JPS63244094A - Fast color alteration display method and apparatus for color image - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method and apparatus for rapidly changing and displaying colors of a color image without impairing the naturalness of the colors.

(Prior Art) CAD (computer, aided design) is applied to the field of color design, and there is a need to change colors within it. Specifically, the object of design (
For example, by importing an image containing a car (for example, a car) into a computer system using a scanner or color camera and displaying it on a color display, the color of the object part is changed (for example, the body of a car that was originally red is changed to blue). , it is required to predict the result of a design in various colors without actually making it.

For this purpose, conventionally, the color of a certain surface (finally R (red), G (green), B (blue)) as shown in Figure 3 has been used.
, given by three components) according to the shadow obtained with a camera (monochrome) (Textiles and Industry, Vol. 36, No. 6, 1980, pp. 195-199). In this case, a gray original image 101 in which the parts of the object whose colors are to be changed are painted with different densities is inputted by a monochrome television camera 102, the signal is shaped by a false signal correction circuit 103, and then converted into a digital image by a zero converter 104. The signal is converted into a value and separated into each part, and a color controller 105 gives R, G, and B values, and a color encoder 106 converts the signal into a color television signal. At this stage, the same color portions have colors shown as flat (R, G, B). At the same time, the actual product 107 is aligned with the original image 101 and photographed by another monochrome television camera 108, and the resulting image signal N with shadows and the previous color television signal are sent to a shadow synthesis circuit 109. Synthesize. This allows the color television 110 to simulate a color image with shading while freely changing the colors.

At this time, if the color of the object is given as (R, G, B),
Based on the brightness N of each pixel given by the monochrome camera, the color (R'', α, B) of each pixel is determined as follows.

Here, it is assumed that N takes a value of O to 1.

This method is based on the following method: ``The colors of one color area are originally (R, G, B
), and some parts are darker due to shading. ” is the basis. In other words,
When considering the three-dimensional color space in Figure 4, - the color of the horn area (
R', G', B') is black (0,0,0) and object color (R,
It is assumed that it is on a straight line connecting G and B).

(Problem to be solved by the present invention) However, in reality, even in one color area, because the light reflects back and is bright, it is normal for there to be colors that are close to white, as shown in Figure 4, P. . However, the above circuit cannot properly handle such parts.

It is an object of the present invention to solve this problem and provide a method and apparatus for displaying a color area of an image having a reflective portion by changing the color naturally and at a very high speed.

(Means for Solving the Problems) The first invention is to calculate the three primary color values of each pixel in the color region that is the target of a color image by the three colors of black, object color, and light source color in a three-dimensional color space. A small number of representative colors are selected from the distribution by clustering, and the representative colors are determined according to the clustering criteria for each pixel in the color area. A color code is given, a color code image is created, and a change color corresponding to each color code is determined for the representative color using the light source color and the newly given second object color, and is registered in a lookup table. and, by switching between and displaying the color image and an image obtained by applying a lookup table to the color code image, a color image that quickly displays an image in which a desired color change is naturally made only in the color area. This is a fast color changing display method.

In addition, a second invention includes 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 that is a target of the color image, and a light source for the color image. A light source color storage means for storing colors, and the three primary color values of each pixel in the target color region of the color image are stored on a plane defined by the three colors of black, object color, and light source color in a three-dimensional color space. Intermediate pixel calculation means for converting into intermediate coordinate values in a two-dimensional color space assuming that it represents a color, and clustering means for clustering the color distribution obtained from the intermediate pixel value calculation means and selecting a small number of representative colors. , a cluster storage means for storing the clustering standard obtained in the clustering process and the representative color, and an intermediate coordinate value obtained from the intermediate pixel value calculation means and corresponding to the representative color of each pixel determined by the clustering standard. a color code image storage means for storing a color code as an image, and a second object color storage means for storing an object color after changing the color of the color area;
The three primary color values corresponding to the color code calculated from the representative color using the second object color and the light source color are stored, and when displaying an image, the color code read from the color code image storage means is stored as the three primary color values. a look-up table for converting the image into a pixel, and, when displaying an image, replacing the three primary color values of pixels read from the color image storage means with the three primary color values output from the look-up table for pixels belonging to the color area. The present invention is a high-speed color change display device for a color image, which includes a display controller and quickly changes and displays the color of a target color area of a color image.

