JP2000209449A - Color matching method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform color conversion with less feeling of incongruity between the devices of different color reproducing areas such as a CRT and a printer for instance. SOLUTION: This color matching method between the different devices of the different color reproducing areas which are physical property parameters intrinsic to the respective devices is provided with a step for deciding the type of images, the step for selecting a color conversion method corresponding to the decided type of the images and the step for executing the selected color conversion method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a printed matter having no apparent discomfort with an original on a CRT monitor between two devices having different color reproduction ranges, for example, between a CRT monitor and a printing press. Color matching method between different devices that enables color conversion
The present invention relates to an apparatus and a recording medium on which a program for performing such a method is recorded.

[0002]

2. Description of the Related Art Generally, a CRT monitor and printing have different color reproduction mechanisms (coloring mechanisms).
CRT monitor has three primary colors of light: R (red), G (green), B
Additive color mixture that reproduces color by color mixture of (blue) is used.
On the other hand, printing is performed for the three primary colors C (cyan) and M
(Magenta) and Y (yellow) using subtractive color mixture. The CMYs correspond to the complementary colors of RGB (that is, C and R, M and G, and Y and B together become achromatic).

In additive color mixing, R (red), G (green), B
The three primary colors (blue) are used to form different colors depending on the ratio of light, and the higher the light intensity, the higher the brightness. On the other hand, in subtractive color mixture, the color materials of C (cyan), M (magenta), and Y (yellow)
A color is formed by absorbing (red), G (green), and B (blue) light and selectively absorbing a specific color from white light. For example, a C (cyan) color material absorbs R (red) light and reflects G (green) and B (blue) components. Therefore, as the colors mix, the degree of absorption increases and the color becomes lower in brightness.

As described above, the color reproduction method is different between the CRT monitor and the printing.
Because the color gamut of the monitor is wider than that of printing,
Among the colors of the RT monitor, there are colors that cannot be reproduced by printing. Therefore, when printing the color of the CRT monitor,
Each color on the original picture of the CRT monitor cannot be faithfully reproduced on the printed matter, and often causes a problem that a viewer feels strange.

[0005] In the conventional color reproduction method at a printing site, a skilled operator first compares an image captured from a document photograph through a scanner with a color separation condition which is expected to predict the finish of a printed matter while comparing the image with the document photograph. Therefore, the degree of color matching between the document (photograph) and the printed matter must depend on the skill of the operator.

However, in recent years, digitalization of printing has been advanced, and especially in offices, DPT (Desk Top Publish
Document creation using computers called g) has become popular. Such DTP is C
The font type, size and layout are changed on the RT monitor, and editing is advanced. In DTP, it is required that information displayed on a CRT monitor be reproduced as it is, including colors. In order to satisfy such demands, attempts have been made to faithfully reproduce each color of an original image on a CRT monitor and to produce a printed matter with less discomfort to humans. A system for this is generally called a CMS (Color Management System).

[0007] The basic principle of the CMS is as follows. (1) In order to grasp the relative relationship between different colors for each adopted device, a device-independent color space (for example, L
ab space), and all are converted to such a color space. Hue (color type), lightness (brightness), and saturation (brightness), which are three attributes of human color perception, are expressed in a three-dimensional space having three axes L, a, and b orthogonal to each other. It can be represented by coordinates. (2) Device characteristics are described by a data file called a device profile. That is, the color reproduction characteristics that are different for each device are described in the device profile. (3) Absorb differences in color gamut by mapping in a device-independent color space. For example, conversion of colors on a CRT monitor to colors that can be expressed on a printing press (mapping of color gamut)
This minimizes discomfort.

The above system is an ICC (International Co.)
lor Consortium).
For example, Lab is one of the device-independent color spaces.
A color space is adopted, and the color characteristics of each device are defined as a device profile, and the mapping is defined as an ICC profile and a color management module. In response to this, a device maker only needs to use a Lab space, prepare a profile describing characteristics of its own device, and a mapping function most suitable for the device itself, and some device manufacturers have already sold them. . The contents of such a mapping function called a color management module are almost not disclosed.

