JPH0918727A - Color reproducing processor - Google Patents

Abstract

PURPOSE: To form an output image where a color change is unremarkable from an image including a high saturation color and to generate an output image in which deformed gradation or skipped gradation is not caused. CONSTITUTION: After color image information in a frame memory 1 is received by a CPU 4 via an external interface 3, conversion circuits 5, 6 convert an RGB signal into an LCH (brightness, saturation, hue) signal. The LCH signal is converted into an LCH signal within a color reproducing range of an output system with a color conversion processing circuit 7 and then converted into a CMY signal for a printer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color for mapping input system color image information to color image information within the output system color reproduction range when the input device color reproduction range and the output device color reproduction range are different. The present invention relates to a reproduction processing device.

[0002]

2. Description of the Related Art A conventional color reproduction processing method will be described by taking a case where a color CRT is used as an input system device and a color inkjet printer is used as an output system device as an example.

Generally, these input / output devices are different in the color reproduction range of the input system and the color reproduction range of the output system.
Will be described. FIG. 14 shows the color reproduction range when the hue is red in each input / output device, in which the vertical axis represents lightness and the horizontal axis represents saturation. The area surrounded by the lightness axis and the broken line in FIG. 14 is the color reproduction range of the color CRT, and the area surrounded by the broken line is the inkjet color reproduction range.

As described above, since the color reproduction range of the color CRT is wider than that of the ink jet, the color CRT is
There are some colors that cannot be output by inkjet even if they are colors that can be displayed above. Therefore, conventionally, a method of performing color reproduction processing on a color CRT image, converting the color into a color within a color reproduction range of an inkjet, and then outputting with an inkjet has been adopted.

As a conventional color reproduction technique, for example, when a color that cannot be reproduced by ink jet is converted into a color within a reproduction range, a color correction for switching a target point in the mapping direction according to the brightness of an input color. Method (first technique, see Japanese Patent Laid-Open No. 63-195777), a color correction processing device that switches the target point in the mapping direction according to the hue of the input color (second technique, Japanese Laid-Open Patent Publication No. 4-101566) Color image processing apparatus for mapping the input color to the color having the smallest color difference within the color reproduction range of the output system (third technique, Japanese Patent Laid-Open No. 4-1).
89669).

[0006]

The first and second techniques described above are performed by either method in which the direction (target point) of the color conversion map in the color reproduction processing is switched according to the hue and lightness of the input color. Also has the characteristic that there is relatively little color change in the brightness direction.

However, in the above-mentioned method, the color change in the saturation direction becomes large, so that there is a problem that the color change is conspicuous for an image including many highly saturated colors such as a computer graphic image.

The above-mentioned third technique has a feature that the color conversion mapping in the color reproduction processing is switched to a direction having the smallest color difference according to the shape of the color reproduction range, and the color change before and after the color reproduction processing is small. ing. However, in this method, the mapping direction depends on the shape of the color reproduction range of the output system, and the continuity of the mapping direction may not be maintained. In such a case, the continuously changing input color is mapped to the color of the discontinuous mapping direction destination by the color reproduction processing, so that the deterioration of the image quality such as the gradation collapse and the jump occurs.

As described above, the conventional first and second techniques have a drawback that the color change in the saturation direction is large, and the third technique has a drawback that the gradation is distorted or the gradation is skipped. is there.

It is an object of the present invention to produce an output image in which the color change is inconspicuous with respect to an image containing a highly saturated color, and to produce an output image in which the gradation is not collapsed or the gradation is not skipped. It is to provide a processing device.

[0011]

In order to achieve the above object, according to the invention of claim 1, the color gamut of the output color image is different from the color gamut of the input color image, and the input color In a color reproduction processing device for mapping image information onto color image information within a color reproduction range of an output system, means for determining a mapping direction based on at least saturation of input colors, and the input color being determined. It is characterized in that a means for converting into a color within the color reproduction range of the output system in the mapping direction is provided.

According to a second aspect of the present invention, the mapping direction is represented by a target point.

According to a third aspect of the present invention, the saturation of the target point has a monotonically increasing relationship with the saturation of the input color.

According to a fourth aspect of the invention, when the saturation of the input color is the maximum saturation of the color reproduction range of the input system, the saturation of the target point is the maximum saturation of the color reproduction range of the output system. It is characterized by being.

According to a fifth aspect of the invention, the lightness of the target point is equal to the lightness of the maximum saturation point in the color reproduction range of the output system in the hue of the input color.

