JPH1075372A - Color information conversion processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reflect preference of persons with respect to color reproduction with fidelity while storing lightness difference bonafide by converting a non- reproduction color of an outputted image into a reproducible color on the basis of an inverted lightness. SOLUTION: When received image color information is discriminated to be a non-reproduction color, at first a lightness LP is extracted (S701) and the relation of quantity between a lightness L of a non-reproduction color and the lightness LP is compared and discriminated (S702). When it is discriminated that the lightness of the non-reproduction color is lower than the LP, constants C1, D1 are used to obtain a lightness L2 of a reproduction light (S703). On the other hand, when it is discriminated that the lightness of the non- reproduction color is higher than the LP, constants C2, D2 different from the constants C1, D1 in the case of lower lightness are used to obtain a lightness L2 of a reproduction light (S704). Then a color coordinate on a border line within a color reproduction range with the lightness L2 is obtained (S705). That is, a desired reproduction color (L2, a2, b2) is obtained by obtaining points on the border line within the reproduction range with the lightness of L2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color information conversion processing method for transferring color image information between devices having different color reproduction ranges, such as a CRT, a color printer, and a color copy. Note that the difference between the lightness of the non-reproduced color and the lightness of the reproduction destination is reversed by the predetermined lightness value regardless of the gamut boundary based on the result of The present invention relates to a color information conversion processing method for converting non-reproducible colors into reproducible colors and faithfully reflecting a person's taste regarding color reproduction.

[0002]

2. Description of the Related Art In recent years, media handling color images have been developed in various forms. For example, there is well known a system in which a character or image is read by a color scanner, edited and processed on a computer display, and the result is printed out by a color printer or the like.
However, in this case, the color reproduced on the display and the color printed out are determined by a color reproduction method or a mixed color system (RG
(B, YMC), and the fact that colors differ from each other due to the mismatch of color reproduction ranges.

As described above, since the gamut of colors that can be expressed by a device is usually different from each other, of the input colors, colors that cannot be output by an image output device are replaced with reproducible colors and converted. Performs color gamut compression processing.

However, in general, when a non-reproduced color is included in an output image, the above-described compression processing is performed irrespective of colors around the non-reproduced color. Therefore, the color may be reproduced in the same color as the periphery of the non-reproduced color, and as a result, the gradation may be lost.

Therefore, conventionally, for example, Japanese Patent Publication No. 6-365
As disclosed in “Color Image Signal Processing Method” of JP-A-48-48, a compression ratio suitable for the characteristics of an image represented by an input color image signal is determined for both lightness and saturation, and the lightness and saturation are determined. Compression and mapping within the color reproduction range of the output system so as to preserve the gradation of

[0006] In addition to the above, JP-A-61-2886.
In the "color image processing method" disclosed in Japanese Patent Publication No. 90, a hue is fixed around a white point on a chromaticity diagram, and points outside the color reproduction range of the output system are compressed and mapped within the color reproduction range of the output system. Things are disclosed.

Further, in Japanese Patent Application Laid-Open No. 4-284579, "Color Image Processing Method and Apparatus", color image information is coded according to lightness, saturation and hue,
There is disclosed one that converts a color outside the color reproduction range of the output system to the outer edge of the color reproduction range.

FIG. 11 shows a conventional non-reproduction color compression method. In general, there are a method (a) of determining the compression angle (θ) with respect to the boundary of the reproduction range and compressing in the direction, and a method (b) of compressing the white point.

Conventionally, a gamut vertex of a gamut boundary line, that is, a lightness of a color having the highest saturation in a color reproduction area of a certain lightness is used as a reference. For example, the lightness of a non-reproduced color is higher than the reference lightness. In this case, a compression process is performed in which the brightness of the non-reproduced color is set to a low brightness, and when the brightness of the unreproduced color is lower than the reference brightness, a converted color having a high brightness is used.

[0010]

However, the conventional Japanese Patent Publication No. 6-36548 and the Japanese Patent Application Laid-Open No. 61-288690 described above all dissolve gradation loss. However, since not only the non-reproduced colors of the output image are converted into reproducible colors but also the colors of the reproducible output image are converted, they are reproduced in colors different from the output image. However, there is a problem that the operation may be performed.