Conventionally, there are a compression type and a common area preserving type as a type of mapping for obtaining a printed matter having little apparent discomfort with respect to an original image on a CRT monitor, for example. In the case of the compression type, color conversion is performed by compressing the color gamut of the CRT monitor to the color gamut of printing at the same ratio toward the center of the coordinates. On the other hand, in the case of the common area preservation type, while keeping the common area of the CRT monitor and the color reproduction area of printing and printing, only the area that cannot be reproduced by printing is moved to the outline of the color reproduction area. Here, the common area saving type is roughly classified into a method for saving lightness and a method for saving saturation. In addition, in Japanese Patent Application No. 10-145520, which has not been published yet at the time of filing the present application,
The present inventors have proposed a new method.

[0010]

However, these color matching methods, that is, the color conversion rules are generally changed depending on the type of the image to be converted. There is a problem that involves trial and error. In many cases, since color conversion is performed without considering the actual components of the image to be converted, the entire image area is color-converted in the same manner using the same color conversion rule, which causes discomfort. May result. For example, in many types of printed matter, there is a problem in that a portion that does not originally need to be changed in color is changed.

An object of the present invention is to solve the above-mentioned problem and achieve color conversion with less discomfort by dividing an image to be converted into several parts and actually analyzing the constituent elements. . More specifically, the present invention seeks to automatically determine the type of an image and select an optimal color conversion rule for the image type. In addition, the color conversion is not performed or the degree of the color conversion is reduced in a part of the area, not in the entire image area. This is to analyze the components of the image and to keep the color of a region of interest (called an attraction point) as little as possible.

[0012]

[Means for Solving the Problems]

The present invention is a color matching method between different devices having different color gamut, which is a physical property mass unique to each device, wherein a type of an image is determined, and a color corresponding to the determined type of the image is determined. A color matching method using a conversion method is provided.

The present invention further relates to a color matching method between different devices having different color reproduction ranges, which are physical masses unique to each device, wherein an image type and a region of high attractiveness are determined. Provided is a color matching method that uses a color conversion method according to the type of an image and reduces the conversion amount of color conversion in an area with a high attractiveness separately from other parts.

The above-described method of the present invention can be implemented by being incorporated in a color matching apparatus including a computer having a CPU and a memory, and the present invention also includes such a color matching apparatus. The color matching apparatus between different types of devices having different color gamut, which is the physical property mass unique to each device of the present invention, analyzes input image data to determine an attractive point, It comprises means for selecting a color conversion method according to the characteristics of an image, and means for implementing the selected color conversion method. The color conversion method can be stored in advance in the apparatus of the present invention in association with the characteristics of the image. The determination of the attraction point can be performed based on the attraction degree expressed as a function of parameters such as hue, saturation, brightness, and area. This function is also stored in the apparatus of the present invention, and the degree of attraction can be calculated using the analysis result of the input image data.

In another aspect, a color matching apparatus according to the present invention comprises a first detecting means for detecting color gamut data based on an LCH color space of a source device, and a color reproduction device based on an LCH color space of a destination device. Second detection means for detecting the area data, and at least a part of the color reproduction range of the conversion source device detected by the first detection means, the color of the conversion destination device detected by the second detection means If the data is outside the reproduction range and cannot be reproduced by the destination device, conversion means for converting the hue, lightness, and saturation components of the color reproduction range data of the source device into the color reproduction range of the destination device; Output means for outputting the color reproduction area data to the conversion destination device, wherein the conversion means analyzes the input image data to determine the attraction point, and Means for selecting a color conversion method by Flip,
And means for implementing the selected color conversion method.

Further, the above-described method of the present invention can be embodied as a computer program. The present invention also includes a computer-readable recording medium on which a color matching program for implementing the method of the present invention is recorded.

