JP2000253264A - Color image signal processing unit and color image signal processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image signal processing unit that converts a received color image signal into a desired color image signal at an output side so as to attain color reproduction with thigh image quality. SOLUTION: The dolor image signal processing unit obtains external data denoting the border of an output side color reproduction area with prescribed accuracy in advance and stores the result to a color reproduction area data storage section 1. When receiving an input color image signal, a color reproduction area shaping section 2 acquires exterior data from the color reproduction area data storage section 1 to obtain the exterior of a color reproducible area at an output side at a hue cross section corresponding to the color of an input color image signal. Then approximation processing is applied to at least part of the exterior to approximate undesired ruggedness as a convex contour. A color conversion section 3 converts the input color image signal into an output color image signal on the basis of the shaped color reproducible area. In this case, unfied color conversion processing is preferable for the purpose. Moreover, the step-wise difference of colors due to the exterior shape of the color reproducible area is eliminated and color reproduction with high image quality is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to various apparatuses for handling color images, such as digital copiers and printers, and more particularly, to a method for converting a color image signal on an input side into a color image in a color reproducible area on an output side. The present invention relates to a color image signal processing device and a color image signal processing method for performing a color conversion process on a signal.

[0002]

2. Description of the Related Art As a device for outputting a color image, there are a display device such as a CRT and a color LCD, and a printing device such as a printer. In these output devices, the reproducible color range (color reproducible area) differs depending on the difference in each output method. However, the input color image signal is often input without considering the color reproducible area on the output side. Therefore, in each output device, at least a color that cannot be reproduced is replaced with a color considered to be the closest, and output, so that the entire image can be reproduced with the best image quality in the output device. At this time, a color mapping (Col) for replacing the given color image signal with a color in the color reproducible area of the output device.
or Mapping) is required.

In order to perform such color mapping, it is necessary to first find the boundary of the color reproducible area in the output device. For example, in the technology described in Japanese Patent Application Laid-Open No. 7-203235, eight saturated colors R (red), G (green), and
B (blue), Y (yellow), M (magenta), C (cyan),
K (black) and W (white) are converted into colors in the L ^* a ^* b ^* color space, and the obtained eight points are connected to three neighboring points by a triangle to obtain 12 points.
The boundary surface of the color reproducible region is approximated by a plane. However, since the boundary surface of the actual color reproducible region is a solid having more irregularities than the dodecahedron, approximation of the color gamut by a simple dodecahedron is very large in loss and overhit of the color gamut. There's a problem.

[0004] For example, Japanese Patent Application Laid-Open No. 7-30774 is disclosed.
In the method described in^*a ^*b^*Smell in color space
The color reproducible area is L^*Cut at K planes perpendicular to the axis
You. Then, for each of the K cross sections, 3
60 degrees are divided into S, K × S points on the boundary are obtained, and K × S
Generate a plurality of triangles from S points,
The boundaries are approximated. As a result, the color
The boundaries of the feasible area can be obtained.

However, this method is inefficient because a large amount of calculations and a large number of boundary signals need to be generated in order to find the saturated color and to generate the data of the boundary of the color reproducible region with high accuracy. In order to improve this, for example, a method has been proposed in which a block is formed based on adjacent sample data on the boundary of the color reproducible region, and the boundary of the color reproducible region is obtained while dividing the block. By these various methods, the boundaries of the color reproducible regions can be obtained finely.

On the other hand, using the color reproducible area obtained in this way, for example, when the input color image signal is a color outside the color reproducible area, the color image signal is converted to a color in the color reproducible area. . When the color area that can be taken by the input color image signal is at least partially smaller than the output-side color reproducible area, the color can be expressed using the entire output-side color reproducible area as much as possible. In some cases, color conversion is performed. As a method of such a color conversion, for example, there is a method of changing the saturation while keeping the brightness constant, and converting the color into a color within a color reproducible region. As another method, there is a method in which one point in a color reproducible region, for example, one point on a lightness axis is set as a target point, and both the saturation and the lightness are changed in a direction toward the target point or in the opposite direction.

