JPH08149320A - Method for generating color conversion lookup table and its device - Google Patents

Abstract

PURPOSE: To generate a color conversion lookup table at a high speed by starting the retrieval this time from a space obtained by preceding retrieval and retrieving a space in the vicinity sequentially when a color being an object of retrieval this time is not in existence in the space. CONSTITUTION: An address of each point of an object image signal generated from an address generating means 1 is given to a lookup table(LUT) 2, from which a corresponding color is outputted. The color is given to a medium space inside outside discrimination means 3, which checks whether or not the color obtained from the LUT 2 is between a maximum value and a minimum value obtained from a maximum/ minimum value calculation means 6 to discriminate whether or not the color of an object image signal this time is in existence in the medium space this time. The medium space inside outside discrimination means 3 provides the output of a discrimination result as a control signal to an address generating means 4 and a small space inside outside discrimination means 7. The address generating means 4 receiving the discrimination result that the color of the object image signal this time is not in existence in a medium space this time generates addresses as to points forming a succeeding medium space.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color conversion lookup table creating method and apparatus, and more particularly to a color conversion lookup table creating method and apparatus used for color system conversion.

[0002]

2. Description of the Related Art Generally, when a color image is displayed on a display or the like, the image is formed by a color addition method and, for example, a BGR color system is used as a color system, but a color image is printed by a printer or the like. In this case, an image is formed by a subtractive color method, and for example, the YMC color system is used as the color system. Therefore, in order to reproduce the color of the color image displayed on the display in printing by the printer, it is necessary to convert the color system of the display color. For example, when the color displayed on the display is to be printed by the printer, color masking is required. The color separation system is converted by a color separation image correction device such as a device.

By the way, in this color separation image correction apparatus, if the conversion is performed by performing the calculation for each printing, for example, it causes a problem in processing speed. A color conversion lookup table in which the correspondence between the image signal (for example, BGR value) in the system (for example, BGR color system) and the image signal (for example, YMC value) in the color system after conversion (for example, YMC color system) is tabulated. (Hereinafter, referred to as “color conversion LUT”) is created and stored in advance, and when the conversion of the color system is necessary, the calculation is not performed, and the target image device (eg, display) is used by using this color conversion LUT. The image signal to be input to the reproduction image device in order to reproduce the color output to the target image device with the reproduction image device (for example, a printer) is obtained based on the image signal in It has to so that.

As a method for creating this color conversion LUT, Japanese Patent Laid-Open No. 2-226870 and "Po-Chieh Hung," C
olorimetric calibration in electronic imaging devi
cesusing a look-up-table model and interpolations,
"Journal of Electronic Imaging, 2-1, pp53-61"
The method disclosed in (hereinafter referred to as "Hung's paper") is known.

Here, based on FIG. 8, Japanese Patent Application Laid-Open No. 2-22
A method of creating the color conversion LUT disclosed in Japanese Patent No. 6870 and the article by Hung will be described. The image signals in the target image device and the reproduction image device are BGR.
(Blue, Green, Red) and YMC (Yellow, Magenta, Cyan) 3D image signals, YMCK
4 like (yellow, magenta, cyan, black)
Although there are two-dimensional image signals and the like, here, for simplicity, it is assumed that the image signals are two-dimensional.

First, an image signal represented by a color system used in the target image device (hereinafter referred to as "target image signal"),
A value that is the color that is output when this image signal is input to the target image device in the L ^* a ^* b ^* color system (hereinafter "color value").
A) and a lookup table (hereinafter referred to as “first LUT”) that are associated with each other.

The first LUT may be created by directly measuring the color output from the target image device with a colorimeter to obtain the color value, or based on the Neugebauer equation or the density addition law. It may be created by obtaining a color value.

Next, an image signal represented by a color system used in a reproduction image device (hereinafter referred to as "reproduction image signal"),
A look-up table (hereinafter, referred to as "second LUT") that associates the color value of the color output when the image signal is input to the reproduction image device is created.