(Operation) The operation of the present invention will be explained with reference to FIG. light source 120
The light that hits the object 121 and enters the camera 122 from
The light can be roughly divided into specular reflection light 123 and diffuse reflection light 124. Specular reflected light is reflected from the surface of an object, and its spectral composition is the same as that of the light source, with only the intensity changing. Diffuse reflected light is light from a light source that enters an object, undergoes spectral absorption specific to the material, and then is emitted to the outside in the same direction.

The spectral composition of the diffusely reflected light is usually different from that of the light source. Therefore, the three color components (R, G
, B) can be written as . Here, (Ro, Go, Bo) are three components of the diffusely reflected light, and since they differ depending on the object, they are hereinafter referred to as "object colors" in this specification.

(Rs, Gs, Bs) are three components of specularly reflected light and are equal to the color of the light source, so they are hereinafter referred to as "light source color" in this specification. α and I3 indicate the degree of contribution of diffusely reflected light and specularly reflected light to the amount of emitted light, and are related to the surface material, direction, etc. This differs from pixel to pixel, so if the pixel position within a pixel is (X, y), then it is written as: Such models are used in computer graphics, and for example, according to Phong's model, (13th Image Engineering Conference, 1982, pp. 55-58).

Uni, 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 that indicates the intensity of diffuse reflected light and ambient light, W(θ) is also a term indicating the degree of specular reflection light relative to diffuse reflection light.

When the surface of a certain object is expressed by equation (3), if objects are made of the same material but have different colors, only the object color is expressed as (Ro'+GO'y
BO'), each pixel value can be calculated as shown in equation (5).

In the present invention, it is assumed that the color of each pixel in one color region in a color image follows equation (3). This will be explained with reference to FIGS. 6 to 8. In FIG. 6, a color distribution 200 in one color area in a color image is included in a plane formed by the origin 0, the object color C8, and the light source color Cs in the R, G, B color space. The color of each pixel can be expressed by a coordinate axis α connecting 0 and C8, and a coordinate axis p connecting 0 and Cs. This color distribution becomes as shown in FIG. 7 if the two coordinate axes α and 13 are viewed as orthogonal coordinates. On the other hand, by changing only the object color to Col, the α axis changes to the α' axis in FIG. 8, and by keeping the color distribution unchanged, a natural color change can be obtained.

To achieve this, it is necessary to determine co and cs for the color region of a given color image, and to find the α and p values for each pixel. In reality, there is no color where α=o or p=0, so it is not possible to accurately determine C8 and cs from the image. In the case of a car, it is practically sufficient to read the image value of the part that looks very red and set it as co, and read the image value of the part that looks pure white due to specular reflection and set it as Cs.

To obtain α, 13 for each pixel, for convenience, a third color vector cd perpendicular to C8 and cs is determined as, for example, the vector product (cross product) of co and Cs, as follows: cd=coXC8(6). Expression (7) of this cd in R, G, B space
When expressed as, the color (R, G, B) of each pixel in the image is expressed as
It can be written as Here γ is 0, C8, c of each color
The pixels in the target color region corresponding to the distance from the plane created by o are considered to be noise.

By reversing equation (8), equation (9) holds true, so αt13tγ can be found from the R, G, and B values for each pixel. Since γ is a noise component, it can be ignored.

In this way, α and p are determined for each pixel.

In order to convert the image part that had the object color co to C8' and to convert the other parts of this color area accordingly so that they look natural, it is best to use equation (5) first. As stated above.

However, according to the above method, it is necessary to determine whether or not each pixel in the color image is in the target color area, and then to execute equation (5) for all pixels that satisfy this condition. , it is necessary to create a very high-speed dedicated arithmetic circuit to make changes many times and observe the results continuously. In order to solve this problem, a display device as shown in FIG. 9 is used. This display has two types of image memory for refreshing. The color image memory 1 stores a color image in R, G,
B has 8 bits each. The color code image memory 2 has, for example, an 8-bit color code for each pixel, and the next stage look-up table (LUT) 3 has preset R, G, B color codes according to the color code of each pixel. Output the value.