FIG. 10 is an explanatory view of a problem at the time of color conversion in an example of a color reproducible area, and FIG. 11 is an enlarged view of the same. Here, a cross section at a certain hue is shown by a lightness-chroma plane. By acquiring the boundary of the color reproducible region finely as described above, it is possible to express unevenness of the boundary surface of the color reproducible region. As a result, the input color image signal can be converted to an appropriate color within the color reproducible area. However, when the boundaries of the color reproducible regions are actually obtained in such a fine manner, large irregularities may occur in some portions, such as the portion surrounded by an ellipse in FIG. When such large irregularities occur, there is a problem that color conversion processing cannot be performed accurately.

For example, consider a case where a method of changing both the saturation and the brightness in the direction toward the target point or in the opposite direction is used as the color conversion method. One point on the lightness axis is set as a target point, and a vector heading for this target point is shown in FIG.
And in FIG. 11 are indicated by arrows. The brightness and saturation are changed in the direction of this vector or in the opposite direction. At this time, the colors A to B and the colors C to D shown in FIG. 11 are within the color reproducible region, but the colors B to C are colors outside the color reproducible region. Therefore, when trying to change the color E to a color in the color reproducible area, it is uniquely determined whether to convert the color E to a color between the colors A and B or to a color between the colors A and D. Will be gone.

In any case, there is a possibility that the converted color greatly changes between the color E and a color having a slightly different saturation, and a color step may occur. For example, color F is converted to a color close to color B, while color G is converted to a color close to color D. The color E is converted into one of the colors B and D or a color close to them, but a large color difference appears between the color E and the other color.

Further, although the colors C to D are not color-converted, the colors B to C are subjected to the color conversion into the color reproducible region, and the color reproduction in this portion is also non-uniform. There are also problems.

FIG. 12 is an explanatory diagram of a problem in a case where the color area on the input side is matched with the color reproducible area on the output side. As in FIG. 11, a color conversion method that changes both the saturation and the brightness in the direction toward the target point or in the opposite direction is used.
The color conversion is performed so that the color region on the input side matches the color reproducible region on the output side as much as possible, and color reproduction is performed by effectively utilizing the color reproduction capability on the output side. However, if there are large irregularities on the boundary of the color reproducible area on the output side, for example, the color B or the color D is a candidate for the outer color H of the color area on the input side, and a uniform conversion point can be found. Disappears. FIG.
As in the case of No. 1, there is a possibility that the color after conversion may greatly change even if the saturation and lightness slightly change, and the color reproduction may be non-uniform.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is capable of converting an input color image signal into a desired output side color image signal, thereby achieving high-quality color reproduction. It is an object of the present invention to provide a color image signal processing device and a color image signal processing method capable of performing the following.

[0013]

SUMMARY OF THE INVENTION The present invention relates to a color image signal processing device and a color image signal processing method for converting an input color image signal into an output color image signal in a color reproducible area on the output side. An approximation process is performed on at least a part of an outline of a color reproducible region on the output side in a hue cross section corresponding to a color of a color image signal, and an output color in a color reproducible region having an outline approximated to an input color image signal It is characterized in that it is converted into an image signal. The approximation process can be approximated by a curve or a plurality of line segments, and can be approximated as a smooth convex contour. An error due to the approximation process can be absorbed during the color conversion process.

For example, when large irregularities occur at the boundary of the color reproducible area on the output side as described above, approximation processing can be performed on a section including that part. As a result, a plurality of boundaries of the color reproducible area on the output side do not occur at the time of color conversion processing, and uniform conversion processing can be performed. In addition, the approximation process does not cause a step in the color after the color conversion process, and can improve the image quality.

[0015]

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 is a color gamut data holding unit, 2 is a color gamut shaping unit, and 3 is a color conversion unit. The color gamut data holding unit 1 holds at least outline data indicating a boundary of a color reproducible area on the output side. The outline data is converted to a color in the color reproducible area with high accuracy when performing color conversion processing in the color conversion unit 3 in the subsequent stage.
It is better to obtain it with a predetermined accuracy. For example, using a color considered to be clearly on the boundary of the color reproducible region, for example, a saturated color R, G, B, Y, M, C, K, W, etc., a square or triangle formed by adjacent colors is used. By the method of sequentially dividing, it is possible to obtain the outline data of the color reproducible region with a predetermined accuracy.

