JPH05292303A - Color picture printer - Google Patents

Abstract

PURPOSE:To attain the print of color reproduction with high precision and to adjust color by blightness, hue and saturation by converting the hue and saturation adjusted based on a lookup table into the hue and saturation on an orthogonal coordinate, adding the blightness to them and applying Y, M, C conversion to the result. CONSTITUTION:A standardizing circuit 1 converts picture data into R, G, B data in compliance with standards. In order to express picture data on the Munsell system based on the R, G, B system, an RGB-VHC conversion circuit 2 converts the RGB data into VHC data. The blightness and the contrast are adjusted by using a V adjustment LUT 3 to make compression/expansion based on a range of the blightness of a printer from the blightness of input picture data, the hue is adjusted based on an H adjustment LUT 4, the saturation is adjusted by a C adjustment LUT 5, the VHC data are converted into signals S1, S2 by the H, C adjustment LUT 4, 5, and the VHC data are mapped into YMC data via an S1, S2-YMC conversion circuit 7 together with an output V of the V adjustment LUT 3. Thus, the YMC data with respect to the object VHC data are outputted with high precision and then the color displayed on a display device is printed out with high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image printing apparatus, and more particularly, to a color image printing apparatus for performing color adjustment with lightness, hue and saturation which a user can easily adjust.

[0002]

2. Description of the Related Art Conventionally known color image printing methods and apparatuses of this type include those disclosed in JP-A-1-234251 and JP-A-1-234252. JP-A-1-
The color correction method presented in Japanese Patent No. 234251 divides a color space formed by R, G, and B into a plurality of colors, and determines the Y, M, and C ink amounts having the best reproducibility for each division point. It is stored in a look-up table, and the intermediate values other than the division points are obtained by linear interpolation. Color adjustment is performed by changing the value corresponding to the division point. Further, the color correction method and apparatus presented in JP-A-1-234252 convert the input data into density data Y, M, C, and
The maximum value, the intermediate value, and the minimum value of M and C are obtained, and Bk, which is an achromatic color component, is subtracted from the minimum value, and R, G, and B, which are the colors obtained by subtracting the minimum value from the intermediate value and overlapping two color inks. , A single color Y, M, and C obtained by subtracting the intermediate value from the maximum value, each component is adjusted by a look-up table, and then combined.

[0003]

[Patent Document 1] Japanese Patent Laid-Open No. 1-234
In the technology disclosed in Japanese Patent No. 251, the corresponding R is adjusted in order to adjust the three attributes of the color to be originally adjusted (brightness or lightness, hue or hue, vividness or saturation).
There is no formula for changing the GB data in what direction, and it cannot be done unless complicated setting work is performed. Further, in the technique disclosed in Japanese Patent Application Laid-Open No. 1-234252, there is no formula for adjusting the hue and saturation, and setting of each adjustment amount is complicated.

It is an object of the present invention to provide a color image printing apparatus capable of highly accurate color reproduction printing and easy adjustment by three attribute parameters (lightness V, hue H, saturation C) of a color which a user can easily adjust. It is in.

[0005]

In order to achieve the above object, the present invention inputs RGB image data captured from a color scanner, a color camera or the like or RGB image data from a computer and outputs these image data. In a color image printing apparatus for printing after correction processing, a unit for converting input RGB image data into color image data conforming to a certain standard, and color data of the converted image data having lightness V, hue H, and saturation C. And a means for adjusting the lightness V, hue H, and saturation C by a look-up table in which various conversion curves are stored and which are selected in advance by instruction data from a panel or a computer. , The adjusted hue H and the saturation C are two parameters S of the orthogonal coordinate system.
1, S2 conversion means, V, S1, S2 Y, M,
A color image printing apparatus for converting into C and printing is provided.

Since the V, S1, S2-YMC conversion is non-linear, the conversion may use a mapping method other than the calculation.