The conversion source device includes a CRT, a flat display and other image display devices, and the conversion destination device includes a color printer connected to a personal computer and a printing machine including a printing machine for electronic publication. There is a machine. However, the present invention is widely applicable to any combination of devices having different color reproduction ranges, in addition to the combination of the conversion source device and the conversion destination device.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be further described below with reference to the drawings. FIG. 1 shows the flow of an embodiment of the method of the present invention. There are regions of interest in the image, which are commonly referred to as eye-catching points. By analyzing the characteristics of these regions in the image, the image type (natural image, business document, CG, etc.) can be determined based on the portion that has the greatest impact on what is viewed. As a method of extracting the attraction points in the image, there is a method of elucidating the attraction points by line-of-sight analysis and using a correlation analysis with image features (brightness L, hue H, saturation C, area ratio A, etc.) of the area. . Instead of the eye gaze analysis, a method of allowing the subject to answer verbally is also possible. As the image features, in addition to those described above, brightness differences, hue differences, saturation differences, and the like from the surroundings can be considered. Such an attractiveness is a property that is better defined by collecting actual data experimentally through a questionnaire survey or the like.

Here, an example using hue H, saturation C, lightness L, and area ratio A will be described. Using several subjects and image types,
Investigate the image features of the attraction points and the area. These are statistically analyzed, and an attractiveness y defined by the following equation is defined. Here, the weighting coefficient of each feature amount can be, for example, a factor load amount of the result of the principal component analysis, and an amount that is considered to be most preferable empirically can be defined. It should be noted that there is no need to stick to this method for obtaining these weighting factors.

[Equation 3] y (L, C, H, A) = w _L L + w _C C + w _H H + w _A A where L is lightness, C is saturation, H is hue, A is area ratio,
w _L , w _C , w _H , and w _A each represent a weight coefficient. Note that the above equation is merely an example, and any analysis method may be used as long as it can describe the relationship with the attractiveness, but it must be quantified as some function.

Using this degree of attraction, it is possible to extract a region having high attraction. FIG. 2 shows the procedure. First, the image area is divided into an appropriate number. Although the number of divisions at this time is arbitrary, for example, 3 × 3 = 9 to 8 × 8 =
It is conceivable to divide the image into a grid such as 64 or 6 × 4 = 24 (vertical 6 rows, horizontal 4 columns). Alternatively, the image segmentation for the method of the present invention is possible by covering a plurality of round areas substantially with the image. Then, the attractiveness y is calculated for each image area by the above formula. Then, an area having a high degree of attraction y is set as an attraction point. With this method, for example, an attractive point (apple) is extracted as shown in FIG.

Next, the image type is determined by analyzing the extracted points of interest. Here, as an example, consider classifying images into business documents, computer graphics images, and natural images. A business document is an image composed of text, graphs, and the like, and generally having no gradation and high saturation. In this case, the number of the attraction points is generally small, or the attraction point is zero in the case of only text. Also, if there is an eye-catching point, it is expected that the eye-catching point has high chroma and no gradation such as a graph. An image satisfying these characteristics is determined to be a business document. Computer graphics images are characterized by having extremely high saturation compared to general images. If the saturation of the attraction point is very high, it is determined that the image is a computer graphics image. The natural image refers to a photograph of a landscape, a scene, or the like. These include various things such as nature, city scenery, indoors, etc., but have a feature that there are multiple points of interest and that there is no extreme bias in the distribution of saturation and brightness. An image satisfying these characteristics is determined as a natural image. Of course, such a classification is not limiting, and different classifications can be considered. Furthermore, even if the image is classified into computer graphics images, the image is classified into two or more types depending on the level of the saturation, and the natural image is further classified according to the difference in brightness between parts. Can be.