This second LUT may also be created by directly measuring the color output from the reproduction image device with a colorimeter to obtain the color value, or based on the Neugebauer equation or the density addition law. It may be created by obtaining a color value.

In FIG. 8, FIG. 8A is a diagram showing a target image signal and FIG. 8C is a diagram showing a reproduced image signal. As described above, the case where the image signal is two-dimensional will be described here. The target image signal and the reproduced image signal can be represented two-dimensionally on the vertical axis and the horizontal axis. On the other hand, FIG. 8 (b) and FIG. 8 (d) are views showing the L ^* a ^* b ^* space,
The vertical axis represents L ^* and the horizontal axis represents c ^* (= √ (a ^{* 2} + b ^{* 2} )).

In FIG. 8 (a), 25 types of target image signals are indicated by black circles in a combination of 5 types of vertical axis and 5 types of horizontal axis. The color value of the color output when these 25 types of target image signals are input to the target image device is the first LU.
It is calculated by T and is pointed by a black circle in FIG. That is, the points d, e, f, and h in FIG. 8A correspond to the points d ′, e ′, f ′, and h ′ in FIG. 8B, respectively.

Also in FIG. 8C, white circles point to 25 kinds of reproduced image signals in a combination of 5 kinds of vertical axes and 5 kinds of horizontal axes. The color value of the color output when these 25 types of reproduction image signals are input to the reproduction image device is the second value.
8D, and is pointed by a white circle in FIG. That is, points j, k, and
p and q are points j ′, k ′, p ′, and q in FIG. 8D, respectively.
Corresponds to ´.

Next, consider a frame surrounded by a broken line by connecting the points shown in FIG. 8C as shown by broken lines and the points shown in FIG. 8D as shown by broken lines. Then, the frame in FIG. 8D in which each point pointed to FIG. 8B is located is searched. For example, when the target image signal at the point s in FIG. 8A is given to the target image device, the point s ′ in FIG.
The color corresponding to is output, but here, it is determined that this point s ′ exists within the frame formed by the triangle t′u′w ′ in FIG. 8D. Thus, in FIG. 8D, the point s
Once the frame in which ′ is present is obtained, in order to output the color corresponding to the point s ′ from the reproduction image device, a specific reproduction image signal within the frame formed by the triangle tuw in FIG. You can see that you can enter in.

At this stage, it is only known that this particular reproduced image signal is within the frame formed by the triangle tuw in FIG. 8C, but it was disclosed in the above-mentioned Japanese Patent Laid-Open No. 2-226870 and the article by Hung. According to the method
This specific reproduction image signal can be obtained from the coordinates of the vertices of the frame of FIG. 8C and FIG. 8D where the point exists. Since this point is not the gist of the present invention, detailed description thereof is omitted here.

In this way, the target image signal and the reproduction image signal to be input to the reproduction image device when the color output when the target image signal is input to the target image device is desired to be output by the reproduction image device. You can ask for correspondence with
A color conversion LUT can be created.

[0016]

By the way, in the above-mentioned conventional method, when searching for in which frame in FIG. 8 (d) each point in FIG. 8 (b) exists, in what order There is no mention of how to search. Therefore, it is generally conceivable that the frame shown in FIG.
This is a method of performing inside / outside determination as to whether or not each point in (b) is within the frame. Here, the frame in FIG. 8D is a quadrangle t'u.
Considering a case where a rectangular frame such as'v'w 'is present and each point in FIG. 8 (b) is present in the rectangular frame, the number of target image signals is calculated. Is (N _i × N _i ), and the number of reproduced image signals is (N _o × N _i ).
_o )), each point is searched for each frame and the search is terminated at the time when a frame in which the point is present is found, but the number of searches is (N _i × N _i × (N _o −1) ) × (N
It becomes _o −1) × 1/2) times, resulting in a huge amount of calculation.