As disclosed in Japanese Patent Application Laid-Open No. 4-284579, non-reproducible colors are replaced with various colors on the boundary of a reproducible range of an image output system and converted. Since it is not always clear and the compression processing method is not formulated to reflect the subjective evaluation result, the taste about human color reproduction is not faithfully reflected. Further, even when non-reproduced colors having different lightness exist, there is a problem that the lightness difference is not faithfully reproduced if the compression direction is the same.

This will be described with reference to FIG.
a, b, and c are the lightness of the non-reproduced color, a ', b',
When c ′ is the brightness of the color to be reproduced, a> b, a = c,
If c> b, a ′ = b ′, a ′> c ′, b ′> c ′
Thus, it can be seen that the relationship of the gradation difference (brightness) between a, b, and c changes. Similarly, d <
If f, d = e, e <f, d ′ = f ′, d ′ <
The relationship of the gradation difference (brightness difference) between d, f, and e changes as e ', f'<e'.

The present invention has been made in view of the above, and based on the result of the subjective evaluation, the difference between the lightness of the non-reproduced color and the lightness of the reproduction destination is determined by a predetermined lightness value regardless of the gamut boundary. Paying attention to the fact that it is reversed, the non-reproduced colors of the output image are converted into reproducible colors based on the reversed lightness value, so that the lightness difference is faithfully preserved and the taste about human color reproduction is improved. The purpose is to reflect faithfully.

[0014]

According to a first aspect of the present invention, there is provided a color information conversion processing method.
When at least a part of the image information is a non-reproducible color that cannot be reproduced in the color reproduction range of the image output system, a color information conversion processing method of converting the non-reproducible color into a reproducible color of the image output system is considered. A judgment step of judging whether or not the pixel is inside the color reproduction range of the image output system; a lightness value setting step of presetting a lightness value in which the sign of the lightness difference between the non-reproduction color and the reproduction destination is reversed; A brightness comparison step of comparing the color information of the pixel of interest determined to be outside the color reproduction range in the determination step with respect to the brightness value set in the brightness value setting step; A lightness determining step of determining the lightness of the non-reproduced color after conversion based on a comparison result of the steps; and a conversion color determining step of determining a converted color having the lightness determined in the lightness determining step. Than it is.

That is, when a non-reproducible color is assigned to a color on the boundary of the reproduction range, the result of the subjective evaluation is reflected, and regardless of the brightness of the gamut vertex (the color having the highest saturation in the color reproduction range of a certain brightness), Based on a preset brightness value, the color is converted into a desired color using the brightness uniquely determined by the brightness of the original color. Therefore, the taste of human color reproduction is faithfully reflected, and the brightness difference is faithfully reflected. As well as realizing the color reproduction to be preserved, the color of the reproduction color can be easily obtained only by the brightness of the non-reproduction color, and the compression direction of the non-reproduction color based on the subjective evaluation becomes clear. Natural color reproduction is possible without becoming too whitish.

Further, in the color information conversion processing method according to the second aspect, the brightness value setting step sets a brightness value based on a hue of a non-reproduced color.

That is, by determining the reference point of the conversion in the compression for each hue, the color is converted into a desired color for each hue, so that a highly accurate color reproduction according to the hue is realized.

According to a third aspect of the present invention, in the color information conversion processing method, the lightness value setting step includes the step of setting a boundary of a reproduction range having the same lightness as the saturation of the non-reproduction color and the lightness of the non-reproduction color. The brightness of the converted color is set based on the difference from the saturation of the converted color.

That is, by paying attention not only to the brightness difference but also to the saturation difference of the non-reproduced color from the gamut boundary, the non-reproduced color near the gamut boundary is smoothly reproduced.

Further, in the color information conversion processing method according to claim 4, the lightness value determining step includes the step of comparing the lightness comparing step using the lightness value set in the lightness value setting step. The brightness of the converted color is determined based on the difference between the saturation of the non-reproduced color and the saturation of the boundary of the reproduction range having the same brightness as the brightness of the non-reproduced color.

That is, by simultaneously providing the features of claim 1 and claim 3, it is possible to maintain a gradation that is more suitable for human vision.

In the color information conversion processing method according to a fifth aspect, in the brightness value setting step according to the fourth aspect, a brightness value is set based on a hue of a non-reproduced color set in advance. Things.

That is, by simultaneously providing the features of the second and third aspects, it is possible to adjust so as to maintain the gradation for each hue.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a color information conversion processing method according to the present invention will be described in detail in the order of (subjective evaluation experiment) and (processing operation example) with reference to the accompanying drawings.

