JPH06100900B2 - Method and apparatus for high-speed color change display of color image - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for rapidly changing and displaying a color image without impairing the naturalness of the color.

(Prior Art) CAD (Computer Aided Design) is applied in the field of color design, and it is required to change the color in it. Specifically, after capturing an image including a design target (for example, an automobile) into a computer system with a scanner or a color camera and displaying the image on a color display, the color of the target portion is changed (for example,
Originally, by making the body of a red car blue), it is required to predict the design results of various colors without actually making things.

For such a purpose, conventionally, as shown in FIG. 3, the color of a certain surface (finally R (red), G (green), B
(Blue), given by the three components) TV camera (monochrome)
It is known that a circuit is added depending on the shade obtained in (Fiber and Industry, Vol. 36, No. 6, 1980, pp. 195-199). In this case, a grayscale original image 101 in which a portion of which the color of the object is desired to be changed is painted with different densities is input by the monochrome television camera 102, the signal is shaped by the false signal correction circuit 103, and then by the A / D converter 104, It is converted into a digital value and each part is separated, and R, G, B values are given by a color controller 105 and a color television signal is made by a color encoder 106. At this stage, the same color part has a flat plate color (R, G, B). At the same time, the actual product 107 is aligned with the original image 101, and another monochrome TV camera 108
The image signal N having a shadow obtained by the above is combined with the previous color television signal by the shadow combining circuit 109. This allows the color television 110 to simulate a shaded color image while freely changing the color.

At this time, if the color of the object is given as (R, G, B), the color (R ', G', B ') of each pixel is as follows according to the lightness N of each pixel given from the monochrome camera. Desired.

Here, it is considered that N takes a value of 0 to 1.

This method is based on the ground that "the color of one color area is originally a bright color (R, G, B), and there is a portion that is dark due to shading." In other words, the fourth
When considered in the three-dimensional color space of the figure, the color (R ', G', B ') of one area is on the straight line connecting black (0,0,0) and object color (R, G, B). It is supposed to be on board.

(Problems to be Solved by the Present Invention) However, in reality, even in one color region, since light is reflected and bright, it is common that a color near white exists as shown in FIG. 4P. . However, the above circuit cannot correctly deal with such a part.

SUMMARY OF THE INVENTION It is an object of the present invention to solve this problem and provide a method and an apparatus for displaying a color area of an image having a reflection part by changing the color naturally and at a very high speed.

(Means for Solving the Problems) In the first invention, the three primary color values of each pixel in a color region targeted for a color image are converted into three colors of black, an object color, and a light source color in a three-dimensional color space. Converted to a two-dimensional intermediate coordinate value assuming that it shows a color on a stretched plane, select a small number of representative colors from the distribution by clustering, and the representative color according to the clustering criterion for each pixel in the color region. Color code image is created, a changed color corresponding to each color code is obtained for the representative color using the light source color and the newly provided second object color, and registered in a lookup table. Then, by switching and displaying the color image and the image in which the rulicup table is applied to the color code image, the image in which the desired color change is naturally performed only in the color area can be displayed at high speed. This is a high-speed color change display method of the color image displayed on.

A second aspect of the present invention is to provide a color image storage unit that stores a color image, a first object color storage unit that stores an object color of a color region that is a target of the color image, and a light source color of the color image. A light source color storage unit that stores the three primary color values of each pixel in the color region that is the target of the color image, in a three-dimensional color space, a color on a plane formed by three colors of black, an object color, and a light source color. Assuming that, intermediate pixel calculation means for converting into intermediate coordinate values of a two-dimensional color space, clustering means for clustering the color distribution obtained from the intermediate pixel value calculation means, and selecting a small number of representative colors, In front of each pixel obtained by the clustering reference obtained in the clustering process and the cluster storage means for storing the representative color, the intermediate coordinate value obtained by the intermediate pixel value calculation means, and the clustering reference. Color code image storage means for storing a color code corresponding to a representative color as an image, second object color storage means for storing the object color after the color change of the color area, the second object color and the light source. A lookup table that stores the three primary color values corresponding to the color code calculated from the representative color by color, and converts the color code read from the color code image storage means into the three primary color values when displaying an image; A display controller that replaces the three primary color values of the pixels read from the color image storage means with the three primary color values output from the look-up table for the pixels belonging to the color area when displaying the image; It is a high-speed color change display device for a color image that changes and displays a color of a target color region at high speed.