Now that the image type has been determined, a color conversion rule is determined. That is, the optimum color conversion rule is changed according to the image type. In the present invention, various color conversion rules can be used, and are not restricted by any of the conversion rules. Conventionally known conversion rules include, for example, a compression type and a common area saving type. In the case of the compression type, color conversion is performed by compressing the color gamut of the CRT monitor to the color gamut of printing at the same ratio toward the center of the coordinates. In the case of the common area preservation type, only the area that cannot be reproduced by printing is moved to the outline of the color reproduction area while maintaining the common area between the CRT monitor and the color reproduction area of printing and printing. Here, the common area saving type is roughly classified into a method for saving brightness and a method for saving saturation. Further, as described below, the present inventor has shown a visual characteristic consideration compression type and a visual characteristic consideration common area storage type, and roughly classifies images into business documents, computer graphics images, and natural images for each image. (Japanese Patent Application No. Hei 10 (1998)) which has not been published at the time of filing the present application.
145520). In addition to these conversion rules, other conversion rules are also objects of the present invention. The outline of these conversion rules will be described separately below.

For example, the above-mentioned Japanese Patent Application No. 10-145520.
According to the questionnaire evaluation result shown in the above item, it is conceivable that the business document image is of the saturation preservation type, the computer graphics image is of the visual characteristic consideration common region preservation type, and the natural image is the visual characteristic consideration common region preservation type. It is not always necessary to use these color conversion rules, and they can be changed if more suitable color conversion rules are devised in the future. Finally, color conversion is performed using the determined color conversion rule. The converted image data is input to the printing machine and printing is performed.

By performing the color conversion in this manner,
It is possible to use a color conversion rule that can preserve the feature of the color of the attraction point as much as possible, and it is possible to further reduce the discomfort of the printed matter.

As a further embodiment, a method shown in FIG. 4 can be considered. The process is the same as that of the above-described embodiment until the image area including the attraction point is found. The difference is that the color of the attraction point, the area including the attraction point, or the area of the attraction point and the area near the attraction point is not changed as much as possible after the attraction point is found. This is because, at the point of interest or at or near the point of interest, the color is not significantly changed by reducing the amount of color conversion based on the color conversion rule by a uniform amount or by a different reduction amount for each color characteristic such as saturation or lightness. Can be achieved. This is effective when performing compression type color conversion. The reduction of the color conversion amount can be achieved by subtracting a certain amount or by multiplying the color conversion amount by a coefficient of 0 or more and less than 1. That is, the fact that the coefficient is 0 means that the area including the attraction point,
Alternatively, the color conversion is not performed at all in the area including the attraction point and the surrounding area. Of course, if the color at the eye-catching point is a color that cannot be reproduced by the device, it is desirable that conversion into a color region that can be reproduced be performed.

Next, an example of a color matching method to which the method of the present invention is applied, that is, an example of a color conversion rule will be outlined. First, FIG. 5 shows a relationship between the Lab color space and the LCH space. As described above, all colors that can be perceived by humans are composed of three attributes of color, that is, hue (color type), lightness (brightness), and saturation (brightness). ,
It can be shown in a three-dimensional space (Lab color space) with b as three axes. That is, the lightness is represented by the height on the L axis, the hue is represented by the inclination angle with respect to the a axis, and the saturation is represented by the distance from the L axis.

The Lab color space can be converted to the LCH space by the following equation. [Equation 1] L = LC = (a ² + b ² ) ^1/2 H = tan ⁻¹ (a / b) where L represents lightness, C represents chroma, and H represents hue.

C and H correspond to the distance from the origin on the ab plane and the rotation angle from the a-axis. Since humans are sensitive to changes in hue, hue H is generally kept unchanged without change. Specifically, the color conversion is performed on the LC plane under the uniform hue condition where the hue H is constant.

The Lab color space is also referred to as a color matching perception space, and is defined such that if the color differences are the same, the perceived color differences are uniform in the entire color space. For example, A color and B
If there is a color, the color difference is determined by the distance between the two in the Lab color space, and the color coordinates are (L1, a1,
For b1) and (L2, a2, b2), the color difference ΔE is defined by the following equation.