Embodiment (Subjective Evaluation Experiment) First, a subjective evaluation experiment will be described with reference to FIGS. FIG. 1 is an explanatory diagram showing the lightness position of a continuous color patch of an arbitrary non-reproduced color and the compression direction of a reproduced color of a non-reproduced color in a subjective evaluation experiment.
Is an explanatory diagram showing the compression direction of a color reproduced from a non-reproduced color as a result of processing based on the expression (A) described later. FIG. 3 is a diagram showing a continuous color patch as shown in FIG. FIG. 4 is a graph showing the result of regression analysis from the reproduction results of non-reproduced colors by subjective evaluation. FIG. 4 shows the lightness before and after compression when the distribution of non-reproduced colors in a continuous color patch is distributed at a place higher than the lightness value of 35. A graph showing the relationship between the values,
FIG. 5 shows that the distribution of non-reproduced colors in a continuous color patch has a brightness value of 3
It is a graph which shows the relationship of the lightness value before and after compression in the case where it is distributed at a place lower than 5.

Here, the reference numerals shown in the above figures will be described. L1: Arbitrary continuous color patches of the same hue and non-reproducible colors p1 to p6: Brightness of the color patches, each of which is uniform L2: Color of the same hue on the boundary of the reproduction range and subjectively original Color patches determined by comparison with color p1 'to p6': Lightness of reproduced patch GP: Lightness of vertex of reproduction range of image output system (lightness of gamut vertex) LP: Non-reproduced color and reproduction destination Brightness value where the sign of the brightness difference is reversed

In order to estimate a desired compression direction, each color (L1: p1 to p6 in FIG. 1) of the same hue, non-reproduced color, and any continuous color patch is converted into the color reproduction range of the image output system. Which color on the border line should be converted (Fig. 1
L2: p1 ′ to p6 ′), an experiment was performed based on the subjective evaluation.

According to the results of this subjective evaluation experiment, as shown in FIG. 2, the desirable compression direction is such that the brightness tends to decrease even in a portion darker than the vertex of the gamut, and the compression direction is reversed by the vertex of the gamut. It turns out that it is not.

The brightness difference is gradually increased from the low brightness portion to the high brightness portion up to the brightness LP, and the color of the brightness LP is constant brightness, and the portion lower than the brightness LP is changed from the low brightness portion to the high brightness portion. To gradually reduce the brightness difference. That is, it is desirable to compress the image in a direction to gradually decrease the brightness as the image becomes darker, and to increase the brightness as the image becomes darker.

In FIG. 2, C1, C2, D1,
D2 is arbitrary, and when LP ≦ p1 to p6 and p1> p6, p1 ′ = C1 × (p1−LP) + LP + D1... P6 ′ = C1 × (p6-LP) + LP + D1 LP> pp1 to pp6 When pp1> pp6, pp1 ′ = C2 × (pp1-LP) + LP + D2... pp6 ′ = C2 × (pp6-LP) + LP + D2 Therefore, the brightness difference is p1-p1 ′> p6-p6 ′, pp1-pp1 '<pp
6-pp6 '.

As a result of the regression analysis of the experimental values, the relationship between the brightness before and after the compression from the graph of FIG. 3 shows that when the maximum value of the brightness is normalized to 100, the brightness value at which the sign of the brightness difference is reversed. Is approximately 35, and further analysis using this value yields graphs shown in FIGS. 4 and 5.
This shows that the slopes having a linear correlation are slightly different.

Therefore, it was found from the above results that the lightness difference before and after compression can be represented by the following simple linear correlation. However, as the lightness, a value obtained by normalizing the white lightness value to 100 is used.

That is, from the graph of FIG.
At the time of L2 = 0.91 × (L1-LP) + LP + 0 From the graph of FIG. 5, when L1 <LP, L2 = 0.87 × (L1-LP) + LP + 0, and the following equation (A) is obtained. Can be represented.

L2 = C × (L1−LP) + LP + D (A) where C and D are constants.

Next, based on the results of the subjective evaluation described above, the processing operation example of the embodiment will be described with reference to flowcharts (processing operation example 1), (processing operation example 2), (processing operation example 3), (processing operation example 3). Operation example 4) and (processing operation example 5) will be described in this order.

