optical disk driver 1.
(Red), G (green), and B (blue). The original image signal in the first frame memory 10 is output to the image monitor 3 via the internal switch SW to be displayed as an image. When the operator operates the pointing device such as the mouse 7 of the data input device 4 while viewing the screen to specify the display location of the color to be corrected, the data input device 4 is displayed on the screen of the image monitor 3. The coordinate data of the point is output as a read address to the first frame memory 10.

Here, the read three primary color signals of R, G, and B are defined as R _U, G _{U, and} B _U signals. The _RU, GU _{, and BU} signals are
The R, G, and B signals of the point (pixel) designated by the mouse 7 described above, but the color of the point designated by the operator, that is, the color of the signal to be corrected visually determined by the operator (hereinafter, the color of the signal to be corrected) Strictly speaking, not only the color of the specified point on the screen but also the color around the specified point is affected. Therefore, as the R _U, G _{U, and} B _U signals, the R _, G _{, and} B signals of the four pixels adjacent to the point designated by the mouse 7 or the eight pixels around the pixel are used.
The average of the values of the G and B signals may be used.

The R _U, G _{U, and} B _U signals can be obtained by, for example, directly specifying the pixels of the original image displayed on the image monitor 3 with the mouse 7 or the like from the keyboard 6 as described above. , G, and B signals. At this time,
For example, R, G,
If B signal is a digital signal of 8 bits each, R _U, G it numerically to "0 to 255", which is converted to a decimal
_{U, BU} signal may be specified, or "0-255"
May be specified by a numerical value of "0 to 100 (%)" which is a percentage of the numerical value of "." If all pixels in the original image corresponding to the R _U, G _{U, and BU} signals of the color to be corrected are displayed on the image monitor 3 in a special color display or blinking display, etc. The operator can easily grasp the distribution of the corrected colors.

The R _U, G _{U, and BU} signals are stored in the first pixel value memory 11.
And output to the parameter calculation unit 12 and the color patch display memory 13, and further stored in the RGB / C
After being converted into C, M, Y, K signals via the MYK conversion unit 14, the signals are also supplied to the data input device 4.

These memories and a memory described later exist, for example, as a part of a storage area of an internal memory (main storage device) of the computer main body 8, and each arithmetic processing unit executes a program according to the processing algorithm. It corresponds to a CPU (Central Processing Unit) that executes.

The color patch display memory 13, the area being predefined on the screen of the image monitor 3 (e.g., the lower left corner near the like of the screen) of the above address corresponding to R _U, G _U, B _U The signal is stored and output to the image monitor 3, and the color patch of the color to be corrected is superimposed and displayed on the original image.
The color patch refers to a color in which a predetermined area of the image monitor 3 is filled with the color so that the operator can independently observe the color to be corrected specified on the original image.

[0026] Incidentally, as described above R _U, G _U, B and _U signals to specify a numeric value from the keyboard 6, the image monitor 3 to be revised color specified (color patch) is in real time
Are displayed on the screen, the operator can specify the designated R _U, G _U, B
The correlation between the numerical value of the _U signal and the color to be corrected can be immediately grasped. If the color of the color patch is different from the color to be corrected _, RU, _GU, B _The color to be corrected can be easily and accurately specified by updating the value of the _U signal.

The RGB / CMYK conversion section 14 converts the supplied RGB signals (R _X, G _X, B _X ) into CMYK signals (C _X, M _X, Y _X, K _X ). , And this is converted, for example, by the following equation. _{C X = α 11 R X -α} 12 G X -α 13 B X M X = -α 21 R X + α 22 G X -α 23 B X Y X = -α 31 R X -α 32 G X + α 33 B _X K _X = MAX (C _X, MX _, Y _X ) where α _ij (i = 1 to 3, j = 1 to 3) is a predetermined coefficient (positive value), and MAX (C _{X ,} M _X, Y _X) is, C _X,
A function for extracting the largest one of M _{X and} Y _X is shown. It should be noted that the relationship between the CMYK signals corresponding to the RGB signals obtained by the above conversion equation is set as a table,
The B / CMYK conversion unit 14 may be configured.