In FIGS. 8A to 8D, the image signal is 2
The case of dimension is shown, but it is often used in practice.
When the image signal is three-dimensional like the GR color system or the YMC color system, the number of searches described above further increases, and (N _i × N _i
× N _i × (N _o −1) × (N _o −1) × (N _o −1) ×
It became 1/2) times, and the amount of calculation was enormous.

Therefore, conventionally, it takes much time to create a color conversion LUT.

The present invention has been made in view of the above points, and an object thereof is to provide a method and apparatus for creating a color conversion lookup table at high speed.

[0020]

According to the present invention, in order to achieve the above object, each of a first color value group in a color space of a color output when a target image signal is input to a target image device is , Which one of the plurality of spaces defined by the second color value group in the color space of the color output when the reproduction image signal is input to the reproduction image device is sequentially searched. In the color conversion lookup table creating apparatus for creating the color conversion lookup table storing the correspondence between the target image signal and the reproduced image signal by obtaining, the current search in the first color value group. And a first color value selecting means for selecting the first color value as a target from the vicinity of the first color value that was the target of the previous search, and the plurality of spaces obtained in the previous search. Space It started this search, if the first color value of interest of said current retrieval does not exist in this space, and a retrieving means for retrieving from the space in the vicinity of this space in order.

[0021]

With the above arrangement, the first color value selecting means sets the first color value, which is the target of the current search, in the first color value group, as the target of the previous search. The search means selects from the vicinity of the first color value, and the search means starts the current search from the space obtained by the previous search among the plurality of spaces,
When the first color value to be searched this time does not exist in this space, the spaces near this space are searched in order.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

First, the principle of the present invention will be described.

Here, a quadrangle frame having four points of the reproduced image signal as vertices (for example, quadrangle t'u'v in FIG. 8D).
'W') is called a medium space, and this medium space is divided into two and a triangular frame having three points of the reproduced image signal as vertices (for example, FIG. 8).
The triangle t'u'w 'and the triangle u'v'w' in (d) are called a small space. When the target image signal and the reproduced image signal are two-dimensional, the medium space is a quadrangle and the small space is a triangle, but when the target image signal and the reproduced image signal are three-dimensional, the medium space is a reproduced image. It becomes a hexahedron having 8 points of signals as vertices, and the small space divides the medium space into 6 and becomes a triangular pyramid having 4 points of reproduced image signals as vertices.

The present invention can be applied to the case of searching a medium space where each point of a target image signal exists and the case of searching a small space where each point of a target image signal exists. In the case of searching a medium space where each point of the target image signal exists, when searching in which medium space each point of the target image signal exists, the point of the target image signal that has been searched immediately before (hereinafter referred to as “ It is assumed that the next search is performed for a point (hereinafter referred to as "the current point") near the "previous point", and in the search for the current point, the medium space in which the previous point exists (hereinafter referred to as "the previous point"). The search starts from the middle space near the space) or the previous middle space, and gradually searches the middle space far from the last middle space.
As described above, the present invention utilizes that the middle space in which the current point exists is near the previous middle space because the color characteristic of the current point is close to the previous point. .

As described above, in the conventional method, the search is always performed in order from the middle space at the edges, so that both image signals are
In the case where the number of target image signals is (N _i × N _i × N _i ) and the number of reproduced image signals is (N _o × N _o × N _o ), the number of searches is (N _i × N _i × N). _i × (N _o −1) × (N _o −
1) × (N _o −1) × 1/2) times. However, according to the method of the present invention, since the search can be almost completed in the previous midspace and the midspace adjacent to the previous midspace (the number of which is 27), the number of searches is almost (N _i × N _i × N _i × 27) times.

In particular, in order to improve the accuracy of color conversion, it is necessary to increase the number of target image signals and the reproduced image signals corresponding thereto in the color conversion LUT. The difference between the number of searches and the number of searches of the present invention becomes larger and larger. Table 1 is a table showing a comparison between the number of searches of the conventional example and the number of searches of the present invention when the number of target image signals and the number of reproduced image signals are the same.