This allows images in 256 colors to be displayed simultaneously. Generally, displaying a color image with 256 colors will inevitably result in significant deterioration in image quality, but it is often possible to display color changes in one color area by appropriately selecting 256 colors. In the present invention, the entire image is displayed using R, G, and B values from a color image memory 1, and only the color area whose color is to be changed is displayed using a color code image memory 2 and a look-up table 3. By rewriting the contents of the up table 3, it is attempted to realize high-speed color change display. The display controller 5 is
The signals from these two image memories are switched for each pixel using the pixel value of the mask image memory 4. That is,
The mask image memory 4 is a memory having one 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 part of the body of the car whose color is to be changed. When displaying an image, the display controller 5 checks the pixel value of the mask image for each pixel, and if it is "01'", the (R, G, B) value from the look, up, table 3 is set to "01'". θ
If it is a color image memory 1, the (R, G, B) values from the color image memory 1 are given to the D/A converter 6, and a color image in which the naturally colored parts are combined is displayed on the color monitor 7. .

In this way, when Co′ is changed, the only calculation required to change the color is the contents of lookup table 3, and 256 calculations of equation (5) are required, resulting in a significant speed increase. is realized.

Next, an appropriate color selection method for expressing a target color area with a small number of colors will be described with reference to FIGS. 11 to 14. All colors existing in the color area are α-
Even if the colors are distributed in the diagonally shaded area 200 in p-space, if the frequency of each color is represented by isocapital lines, most of the colors have a very low frequency as shown in FIG. 11, and the cluster 101-
The frequency is high only in some parts such as 105. Therefore, even if only such parts are accurately reproduced and other parts are inaccurate, there is almost no problem in practice.

Therefore, the 256 colors to be registered in the lookup table are
By concentrating on the raster colors in this way, natural color reproduction is achieved.

An example of a clustering method for determining clusters will be described below. For the sake of simplicity, a method for obtaining four-color clusters will be exemplified here. Here, the color of the target color area is
Assume that the distribution is as shown in the figure. These 18 colors (α
, β) coordinates are as shown in FIG. Clustering is usually performed by a computer program, but (α
FIG. 14 shows the processing flow when dividing the dataset of stages , , into two clusters. The data set is divided into two equal parts by finding the median position C in the direction of the principal axis with the largest variance. In the case of clustering into 2n colors, the same process may be repeated for this divided data set, performing n stages in total. As the representative color of the cluster obtained in this way, the result of finding the average color of the pixels included in each cluster is shown in Figure 12.
Shown as a mark.

By such a method, 256 representative colors are selected and the color codes are set from color code O to color code 255. Furthermore, by using the principal axis and median for clustering described above, a color code is given to each pixel in the color area and stored in the color code image memory 2 of FIG. In addition, lookup table 3 contains formula (5) from (α, 13) of each representative color.
Find (R'', G', B) for each color code and write them. By doing this, a natural color change display can be obtained.

Note that if there is no part that is considered to be specular reflection in the target area of the color image, C6 is a value that is normally considered white on the display device (for example, R, G, B
In a display device that allocates 8 bits to each, there is no practical problem in giving BIRD=Gs:B,=,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, mask image memory 4, display controller 5, D/A converter 6, and color monitor 7 are as already explained in FIG.

The color image memory 1 stores full color images including, for example, cars, and the mask image memory 4 stores,
It is assumed that a mask image has already been created using a known technique such as observing a color image on a CRT, drawing an outline with a pointing device, and filling in the inside.

A color specifying means 8 uses a CRT 7 and a pointing device 9 to select an object color C from an image according to a user's instruction.
8 and light source color C8 are picked up and stored in the first object color storage means 10 and light source color storage means 11, respectively, and can be realized by a microcomputer or the like. The intermediate pixel value calculation means 12 scans each pixel of the mask image memory 4, and calculates the formula for the pixel whose value is "1" from (R, G, B) stored in the color image memory 1. The intermediate pixel value (α, I3) is calculated according to (9) and first provided to the color distribution memory 13. The color distribution memory 13 is a two-dimensional (α, p) memory, and stores the color distribution of the target color area as the frequency of each address in the form shown in FIG. 11.

The clustering means 14 performs rastering on this color distribution as described above, and stores the results in the cluster storage means 15. The clustering means 14 can be realized by a microcomputer or the like. The contents of the cluster storage means 15 are shown in FIG. The average value of each cluster corresponding to the representative color (page 32) is stored in the cluster average value table 153, and the values of the principal axis vector at each stage and the dividing point in that direction, determined in the process of obtaining this, are stored in the principal axis vector table 151 and the dividing point, respectively. It is stored in the point table 152. When the representative colors are 28:256 colors, the capacity of the cluster average value table 153 is 256, and this is determined by repeating 8 stages of bisection, so 1+2+4+8+16+32+64+128=255 creates the principal axis vector table 151 and the division point table. 15
2 each have a capacity of 255.

