JPS63237172A - Method and device for color change of color picture - Google Patents

Abstract

PURPOSE:To change a color region into a desired color naturally by converting a three primary colors value into an intermediate coordinate value of a two-dimensional color space, and next, calculating the changed three primary colors value. CONSTITUTION:A full color picture is stored in a color picture memory 1, and the contents are displayed on a CRT 3. A mask picture memory 4 stores a mask picture. A color designating means 5 picks up an object color and a light source color in the picture by using the CRT 3 and a pointing device 6, and stores them in an object color storing means 7 and a light source color storing means 8 respectively. An intermediate picture calculating means 9 scans the respective displayed picture of the mask picture, and calculates the intermediate picture from the three primary colors value, stored in the color picture memory 1, and writes it in an intermediate picture memory 10. Next, the intermediate picture, obtained from the intermediate picture memory 10, is given to a changed picture calculating means 13 by the color designating means 5, and changed to the desired three primary colors value.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method and apparatus for changing the colors of a color image without impairing their naturalness.

(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 (
The process of importing an image containing a car (for example, a car) into a computer system using a scanner or color camera, displaying it on a color display, and then changing the color of the resultant part (for example, changing the body of a car that was originally red to blue). Therefore, 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 by a TV camera (monochrome) (Fiber and Industry, Vol. 36, No. 6, 1980, Ko, pp. 95-199). 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 input to 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 digital converter 104. The color controller 105 converts into values and separates each part.
The R, G, and B values are given by the color encoder 106 and converted 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, resulting in an image signal N with shadows,
The previous color television signals are synthesized by a shadow synthesis circuit 109. 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),
The color (R', G', B') of each pixel is determined as follows based on the brightness N of each pixel given by the monochrome camera.

Here, it is assumed that N takes a value of θ˜1.

This method [colors in 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 shown in Figure 4, the color of one area (
R'', G', B') are 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.

SUMMARY OF THE INVENTION An object of the present invention is to solve this problem and provide a method and apparatus that can naturally change colors even in color areas of images that have reflective parts.

(Means for Solving the Problems) The first invention is based on the three primary color values of six pixels in the color area that is the target of a color image, which are the three colors of black, object color, and light source color in a three-dimensional color space. Assuming that the colors on the plane are expressed, the colors are converted to intermediate coordinate values in a two-dimensional color space, and then the intermediate coordinate values, the light source color, and the three primary colors changed from the newly given second object color are This method of changing the color of a color image is characterized in that the color area is naturally changed to a desired color by calculating a value.

A second invention also provides a color image storage means for storing a color image, a first object color storage means for storing an object color of a target color region of the color image, and a first object color storage means for storing an object color of a target color region of the color image; A light source color storage means for storing the three primary color values of each pixel in the target color region of the color image, and a color on a plane defined by the three colors of black, object color, and light source color in a three-dimensional color space. intermediate image calculation means for converting into intermediate coordinate values in a two-dimensional color space; intermediate image storage means for storing pixel values obtained by the intermediate image calculation means as images; a second object color storage means for storing a changed object color; and intermediate coordinate values stored in the intermediate image storage means based on the object color stored in the second object color storage means and the light source color. and a changed image calculation means for converting the three primary color values into new three primary color values and writing them into the color image storage means, the color changing device for a color image naturally changing the color of the target color area of the 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 is then isotropically emitted to the outside.

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*GOtBo) is the three components of the diffusely reflected light, and since it differs depending on the object, it is hereinafter referred to as "object color" in this specification.

(Rs, Gs, Bs) are the three components of specularly reflected light and are equal to the color of the light source, so they will be referred to as [light source color J] hereinafter. α,! 3 indicates the degree of contribution of diffusely reflected light and specularly reflected light to the amount of emitted light, and is 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).

Here, θ is the angle between the surface normal and the camera direction, a is the angle between the specular reflection direction and the camera direction, d is a constant that indicates the intensity of the diffuse reflected light and the 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 (Fto'sGo'
*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 an origin O1, an object color C6, and a light source color Cs in the R, G, B color space. The color of each pixel can be represented by a coordinate axis α connecting 0 and Co, and a coordinate axis p connecting O and C5. This color distribution becomes as shown in FIG. 7 if the two coordinate axes α and p 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.

In order to realize this, it is necessary to determine C0 and C8 for the color area of a given color image, and to obtain the a and p values of each pixel. Actually, α=0. Or, since there is no color with p=0, it is not possible to accurately determine C8 and C8 from the image, but the part in the image that is most likely to be the color of that color region (for example, in the case of a car with a red body, the part that looks very red) ) is read as C0, and reading the image value of the part that appears pure white due to specular reflection as Cs is sufficient for practical purposes.