[0028]

[Table 1] As can be seen from Table 1, in the conventional example, the number of searches increases exponentially as the number of image signals increases, but according to the present invention, the number of searches does not significantly increase. That is, the greater the number of image signals, the greater the effect of the present invention.

Next, an embodiment of the color conversion LUT creating apparatus according to the present invention will be described.

FIG. 1 is a block diagram of an embodiment of a color conversion LUT creating apparatus according to the present invention.

The address generating means 1 generates the address of each point of the target image signal for obtaining the corresponding reproduced image signal.

FIG. 2 is a diagram for explaining the address generation order of the points of the target image signal in the address generation means 1, and FIG. 2A is an example of the address generation order in the present invention.
(B) is an example of an address generation order which is not performed in the present invention.

FIGS. 2 (a) and 2 (b) show an example in which the target image signal is two-dimensional and the number thereof is (5 × 5). The numbers in the figure are points of the target image signal. The address generation order is shown, and the middle space where each point of the target image signal exists is searched in this order.

In the address generation order of the target image signal in the present invention, as in the example of FIG. 2A, when an address for a certain point is generated, next, an address is generated for a point adjacent to the previous point. There is a need to. Therefore,
In the present invention, the address generation order should not be skipped as in the case of moving from the point of order "5" to the point of order "6" in the example of FIG. 2 (b). Figure 2 (a)
In the above example, the starting point of address generation, that is, the point of sequence "1" is the lower left point, but the present invention is not limited to this, and the starting point may be any point.

Returning to the description of FIG. 1, the address of each point of the target image signal generated by the address generating means 1 is input to the LUT 2 and the corresponding color value is output. Then, this color value is input to the medium space inside / outside determination means 3. here,
LUT2 corresponds to the first LUT in the conventional example. The address generating means 1 and the LUT 2 correspond to the first color value selecting means in the claims.

On the other hand, the address generating means 4 generates the address of each point of the reproduced image signal forming the medium space for each medium space, and this address is inputted to the LUT 5 and the corresponding color value is outputted. Then, this color value is input to the maximum value / minimum value calculating means 6, the small space inside / outside determining means 7, and the target image signal estimating means 8. Here, the LUT 5 corresponds to the second LUT in the conventional example. Address generating means 4
The generation order of the middle space in which the address is generated will be described later.

The maximum value / minimum value calculating means 6 calculates the maximum value and the minimum value of the color value of the medium space formed by each point of the reproduced image signal indicated by the address obtained from the address generating means 4, It outputs to the space inside / outside determination means 3.

In this embodiment, a medium space in which the color value of the target image signal may exist is obtained, and then the color value of the target image signal exists in a small space obtained by dividing the obtained medium space. It does not search all small spaces, and if the color value of the target image signal is not clearly in the middle space at the middle space stage, the middle space is searched. This is intended to speed up the processing by not performing a search for the divided small space.

That is, the medium space inside / outside determination means 3 is
It is checked whether or not the color value obtained from T2 is between the maximum value and the minimum value obtained from the maximum value / minimum value calculation means 6, and the color value of the target image signal of this time is clearly the middle space of this time. It is judged whether it is not inside or there is a possibility that it is inside the medium space this time. For example, in the color space shown in FIG.
When the color value of the target image signal is point J, points D, E, F,
Since it is between the maximum value and the minimum value of the medium space consisting of H, it is determined that it may be in the medium space this time (although it is not actually in this medium space). Since the L ^* value exceeds the maximum value, it is determined that it is not in the medium space this time.
The medium space inside / outside judging means 3 outputs this judgment result to the address generating means 4 and the small space inside / outside judging means 7 as a control signal.

The address generating means 4, which has received the control signal of the determination result that the color value of the target image signal of this time is not in the middle space of this time, generates an address for each point forming the next middle space.

Here, the generation order of the medium spaces (that is, the search order of the medium spaces) in which the address generating means 4 generates the addresses will be described.