[0007]

[Function] Display standards include NTSC standard and HDT
There are some standards such as V standard and CRT used in personal computers, etc., which are slightly changed, and the RGB signals or RGB data generated from them are different even for the same display color, so on the printer side ,
Standard RGB is determined and the input image data is converted to match it. Furthermore, this RGB image data is CIE
(Commission Internationale de l'Eclairange)
It may be converted into standard XYZ chromaticity coordinate values. XY
The Z chromaticity coordinate is a standard coordinate that quantitatively represents a color. The converted image data is converted into lightness V, hue H, and saturation C, which are said to be three attributes of a color that are easy to adjust. This conversion is non-linear, and the method uses an arithmetic circuit or a mapping circuit that determines and maps a representative point and interpolates other than the representative point. When the mapping method is used, since it is more accurate to perform it between orthogonal coordinate systems, the mapping is performed from RGB which is an orthogonal coordinate system to V, S1 and S2 which are orthogonal coordinate systems. Then, S1 and S2 are converted into hue H and saturation C. As a means for adjusting V, H, and C, a look-up table storing some conversion curves is prepared and the conversion curve is selected in advance. V, H and C are adjusted by this curve. For example, in the V adjustment curve,
When the brightness of the input image data is larger than the brightness expression range of the printer, the brightness is compressed. When the brightness of the input image data is small, the brightness is extended, and there are curves for adjusting contrast and brightness. Next, the adjusted VH
This cannot be done without converting the C data into the print data Y, M, C, but VHC and YMC have a non-linear relationship, and
Convergence calculation is involved in obtaining YMC from HC. Therefore,
VHC is converted into orthogonal coordinate values V, S1, S2, the color space created by all V, S1, S2 is divided into a plurality of regions, and the values of Y, M, C corresponding to these division points are set. It is determined experimentally or by using a color reproduction model of the printer and corresponding. Except for the division points, they are obtained by interpolation calculation. In addition,
YMC with the smallest color difference when there is no corresponding YMC point
Match the points.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a color image processing apparatus according to an embodiment of the present invention. In the figure, a standardization circuit 1 defines output signals from a video camera or a color scanner and image data output from a computer to a certain standard (for example, N.
It is converted into R, G, B data according to the TSC method). In general, output data from a video camera or a computer is subjected to a conversion curve called video gamma as shown in FIG. 2, and in order to obtain RGB data of NTSCRGB standard, a standardization circuit 1 is used as shown in FIG. Performs inverse video gamma correction. In addition, RGB data other than NTSC is
Convert to RGB of NTSC standard by matrix conversion. As a result, the subsequent process only needs to support NTSC RGB data.

The RGB-VHC conversion circuit 2 converts the RGB color space into a Munsell color space (lightness V,
It is a cylindrical coordinate system that represents a color with a hue H and a saturation C. ) Convert RGB image data to VHC to represent the image data above. The method to convert from RGB to VHC is MTM
The law is known and converted by the following procedure.

(1) The RGB data is converted into chromaticity coordinate values XYZ in the XYZ color space.

[0012]

[Equation 1]

(2) Non-linear conversion is performed from X, Y and Z in consideration of the characteristics of human color perception.

[0014]

[Equation 2]

(3) H1, H2, and H3 are replaced by (M1, M2,
V).

[0016]

[Equation 3]

(4) Color planes S1 and S using M1 and M2
2 is calculated by the following formula.

[0018]

[Equation 4]

(5) Conversion to H, V, C data is performed using S1 and S2.

[0020]

[Equation 5]

As described above, the conversion from RGB to VHC is performed.

The V adjustment LUT 3 performs lightness compression when the lightness of the input image data is larger than the lightness expression range of the printer, and when the lightness expression range of the input image data is small,
It has the function of extending brightness and adjusting contrast and brightness. There is a conversion curve as shown in FIG. 3, in which lightness compression conversion is performed, and lightness extension conversion is performed. Emphasizes contrast, and emphasizes halftones. Is a curve that brightens overall,
Is an overall darkening curve. These curves are selected by the user from a panel or keyboard not shown.

The H adjustment LUT 4 can perform various color tone adjustments. For example, as shown in FIG. 4, the curve of is for converting a red color to a yellow color, and the curve of is a blue color. The color is converted to a cyan color. The curve of is a function of color assignment that converts a specific color to a different color. In this way, the H adjustment circuit 5 can adjust the hue of the specific color gamut of the input image data.