(Operation) The operation of the present invention will be described with reference to FIG. Light that strikes the object 121 from the light source 120 and enters the camera 122 can be roughly classified into specular reflection light 123 and diffuse reflection light 124. The specularly reflected light is reflected by the surface of the object, its spectral composition is the same as that of the light source, and only the intensity changes. Diffuse reflected light, after the light from the light source enters the object and undergoes spectral absorption peculiar to the substance,
It is isotropically injected to the outside. The spectral composition of diffusely reflected light is usually different from that of the light source. Therefore, the three components (R, G, B) of the color of each point on the target surface are Can be written. Here, (R ₀ , G ₀ , B ₀ ) is the three components of the diffuse reflected light, and varies depending on the object, and is henceforth referred to as “object color” in the present specification. (R _S , G _S , B _S ) is the three components of the specularly reflected light and is equal to the color of the light source, and is henceforth referred to as "light source color" in this specification. α and β indicate the degree of contribution of diffuse reflection light and specular reflection light to the amount of emitted light, and are related to the material and direction of the surface. This is different for each pixel, so if the pixel position within a pixel is (x, y), Is written. Such models are used in computer graphics. For example, according to Phong's model, (13th Imaging Engineering Conference, 1982, 55-
(Page 58).

Where θ is the angle between the surface normal and the camera direction, α is the angle between the specular reflection direction and the camera direction, d is a constant indicating the intensity of diffusely reflected light and ambient light, and w (θ) Is a term indicating the degree of specular reflection light to diffuse reflection light.

When the surface of a certain object is expressed by the formula (3), if the same material and different colors are used, only the object color (R ₀ ′, G ₀ ′,
By changing to B ₀ ′), each pixel value can be calculated as in Expression (5).

In the present invention, it is assumed that the color of each pixel in each one region in the color image complies with Expression (3). This will be described with reference to FIGS. 6 to 8. In FIG. 6, the color distribution 200 in one color area in the color image is included in the plane formed by the origin O, the object color C ₀ , and the light source color C _{S in} the R, G, B color spaces. The color of each pixel is the coordinate axis α connecting O and C ₀ , and O and C _S
It can be represented by a coordinate axis β connecting the two. This color distribution is as shown in FIG. 7 when the two coordinate axes α and β are regarded as orthogonal coordinates. On the other hand, by changing only the object color to C ₀ ′, the α-axis changes to the α′-axis in FIG. 8 and the color distribution remains unchanged, so that a natural color change can be obtained.

In order to realize this, it is necessary to determine C ₀ and C _S for the color region of a given color image and obtain α and β values of each pixel. Actually, since there is no color with α = 0 or β = 0, it is not possible to accurately obtain C ₀ and C _S from the image, but in the image, the most likely color part of the color region (for example, In the case of a car with a red car body, it is sufficient for practical use to read the image value of the part that looks very red) and set it to C _0, and read the image value of the part that appears to be pure white due to specular reflection and set it to C _S.

To obtain α and β of each pixel, for convenience, a third color vector C _d perpendicular to C ₀ and C _S is defined as a vector product (outer product) of C ₀ and C ₀ , and C _d = C ₀ × C _S ( 6) Set as follows. When this C _d is expressed in R, G, B space as shown in equation (7), The color (R, G, B) of each pixel in the image is introduced by γ, Can be written. Here, γ corresponds to the distance from the plane formed by O, C _s , and C ₀ of each color, and the pixel in the target color area is considered to be noise.

Since equation (9) is established by solving equation (8) in reverse, α, β, γ can be obtained from the R, G, B values for each pixel. Since γ is noise, it can be ignored.

In this way, α and β are obtained for each pixel.
In order to convert the image part having the object color C ₀ into C ₀ ′ and to convert other parts of this color region so as to look natural, the formula (5) should be used. Is as described above.

However, according to the above method, it is determined whether or not all the pixels of the color image are in the target color area and the equation (5) is executed for all the pixels that satisfy the condition. Therefore, C ₀ ′ is set to 1 second. In addition, it is necessary to make a very high-speed dedicated arithmetic circuit in order to change it many times and continuously observe the result. To solve this problem, a display device as shown in FIG. 9 is used. This display has two types of image memories for refreshing. The color image memory 1 stores a color image for each pixel in each of R, G, B 8
Even a bit. The color code image memory 2 has, for example, an 8-bit color code for each pixel, and the look-up table (LUT) 3 in the next stage has R, G, B preset according to the color code of each pixel. Output the value. As a result, an image of 256 colors can be displayed at the same time. In general,
Displaying a color image with 256 colors inevitably causes a significant deterioration in image quality, but displaying a color change in one color region is often possible by appropriately selecting 256 colors. The present invention displays the entire image with R, G, B values from the color image memory 1 and displays only the color area for changing the color with the color code image memory 2 and the look-up table 3, By rewriting the contents of the up table 3, high-speed color change display is realized. The display controller 5 switches the signals from the two image memories for each pixel according to the pixel value of the mask image memory 4. That is, the mask image memory 4 is a memory having 1 bit for each image. FIG. 10 shows the relationship between the image stored in the color image memory 1 and the mask image stored in the mask image memory 4. The mask image has a pixel value of "1" only in the body part of the car that is the target of color change. The display controller 5 checks the pixel value of the mask image for each pixel when displaying the image,
If it is "1", (R,
If the G, B) value is "0", (R,
G, B) values are given to the D / A converter 6, and a color image in which the naturally changed color portions are combined is displayed on the color monitor 7.