The color gamut shaping unit 2 performs an approximation process on at least a part of the outline of the color reproducible area on the output side in the hue cross section corresponding to the color of the input color image signal. The outline data held in the color gamut data holding unit 1 is obtained with high accuracy as described above. In the process of obtaining such accurate contour data, large irregularities such as those shown in FIGS. 10 to 12 actually occur, for example. The color gamut shaping unit 2 smoothes such irregularities to some extent by approximation processing. This makes it possible to prevent the color reproducible area from being divided into a plurality of areas or to prevent the occurrence of color steps when the next color conversion unit 3 performs the color conversion processing.

The color conversion unit 3 converts an input color image signal into an output color image signal by using the outline data approximated by the color gamut shaping unit 2. At this time, when the input color image signal is a color outside the color reproducible range on the output side, a process of converting the color into a color within the color reproducible range on the output side can be performed. Alternatively, color conversion processing can be performed so that the color of the input color image signal within the color range on the input side matches the color reproducible range on the output side. As the color conversion processing method, as described above, for example, various methods such as a method of changing the saturation by fixing the brightness and a method of changing both the brightness and the saturation toward a certain target point can be used. it can. Of course, these methods may be used in combination.A method in which the brightness is fixed and the saturation is changed at a brightness higher than the brightness having the maximum saturation in the color reproducible range. And a method of changing the saturation. Prior to such a color conversion process, a certain degree of hue conversion may be performed. When performing hue conversion, the color gamut shaping unit 2
It is preferable to receive a result obtained by performing an approximation process on outline data in a hue cross section including a color after hue conversion. In such a color conversion process, since the outline data indicating the outline of the color reproducible area on the output side is obtained with high accuracy, the colors in the limited color reproducible area are effectively used to achieve the desired color reproduction. A feasible output color image signal can be output. Also, among the contours of the color reproducible area on the output side, large irregularities that are inconvenient in uniform conversion processing have been smoothed by approximation processing.
Even if uniform conversion processing is performed, no color difference or the like occurs, and an output color image signal that can realize good color reproduction can be obtained.

FIGS. 2 and 3 are flowcharts showing an example of the operation in the embodiment of the present invention. S1 in advance
In step 1, the outline data of the boundary surface of the color reproducible area on the output side is obtained with a predetermined accuracy, and stored in the color reproduction area data storage unit 1. The outline data may be obtained in a device-independent color space, for example, a CIE-L ^* a ^* b ^* color space. In the following description, the internal processing is CIE
-L ^* a ^* b ^* color space. FIG.
FIG. 3 is a conceptual diagram showing an example of a color reproducible region. Generally, the color reproducible area is not uniform and has a complicated three-dimensional shape as shown in FIG. The inside of the solid shown in FIG. 4 is a region where color reproduction is possible, and the outside is a region where color cannot be reproduced. Here, outline data indicating a boundary surface between a region where color reproduction is possible and a region where color cannot be reproduced is obtained in advance. As described above, since the shape of this boundary surface is not uniform, it is preferable to represent the boundary surface by dividing it into a polygonal shape such as a triangle. In FIG. 4, only a part of the boundary surface is divided into triangular shapes, but such division is performed on the entire boundary surface.

When an input color image signal is input, S1
2, the hue cross section corresponding to the input color image signal, for example, the color of the input color image signal unless the hue is changed;
When the hue is changed, a plane including the color of the changed hue and passing through the lightness axis is determined. FIG. 5 is an explanatory diagram of an example of a hue cross section. Here, the input color image signal is C
It is shown as an input color in the IE-L ^* a ^* b ^* color space.
The CIE-L ^* a ^* b ^* color space includes this input color,
A plane P passing through the L ^* axis is determined. Then, the contour of the output-side color reproducible area on the determined plane P is obtained from the outline data held in the color gamut data holding unit 1. Thus, for example, FIG. 6A and FIG.
The outline of the color reproducible area as shown in FIG.
Generally, the contour of such a color reproducible region has a different shape for each hue because the shape of the color reproducible region is not uniform as shown in FIGS.

S13 and S14 (and the processing of FIG. 3)
In, the outline of the color reproducible region in the hue cross section obtained in S12 is subjected to approximation processing to shape the outline.
Here, as the outline range of the color reproducible area to be shaped,
It is between the color B having the maximum chroma and the color A on the lightness axis having the minimum lightness. Within this range, it is approximated by one or more line segments. For this purpose, the color B and the color A are obtained in S13, and one or more approximate line segments are obtained for the line segment AB connecting these two colors by the processing shown in S14 and FIG. In step S15, a color conversion process is performed on the input color image signal based on the outline data indicating the outline of the color reproducible region on which the approximation process has been performed to obtain an output color image signal.