According to a sixth aspect of the invention, the lightness of the target point has a monotonically increasing relationship with the lightness of the input color.

According to a seventh aspect of the invention, when the lightness of the input color is the maximum lightness of the color reproduction range of the input system, the lightness of the target point is the maximum lightness of the color reproduction range of the output system. I am trying.

According to an eighth aspect of the invention, when the lightness of the input color is the minimum lightness of the color reproduction range of the input system, the lightness of the target point is the minimum lightness of the color reproduction range of the output system. I am trying.

According to a ninth aspect of the present invention, the mapping direction determining means is a storage means that outputs the mapping direction corresponding to the input color using the input color as an address.

[0020]

[Function] The input RGB signal is converted into a LAB signal,
This LAB signal is converted into an LCH signal. Converted L
After mapping the CH signal within the color reproduction range of the output system,
It is converted into a signal and converted into a CMY signal of a printer which is an output system. This makes it possible to generate an output image in which the color change is inconspicuous even for an image including a high saturation color.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be specifically described below with reference to the drawings. <Embodiment 1> FIG. 1 shows the structure of an embodiment of the present invention. In the configuration of this embodiment, the color CRT is used as the input system device and the printer is used as the output system device, but the same can be realized when other input / output devices are used.

In FIG. 1, 1 is a frame memory for storing color image information, and 2 is a color C which is an input system device.
RT, 3 is an external interface for connecting a bus and a frame memory, 4 is a CPU, 5 is a conversion circuit for converting RGB signals into LAB signals, 6 is a conversion circuit for converting LAB signals into LCH signals, and 7 is a color of an output system. A color conversion processing circuit for converting an LCH signal within a reproduction range, a conversion circuit for converting an LCH signal into a LAB signal, a conversion circuit for converting a LAB signal into a CMY signal, an external interface 10 and an output system 11. The device is a printer, and 12 is a bus.

The frame memory 1 stores R, G, B signals (0 to 255) representing color image information in pixel units, and is displayed on the color CRT 2. Further, the color image information of the frame memory 1 is fetched by the CPU 4 via the external interface 3 and the bus 12.

FIG. 2 is a processing flowchart of this embodiment. The processing operation of FIG. 1 will be described with reference to FIG. The RGB signal is input from the frame memory 1 (step 101), and the pixels fetched by the CPU 4 are RGB →
The LAB conversion circuit 5 converts the coordinates into the coordinate values (L * _in , a * _in , b * _in ) of the CIE LAB color space (step 102).

Next, in the LAB → LCH conversion circuit 6, the (L *, a *, b *) signals are converted into lightness L,
It is converted into a color space composed of three variables representing saturation C and hue H (step 103).

<Lightness> L = L * <Saturation> C = √ (a *) ² + (b *) ² <Hue> H = arctan (a * / b *) By the above conversion, (L * _in , A * _in , b * _in ) is (L
_in , C _in , H _in ). Transformed (L _in , C
_{The in} , H _in ) signals are converted into LCH signals (L _out , C _out , H _out ) within the color reproduction range of the output system in the color conversion processing circuit 7 (step 104). The color conversion processing circuit 7
The present invention is particularly characterized and will be described in detail later.

Converted within the color reproduction range of the output system (L
_out , C _out , H _out ) are LCH → LAB conversion circuit 8,
It is converted into a printer signal through the LAB → CMY conversion circuit 9 and output to the printer 11 (steps 105, 10).
6, 107). The printer signal may be either a CMY signal or a CMYK signal, and the output system device is a color CRT.
In the case of, it is converted into an RGB signal.

When the CPU performs the above-described processing on the entire image on the frame memory (step 108), the R, G, and B signals of the input system are subjected to color reproduction processing, and the output system printer signal (C, C, M, Y signals).

FIG. 3 shows a detailed configuration of the color conversion processing circuit. The color conversion processing circuit 7 includes a color reproduction range determination circuit 21, a printer color reproduction range table 22, a color CRT color reproduction range table 23, a color reproduction range outside point conversion circuit 24, and a selector circuit 25.

FIG. 5 is a processing flowchart of the color conversion processing circuit. The color conversion processing circuit 7 has (L _in , C _in ,
H _in ) is input (step 201), and the color gamut determination circuit 21 determines whether or not the input value (L _in , C _in , H _in ) is a color within the color reproduction range of the printer by the printer color reproduction. The determination is made by referring to the range table 22 (step 202). The printer color reproduction range table 22 and the color CRT color reproduction range table 23 store the boundary values of the color reproduction ranges of the respective devices.