(Processing Operation Example 1) FIG. 6 is a flowchart showing a processing operation example 1 of the embodiment. In FIG. 6, this color reproduction processing is performed in the following procedure.

First, image color information is input (S601).
The image color information is converted into, for example, Lab coordinate values (S
602). Subsequently, it is determined whether the color is a non-reproduction color (S603). If it is determined that the color is a non-reproduction color,
The converted color information is determined using the lightness difference that is uniquely determined from the lightness of the original color with the same hue, and the color on the boundary of the reproduction range is determined (S604).

On the other hand, if it is determined in step S603 that the color is not a non-reproduction color, the color reproduction processing is not performed.
It is converted into color information that can be output to the image output system (S605),
The image output is executed (S606). Also, after executing the above step S604, this step S605 is also performed.
Execute

FIG. 7 is a flowchart showing the detailed processing operation of step S604 in FIG. In the figure, first, the lightness value LP is extracted (S701). In other words, the value of the lightness value LP is predetermined, and
The value of P is always given the same value regardless of the hue.

Next, judgment of LP ≧ L, that is, the magnitude relationship between the lightness of the non-reproduced color and the lightness value LP is compared and judged (S702). Here, if it is determined that the lightness of the non-reproduced color is higher than LP, the constants C1 and D1 are substituted into the above-described equation (A) to obtain the lightness L2 of the reproduction destination (S703).

That is, C1 × (L−LP) + LP + D
The calculated value of 1 is defined as L2. As a result, the compression direction becomes p1 → p1 ′ and p6 → p6 ′ in FIG. For example, if the constants are C1 = 0.91, D1 = 0.
Set to 0.

On the other hand, if it is determined in step S702 that the lightness of the non-reproduced color is lower than LP, constants C2 and D2 different from the constants C1 and D1 when the lightness is high are substituted into equation (A) and reproduced. The lightness L2 is obtained (S70).
4).

That is, C2 × (L−LP) + LP + D
Let L2 be the calculated value of 2. Accordingly, the compression direction is pp1 → pp1 ′, pp6 → pp6 ′ in FIG. For example, let the constant be C2 = 0.87, D
2 = 0.0.

When the processing in step S703 or S704 is completed, the color coordinates on the boundary of the color reproduction range having the lightness L2 are obtained (S705). That is, the brightness is L2, and a point on the boundary of the reproduction range is obtained to obtain a desired reproduction color (for example, (L2, a2, b
2)) is required. For example, the hue of the non-reproduced color is examined, and a point on the boundary of the reproduction range of the same hue is obtained. In this case, it is not necessary to limit to the same hue.

(Processing operation example 2) In this processing operation example 2,
The process of step S701 in FIG. 7 described above is executed in the following procedure.

For each of the N-divided hues created in advance, a table corresponding to N reference values LP is used, and the LP values are interpolated by using the preceding and succeeding LP values in the hue values of the non-reproduced colors. To determine.

Next, according to the graph shown in FIG. 8, since the value of C in the above equation is in the range of 0 to 0.9, attention is paid to the chroma difference from the gamut boundary as a feature amount for determining this C value. As a result, a graph shown in FIG. 9 is obtained, and the following relational expression is established. However, in the graph of FIG.
0.94.

That is, Lratio = (L1-L2) /
Assuming that ((1−Az) × L1), a relational expression of L2 = L1−Lratio × ((1−Az) × L1) = (1−Lratio × (1−Az)) × L1 is established.

Assuming that the difference in saturation from the gamut boundary is ΔC, Lratio is Lratio where ΔC is close to 0.
= 0, that is, reproduction with L2 = 1 (reproduction in the direction of constant lightness) is desirable. On the other hand, when the saturation difference from the gamut boundary increases, the maximum value of Lratio gradually increases. I have. In other words, as the saturation difference goes away from the saturation value of the gamut boundary, the desired compression destination range “constant lightness direction—Az × lightness L1” expands,
Az that determines this range monotonically increases as ΔC increases.

Therefore, it can be described as Lratio = f (ΔC). When the value of ΔC is large, the function becomes a monotonically decreasing function that converges to the constant C of the above-described equation (A), and the relation of the following equation (B) is obtained. Can be represented by

(Processing operation example 3) In this processing operation example 3,
The processing operation is performed based on the processing operation example 2 described above. That is, when the non-reproduced color is near the gamut boundary, it is desirable that the value from the non-reproduced color be closest to the gamut boundary. Therefore, the above equation (A) is modified to the following equation (B).