C, M, Y, K for R _U, G _{U, BU} signals
The data input device 4 to which the signal is given is assigned to its C, M,
The Y and K signals are converted into numerical values, and the numerical values are output and displayed on the operation monitor 5. For example, if each of the C, M, Y, and K signals is an 8-bit digital signal, the C, M, Y, and K values are converted into decimal numbers and represented by numerical values from "0 to 255".
The signal may be expressed, or a numerical value of "0 to 255" may be expressed as a percentage of "0 to 100 (%)".

[0029] The operator, the color patches of the revised color displayed on the image monitor 3 above, R _U, which is displayed on the operation monitor _5, G _U, C for B _U signal, M, Y, K signals , C, M, and C of a color (hereinafter, a target color) to be obtained after color correction for the color selected as the signal to be corrected.
Numerical values of the Y and K signals (target signals) are input from the keyboard 6.

The data input device 4 generates C, M, Y, and K signals corresponding to the input values, outputs the generated signals to the parameter calculation unit 12, and outputs the C, M, Y, and K signals via the CMYK / RGB conversion unit 15.
After being converted into R, G and B signals, the signals are supplied to the color patch display memory 13. The C, M, Y, K signals of the target color are
_{T, M T, Y T,} K T signal, denoted the _{C T, M T, Y T} , K T R the signal is converted, G, and B signals R _T, G _T, and B _T signal.

The color patch display memory 13 stores the R
_U, G _U, to another storage location with the same area as the storage area storing the B _U signal (e.g., a storage location corresponding to the next display location of the modification of color patches of the), R _T, G _T,
The _BT signal is stored and output to the image monitor 3, and the color patch of the target color is superimposed and displayed on the original image.

As described above, when the operator sets C _T, M _T, Y _T, K
_When the value of the _T signal is input, the R,
Since an image (color patch) corresponding to the G and B signals is displayed on the image monitor 3, the operator can set the C _T,
The approximate correlation between the values of the MT _, YT _{, and KT} signals and the assumed target color can be immediately grasped. If the color of the color patch is different from the assumed target color, C _T, M _T,
The target color can be designated by updating the numerical values of the Y _{T and} K _T signals, for example.

The CMYK / RGB converter 15 converts the supplied CMYK signal into an RGB signal and outputs the signal. For example, this conversion is performed by Neugebaue.
This is performed by a known conversion formula using the r (Neugebauer) equation or the like.

Note that C obtained by a known conversion formula
The relationship between the RGB signals corresponding to the MYK signals may be set as a table to configure the CMYK / RGB conversion unit 15.

When the designation of the color to be corrected and the target color is completed,
Subsequently, the operator specifies the effective range of the color correction from the color to be corrected to the target color. In the present apparatus, the designation of the effective range is determined by the hue H, which is the three attribute values of the human perceived color.
(Hue), saturation S (Saturation), and lightness L (Lightness)
It is done with two parameters. The effective range is such that the hue corresponding to the R _U, G _{U, and} B _U signals of the color to be corrected is H _U,
When the saturation is S _{U and the} lightness is L _U , H _U ± dH, S _U
It is input as dH, dS, dL represented by ± dS, L _U ± dL, and stored in the effective range memory 16.

The present apparatus uses the information input or extracted so far, that is, the "R, G, B signals (R
_U, GU _{, BU} signals), "C, M, Y, K signals of target colors ( _CT, MT _, YT _{, KT} signals)", "Data dH, dS of the effective range of color correction" , DL ”, it is determined whether or not the color components of each pixel of the original image stored in the first frame memory 10 are within the effective range of the color correction. Is determined, and the RGB signals of each pixel of the original image are converted to C
The color correction processing after the conversion into the MYK signal is performed.

First, the color component of each pixel of the original image is HSL
A lookup table 17 for converting the values of R, G, and B into the values of hue H, saturation S, and lightness L in order to determine whether or not the color correction is within the effective range of color space in the following procedure. Create and keep.

Since the values of R, G, and B do not directly correspond to the values of hue H, saturation S, and lightness L, the values of R, G, and B are represented by a Lab color system (this display system is , International Commission on Lighting (CI
E) is a display system recommended in 1976 as a uniform perceived color space. ), And the value of the Lab color system is H
A procedure of converting to a value in the SL color space is adopted.