[Equation 2] ΔE = ｛(L1-L2) ² + (a1-a2) ² + (b1-
b2) ² ｝ ^1/2

Next, the color perception sensitivity ratio will be described.
The perceptual sensitivity ratio can be calculated by preparing a sample group with the same color difference in the hue, lightness, and saturation directions from the reference sample and comparing the sample group with the color difference actually perceived by humans. , Hue, lightness, and saturation ("Evaluation of color difference by object (I)", Hitoshi Komatsubara et al., Color Research, vol. 2).
9, No. 2, 1982). Japanese Patent Application No. 10-
As described in 145520, the results of the survey
When the hue is fixed to 1.0, the perceptual sensitivity ratio is known to be 1.0 to 0.7 for lightness and 0.7 to 0.3 for saturation.

Next, a specific color conversion method will be described for each type. [Compression type] FIG. 6 shows a state in which the color reproduction range D1 of a certain device is converted to the color reproduction range D2 of printing at the same ratio toward the center of coordinates by the so-called compression type.
In the compression type, the area in D1 is compressed at the same ratio so as to be directly in D2.

[Brightness Saving Common Area Saving Type] In the common area saving type, in an area common to a certain device and printing, that is, in an area where D1 and D2 overlap, the color is not changed and is held as it is. Only the area that cannot be reproduced by printing (the area outside D2) is the color reproduction area (D
Move to the outline of 2). At this time, when mapping a point outside the D2 area, it is possible to select to save either the saturation or the lightness. In the brightness preservation type, FIG.
As shown in the figure, the brightness is kept constant and is not changed, and the saturation is changed from D1 to the color gamut D2 of printing from the color gamut of a certain device.
It maps to D whose brightness cannot be saved
In an area such as the area below one area, it can be mapped to a peripheral point on the L axis of the area D2.

[Saturation Saving Common Area Saving Type] In the example of the common area saving type shown in FIG. 8, saturation is saved. However, a region further to the right of the right vertex of the D2 region where saturation cannot be preserved can be mapped to this D2 vertex. This saturation preservation common storage type has been found to be particularly suitable for business documents having high saturation and no gradation (that is, good color reproducibility after conversion).

[Common area preserving type considering visual characteristics] The common region preserving type considering visual characteristics can be considered as a modification of the above-described common region preserving type. From the color coordinates of the LCH color space, the hue component having the highest human sensitivity is not changed, and the conversion ratio is inversely proportional to the sensitivity ratio (for example, 2: 1) between the lightness component and the saturation component. (For example, 1: 2). Further, the color conversion direction (S) determined as shown in FIG.
To convert from the wide reproduction range D1 to the narrow reproduction range D2. That is, this color conversion vector is the sum of the conversion vector of brightness 17 and the conversion vector of saturation 18.

In FIG. 10, the wide reproduction range D1 is approximately represented as a triangular area surrounded by the L axis, the side D1 ', and the side D1 ". It is approximately represented as a triangular area surrounded by an axis, a side D2 ′, and a side D2 ″. These regions can of course be approximated by any polygon other than a triangle.
It is also possible to carry out the method of the present invention without any approximation with an arbitrary region shape. As shown in FIG. 10, of the colors in the wide reproduction range D1, the portion overlapping with the narrow reproduction range D2, that is, the color in the common region is kept as it is. At the same time, the color of the portion that does not overlap with the narrow reproduction range D2 is converted to the color conversion direction determined by the predetermined conversion ratio as described above. That is, the components of the brightness and the saturation are moved onto the outlines D2 ′ and D2 ″ of the narrow reproduction range D2 along the direction (S) determined by the conversion ratio inversely proportional to the perceptual sensitivity ratio. Either a parallel line PL or a lightness axis L which passes through a portion of the reproduction range D2 where the saturation is relatively large (the vertex I where the saturation is maximum in the figure) and is parallel to the saturation axis C, and the conversion destination device When they cross outside the color reproduction area D2,
Move to vertices I, J, K closest to the intersection. The direction of movement is
In either case, the direction is toward the parallel line PL. That is, as can be easily seen from FIG. 10, the direction (S) is different above and below the parallel line PL, and although the absolute value ratio of the lightness component and the saturation component in this direction is constant, the direction (S) is shifted. The sign of the brightness component is reversed above and below the parallel line PL so that the direction approaches the parallel line PL.