FIG. 4 is a diagram showing an example of the generation order of the medium space in which the address generation means 4 generates an address.

FIG. 4 shows an example in which the reproduced image signal is two-dimensional and the number thereof is (5 × 5). In this case, the number of medium spaces is (4 × 4). The numbers in the figure indicate the generation order of each medium space.

As described above, according to the present invention, the search is started from the midspace near the previous midspace (the midspace in which the point of the target image signal that has been searched immediately before exists) or the previous midspace, This is to gradually search for a medium space far from the previous medium space. Therefore, the address generating means 4 may generate the addresses in the order shown in FIG. 4, for example.

Returning to the explanation of FIG. 1, the small space inside / outside judging means 7 having received the control signal of the judgment result that the color value of the target image signal of this time may be in the middle space of this time, It is determined whether or not the color value of the target image signal is within each small space formed by dividing the current medium space. The small space inside / outside judging means 7 outputs the judgment result to the address generating means 4 and the reproduced image signal estimating means 8 as a control signal. By the way, the address generating means 4, the LUT 5, the maximum value / minimum calculating means 6, the medium space inside / outside judging means 3, and the small space inside / outside judging means 7.
And correspond to the search means in the claims.

Now, the address generating means 4 which has received the control signal of the judgment result that the color value of the target image signal of this time is not within the small space formed by dividing the medium space of this time forms the next medium space. Generate an address for each point.

On the other hand, the reproduced image signal estimating means 8 which has received the control signal of the determination result that the color value of the target image signal of this time is within the small space obtained by dividing the medium space of this time Based on the coordinates of the color value of the signal, the coordinates of the vertex of the small space where the color value of the target image signal exists, and the coordinates of each point in the coordinate system of the reproduced image signal corresponding to this vertex, the target of this time A reproduced image signal corresponding to the image signal is obtained. The LUT 9 is a color conversion LUT created by storing the correspondence between the target image signal and the reproduced image signal.

By the way, the color value of the target image signal may not be within the color gamut of the reproduced image signal depending on the combination of the target image device and the reproduced image device. Here, the processing in this case will be described.

FIG. 5 is a diagram for explaining the case where the color value of the target image signal is not within the color gamut of the reproduced image signal.

In FIG. 5, the color gamut of the reproduced image signal has points M ₀ , M ₁ , M ₂ , M ₃ , N ₀ , N ₁ , N ₂ , N ₃ and P.
_The area is surrounded by ₀ , P ₁ , P ₂ , P ₃ , Q ₀ , Q ₁ , Q ₂ , and Q ₃ , and the reproduction image device can output only colors within this color gamut. Therefore, when the color value of the target image signal exists outside the color gamut of the reproduced image signal as at point R, a color that is within the color gamut of the reproduced image signal and similar to the color value of the target image signal is used instead. Must be done.

As this similar color, for example, a color having the same hue as the color value of the target image signal but the maximum saturation that does not significantly differ in lightness may be used. Therefore, a reproduced image signal that associates the color value at the intersection of the straight line connecting the point R and the gray axis and the boundary line of the color gamut of the reproduced image with the target image signal that outputs the color value of the point R in the color conversion LUT. The color value of

Here, points M ₀ , M ₁ , M ₂ and M _{3 in FIG.}
Is a side M, points N ₀ , N ₁ , N ₂ , N ₃ are sides N, points P ₀ , P ₁ , P ₂ , P ₃ are sides P, points Q ₀ , Q _The side composed of ₁ , Q ₂ and Q ₃ is called side Q. In order to obtain the above-mentioned intersection, this side M, N,
You must search P and Q to check if there is an intersection.

The present invention also speeds up the creation of the color conversion LUT by defining the order in which each side that is the boundary line of the color gamut of the reproduced image is searched.