In order to convert the values of R, G, and B into a Lab display system, first, the tristimulus values Xima obtained when the maximum values Rmax, Gmax, and Bmax of R, G, and B are added to the image monitor 3.
x, Yimax, Zimax (i = R, G, B) are measured with a spectroradiometer.

Next, using the gamma of the image monitor 3 (constant indicating the relationship between the input signal of the color monitor and the light emission output: hereinafter referred to as a symbol t for convenience), arbitrary RGB values r, g, The tristimulus values X, Y, and Z when b is input are obtained by the following equations. X = Σ (j / imax) ^t · Ximax: (i = R, G, B,
j = r, g, b) Y = Σ (j / imax) ^t · Yimax: (i = R, G, B,
j = r, g, b) Z = Σ (j / imax) ^t · Zimax: (i = R, G, B,
j = r, g, b) In each of the above equations, each time i = R, G, B, j = r, g, b.

Using these tristimulus values X, Y, Z, R, G,
The value of B is converted into a value of the Lab color system by the following equation. This conversion formula is determined by the CIE. L = 116 · (Y / Yn) ^1/3 -16 a = 500 · [(X / Xn) ¹ /3-(Y / Yn) ^1/3 ] b = 200 · [(Y / Yn) ^1/3 − (Z / Zn) ^1/3 ] where Yn = ΣYimax (i = R, G, B) and Xn =
ΣXimax (i = R, G, B), Zn = ΣZimax (i
= R, G, B).

FIG. 3 shows the relationship between the Lab color system and the HSL color space. In FIG. 3, the L axis of the Lab color system is HS
It corresponds directly to the lightness L of the L color space, the moving radius on the two-dimensional coordinates of the a-axis and the b-axis corresponds to the saturation S, and the angle θ between the a-axis and the moving radius corresponds to the hue H. . Therefore, the value of L obtained as described above is directly used as the value of lightness in the HSL color space, and the saturation S and the hue H are obtained using the following equations.

S ² = A ² + B ² H = tan ⁻¹ (B / A) However, when A <0, 180 degrees are added to the calculation result of the hue H, and when A> 0 and B <0, Add 360 degrees. This is because a negative value is not output as a calculation result.

In the look-up table 17 of FIG. 2, the values of H, S, and L corresponding to the values of the R, G, and B signals obtained by the above arithmetic expressions are stored. But,
Assuming that the number of bits of the digitized R, G, and B signals is n, the combination of the values of R, G, and B is n ³ , and if the values of H, S, and L corresponding to all of them are tabulated, it is enormous. Since the data amount is n, for example, the lower few bits of n bits are deleted to make m bits (n> m).
The values of H, S, and L corresponding to the G and B signals (represented by n bits because there is no need to reduce this data) may be stored in the look-up table 17.

The reason why the values of the R, G, and B signals are converted to values in the HSL color space is to determine whether the color components of each pixel of the original image are within the specified effective range of color correction. Yes,
A decrease in accuracy due to a reduction in the number of bits of the R, G, and B signals is not particularly problematic.

Therefore, of the R _U, G _{U, and} B _U signals (n bits) of the color to be corrected stored in the first pixel value memory 11, only the m bits excluding the lower several bits are looked up in the look-up table 17. To obtain the n-bit values of H, S, and L. This is represented as H _U, S _U, L _U. H _U, S _{U, and} L _U are stored in another storage area of the first pixel value memory 11.

The parameter calculating unit 12 to which the R _U, G _{U, and} B _U signals of the color to be corrected and the C _T, M _T, Y _{T, and} K _T signals of the target color are given firstly. R _U, GU _{, BU} signal
The corrected conversion signal (C _U,
M _U, Y _{U, and} K _U signals), and the parameters kc, km, ky, and kk required for the color correction processing are calculated by the following equations. _{kc = C T / C U -1} km = M T / M U -1 ky = Y T / Y U -1 kk = K T / K U -1 calculated kc, km, ky, kk parameter memory
Stored at 18.