That is, paying attention to the saturation difference ΔC from the gamut boundary, it is shown that when ΔC is close to 0, reproduction by L2 = L1 (reproduction in a constant brightness direction) is desirable. When the saturation difference ΔC from the gamut boundary increases, the relationship of the expression (A) is approached.

Here, f (ΔC) is 1 when ΔC is 0.
And a monotonically decreasing function that converges on the constant C of the equation (A) as the value of ΔC increases. L2 = f (ΔC) × L1 + D ′ (B) In the above equation (B), f (ΔC): 1.00 (C) (monotone decreasing function) in equation (A) ΔC: from the gamut boundary This is the saturation difference between the original colors.

Therefore, in the third example of the processing operation, the processing in the above-described step S604 (see FIG. 6) is executed by calculating by the processing based on the above equation (B).

(Processing Operation Example 4) Here, the processing of step S703 (see FIG. 7) is executed using the following equation (B-3).

L2 = f ′ (ΔC) × (L−LP) + LP + D1 (B-3) In the above equation (B-3), f ′ (ΔC): 1.00 to the equation in step S704 C2
(Monotone decreasing function) ΔC: Saturation difference of the original color from the gamut boundary.

(Processing Operation Example 5) Here, the above-described processing of step S701 (see FIG. 7) is executed according to the following procedure.

That is, for each of the previously created N-divided hues, a table corresponding to N reference values LP is used, and the L values before and after the hue values of the non-reproduced colors are used.
LP is determined by interpolating using the value of P.

(Effects of Embodiment) Next, effects of the above-described embodiment will be listed.

First, as described in the processing operation example 1 of FIGS. 6 and 7, the processing is performed by paying attention to the brightness difference before and after the compression of the non-reproduced color, so that the gradation loss due to the compression is avoided. You. In addition, there is no inversion of brightness, and faithful color reproduction can be performed. Further, the color of the reproduction destination can be easily obtained only by the brightness of the non-reproduction color. This scheme according to the present invention is shown in FIG.

Further, the compression direction of the non-reproduced color based on the subjective evaluation becomes clear. For this reason, the color of the reproduction destination does not become too whitish or too dark, and natural color reproduction is realized.

That is, in FIG. 10, when a, b, and c are the lightness of the non-reproduced color and a ', b', and c 'are the lightness of the color of the reproduction destination, a> b, a = c, c If> b, it can be seen that the relationship of the tone difference (brightness) between a, b, and c is maintained, such as a '>b', a '= c', and c '>b'. . Also, since the saturation difference between a and c is not so much felt, a '= c' holds.

Similarly, if d <f, d = e, e <f, d '<f', d '= e', e '<f', and so on, d, f, e The relationship of the gradation difference (brightness difference) is maintained. Further, since the difference in saturation between d and e is not so much felt, d '= e' holds.

Second, since the compression is made different depending on the hue of the non-reproduced color, it is possible to reproduce with high accuracy in accordance with the hue.

Third, smooth reproduction of non-reproducible colors near the gamut boundary can be realized by focusing not only on the brightness difference but also on the chroma difference of the non-reproducible color from the gamut boundary.

Since these processes are extremely simple processes, they are very easy to realize, and it has been confirmed that even in the processing of natural images including non-reproduced colors, good images can be reproduced.

[0067]

As described above, according to the color information conversion processing method of the present invention (claim 1), when a non-reproducible color is assigned to a color on the boundary of the reproduction range, the subjective evaluation result is reflected. , Irrespective of the brightness of the gamut vertex (the color with the highest saturation in the color gamut of a certain brightness), the desired color is determined by using the brightness uniquely determined by the brightness of the original color based on the brightness value set in advance. , Which reflects the taste of human color reproduction faithfully, realizes color reproduction that preserves the brightness difference faithfully, and makes it possible to easily find the color of the reproduced color using only the brightness of the non-reproduced color. Since the compression direction of the non-reproduced color based on the subjective evaluation becomes clear, the color of the reproduced difference does not become too whitish, and natural color reproduction can be performed.

According to the color information conversion processing method according to the present invention (claim 2), since a conversion reference point in compression for each hue is determined, each hue is converted into a desired color. Highly accurate color reproduction is realized.