With respect to the shaping of the outline of the color reproducible area by the approximation processing, the processing shown in FIG. 3 will be described using a more specific example. FIG. 6 is an explanatory diagram of an example of the approximation processing when the contour shaping portion of the color reproducible region has a convex shape.
It is explanatory drawing of an example of the approximation process in the case of a similarly concave shape.
In S12 of FIG. 2, by determining the hue cross section and acquiring the contour of the color reproducible region, the contour of the color reproducible region as shown in, for example, FIG. 6A or FIG. 7A is obtained. The hue cross section can be represented by a lightness L ^* axis and a saturation C ^* axis.

From the outline of the color reproducible area, S
13, the color B having the maximum saturation and the lightness axis (CI
The color A having the minimum lightness on the EL ^* a ^* b ^* color space (the L ^* axis) is obtained. Thereby, for example, FIG.
And the colors shown as points A and B shown in FIG. Consider a line segment AB connecting point A and point B,
For B, the processing shown in FIG.

In S21 of FIG. 3, the center point of the line segment AB is set as a point C. A straight line L passing through the center point C and perpendicular to the line segment AB is determined, and an intersection D between the straight line L and the contour line of the color reproducible region is determined (see FIGS. 6B and 7B). ).

At step S22, it is determined whether the obtained intersection D is inside or outside the line segment AB. Here, since the line segment AB usually has a positive slope, the side near the L ^* axis is called the inside in the meaning of the color reproducible region, and the side near the C ^* axis is called the outside. For example, the case where the intersection D is inside the line segment AB is the case as shown in FIG. 7B, that is, the case where the contour of the color reproducible region is concave. In this case, the given line segment AB can be regarded as already including most of the boundary of the color reproducible region. Therefore, in S23, the line segment AB is returned as an approximate result. That is, in the example shown in FIG. 7, the line segment AB is an approximation result as shown in FIG.

On the other hand, when the intersection D is outside the line segment AB, that is, when the contour of the color reproducible region is convex as shown in FIG. 6B, the convex portion is approximated.
Further, the approximation process is repeated by dividing into a number of line segments. That is, in S24, the line segment AD and the line segment DB are set as new approximate straight lines. Then, in S25, the approximation accuracy is confirmed, and if desired, the line segment AD and the line segment DB are returned as the approximation result. If it is not the desired accuracy, in S26,
For the line segment AD and the line segment DB, respectively, the line segment AB
The processing shown in FIG. 3 is performed as in the case of (1). Thus, the processing shown in FIG. 3 is executed recursively, and if the contour of a given line is concave or convex, the line is divided until the desired accuracy is reached. The obtained line segment is the approximation result.

For example, in FIG. 6B, the image is divided into a line segment AD and a line segment DB. At this time, it is assumed that the desired accuracy has not been reached. Then, the center point of the line segment AD is obtained, and the intersection F between the straight line passing through the center point and orthogonal to the line segment AD and the contour line of the color reproducible region is obtained. Then, the line segment AD is divided into a line segment AF and a line segment FD. If the desired accuracy has been reached at this point, the line segment AF and the line segment FD are obtained as an approximation result from the point A to the point D. of course,
If the desired accuracy is not obtained, the same processing is repeated for each of the line segment AF and the line segment FD.

Similarly, the center point of the line segment DB is determined, and the intersection E between the straight line passing through the center point and orthogonal to the line segment DB and the contour line of the color reproducible region is determined. Then, the line segment DB is divided into line segments DE and EB. At this point, if the desired accuracy has been reached, the line segment DE and the line segment EB are point D
From the point B to the point B. Of course, if the desired accuracy is not obtained, the same processing is repeated for each of the line segment DE and the line segment EB.