Next, the R, G, and B signals of each pixel of the original image stored in the first frame memory 10 are sequentially read out and temporarily stored in the second pixel value memory 19. Assuming that the number of pixels in the horizontal direction of the first frame memory 10 is x and the number of pixels in the vertical direction is y, the pixel ij (i = 1, 2,... X, j =
1, 2,... Y) Rij, Gij, Bij signals are
, And, like the first pixel value memory 11, m-bit Rij,
Gij and Bij signals are output to the look-up table 17,
The corresponding n-bit Hij, Sij, Lij is stored in another storage area of the second pixel value memory 19.

The Rij, Gij, and Bij signals (the original n-bit signals from which the lower several bits are not deleted) are RGB /
The C, M, Y, and K signals (Cij,
Mij, Yij, and Kij signals) and supplied to the color correction processing unit 21.

The comparing unit 20 compares H _U, S _{U, and} L _U stored in the first pixel value memory 11 with H ij, S ij, and L ij stored sequentially in the second pixel value memory 19. Then, the absolute difference amount is stored in the effective range memory 16 as d
It is determined whether the values are larger than the values of H, dS, dL. The comparison formula is shown below. _{| Hij-H U | <dH} | Sij-S U | <dS | Lij-L U | <dL

When all the values of Hij, Sij, and Lij satisfy the above-mentioned comparison formula (when the value of the HSL color space of the pixel ij read from the first frame memory 10 exists within the effective range). The comparison unit 20 outputs a control signal to the color correction processing unit 21 to instruct execution of the processing. Conversely, Hij, Sij, L
If any one of ij does not satisfy the above comparison formula (when it is out of the effective range), the color correction processing unit 21
Output a control signal instructing the default of the process.

Based on a control signal instructing the execution of the processing, the color correction processing section 21 stores the H _U, S _{U, and} L _U data stored in the first pixel value memory 11 and the second pixel value memory. Hij, Sij, Lij data stored in the memory 19, dH, dS, dL data stored in the effective range memory 16, kc, k stored in the parameter memory 18.
The data of m, ky, and kk are read. Then, the Cij, C, M, Y, and K signals are converted from the second pixel value memory 19 via the RGB / CMYK conversion unit 14, and the supplied Cij,
The Mij, Yij, and Kij signals are subjected to color correction processing as described below. The processed C, M, Y, K signals are stored in another memory 23.
R, G, B signals obtained by converting the same signal through the CMYK / RGB conversion unit 15 are stored in the second frame memory.
Stored at 22.

The color correction processing section 21 receives the control signal instructing the default of the processing from the comparison section 20 and outputs the RGB signal.
Cij, Mij, Y supplied from the / CMYK conversion unit 14
The ij and Kij signals are output as they are and stored in another memory 23. The R, G, B signals obtained by converting the same signal via the CMYK / RGB conversion unit 15 are stored in the second frame memory 22.

The color correction process basically multiplies kc, km, ky, and kk calculated by the parameter calculator 12 with the Cij, Mij, Yij, and Kij signals of the pixel ij determined to be processed. Should be added to the Cij, Mij, Yij, and Kij signals. However, in such a case, the following problem may occur.

That is, as described above, the color correction processing is performed on the pixel group of the portion where the values of the R, G, and B signals of the original image are smoothly changed, based on the designated effective range.
When the default is distinguished, the color suddenly changes in the middle of the smoothly changing pixel group, which may result in an unnatural image. A phenomenon called a so-called tone jump occurs. Therefore, in order to solve such a problem, the following processing is performed before performing the color correction processing.

First, as shown in the following equation, the Rij, Gij, and Bij signals Hij, Sij,
And Lij data, the modified color of R _U, G _U, B _U signal H _U, S _U,
L _U data and the difference absolute value of the amount of [Delta] H, [Delta] S, calculates the [Delta] L. _{| Hij-H U | = ΔH} | Sij-S U | = ΔS | Lij-L U | = ΔL

The parameters kc, kc according to the difference amount
A coefficient for varying m, ky, and kk is obtained by the following calculation. 1-([Delta] H / dH) = kh 1-([Delta] S / dS) = ks 1-([Delta] L / dL) = kl In the above equation, dH, dS and dL are the values of the color correction processing stored in the effective range memory 16. This is a value indicating an effective range, that is, a value indicating a boundary between a pixel to be processed and a pixel not to be processed. Kh, ks, kl are ΔH, Δ
As S, ΔL approaches dH, dS, dL, the minimum value approaches “0”, and ΔH, ΔS, ΔL approach “0”.
That is, the coefficient approaches the maximum value “1” as the distance from dH, dS, dL increases.