This search order is such that, for example, when the previous point (the color value of the target image signal) has an intersection point on the side M, the same side M is searched when the presence or absence of the intersection point on this point is checked. If there is no intersection on this side M, then the side on which the intersection of the two points before the next point was searched is searched. Since the intersection of the points this time often exists on the same side as the points of the previous time and the point of the time before the previous time, the processing speed can be increased by adopting such a search order.

Regarding the search order for obtaining this intersection, not only when the color value of the target image device deviates from the color gamut of the reproduced image device when the color conversion LUT is created, but also in the normal image processing. It can also be applied when performing smooth color compression processing.

By the way, in this embodiment, the image signal is mainly 2
Although the case of the dimension has been described and illustrated, it goes without saying that the present invention can be applied to the case where the image signal has the dimension of n (n is an integer of 2 or more).

In this embodiment, as shown in FIG. 1, the medium space is searched first, and then the small space is searched. However, it is assumed that the small space is not directly searched but the small space is searched. May be specified.

Regarding the order of generation of the addresses of the target image signal at the time of retrieval, in addition to the example shown in FIG.
For example, it may be generated obliquely as shown in FIG.
Then, if the increase in the number of searches (decrease in processing speed) can be tolerated to some extent, the points may be occasionally generated as shown in FIG. 2B.

Regarding the search order (occurrence order) of the medium space, in addition to the example shown in FIG. 4, for example, FIG.
As shown in FIG. 7B, the search may be started in the vicinity of the previous medium space, or may be performed in the vertical, horizontal, and diagonal directions of the previous medium space.

In order to compensate for the difference between the color gamut of the target image device and the color gamut of the reproduced image device, the color coordinates corresponding to the target image signal are subjected to saturation compression or the like (color compression) in advance to reproduce the image. The color gamut of the device may be maintained.

Further, the present invention may be combined with a method for predicting the medium space to be initially searched by a simple functional expression.

By the way, in the case where the image output is four colors of YMCK (yellow, magenta, cyan, black), under the condition that black is always maximized or the black is always minimized, the target color value is A combination of YMCK may be obtained (see Japanese Patent Laid-Open No. 2-136848). In this case, the three-dimensional color solid (color gamut) is 4
Two conditions (Ay = 0, Am = 0 for maximum black,
Ac = 0, Ak = 1. Ay = 1 when black is minimum,
Am = 1, Ac = 1, Ak = 0. ) Calculated under 4
It becomes one color solid. In this case, it is necessary to search which of the four color solids has the target color value. This search order is based on, for example, the point previously searched for among the target color values. The current search may be started from the existing color solid, or the current search may be started from the color solid closest to the color solid in which the previously searched point exists.

[0063]

As described above, according to the present invention,
The number of times of searching the medium space or the small space in which the color value corresponding to the target image signal exists can be significantly reduced.

According to the present invention, although the processing time in the address generating means 1 and the address generating means 4 in FIG. 1 is longer than in the conventional case, the processing time can be shortened as a whole by greatly reducing the number of searches. For example, using the BGR color system for the target image signal and the YMC color system for the reproduced image signal, the number of each image signal is (33 × 33 × 3).
3) As a result of actual measurement in the case of using 3 pieces, it took about 40 minutes in the conventional example, but according to the present invention, the color conversion LUT could be created in about 3 minutes.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a color conversion LUT creation device according to the present invention.

2A and 2B are diagrams illustrating an address generation order of each point of a target image signal in an address generation means, FIG. 2A is an example of an address generation order in the present invention, and FIG. 2B is an address generation not performed in the present invention. It is an example of an order.

FIG. 3 is a diagram illustrating a determination process in a medium space inside / outside determination unit.

FIG. 4 is a diagram showing an example of a generation order of a medium space in which an address generation unit generates an address.

FIG. 5 is a diagram illustrating a case where the color value of the target image signal is not within the color gamut of the reproduced image signal.

FIG. 6 is an example of an address generation order of points of a target image signal in the address generation means, which is another example different from FIG. 2A.