For example, along a line segment parallel to the direction S, the color components of the wide reproduction area D1 corresponding to the outline of the narrow reproduction area D2 are converted along the line segments S1 to S6 parallel to the direction S. The color components of the wide reproduction range D1 that correspond to portions that do not correspond to the outlines of the narrow reproduction range D2 even if they move on the outlines D2 ′ and D2 ″ of the narrow reproduction range D2 and move along the direction S,
A point I, on a contour line of the color reproduction area D2 closest to an intersection where a line segment parallel to the direction S, for example, S7, S8, S9 intersects either the parallel line PL or the lightness axis L outside the color reproduction area D2. Transfer to J and K. Note that the direction of conversion S in the figure is
Is above and below the parallel line PL parallel to the saturation axis C,
In the lower part, it points to the upper left.

Further, since the color gamut of any device can be approximated by a triangle in practice, it can be expressed as follows. That is, the portion of the wide reproduction range D1 that does not overlap with the narrow reproduction range D2 has a predetermined inclination in the color conversion direction S, and is narrow with the dotted lines P, Q, R, and T starting from the vertices J, I, and K. The outlines D2 'and D2 "of the reproduction region D2 and the outlines D1' and D1" of the wide reproduction region D1 are divided into regions W1, X, Y1, and Z as shown in FIG. Of the colors in the wide reproduction range D1, the portion that overlaps with the reproduction range D2 is stored as it is, but the color that fits in the areas W1 and Y1 is moved to the outline of the narrow reproduction range D2 and included in the areas X and Z. The colors are moved to vertices J, I, and K, respectively. In FIG. 10, there is no region formed by the dotted line P and the outlines D1 "and D2", but this is merely a coincidence.

Such a common area preserving type color conversion rule considering visual characteristics can be implemented by executing the following steps. That is, the color conversion method of the common area preserving type in consideration of the visual characteristics is that the color gamut (D1, D2) of the conversion source device and the conversion destination device is set to a value and a saturation in which the hue (H) is constant based on the LCH color space. Expressing the lightness axis (L) as one side in the two-dimensional space, and in the two-dimensional space, the color components of the color reproduction range (D1) of the conversion source device overlap with the color reproduction range (D2) of the conversion destination device. If the color is present in the portion, the color is held as it is and the output is held, and the color of the portion that does not overlap with the color gamut (D2) of the destination device is the color gamut (D2) of the destination device. Goes to a parallel line (PL) parallel to the saturation axis (C) passing through a portion where the saturation is relatively large, and is inversely proportional to a previously determined perceptual sensitivity ratio regarding brightness and saturation in the two-dimensional space. Determined by conversion ratio Determine the direction that,
From the point parallel to the direction and representing the color, the parallel line (PL)
Or a step of obtaining a straight line extending to the lightness axis (L), wherein the straight line is the parallel line (PL) or the lightness axis (L).
Is determined to intersect or not intersect outside the color gamut (D2) of the conversion destination device, and if intersected outside the color gamut (D2), the color of the portion that does not overlap with the color gamut (D2) of the conversion destination device is determined. To the point (I, J, K) on the outline of the color gamut (D2) of the conversion destination device closest to the intersection.
If they do not intersect on the outside, the color of the part that does not overlap the color gamut (D2) of the destination device is drawn along the straight line parallel to the direction on the outline of the color gamut (D2) of the destination device. And a step of physically displaying the held output and the converted output.

It has been found that such a conversion method of the common area preserving type in consideration of visual characteristics is suitable for computer graphics images and natural images.