Therefore, the coefficients kh, ks, and kl are calculated by using the following equations to obtain the color correction parameters kc, km, ky,
When acting on kk, kc, km, ky, kk are reduced as the boundary value is approached (farther from the color to be corrected), and kc, km, ky, and kk are reduced as the distance from the boundary value (closer to the color to be corrected) is increased. , Km, ky, kk are obtained. The parameters are KC,
Expressed as KM, KY, KK. KC = kc-kh-ks-kl KM = km-kh-ks-kl KY = ky-kh-ks-kl KK = kk-kh-ks-kl

The parameters KC, KM, K
By using Y and KK in the color correction process, natural color correction can be performed without suddenly changing the color of the image in the middle of the smoothly changing pixel group. In addition, kh · ks · on the right side of each of the above parameters KC, KM, KY, and KK.
Instead of kl, the square root of kh · ks · kl (√ (kh ·
ks · kl)) may be used.

The color correction processing section 21 includes a second pixel value memory 19
, C, M, Y, K via the RGB / CMYK conversion unit 14
Cij, which is converted into a signal and is supplied to the processing target pixel.
The above parameters KC, K are added to the Mij, Yij, Kij signals.
A value obtained by multiplying M, KY, and KK is added to perform a color correction process. cij = Cij · (1 + KC) mij = Mij · (1 + KM) yij = Yij · (1 + KY) kij = Kij · (1 + KK) These cij, mij, yij, and kij are C, M, and Y of the pixel ij after the color correction processing. , K signal and stored in another memory 23.

The image signal after the color correction processing stored in the second frame memory 22 (the CMYK /
The Rij, Gij, and Bij signals converted via the RGB converter 15 and the unprocessed image (original image) signal stored in the first frame memory 10 are output from the data input device 4 such as the mouse 7. The data is selectively output to and displayed on the image monitor 3 by an internal switch SW that is switched by a switch or the like. The image before color correction and the approximate image after color correction can be compared alternately, which is practically convenient. The two images may be divided and displayed in parallel on the image monitor 3.

The operator looks at the image after the color correction displayed on the image monitor 3 and if the color correction is performed as expected, the color-corrected Cij, Cij, stored in another memory 23. An instruction is issued to output the Mij, Yij, and Kij signals to the magneto-optical disk driver 1, and the signals are recorded on the magneto-optical disk.
Then, using the magneto-optical disk as a medium, the Cij, Mij, Yij, and Kij signals after color correction are transferred to another plate making system or the like. The medium for recording the Cij, Mij, Yij, and Kij signals after color correction is not limited to a magneto-optical disk, but may be a magnetic tape or a hard disk. Further, it may be output to a film recorder or a hard copy device.

According to the above-described embodiment, the color correction processing is performed only on the pixels within the designated effective range, but this processing is performed on all the pixels of the original image. That is,
In one image, all the pixels within the specified color range are subjected to the color correction processing. If this is inconvenient, the above processing may be performed only on the area specified by the mouse 7 or the like of the data input device 4.

In the above embodiment, the operator is 1
Although the configuration is such that a set of colors to be corrected (signals to be corrected) and target colors (target signals) are specified, a plurality of sets of colors to be corrected (signals to be corrected) and target colors (target signals) are specified. Alternatively, the color correction processing may be performed. By doing so, the accuracy of color correction can be further improved.

The system described in the above embodiment may be configured to be incorporated in a color scanner for plate making. That is, R, R of the original image color-separated by the input scanner
The G and B signals are transferred to the first frame memory 10 in this embodiment.
After performing the processes shown in the system block diagram of FIG. 2, the Cij, Mij, Y
In this configuration, ij and Kij signals are supplied to an output scanner. With this configuration, when performing color correction using a color scanner, complicated operations in the conventional color correction are not required, and the efficiency of the plate making process can be increased.