The selector circuit 25 is the color gamut determination circuit 2
The output value is selected based on the judgment result of 1. If the determination result is within the color gamut (YES in step 202), the input value (L _in , C _in , H _in ) is selected (step 20).
3) On the other hand, when the determination result is outside the color reproduction range (NO in step 202), the output value (L _tmp , C _tmp , H _tmp ) of the color reproduction outside point conversion circuit 24 is selected.

FIG. 4 shows the configuration of the color reproduction outside point conversion circuit. The out-of-color-reproduction-range point conversion circuit 24 includes a color conversion target point determination circuit 31 and a mapping point calculation circuit 32. In the color conversion target point determination circuit 31, the target points (L _cnt , C _cnt , H _cnt ) in the mapping direction are input values (L _in , C _in , H).
_in ), the color CRT color reproduction range table 23, and the printer color reproduction range table 22, for example, by an arithmetic circuit that realizes the following relational expression (step 20).
4).

L _cnt = L _prntMID C _cnt = C _in × (C _prntMAX / C _crtMAX ) H _cnt = H _in , where L _prntMID is the lightness of the maximum saturation point in the color reproduction range of the printer _{in the} hue H _in . C _prntMAX is hue H
maximum saturation value of a printer in _in, C _crtMAX color C
It represents the maximum saturation value of RT and is a constant obtained by referring to the printer color reproduction range table 22 and the color CRT color reproduction range table 23, respectively.

[0034] FIG. 6, (L _cnt in hue H _in,
The relationship between (C _cnt ) and (L _in , C _in ) is shown. The start point of the arrow in FIG. 6 represents each color (L _in , C _in ) outside the reproduction range (6 points in the case of FIG. 6), and the end point of the arrow is the target point (L _cnt , C _cnt ) in the mapping direction. Is represented. FIG. 7 shows the relationship between C _cnt and C _in in this embodiment. When the color C _in = C _crtMAX of the maximum saturation point is input _{in the} color CRT, the saturation of the target point is set to C _cnt = C _prntMAX, and the color on the achromatic axis, that is, C _in = 0 is input. Then, the target point becomes the color C _cnt = 0 on the achromatic axis. The saturation of the target point when the intermediate saturation is input takes a value between the achromatic color and C _crtMAX .

As described above, the saturation of the target point has a monotonically increasing relationship with the saturation of the input color, and the hue of the target point becomes equal to the hue of the input color.

The present invention is not limited to the above linear relational expression, but the target point (L _cnt , C _cnt , H _cnt ) can be obtained based on the input value (L _in , C _in , H _in ). If so, the saturation of the target point may have a non-linear relationship as shown in FIG.

As described above, the color conversion target point determination circuit 31
At the target point (L _cnt , C _cnt ,
H _cnt ) is obtained. The mapping point calculation circuit 32 calculates points (L _tmp , C _tmp , H _tmp ) which are colors in the direction of the target point in the LCH color space and which are on the boundary of the color gamut of the printer. The calculation method is, as shown in FIG. 11, the input value in = (L
_in , C _in , H _in ) and the target value cnt = (L _cnt , C _cnt , H
_cnt ) is obtained, and a point on this line, prntAREA on the boundary of the reproduction range obtained by referring to the printer color reproduction range table 22, is obtained, and this value is set to (L
_tmp , C _tmp , H _tmp ) (step 205).

In the present invention, if the mapping direction is a point in the direction of the target point, it is not limited to a point on the boundary of the printer reproduction area, but may be any point within the reproduction area of the printer.

<Embodiment 2> Another embodiment of the color conversion target point determination circuit will be described. The overall configuration is the same as that of the first embodiment, so the description thereof is omitted.

In the second embodiment, the target point (L
_cnt , C _cnt , H _cnt ) is calculated by an arithmetic circuit that realizes the following relational expression. The method of _obtaining L _cnt is different from that of the first embodiment. That is, when L _in > L _prntMID , L _cnt = L _prntMID + (L _in −L _prntMID ) × (L _prntWP
−L _prntMID ) / (L _crtWP −L _prntMID ) L _in ≦ L _prntMID L _cnt = L _prntMID − (L _prntMID −L _in ) × (L _prntMID
−L _prntBP ) / (L _prntMID −L _crtBP ) C _cnt = C _in × (C _prntMAX / C _crtMAX ) H _cnt = H _in where L _prntMID is the maximum saturation point of the printer color reproduction range _{in the} hue H _in . Lightness, and C _prntMAX is hue H
maximum saturation value of a printer in _in, C _crtMAX color C
It represents the maximum saturation value of RT and is a constant obtained by referring to the printer color reproduction range table and the color CRT color reproduction range table, respectively. Also, L _prntWP , L
_crtWP is the maximum brightness value of the printer and color CRT, L _prntBP and L _crtBP are the printer and color C, respectively.
It is a constant representing the minimum brightness value of RT.