At the stage when clusters are determined, intermediate pixel value calculation means 12
scans each pixel in the target color area again and sends (α, 13) to the color code calculation means 16 this time. The color code calculation means determines the color code by determining each intermediate pixel value (α, !3) in eight steps according to the contents of the principal axis vector table 151 and the division point table 152, and stores the color code in the color code image memory 2.
write to the corresponding pixel. Once the color code image is completed, preparations for color change display are complete.

To actually change the color, the user first uses the pointing device 9 or the keyboard 18 to change the R, G, and B values (RO'+GO'y) of a new object color Co' instead of the object color C8.
BO') is given to the color specifying means 8, and this is stored in the second object color storage means 19, thereby starting the process. The change color calculation means 17 calculates CI! for each α and p stored in the cluster average value table 153. and C. ′ to form the formula (
5) calculate the respective R, G, B values and use the LUT
Write in 3.

As a result, “1” is added to the pixels of the mask image in the color image.
Only the part with “” is the color code image memory 2 and LU.
The color is replaced with the color generated by T3 and changed to a desired color for natural display.

(Effects of the Invention) With the method and device described above, colors in areas that are originally constant colors but have shading due to shading or reflection can be specified quickly and without sacrificing naturalness. You can change the color and display it. It is possible to display the colors of products designed according to the present invention while changing them naturally and one after another without changing the surrounding conditions, so it is possible to change the color scheme without actually creating a product with that color. can be checked, and has great industrial and economical effects.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing the detailed configuration of the cluster storage means, FIG. 3 is a block diagram of a conventional device, and FIG. 4 is a block diagram of the principle of the conventional device. 5 is a detailed explanatory diagram of the present invention, FIG. 6 is an explanatory diagram showing the color distribution of one color area in a color space, and FIG. 7 is an explanatory diagram showing this in a different coordinate system. 8 is a diagram showing the color distribution in the color space when the color of the color area is changed according to the present invention, and FIG. 9 is an explanatory diagram of the configuration for high-speed color change display of the present invention. Fig. 10 is an explanatory diagram showing the relationship between color image memory and mask image memory, Fig. 11 is an explanatory diagram of color distribution in the target color area, Figs. 12 and 13 are explanatory diagrams of an example of clustering of color distribution, and Fig. 14 is clustering 1
This is a step-by-step process flow. DESCRIPTION OF SYMBOLS 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 specifying 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 10 Figure 2 Figure 4 B Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14

Claims (1)

[Claims] 1. The three primary color values of each pixel in the target color region of a color image are expressed as colors on a plane defined by the three colors black, object color, and light source color in a three-dimensional color space. A small number of representative colors are selected from the distribution by clustering, a color code indicating the representative color is given to each pixel in the color area according to the clustering criteria, and the color is converted into two-dimensional intermediate coordinate values. A 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 given second object color, and registered in a lookup table, and the color image and the A high-speed color change display method for a color image, in which an image in which a desired color change is naturally made only in the color area is displayed at high speed by switching and displaying images obtained by applying a look-up table to a color code image. 2. Color image storage means for storing a color image, first object color storage means for storing an object color of a color region that is a target of the color image, and light source color storage means for storing a light source color of the color image. Assuming that the three primary color values of each pixel in the target color region of the color image represent the colors on a plane defined by the three colors of black, object color, and light source color in a three-dimensional color space, intermediate pixel value calculation means for converting into intermediate coordinate values in 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; a cluster storage means for storing the obtained clustering standard and the representative color, and a color code corresponding to the representative color of each pixel determined by the intermediate coordinate value obtained from the intermediate pixel value calculation means and the clustering standard as an image. a second object color storage means for storing an object color after changing the color of the color region; and a color code image storage means for storing an object color after changing the color of the color region, and the color calculated from the representative color using the second object color and the light source color. a look-up table that stores three primary color values corresponding to the codes and converts the color code read from the color code image storage means into the three primary color values when displaying an image; and a display controller that replaces the three primary color values of the pixels read from the means with the three primary color values output from the look-up table for pixels belonging to the color area, and the display controller is configured to quickly change the colors of the target color area of the color image. A fast color changing display device for changing and displaying color images.