The C adjustment LUT 5 mainly performs saturation expansion when the saturation of the input image is low. There is a conversion curve as shown in FIG. 5, where is a curve for expanding the saturation when the saturation of the input image data is low, and is a curve for decreasing the saturation.

Next, the adjusted VHC data must be converted into print data Y, M, C, but VHC and YMC have a non-linear relationship, and convergence calculation is required to obtain YMC from VHC. Therefore, VHC is converted into rectangular coordinate values V, S1, and S2, and mapped to YMC. Here, the reason for converting VHC into V, S1, S2 is
This is because mapping accuracy is better when mapping from the orthogonal coordinate system V, S1, S2 to YMC which is the same orthogonal coordinate system than when mapping from VHC of the cylindrical coordinate system to YMC of the orthogonal coordinate system.

The HC-S1, S2 conversion circuit 6 converts HC into S1, S2 according to the following equation.

[0027]

[Equation 6]

The result of calculating this conversion formula for all HCs may be stored in the LUT and may be calculated by a lookup table formula.

The V, S1, S2-YMC conversion circuit 7 has
V, S1, S2 are mapped to YMC. This is to divide the color space created by all V, S1, S2 into a plurality of areas, and obtain the Y, M, C values corresponding to these division points experimentally or by using the color reproduction model of the printer. Let Except for the division points, they are obtained by interpolation calculation. If the interpolation calculation is rough, the color reproduction model may be used to further increase the number of division points. If there is no corresponding YMC point, the YMC point with the smallest color difference is associated. According to this mapping method, highly accurate color correction is possible.

The mapping method will be described in more detail. FIG. 6 shows a state in which the V, S1, S2 color space is divided into a plurality of areas in equal divisions, and the YMC corresponding to each division point.
The state of grid points of values is shown. The displayable area on the V, S1, S2 color space has an oval shape as indicated by the diagonal lines. FIG. 7 shows one set of divided blocks, and shows eight lattice points in the Y, M, and C color spaces corresponding to eight divided points in the V, S1, and S2 color spaces. YMC corresponding to arbitrary color data V, S1, S2 in the block is obtained according to the following equation.

[0031]

[Equation 7]

From these equations, V, S1 and S2 are YM
It is converted to C, but may be mapped using a lookup table.

FIG. 8 is a block diagram of a circuit for mapping from V, S1, S2 to YMC by a look-up table method. The V, S1, S2 color space is a combination of the high-order 6 bits of V and the high-order 4 bits of S1, S2 of 64 × 16.
It is equally divided into × 16 blocks.

First, according to the output value selection data, LUTa
8, the outputs of LUTb9 and LUTc10 are set to Y. In the LUTa 8, the result of calculating the term relating to V by the expression 7 is stored for each block designated by a combination of the upper 6 bits of V and the upper 4 bits of S1 and S2. Similarly, in LUTb9, the result of calculating the term relating to S1 in Equation 7 is stored for each block designated by a combination of the upper 6 bits of V and the upper 4 bits of S1 and S2. Similarly, in the LUTc 10, the result of calculating the term relating to S2 in Equation 7 is stored for each block designated by a combination of the upper 6 bits of V and the upper 4 bits of S1 and S2. When V, S1, and S2 of the input image data address the LUT, LUTa8, LUTb9, and LUTc10 to V terms,
The calculation results of the terms S1 and S2 are output, and the adder 11
Is added and output Y.

Next, according to the output value selection data, LUTa8,
The outputs of LUTb9 and LUTc10 are set to M. Similar to the Y operation, the LUT is set by V, S1, and S2 of the input image data.
The calculation results of the V term, the S1 term, and the S2 term related to M are output from a8, LUTb9, and LUTc10, and added by the adder 11 to output M.