According to the color information conversion processing method according to the present invention (claim 3), not only the brightness difference but also the saturation difference of the non-reproduced color from the gamut boundary is noticed. Colors can be reproduced smoothly.

Further, according to the color information conversion processing method of the present invention (claim 4), since the features of claim 1 and claim 3 are simultaneously provided, it is possible to maintain a gradation more suited to human vision. It becomes possible.

According to the color information conversion processing method according to the present invention (claim 5), in order to simultaneously provide the features of claim 2 and claim 3, it is possible to adjust so as to maintain the gradation for each hue. It becomes possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a position of lightness of a continuous color patch of an arbitrary non-reproduced color and a compression direction of a reproduced color of a non-reproduced color in a subjective evaluation experiment according to the embodiment.

FIG. 2 is an explanatory diagram showing a compression direction of a color reproduced from a non-reproduced color as a result of processing based on Expression (A) according to the embodiment;

FIG. 3 shows a continuous color patch as shown in FIG. 1;
9 is a graph showing a result of regression analysis of a reproduction result of a non-reproducible color by subjective evaluation.

FIG. 4 shows a distribution of non-reproduced colors of a continuous color patch having a brightness value of 3
It is a graph which shows the relationship of the lightness value before and after compression when it is distributed at a place higher than 5.

FIG. 5 shows a distribution of non-reproduced colors of a continuous color patch having a brightness value of 3
It is a graph which shows the relationship of the lightness value before and after compression in the case where it is distributed at a place lower than 5.

FIG. 6 is a flowchart illustrating a processing operation example 1 of the embodiment;

FIG. 7 is a flowchart illustrating an example of a detailed processing operation in step S604 in FIG. 6;

FIG. 8 is a graph showing the relationship (1) between the tendency of the entire continuous color patch and the brightness before and after compression according to the second example of the processing operation of the embodiment.

FIG. 9 is a graph showing a relationship (2) between the tendency of the entire continuous color patch and the brightness before and after compression according to the second example of the processing operation of the embodiment.

FIG. 10 is an explanatory diagram showing a non-reproduced color compression method according to the present invention.

FIG. 11 is an explanatory diagram showing a conventional non-reproduced color compression method.

[Explanation of symbols]

L1 Arbitrary continuous color patches of the same hue and non-reproducible colors p1 to p6 Lightness of patches L2 Color patches p1 'to p1' to colors on the boundary of the reproduction range of the same hue and subjectively determined by comparison with the original color p6 'The brightness of the reproduced patch GP The brightness of the vertex (gamut vertex) of the reproduction range of the image output system LP The brightness value at which the sign of the brightness difference between the non-reproduced color and the reproduction destination is reversed

Claims (5)

[Claims] 1. A color information converter for converting a non-reproducible color into a reproducible color of an image output system when at least a part of the image information is a non-reproducible color that cannot be reproduced in a color reproduction range of the image output system. A determination step of determining whether a pixel of interest is inside the color reproduction range of the image output system; and a brightness value for presetting a brightness value at which the polarity of the brightness difference between the non-reproduction color and the reproduction destination is reversed. A setting step, and a brightness comparing step of comparing the color information of the pixel of interest determined to be outside the color reproduction range in the determining step with the brightness value set in the brightness value setting step, which is higher or lower. A lightness determining step of determining the converted lightness of the non-reproduced color based on the comparison result of the lightness comparing step; and a conversion color determining step of a converted color having the lightness determined in the lightness determining step. And a color information conversion processing method comprising: 2. The color information conversion processing method according to claim 1, wherein the brightness value setting step sets a brightness value based on a hue of a non-reproduced color. 3. The brightness value setting step includes the steps of: determining the brightness of the converted color based on a difference between the saturation of the non-reproduced color and the saturation of a boundary of a reproduction range having the same brightness as the brightness of the non-reproduced color. 2. The color information conversion processing method according to claim 1, wherein the setting is performed. 4. The lightness value determining step includes the step of comparing the lightness comparing step using the lightness value set in the lightness value setting step and the same lightness as the saturation of the non-reproducible color and the lightness of the non-reproducible color. 2. The color information conversion processing method according to claim 1, wherein the brightness of the converted color is determined based on a difference between the saturation of the point at the boundary of the reproduction range having the following. 5. A color information conversion processing method according to claim 4, wherein in the lightness value setting step, a lightness value is set based on a preset hue of a non-reproduced color.