The start point (6 points in the figure) of the arrow shown in FIG. 9 represents each color outside the reproduction range, and the end point of the arrow represents the target point in the mapping direction. Compared with the first embodiment, the saturation of the target point is the same (vertical dotted line in the figure), but the brightness of the target point is different. The lightness of the target point has a monotonically increasing relationship with the lightness of the input color.

When L _cnt is realized as described above, since the lightness of the target point is switched according to the input color, the decrease in lightness in the high lightness portion is reduced and a good output image can be obtained.

FIG. 10 shows L _cnt and L _in in this embodiment.
Shows the relationship. Color L of the maximum brightness point in a color CRT
_{When in} = L _crtWP is input, the lightness L _{cnt of the} target point is set to the maximum lightness point L _prntWP of the printer, and when the color L _in = L _prntBP is input, the lightness L of the target point is input.
_cnt is set to the minimum lightness point L _prntBP of the printer. When the intermediate brightness is input, the brightness of the target point takes an intermediate value between the maximum brightness point and the minimum brightness point of the printer.

The present invention is not limited to the above linear relational expression, but the target point (L _cnt , C _cnt , H _cnt ) can be obtained based on the input value (L _in , C _in , H _in ). Any other non-linear relationship may be used as long as it is.

In the above-described first and second embodiments, the arithmetic circuit is used as the circuit for calculating the target point, but it is also possible to use a ROM as shown in FIG. For example, the input color may be associated with the address part, the color of the target point corresponding to the input color may be held in the content of each address, and the content may be read and output.

<Embodiment 3> Another embodiment of the mapping point calculation circuit will be described. The overall configuration is the same as that of the first embodiment, and will be omitted. The output system color (L
_{Although tmp} , C _tmp , and H _tmp are points on the color gamut boundary of the printer, they do not necessarily have to be points on the color gamut boundary in the present invention, and colors slightly inside the boundary should be output. You can also As shown in FIG. 12, the color IN1 on the boundary of the gamut of the input system is replaced with the color OUT1 on the boundary of the gamut of the output system, and the color IN2 outside the color gamut of the output system , And OUT2 respectively. Along with this, the colors within the color reproduction range of the output system and in the vicinity of the color reproduction range are also replaced with values further inside in the same direction.

The calculation method will be described. The target point (L in the mapping direction) obtained by the color conversion target point determination circuit of the first embodiment
_cnt , C _cnt , H _cnt ) to IN1, OUT1, in =
(L _in , C _in , H _in ), out = (L _tmp , C _tmp ,
H _tmp ) and the distances to ΔIN1, ΔOUT1,
When Δin and Δout are set, (L _tmp , C _tmp , H _tmp ) is selected so that the relationship of Δout = ΔOUT1−α (ΔIN1−Δin) is satisfied (where α is a constant). When calculated in this way, it is possible to obtain the effect that gradation collapse does not occur when a color outside the color reproduction range of the output system is compressed.

As is apparent from the above-described embodiments, the color reproduction processing apparatus of the present invention has a small change in color particularly in the saturation direction when output is made by an output system having a different color reproduction range from an input system, and is continuous. It is possible to obtain a color image that maintains the property.

In the first, second and third embodiments described above,
In order to define <lightness, saturation, hue>, the CIE defined L * a * b * uniform color space was used, but other color spaces such as L * u * v * uniform color space and XYZ colors are used. The same can be done using a space.

[0050]

As described above, according to the first and second aspects of the present invention, the mapping direction is controlled according to the lightness, hue, especially saturation of the input color. It is possible to map the input color in the mapping direction most suitable for the input color, and it is possible to obtain an output image in which the color change is inconspicuous with respect to the image including the high saturation color.

According to the third aspect of the present invention, the saturation of the target point that determines the mapping direction is controlled so as to have a monotonically increasing relationship with the saturation of the input color. It is possible to obtain an output image in which the color change in the saturation direction is small without causing the distortion of the image and the gradation skipping.