Finally, by the output value selection data, LUTa
8. Set the outputs of LUTb9 and LUTc10 to C. In the same manner as above, the LUTa is changed by V, S1, and S2 of the input image data
The calculation results of the V term, the S1 term, and the S2 term related to C are output from 8, LUTb9, and LUTc10, and added by the adder 11 to output C. The look-up table method performs the conversion process at high speed. The configuration of another mapping circuit is shown in FIG. This is to calculate the constant term and the integration term separately. Equation 7 is transformed into the following.

[0037]

[Equation 8]

[0038] Similarly to the above equation, M and C are also calculated separately for the constant term and the integration term. For example, the operation of calculating Y will be described. When the output selection signal is Y and the input selection signal is V, the A term is output from the LUTd 12. Also, LUTe1
From B, the B term is output. The outputted B term is multiplied by V outputted from the selector 14 by the multiplier 15 in accordance with the instruction of the input selection signal, and the multiplication result and L by the adder 16.
The output from the UTd 12 is added. The output from the adder 16 is latched by the latch 17. Next, the input selection signal becomes S1, C + D.S1 is added in the same manner as above, and finally the input selection signal becomes S2, E + F.S2
Is added.

As described above, YMC for the target VHC can be output with high accuracy.

According to the present embodiment, the color displayed on the display can be printed with high precision color reproduction, and the color can be easily adjusted by the parameters of brightness, hue and vividness.

FIGS. 10 and 11 are explanatory views of another embodiment, in which RGB is converted into V, S1 and S2 by a mapping method. FIG. 10 shows a state in which the RGB color space is equally divided into a plurality of regions, and a state of grid points of V, S1, and S2 values corresponding to respective division points in the RGB color space. RG
The division point in the B color space and the grid point in the V, S1, S2 color space are 1
Correspond with one to one. FIG. 11 shows one set of divided blocks, and V and S corresponding to eight divided points in the RGB color space.
Eight grid points in the 1, S2 color space are shown. V, S1, S2 corresponding to arbitrary color data RGB in the block is expressed by
Is required according to.

Here, (R ₁ , G ₁ , B ₁ ), (R ₂ , G ₂ ,
B ₂ ) indicates the coordinate values of the initial point and the final point of the divided block, and (V ₁₁₁ , S1 ₁₁₁ , S2 ₁₁₁ ) to (V ₂₂₂ , S1 ₂₂₂ ,
S2 ₂₂₂ ) indicates the coordinate value of the corresponding grid point. 12
FIG. 4 is a block diagram of a circuit for mapping RGB to V, S1, S2. If each of the input data RGB is 8-bit data, the RGB color space is equally divided into blocks of 16 × 16 × 16 by a combination of respective upper 4 bits. The initial point and the final point of one divided block are designated by RGB upper 4-bit data,
R from the dividing point (R1, G1, B1) in the lower 4 bits of
Specify the GB distance.

The outputs V, S1, and S2 are 10, and
8 and 8 bits. V is brightness information, and the accuracy is low with 8 bits because it has high human identification ability. About 10 bits is enough.

First, according to the output value selection data, LUTf18,
The outputs of LUTg19 and LUTh20 are set to V. In the LUTf 18, the result of calculating the term relating to R by the equation 9 is stored for each block designated by the upper 4 bits of R, G, B. As well
In LUTg19, the result of calculating the term related to G in Equation 9 is R,
It is stored for each block designated by the upper 4 bits of G and B.

[0045]

[Equation 9]

Similarly, in the LUTh20, the result of calculating the term relating to B by the equation 9 is stored for each block designated by the upper 4 bits of R, G, B. RG of input image data
From B, LUTf18, LUTg19, LUTh20 to R term, G term,
The calculation result of the term B is output and added by the adder 21 to obtain V
Is output.

Next, according to the output value selection data, LUTf18, LUTg
19. Set the output of LUTh20 to H. LUTf18, LUTg19, LUTh20 depending on the RGB of the input image data as in the Y operation.
To R, G, and B calculation results are output and added by the adder 21 to output H.

Finally, according to the output value selection data, LUTf18,
The outputs of LUTg19 and LUTh20 are set to C. Similar to the above, LUTf18, LUTg19, LUTh20 depending on RGB of input image data
To R, G, and B are calculated, and added by adder 21 to output C.