[0066]

As is apparent from the above description, according to the color tone correcting apparatus of the first aspect of the present invention, the HS indicating the effective range of the color tone correcting process specified by the processing condition specifying means.
The L value is compared with the HSL value obtained by giving the RGB signal of each pixel of the original image to the image data conversion table, and it is determined whether or not the pixel is a target of color tone correction. HSL color with three attribute values of hue H, saturation S, and lightness L, which are the three attribute values of the human perceived color, only for the pixels determined to be Since the target of the color tone correction processing is determined based on the space, for example, it is possible to specify an effective range such as to correct only the bright red portion of the output signal, and the operator can perform the color tone correction as desired. it can. Further, in performing such color tone correction, the operator can perform desired color tone correction simply by specifying the signal to be corrected, the target signal, and the effective range of the color tone correction processing, so that the operator's operation becomes extremely easy.

According to the color tone correcting apparatus of the present invention, the difference value between the HSL value of the pixel corresponding to the signal to be corrected in the original image and the HSL value of the pixel determined to be the target of the color tone correction The effect of the color tone correction process decreases as
Since the parameters are corrected so as to be smaller and used in the tone correction processing, the intensity of the tone correction processing is minimized at the boundary between the pixel subjected to this processing and the pixel not subjected to this processing, and the pixel subjected to this processing is corrected As the value approaches the value of the pixel corresponding to the signal in the color space, the color tone can be smoothly corrected so that the intensity becomes maximum, and a natural color tone correction that avoids a phenomenon called tone jump can be realized.

[Brief description of the drawings]

FIG. 1 is an external perspective view of a color tone correcting device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an internal configuration thereof.

FIG. 3 is an HS in which values of hue, saturation, and brightness are three-dimensional coordinates.
FIG. 3 is a diagram illustrating a relationship between an L color space and a Lab color system.

[Explanation of symbols]

4 Data input device (processing condition specifying means) 10 First frame memory (original image data storage means) 12 Parameter calculating section (Parameter calculating means) 14 RGB / CMYK converting section (RGB / CMYK converting means) 17 … Look-up table (image data conversion table) 20… Comparison unit (processing target determination unit) 21… Color correction processing unit (correction processing unit, parameter correction unit)

Claims (2)

(57) [Claims] 1. A three-primary color signal (RGB signal) of additive color mixture of each pixel of an original image is converted into a predetermined RGB / CMYK signal for each pixel.
A color tone correction device that converts the color into three subtractive primary colors (CMY signals) and black (K signal) by a conversion process, and corrects the color tone of these CMYK signals. An original image data storage unit for storing a signal; and an RGB / RGB signal for converting the RGB signal into the CMYK signal.
CMYK conversion means; an image data conversion table for converting the RGB signals into three perceived color attribute values (hue, saturation, lightness: HSL values); and color tone correction from the RGB signals stored in the original image data storage means Designation of the signal to be corrected which is the center of the processing, designation of the desired signal to be obtained after the tone correction for the signal to be corrected, and designation of the effective range of the tone correction processing based on the signal to be corrected by the HSL value A modified condition signal obtained by converting the signal to be modified specified by the processing condition specifying device into a CMYK signal by the RGB / CMYK conversion device, and an object designated by the processing condition specifying device. A parameter calculating means for calculating a color tone correction parameter based on the signal, and an RGB signal of each pixel of the original image stored in the original image data storing means, A process of comparing the HSL value obtained by giving the data to the data conversion table and an HSL value indicating the effective range of the color tone correction process specified by the processing condition specifying means to determine a pixel to be subjected to the color tone correction process Object determination means; and the processing object determination means of the CMYK signals obtained by sequentially applying the RGB signals of each pixel of the original image stored in the original image data storage means to the RGB / CMYK conversion means. Correction processing means for performing a color correction processing by applying the parameters calculated by the parameter calculation means to the CMYK signals of the pixels within the effective range. 2. The color tone correcting apparatus according to claim 1, wherein an HSL value of a pixel corresponding to the signal to be corrected and an HSL value of a pixel determined as a color tone correction target by said processing target determination means.
A color tone correction device comprising: a parameter correction unit that calculates a difference value from the value, and corrects the parameter such that the effect of the color tone correction processing decreases as the difference value increases.