To obtain α, 13 for each pixel, for convenience, C8 and a third color vector cd perpendicular to C8 are determined as, for example, the vector product (cross product) of C8 and Cs, as follows: cd=coXC8(6). Expression (7) of this cd in R, G, B space
The color (R, G, B) of each pixel in the image can be written by introducing γ. Here, γ is O of each color,
The pixels in the target color area, which correspond to the distance from the plane created by C, , Co, are considered to be noise.

By reversing equation (8), equation (9) holds true, so for each pixel, α, 13. γ can be found. Since γ is a noise component, it can be ignored.

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

As mentioned earlier, in order to convert the image part that had the object color C8 to C6' and naturally convert the other parts of this color area accordingly, it is sufficient to use equation (5). That's right.

Note that if there is no part that is considered to be specular reflection in the target area of the color image, it will be treated as C, and a value that is normally considered white on a display device (for example, R, G,
In a display device in which 8 bits are assigned to each B, there is no practical problem even if R,=G,=B,=255) are given.

(Example) An example of the present invention will be described with reference to FIGS. 1 and 2. In the color image memory 1, a full-color image including an object whose color is to be changed is stored, for example, in R, G, and B gradations of 8 bits each. This content is D/A converter 2
The image is displayed on the CRT 3 as a color image. The mask image memory 4 stores a mask of a color area to be changed in color in this image, with one bit for each pixel. This relationship is shown in FIG. The color image memory 1 includes not only the car but also the background. Mask image memory 4
is 1" only for the parts of the car body that are subject to this white color change, and is "0" for other parts.
It has a mask image whose value is . It is assumed that the mask image has already been created using a known technique such as observing a color image on a CRT, then using a pointing device to outline and fill in the inside.

The color specifying means 5 in FIG.
The object color C6 and the light source color C8 are picked up from the image using the pointing device 6 and are stored in the first object color storage means 7 and the light source color storage means 8, respectively. realizable. The intermediate image calculation means 9 scans each pixel of the mask image memory 4, and calculates the formula (R, G, B) stored in the color image memory 1 for the pixel whose value is "1" by formula ( (α, I3) is calculated according to 9) and the α, 13 values are written into the intermediate image memory IO as two image data.When the intermediate image is completed, preparations for color change are complete.

To actually change the color, the user first uses the pointing device 6 or keyboard 11 to change the R, G, and B values (Ro'+Go'+
Bo') is given to the color specifying means 5, and this is stored in the second object color storage means 12, thereby starting the process. The modified image calculation means 13 also scans each pixel of the mask image memory 4, and calculates (α, I3) and Cs5CO' obtained from the intermediate image memory 10 for pixels whose value is "1".
are the new R, G, B values (R'
, G', B') and write them into the color image memory 1. When this is completed for all pixels, the color of the portion of the color image in the color image memory 1 where "1" stands in the mask image has been naturally replaced with the desired color.

(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 changed to specified colors without impairing naturalness. Can be changed. According to the present invention, the colors of a design can be changed and displayed naturally without changing the surroundings of the image, so it is possible to check the color scheme etc. without actually making a product with that color. , has great industrial and economic effects.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the relationship between the color image memory and mask image memory in FIG. 1, FIG. 3 is a block diagram of a conventional device, and FIG. 4 is an explanatory diagram of the principle of the conventional device, FIG. 5 is a detailed explanatory diagram of the present invention, FIG. 6 is an explanatory diagram showing the color distribution of one color region in color space, and FIG. FIG. 8 is an explanatory diagram showing the color distribution in the color space when the colors of the color area are changed according to the present invention. 1. Color image memory, 2.-D/A converter,
3...CRT, 4...Mask image memory, 5...
...Color specifying means, 6. Pointing device, 7. First object color storage means, 8. Light source color storage means, 9. Intermediate image calculation means,
1O... Intermediate image memory, 11... Keyboard, 12... Second object color storage means, Figure 1 Keyboard Figure 2 Mask image memory Color image memory Figure 3 μml Figure 4 B ↑ Fig. 5 120 light source Fig. 6 R Fig. 7 Fig. 8

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. The above color is converted into an intermediate coordinate value in a two-dimensional color space, and then the changed three primary color values are calculated from the intermediate coordinate value, the light source color, and the newly given second object color. A method for changing the color of a color image, characterized by naturally changing an area to a desired color. 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 image calculation means for converting into intermediate coordinate values in a two-dimensional color space; intermediate image storage means for storing pixel values obtained by the intermediate image calculation means as images; a second object color storage means for storing, and converting intermediate coordinate values stored in the intermediate image storage means into new three primary color values using the object color stored in the second object color storage means and the light source color; and a modified image calculation means for writing into the color image storage means,
A color changing device for a color image that naturally changes the color of a target color area of a color image.