[Compression Type Considering Visual Characteristics] The compression type considering visual characteristics can be considered as a modification of the above-described compression type. As in the case of the above-described common area preserving type in consideration of the visual characteristics, the hue component having the highest human sensitivity than the color coordinates in the LCH color space is not changed, and the lightness component and the chroma component have the same sensitivity ratio (for example, 2). : 1) (for example, 1:
Set 2). Further, both the lightness component and the saturation component are changed in the color conversion direction S determined as shown in FIG. 9 according to the conversion ratio, and the color is converted from the wide reproduction range D1 to the narrow reproduction range D2. .

As shown in FIG. 11, the hue, lightness, and chroma components of the wide color reproduction range D1 are stored without change. At the same time, each component of lightness / saturation is transformed in inverse proportion to the perceptual sensitivity ratio, centering on a parallel line PL parallel to the saturation axis C, which passes through a portion where the saturation of the narrow-angle reproduction range D2 is relatively large. It is converted into a direction S determined by the ratio. In this direction S, the lightness component differs between the upper and lower parallel lines PL as in the case of the visual characteristic-considered common area preservation type. The ratio of the absolute values of the lightness component and the chroma component is constant. The line segments S1 to S6 parallel to the direction S for transferring the color of the wide reproduction range D1 into the narrow reproduction zone D2 correspond to either the parallel line PL or the lightness axis L and the narrow reproduction range D2.
It is divided into the case where they meet inside and the case where they meet outside. Here, the lengths of the line segments S1 to S6 do not indicate the distance of movement. The line segment is simply drawn in FIG. 11 with a sufficient length to verify where the direction of movement and the straight line indicating the direction of movement intersect the parallel line PL or the lightness axis L.

For the case of intersection within the narrow reproduction range D2,
A color on a line segment cut by the outline of the wide reproduction range D1 and either the parallel line PL or the lightness axis L, for example, El
The color on E3 is mapped onto a line segment E2E3 cut by either the outline of the narrow reproduction range D2 and the parallel line PL or the lightness axis L (similarly, the color on FlF3 is mapped on F2F3). At this time, for example, substantially all points on the line segment ElE3 are mapped so as to fall on the line segment E2E3 (the point E3 does not move, of course). As a mapping method, for example, the distance from the point E3 of an arbitrary mapped point of the line segment E1E3 to the ratio of the length of the line segment E2E3 to the length of the line segment ElE3 is multiplied by E3 of the position of the mapping destination. Find the distance from
There is a way to move the point to that position. Not only such a linear compression mapping method but also any non-linear compression mapping method can be adopted. Then, the line segments S1 to S6
Intersects either the parallel line PL or the lightness axis L outside the narrow reproduction range D2 (in the case of S4 and S7), a line segment parallel to the direction S, for example, S7 and S8 are parallel lines PL or lightness A point on the contour line closest to the intersection that intersects any of the axes L outside the color gamut D2 (vertex I, J,
Move to K). After such an operation on the image data, the image is physically displayed on the destination device.

Further, similarly to the visual characteristic consideration common area preserving type, the following expression is also possible. That is,
The wide reproduction range D1 is divided into upper and lower portions by a parallel line PL, and the two portions are further divided into regions W2, X1, X2, and D3 by the same dotted lines P, Q, R, and T as shown in FIG.
Divide into Y2 and Z. The colors in the areas W2 and Y2 are
As described above, the image is mapped within the narrow reproduction area D2, and the areas X1 and X
The colors in 2 and Z are moved to vertices J, I and K, respectively.