In this manner, the line segment AF, the line segment FD, the line segment DE, and the line segment EB are finally obtained as approximation results.
FIG. 6C shows the approximation result obtained in this way. Although unevenness was present in the low brightness portion of the color reproducible region, it was approximated by line segment AF. By such an approximation process, the boundary of the color reproducible region is approximated with a desired approximation accuracy so as to be as convex as possible.
Therefore, for example, as shown in FIGS. 10 to 12, a plurality of color reproducible regions do not appear in the color conversion direction, and uniform color conversion processing can be performed by the color conversion unit 3. In addition, due to the approximation, when the color is slightly changed, a step does not occur in the converted color, and the deterioration of the image quality can be reduced. Note that, for the portion that has not been subjected to the approximation processing, the color conversion is performed using the outline data held in the color gamut data holding unit 1 obtained in advance. Therefore, it is possible to perform a color conversion process so that color reproduction can be performed by making full use of the actual color reproducible region.

FIG. 8 is a flowchart showing another example of the approximation processing according to the embodiment of the present invention, and FIG. 9 is an explanatory diagram of a specific example. As the method of the approximation processing, various methods other than the above-described methods can be applied. For example, when the contour of the color reproducible region has irregularities as shown in FIG. 9A, an approximate contour line that covers the irregularities can be obtained as described below. In this example,
An approximation process is performed between the color B having the maximum saturation and the color A having the minimum brightness on the brightness axis. In addition,
The entire process is the same as in FIG.

First, in S13 of FIG. 2, a line segment AB connecting the points A and B is obtained, and in S14, the process shown in FIG. 8 is called. In S31, a straight line L1 parallel to the line segment AB and in contact with the contour of the reproducible region is determined, and the contact point is set as a point C. In S32, it is determined whether the straight line L1 (or the point C) is outside or inside the line segment AB. If inside, line A
Since B already covers the outline of the color reproducible region in the section from point A to point B, the line segment AB is determined as an approximate straight line in S33.

If the straight line L1 (or the point C) is outside the line segment AB, it is divided at the point C in S34, and the line segments AC and CB are provisionally approximated. For example, FIG.
In (A), the point C is in contact with the straight line L1.
The straight line L1 (point C) at this time is outside the line segment AB.
Therefore, the data is divided at the point C, and the line segment AC and the line segment CB are provisionally approximated as shown in FIG. 9B.

In step S35, it is determined whether or not the desired approximation accuracy has been obtained.
The line segment AC and the line segment CB are determined as approximate straight lines. If it is not obtained with the desired approximation accuracy, in S36, each of the line segment AC and the line segment CB is shown in FIG.
Is performed recursively.

In FIG. 9B, a line segment AC and a line segment CB
It is assumed that the accuracy is not the desired approximation accuracy, and the approximation process is further performed for each of the line segment AC and the line segment CB. That is, a straight line L2 parallel to the line segment AC and in contact with the contour of the color reproducible region is obtained, and the contact point C is obtained. And
The line segment AD and the line segment DC are obtained. In this case, the line segment AD
Is almost the same as the outline of the color reproducible region, and thus becomes an approximate straight line as it is. In addition, even if the approximation accuracy is not within the desired range, the line segment DC is determined as an approximate straight line because the line segment DC encompasses the outline. Similarly, when the process is performed on the line segment CB, a line segment CE and a line segment EB are obtained. Thus, an approximation is made as shown in FIG.

By such an approximation process, the boundary of the color reproducible region on which the approximation process has been performed is approximated by a group of included line segments. Therefore, for example, as shown in FIGS. 10 to 12, a plurality of color reproducible regions do not appear in the color conversion direction, and uniform color conversion processing can be performed by the color conversion unit 3. In addition, due to the approximation, when the color is slightly changed, a step does not occur in the converted color, and the deterioration of the image quality can be reduced. Note that, for the portion that has not been subjected to the approximation processing, the color conversion is performed using the outline data held in the color gamut data holding unit 1 obtained in advance. Therefore, it is possible to perform a color conversion process so that color reproduction can be performed by making full use of the actual color reproducible region.

In the above two examples of the approximation processing, a part of the boundary of the color reproducible region is approximated by one or a plurality of line segments. However, the present invention is not limited to this. For example, the boundary of the color reproducible region can be shaped by various approximation methods such as approximation using a curve.

In the above-described embodiment, each time an input color image signal is input, a hue cross section corresponding to the input color image signal is obtained, and an approximation process is performed on the boundary of the color reproducible region. The present invention is not limited to this. For example, approximation processing is performed in advance by the color gamut shaping unit 2 for all hue sections, and the outline data after the approximation processing is again held in the color gamut data holding unit 1, and color conversion is performed. The unit 3 may be configured to directly acquire the outline data from the color gamut data holding unit 1 at the time of color conversion.