FIG. 7 is a diagram showing an example of a generation order of a medium space in which an address generation unit generates an address, and FIG.
Another example, FIG. 7B is another example.

FIG. 8 is a diagram illustrating a method of creating a conventional color conversion LUT.

[Explanation of symbols]

 1 address generating means 2 LUT 3 medium space inside / outside judging means 4 address generating means 5 LUT 6 maximum / minimum value calculating means 7 small space inside / outside judging means 8 reproduced image signal estimating means 9 LUT

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G06T 7/00 9365-5H G06F 15/62 310 15/66 N 310 9061-5H 15/70 310

Claims (6)

[Claims] 1. Each of a first color value group in a color space of a color output when a target image signal is input to a target image device is output when a reproduced image signal is input to the reproduction image device. Correspondence between the target image signal and the reproduced image signal by sequentially searching for which space among the plurality of spaces defined by the second color value group of the color in the color space In a color conversion look-up table creating device that creates a color conversion look-up table that stores an index, a first color value in the first color value group to be searched this time is set as a target in the previous search. And a first color value selection means for selecting from the vicinity of the first color value, and the current search is started from the space obtained by the previous search among the plurality of spaces, and the target of the current search is set. First
A color conversion look-up table creating device, wherein the color conversion look-up table creating device further comprises a searching unit that sequentially searches the space in the vicinity of the color value of the color space value. 2. Each of the first color value groups in the color space of the color output when the target image signal is input to the target image device is output when the reproduction image signal is input to the reproduction image device. Correspondence between the target image signal and the reproduced image signal by sequentially searching for which space among the plurality of spaces defined by the second color value group of the color in the color space In a color conversion look-up table creating device that creates a color conversion look-up table that stores an index, a first color value in the first color value group to be searched this time is set as a target in the previous search. The first color value selection means for selecting from the vicinity of the first color value and the space near the space obtained by the previous search among the plurality of spaces, and the current search is started. Search When the first color value to elephants is not present in the space, the color conversion look-up table forming apparatus characterized by comprising a retrieving means for retrieving from the space in the vicinity of the space in order. 3. The plurality of spaces are a plurality of medium spaces, each medium space is a small space, and the first color value to be searched by the search means is the medium space. 3. The color conversion lookup table creation device according to claim 1, wherein it is determined whether or not it exists in the small space only when it does not exist. 4. Each of the first color value groups in the color space of the color output when the target image signal is input to the target image device is output when the reproduction image signal is input to the reproduction image device. Correspondence between the target image signal and the reproduced image signal by sequentially searching for which space among the plurality of spaces defined by the second color value group of the color in the color space A method for creating a color conversion look-up table that stores a color conversion look-up table, wherein the first color value to be searched this time is selected from the first color value in the first color value group. Is selected from the vicinity of the first color value, and the current search is started from the space obtained by the previous search among the plurality of spaces, and the first search target
The color conversion lookup table creating method is characterized in that, when the color value of the color does not exist in the space, the color conversion lookup table is searched in order from a space near the space. 5. Each of the first color value groups in the color space of the color output when the target image signal is input to the target image device is output when the reproduction image signal is input to the reproduction image device. Correspondence between the target image signal and the reproduced image signal by sequentially searching for which space among the plurality of spaces defined by the second color value group of the color in the color space A method for creating a color conversion look-up table that stores a color conversion look-up table, wherein the first color value to be searched this time is selected from the first color value in the first color value group. Is selected from the vicinity of the first color value, and the current search is started from a space in the vicinity of the space obtained by the previous search among the plurality of spaces, and the first search target The color value is If not present in the space, the color conversion look-up table forming method characterized in that the space in the vicinity of the space was set to be searched in order. 6. The plurality of spaces are a plurality of middle spaces, each of the middle spaces is a small space, and the first color value to be searched for this time does not exist in the middle space. 5. It is arranged to determine whether or not it exists in the small space only in other cases.
Alternatively, the method of creating a color conversion lookup table described in 5 above.