According to the fourth aspect of the invention, when the saturation of the input color is the maximum saturation of the color reproduction range of the input system, the saturation of the target point that determines the mapping direction is the color reproduction range of the output system. Since the saturation is controlled so as to be the maximum saturation, it is possible to obtain an output image in which the color change of a color having a particularly high saturation is small.

According to the fifth aspect of the present invention, the lightness of the target point that determines the mapping direction is controlled to be the lightness of the maximum saturation point in the color reproduction range of the output system in the hue of the input color. It is possible to obtain an output image in which the color saturation of the high-saturation portion is small and the color change of the lightness is not noticeable.

According to the sixth, seventh and eighth aspects of the present invention, the lightness of the target point that determines the mapping direction is in a monotonically increasing relationship with the lightness of the input color, and the lightness of the input color is the color of the input system. When the maximum brightness (minimum brightness) of the reproduction range is set, the brightness of the target point that determines the mapping direction is controlled to be the maximum brightness (minimum brightness) of the color reproduction range of the output system. It is possible to obtain an output image in which the brightness is small and the brightness change of the high brightness color (low brightness color) is small.

According to the invention described in claim 9, since the target point for determining the mapping direction is set by reading the data stored in the ROM in advance, the color reproduction processing is speeded up and the mapping direction is also increased. It is easy to change the design.

[Brief description of the drawings]

FIG. 1 shows a configuration of an embodiment of the present invention.

FIG. 2 is a processing flowchart of the present embodiment.

FIG. 3 shows a detailed configuration of a color conversion processing circuit.

FIG. 4 shows the configuration of a color reproduction outside point conversion circuit.

FIG. 5 is a processing flowchart of a color conversion processing circuit.

[6] (L _cnt, C _cnt) in the hue H _in the (L _in,
C _in ) is shown.

FIG. 7 shows the relationship between C _cnt and C _in in this embodiment.

FIG. 8 shows C _cnt and C _in having a non-linear relationship.

FIG. 9 shows a case where the lightness of the target point is different _in the relationship between (L _cnt , C _cnt ) and (L _in , C _in ).

FIG. 10 shows the relationship between L _cnt and L _{in in} the present embodiment.

FIG. 11 is a diagram illustrating calculation of a value on the color gamut boundary of the printer.

FIG. 12 is a diagram illustrating calculation of values inside a color gamut boundary of a printer.

FIG. 13 is a diagram when the color conversion target point determination circuit is configured by a ROM.

FIG. 14 shows a color reproduction range in a color CRT and an inkjet printer when a hue is red.

[Explanation of symbols]

 1 frame memory 2 color CRT 3, 10 external interface 4 CPU 5 RGB-LAB conversion circuit 6 LAB-LCH conversion circuit 7 color conversion processing circuit 8 LCH-LAB conversion circuit 9 LAB-CMY conversion circuit 11 printer 12 bus

Claims (9)

[Claims] 1. A color reproduction process in which the color reproduction range of an output system color image is different from the color reproduction range of an input system color image and the input system color image information is mapped to color image information within the output system color reproduction range. The apparatus is provided with means for determining the mapping direction based on at least the saturation of the input colors, and means for converting the input color into a color within the color reproduction range of the output system in the determined mapping direction. A color reproduction processing device characterized by the above. 2. The color reproduction processing apparatus according to claim 1, wherein the mapping direction is represented by a target point. 3. The color reproduction processing apparatus according to claim 2, wherein the saturation of the target point has a monotonically increasing relationship with the saturation of the input color. 4. When the saturation of the input color is the maximum saturation of the color reproduction range of the input system, the saturation of the target point is the maximum saturation of the color reproduction range of the output system. The color reproduction processing device according to claim 3. 5. The color reproduction processing apparatus according to claim 2, wherein the lightness of the target point is equal to the lightness of the maximum saturation point in the color reproduction range of the output system in the hue of the input color. 6. The color reproduction processing apparatus according to claim 2, wherein the lightness of the target point has a monotonically increasing relationship with the lightness of the input color. 7. The lightness of the target point is the maximum lightness of the color reproduction range of the output system when the lightness of the input color is the maximum lightness of the color reproduction range of the input system. Color reproduction processor. 8. The lightness of the target point is the minimum lightness of the color reproduction range of the output system when the lightness of the input color is the minimum lightness of the color reproduction range of the input system. Color reproduction processor. 9. The color reproduction processing apparatus according to claim 1, wherein the mapping direction determining unit is a storage unit that outputs the mapping direction corresponding to the input color by using the input color as an address.