It is also possible to obtain XYZ from RGB by the equation 1 and perform mapping from XYZ to V, S1 and S2 as described above.

The conversion from V, S1, S2 to VHC is a conversion from a rectangular coordinate system to a cylindrical coordinate system, and the conversion formula is shown below.

It is also possible to store the result of calculation of this conversion formula for all HCs in the LUT and use a look-up table formula.

According to this embodiment, RGB can be converted into VHC with a simple structure.

FIG. 13 is a block diagram of a color image processing apparatus of another embodiment according to the present invention. Characteristic value generation circuit 2
A circuit 2 generates a gamma value of the display and a matrix coefficient for converting from RGB to XYZ of the CIE standard by instructing a display type from a panel or a computer.

The gamma correction circuit 23 corrects the video gamma of RGB data by these outputs. RGB-XY
The Z conversion circuit 24 linearly converts RGB into XYZ. This XYZ is the tristimulus value of the color displayed on the display, and the color correction value of the printer is determined with this as the target color. As a result, the color correction of the printer only needs to correct the characteristics of the printer regardless of the characteristics of the input image data. The XYZ-VHC conversion circuit 25 operates similarly to the RGB-VHC conversion circuit 2.

According to the present embodiment, it is possible to provide the only printer that is highly accurately color-corrected with respect to the chromaticity coordinate values of the XYZ color system that do not depend on the characteristics of the display.

[0056]

According to the present invention, the color displayed on the display can be printed with high precision color reproduction, and the color can be easily adjusted by the parameters of brightness, hue and vividness.

[Brief description of drawings]

FIG. 1 is a block diagram of a color image printing apparatus that is an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a video gamma curve.

FIG. 3 is an explanatory diagram showing an example of a V conversion curve.

FIG. 4 is an explanatory diagram showing an example of a C conversion curve.

FIG. 5 is an explanatory diagram showing an example of an H conversion curve.

FIG. 6 is an explanatory diagram showing a state of mapping from a V, S1, S2 color space to a YMC color space.

FIG. 7 shows YM from one block on the V, S1, S2 color space.
Explanatory drawing of the method of mapping to one block on C color space.

FIG. 8 is a block diagram of conversion from V, S1, S2 to YMC using a mapping method.

FIG. 9 is a block diagram for mapping other V, S1, S2 to YMC.

FIG. 10 is an explanatory diagram showing a state of mapping from an RGB color space to a V, S1, S2 color space.

FIG. 11 shows V, S1, from one block on the RGB color space.
Explanatory drawing of the method of mapping to one block on S2 color space.

FIG. 12 is a block diagram of conversion from RGB to V, S1, and S2 using a mapping method.

FIG. 13 is a block diagram of a color image printing apparatus according to another embodiment.

[Explanation of symbols]

1 ... Standardization circuit, 2 ... RGB-VHC conversion circuit, 3 ... V
Adjustment LUT, 4 ... C adjustment LUT, 5 ... H adjustment LUT, 6
... HC-S1, S2 conversion circuit, 7 ... V, S1, S2-Y
MC conversion circuit.

Claims (1)

[Claims] 1. A color image printing apparatus for inputting RGB image data fetched from a color scanner or a color camera or RGB image data from a computer, correcting the RGB image data, and printing the RGB image data. Means for converting the data into color image data conforming to a certain standard; means for converting the color image data into color data of lightness V, hue H, and saturation C; and these lightness V, hue H, and saturation C, Various conversion curves are stored, a means for adjusting the conversion curve by a look-up table in which the conversion curve is selected in advance by instruction data from a panel or a computer, and two parameters of the adjusted hue H and saturation C of the orthogonal coordinate system. S1,
It comprises means for converting to S2 and means for mapping V, S1 and S2 to print data Y, M and C. The input RGB image data is converted to VHC to adjust VHC, and the adjusted VHC is adjusted. A color image printing apparatus, characterized in that it is converted into V, S1, S2 for accurate mapping, and these are mapped to Y, M, C which are print data.