Further, the approximation processing performed by the color gamut shaping unit 2 may cause an error in color conversion. Such an error can be absorbed by performing the conversion in consideration of the error when the color conversion unit 3 performs the color conversion processing. Alternatively, when another color conversion unit is provided downstream of the color conversion unit 3, the color conversion error may be absorbed by the other color conversion unit.

Further, in the above specific example, the approximation process is performed between the color B having the maximum saturation and the color A having the minimum brightness on the brightness axis, but the present invention is not limited to this. is not. Since the boundary surface of the color reproducible region is determined with high accuracy, it is desirable to use the contour data determined at this time as much as possible. Therefore, the section where the approximation processing is performed may be limited to a narrower range. In particular, the inconveniences shown in FIGS. 10 to 12 often occur in a region close to the color A having the minimum lightness on the lightness axis. for that reason,
The approximation process may be performed only in this area.

[0039]

As is apparent from the above description, according to the present invention, the color reproducible region can be effectively used by utilizing the outline data of the color reproducible region on the output side which is obtained with high accuracy as a whole. Desired color conversion can be performed.
At the same time, inconvenient irregularities caused by accurately obtaining the outline data are shaped by approximation processing. As a result, during the color conversion processing, a plurality of boundaries of the color reproducible area on the output side do not occur,
Uniform color conversion processing can be performed. In addition, the approximation process eliminates the occurrence of a color step due to the boundary shape of the color reproducible region, and has the effect of improving image quality.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart illustrating an example of an operation according to the embodiment of the present invention.

FIG. 3 is a flowchart illustrating an example of an operation according to the embodiment of the present invention.

FIG. 4 is a conceptual diagram illustrating an example of a color reproducible region.

FIG. 5 is an explanatory diagram of an example of a hue cross section.

FIG. 6 is an explanatory diagram of an example of an approximation process when a contour shaping portion of a color reproducible region has a convex shape.

FIG. 7 is an explanatory diagram of an example of an approximation process when a contour shaping portion of a color reproducible region has a concave shape.

FIG. 8 is a flowchart illustrating another example of the approximation processing according to the embodiment of the present invention.

FIG. 9 is an explanatory diagram of a specific example of another example of the approximation processing according to the embodiment of the present invention;

FIG. 10 is an explanatory diagram of a problem at the time of color conversion in an example of a color reproducible region.

FIG. 11 is an enlarged view for explaining a problem at the time of color conversion in an example of a color reproducible region.

FIG. 12 is an explanatory diagram of a problem in a case where an input side color area is matched with an output side color reproducible area.

[Explanation of symbols]

1 ... color gamut data holding unit, 2 ... color gamut shaping unit, 3 ...
Color conversion unit.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (5)

[Claims] 1. A color image signal processing apparatus for converting an input color image signal into an output color image signal in a color reproduction area on the output side, wherein color reproduction area data holding outline data of the color reproduction area on the output side. Holding means for obtaining, from the color gamut data holding means, outline data indicating an outline of an output-side color reproducible area in a hue section corresponding to a color of an input color image signal, and performing an approximation process on at least a part of the outline data And a color conversion unit for converting the input color image signal into an output color image signal using the contour data approximated by the color gamut shaping unit. Signal processing device. 2. The color image signal processing apparatus according to claim 1, wherein the color gamut shaping unit approximates a boundary of a color reproducible region indicated by the outline data with a curve or a plurality of line segments. . 3. The color image signal processing device according to claim 1, wherein the color gamut shaping unit approximates a boundary of a color reproducible region indicated by the outline data with a smooth convex contour. 4. The color conversion unit according to claim 1, wherein the color conversion unit performs a conversion process in consideration of an error when the outline data is approximated by the color gamut shaping unit. 2. The color image signal processing device according to claim 1. 5. A color image signal processing method for converting an input color image signal into an output color image signal in a color reproducible area on the output side, wherein color reproduction on the output side in a hue cross section corresponding to the color of the input color image signal. A color image signal processing method comprising: performing an approximation process on at least a part of an outline of a possible region; and converting the input color image signal into an output color image signal in a color reproducible region having an approximated outline. .