The compression type color conversion rule considering the visual characteristics can be implemented by executing the following steps. In other words, the color conversion method of the common area preserving type considering the visual characteristics uses the color reproduction range (D
1, D2) in a two-dimensional space of lightness and saturation with a constant hue (H) based on the LCH color space, with the lightness axis (L) as one side; and in the two-dimensional space, a destination device To a parallel line (PL) parallel to the saturation axis (C), passing through a portion where the saturation of the color reproduction range (D2) is relatively large, and inversely proportional to the perceived sensitivity ratio of brightness and saturation. Determining a direction in the two-dimensional space determined by the conversion ratio to be converted; and a straight line extending from a point representing the color of the color reproduction range (D1) of the conversion source device and parallel to the direction is the parallel line (PL). Alternatively, one of the lightness axes (L) intersects inside the color gamut (D2) of the conversion destination device and the case where it does not intersect inside the nucleus. Outer line of D1) and the parallel line (PL) Other lightness axis color on the line segment to be clipped from the straight line by either (L), the destination gamut of the device the parallel line and outline of (D2) (PL)
Alternatively, the image is mapped on a line segment cut off from the straight line by either the lightness axis (L), and for the latter, a point (I) on the contour line of the color reproduction area (D2) of the conversion destination device closest to the intersection. , J, K) to obtain a converted output, and physically displaying the converted output.

The compression type color conversion method considering the visual characteristics is as follows.
It has been found to be suitable for business documents as well as computer graphics images and natural images.

The method of the present invention can be carried out using the color conversion rules exemplified above or other color conversion rules.

[0050]

As is apparent from the above description, according to the present invention, an image type is determined and a color conversion rule suitable for the image is used, or a color conversion rule suitable for the image is used. In addition, by making the color of the area of the point of attraction not to be changed as much as possible, it is possible to obtain a printed matter with less discomfort.

[Brief description of the drawings]

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

FIG. 2 is a flowchart of extracting an eye-catching point in an image according to the present invention.

FIG. 3 is a diagram illustrating a state of extraction of an attraction point in an image.

FIG. 4 is a block diagram showing a basic configuration of another embodiment of the present invention.

FIG. 5 is a diagram illustrating a relationship between a Lab color space and an LCH color space.

FIG. 6 is a graph showing a “compression type” method which is an example of a color gamut conversion method.

FIG. 7 is a graph showing an example of a method of converting a color gamut, which is a “common area preservation type in which lightness is preserved”.

FIG. 8 is a graph showing a “common area preservation type in which saturation is preserved” method, which is an example of a color gamut conversion method.

FIG. 9 shows a vector representing the direction (S) of color conversion,
7 shows a method of determining as the sum of the conversion vector of 7 and the conversion vector of saturation 18.

FIG. 10 is a graph showing a “visual characteristic consideration type common area saving type” method which is an example of a color gamut conversion method.

FIG. 11 is a graph showing a “visual characteristic consideration compression type” method which is an example of a color gamut conversion method.

[Explanation of symbols]

 C Saturation L Lightness H Hue D1 Wide gamut (color gamut of source device) D2 Narrow gamut (color gamut of destination device)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) 9A001 F term (Reference) 2C087 AA15 BD01 BD24 BD36 CB15 5B021 AA01 AA02 LG07 LG08 LL05 5B057 CA01 CB01 CE17 CH18 DC30 5C077 MP08 PP35 PP37 PP51 PQ08 TT02 5C079 HB06 LA31 LB02 NA03 PA03 9A001 BB04 BB06 EE04 GG01 HH23 HH26 HH31 KK42

Claims (4)

[Claims] 1. A color matching method between different devices having different color gamut, which is a physical characteristic mass unique to each device, comprising: a step of determining an image type; and a color corresponding to the determined image type. Selecting a conversion method;
Performing the selected color conversion method. 2. A color matching method between different devices having different color reproduction ranges, which are physical physical masses unique to each device, comprising the steps of: determining a type of an image and a region having a high degree of attraction; Selecting a color conversion method according to the type of the color conversion method, and, in the selected color conversion method, the conversion amount of the color conversion of the determined area of high attraction or a surrounding area including the area is set as the other part. A color matching method, comprising the steps of separately reducing and implementing a color conversion method so modified. 3. A color matching apparatus for performing the method according to claim 1. 4. A computer-readable recording medium on which a color matching program for performing the color matching method according to claim 1 or 2 is recorded.