In this way, when C ₀ ′ is changed, only the contents of the lookup table 3 need to be calculated for changing the color, and the calculation of formula (5) can be performed 256 times. Is realized.

Next, an appropriate color selection method for expressing the target color region with a small number of colors will be described with reference to FIGS. 11 to 14. Even if all the colors existing in the color area are distributed in the shaded area 200 in the α-β space of FIG. 7, if the frequency of each color is displayed as contour lines, most of the colors are as shown in FIG. Are very infrequent and only in some parts as shown by clusters 101-105. Therefore, only such a portion is accurately reproduced, and the other portions have practically no problem even if they are inaccurate. Therefore, natural colors are reproduced by concentrating the 256 colors registered in the lookup table on the colors of such clusters.

An example of a clustering method for obtaining a cluster will be described below. Here, for simplification, a method of obtaining clusters of four colors will be exemplified. Here, it is assumed that the colors of the target color area are distributed as shown by the crosses in FIG. These 18 colors (α,
β) coordinates are shown in Fig. 13. Clustering is usually performed by a computer program, but (α,
FIG. 14 shows a processing flow for dividing the β) data set into two clusters. The data set is bisected by determining the median position c for the direction of the principal axis with the greatest variance. In the case of clustering into 2 ⁿ colors, the same processing may be further repeated for this divided data set, and n steps in total may be performed. As a representative color of the cluster thus obtained, the result of obtaining the average of the colors of the pixels included in each cluster is shown as a circle in FIG.

With such a method, the 256 representative colors are selected, and the color codes 0 to 255 are selected. A color code is given to each pixel in the color area by using the above-mentioned main axis for clustering and the median, and stored in the color code image memory 2 in FIG. Further, in the lookup table 3, (R ', G', β ') for each color code is calculated from (α, β) of each representative color by the formula (5) and written. In this way, a natural color change display can be obtained.

If there is no specular reflection part in the target area of the color image, C _s is a value that is normally considered white in the display device (for example, 8 bits are assigned to each of R, G, and B). Display device,
It is practically acceptable to give R _s = G _s = B _s = 255).

(Example) An example of the present invention will be described with reference to FIG. Color image memory 1, color code image memory 2, look-up
The functions of the table (LUT) 3, the mask image memory 4, the display controller 5, the D / A converter 6, and the color monitor 7 are as already described with reference to FIG. The color image memory 1 stores a full-color image including, for example, a car, and the mask image memory 4 draws an outline with a pointing device and fills the inside while observing the color image by CRT. It is assumed that it is already made by various known techniques.

The color designating means 8 uses the CRT 7 and the pointing device 9 according to the user's instruction to pick up the object color C ₀ and the light source color C _s from the image, and respectively picks up the first object color storing means 10 and the light source color. It is stored in the storage means 11, and can be realized by a microcomputer or the like. Intermediate pixel value calculation means 12
Scans each pixel of the mask image memory 4, and for the pixel whose value is “1”, from (R, G, B) stored in the color image memory 1 to the intermediate pixel according to the equation (9). Value (α,
β) is first calculated and given to the color distribution memory 13. The color distribution memory 13 stores (α, β) as a two-dimensional address of the memory, and stores the color distribution of the target color area as the frequency of each address in the form shown in FIG.

The clustering unit 14 performs the above-described clustering on this color distribution, and stores the result in the cluster storage unit 15. The clustering means 14 can be realized by a microcomputer or the like. Cluster storage means 15
The contents of the above are shown in FIG. The average value of each cluster corresponding to the representative color is stored in the cluster average value table 153, and the values of the main axis vector at each stage and the division points in that direction, which are determined in the process of obtaining this, are the main axis vector table 151 and the division point, respectively. It is stored in the table 152. Representative color is 2 ⁸
= 256 colors, the cluster average value table 153 has a capacity of 25
Since this is 6 and this is determined by the equal division of 8 steps, the main axis vector table 151 and the division point table 152 each have a capacity of 255 by 1 + 2 + 4 + 8 + 16 + 32 + 64 + 128 = 255.

When the cluster is determined, the intermediate pixel value calculation means 12
Scans each pixel in the target color area again, and sends (α, β) to the color code calculation means 16 this time. The color code calculation means is
Each intermediate pixel value (α, β) is determined in eight steps according to the contents of the main axis vector table 151 and the division point table 152 to determine the color code, and the corresponding pixel of the color code pixel memory 2 writes it. When the color code pixel is completed, the color change display is ready.

Actual color change is first user, for example a new object color C ₀ instead of object color C ₀ from the pointing device 9, a keyboard 18 'R of, G, B values _{(R 0', G 0 '} , B 0 ′) Is given to the color designating means 8 and this is stored in the second object color storing means 19 to start. The changed color calculation means 17 sets C for each of the values stored in the cluster average value table 153.
_{Using s} and C ₀ ′, the respective R, G, B values are calculated according to equation (5) and written in LUT3. As a result, of the color image, only the part where "1" is set in the pixel of the mask image is replaced with the color generated by the color code image memory 2 and the LUT3, and the color is changed to the desired color and displayed naturally. It

(Effects of the Invention) With the method and apparatus described above, a color of a region which is conventionally a constant color but is included in a color image but has a shade due to shading or glare can be specified at high speed and without impairing naturalness. It is possible to change and display it in the specified color. Colors of products designed according to the present invention can be displayed naturally without changing the surrounding conditions, and while being changed one after another, so that colors can be displayed without actually making products of that color. Can be checked, which has a great industrial and economic effect.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing a detailed configuration of a cluster storage means, FIG. 3 is a block diagram of a conventional device, and FIG. 4 is a principle of the conventional device. Explanatory diagram, FIG. 5 is an explanatory diagram of the operation of the present invention, FIG. 6 is an explanatory diagram showing the color distribution of one color region in a color space, and FIG. 7 is an explanatory diagram showing this in another coordinate system. FIG. 8 is a diagram showing a color distribution in a color space when the color of the color region is changed according to the present invention, and FIG. 9 is an explanatory diagram of a configuration for high-speed color change display according to the present invention, FIG. 10 is an explanatory diagram showing the relationship between the color image memory and the max image memory, FIG. 11 is an explanatory diagram of color distribution in the target color region, FIGS. 12 to 13 are explanatory diagrams of clustering examples of color distribution, and FIG. Is a one-step processing flow of clustering. 1 ... Color image memory, 2 ... Color code image memory,
3 ... Look-up table, 4 ... Mask image memory, 5 ... Display controller, 6 ... D / A converter, 7 ... Color monitor, 8 ... Color designating means, 9 ...
Pointing device, 10 ... First object color storage means, 11 ... Light source color storage means, 12 ... Intermediate pixel value calculation means, 13 ... Color distribution memory, 14 ... Clustering means,
15 ... Cluster storage means, 16 ... Color code calculation means, 17
...... Change color calculation means, 18 ...... Keyboard, 19 ...... Second object color storage means.

Claims (2)

[Claims] 1. The three primary color values of each pixel in a target color region of a color image are set to black, object color,
Converted to a two-dimensional intermediate coordinate value assuming that the color of the light source color is on a plane, and select a small number of representative colors from the distribution by clustering, and the clustering for each pixel in the color region. A color code indicating the representative color is given according to the standard of 1., a color code image is created, and a changed color corresponding to each color code is obtained for the representative color using the light source color and the newly given second object color. By registering in the lookup table and switching between the color image and the image to which the lookup table is applied to the color code image to display, an image in which a desired color change is naturally made only in the color region is displayed. High-speed color change display method for color images displayed at high speed. 2. A color image storage means for storing a color image, a first object color storage means for storing an object color of a color region which is a target of the color image, and a light source for storing a light source color of the color image. It is assumed that the color storage means and the three primary color values of each pixel in the target color area of the color image represent a color on a plane formed by three colors of black, object color, and light source color in a three-dimensional color space. Then, an intermediate pixel value calculating means for converting into an intermediate coordinate value of a two-dimensional color space, a clustering means for clustering the color distribution obtained from the intermediate pixel value calculating means and selecting a small number of representative colors, and the clustering Clustering standard obtained in the process of and the cluster storage means for storing the representative color, the intermediate coordinate value obtained from the intermediate pixel value calculating means, and the representative of each pixel obtained by the clustering standard. A color code image storage means for storing the color code corresponding to the image as an image, a second object color storage means for storing the object color after the color change of the color region, and a second object color and the light source color. A look-up table that stores the three primary color values corresponding to the color code calculated from the representative color and converts the color code read from the color code image storage means into the three primary color values when the image is displayed; A display controller that replaces the three primary color values of the image read from the color image storage means with the three primary color values output from the look-up table for the pixels belonging to the color area. High-speed color change display device for color images that changes and displays the color of the color area to be displayed at high speed.