JPH0580704B2 - - Google Patents

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.

(Conventional technology) CAD (computer computer) is used in the field of color design.
A Dated Design) is applied and the color is required to be changed within it. Specifically, an image containing the object of design (for example, a car) is imported into a computer system using a scanner or a color camera, displayed on a color display, and then the color of the part of this object is changed (for example,
By changing the body of a red car to blue), we can see the design results when changing it to various colors.
It requires making predictions without actually making them.

For this purpose, conventionally, the color of a certain surface (final R (red), G
(border), B (blue), given by three components) according to the shading obtained by a TV camera (monochrome) (Textile and Industry, Vol. 36, No. 6,
1980, pp. 195-199). In this case, an original image 101 of shading 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 an A/D converter 104 The signal is converted into digital values, separated into each part, and a color control 105 gives R, G, and B values, and a color encoder 106 converts the signal into a color TV signal. At this stage, the same color portions have the flat (R, G, B) colors shown. At the same time, the actual product 107 is aligned with the original image 101 and photographed using another monochrome television camera 108.
The shadow image signal N thus obtained and the previous color television signal 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 of each pixel (R', G', B') is determined by the brightness N of each pixel given by the monochrome camera as follows. You are asked to do so.

R′ G′ B′=NR G B...(1) Here, it is assumed that N takes a value between 0 and 1.

This method is based on the following method: ``The color of one color region is originally (R,
The colors are bright (G, B), and some parts are darker due to shading. ” This is based on the basis that In other words, when considering the three-dimensional space shown in Figure 4, the color of one area (R', G', B') is black (0,
0, 0) and the object color (R, G, B).

(Problem to be solved by the present invention) However, in reality, even in one color area, because the light is reflected and bright, there is usually a color that is close to white, as shown in Figure 4, P. It is. but,
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 to convert the three primary color values of each pixel of a color change target area, which is a constant color portion of an object surface in a color image, into black, black, and black in a three-dimensional color space. object color,
It is projected onto a plane defined by the three light source colors, regarded as one point on the plane, converted into two parameter values indicating the mixing ratio of the object color and the light source color, and then
By using these parameter values as the mixing ratio of the newly given second object color and the light source color and calculating new three primary color values for each pixel, the color of the color change target area can be changed to a different color. An image color changing method is characterized by changing the color.

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 color change target area which is a constant color portion of an object surface in the color image; A light source color storage means for storing the light source color in the color image; and a light source color storage means that stores the three primary color values of each pixel in the color change target area of the color image, in a three-dimensional color space, black, the object color, and the light source color. an intermediate image calculation means for projecting onto a plane defined by three colors, treating it as one point on the plane, and converting it into two parameter values indicating a mixing ratio of the object color and the light source color; and the intermediate image calculation means. intermediate image storage means for storing pixel values obtained by the above as an image; second object color storage means for storing a second object color after the color change of the color change target area; The two parameter values stored in the intermediate image storage means are used as a mixing ratio for the second object color stored in the color storage means and the light source color stored in the light source color storage means. a changed image calculation means for calculating new three primary color values for each pixel and writing them into the color image storage means, and changing the color of the color change target area of the color image to a different color. It is a color changing device.

(Operation) The operation of the present invention will be explained with reference to FIG. When the light source 120 hits the object 121, the camera 12
The light entering 2 is specular reflection light 123 and diffuse reflection light 1
It can be roughly divided into 24 types. 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) of each point on the target surface can be written as R G B = R ₀ G ₀ B ₀ a + R _S G _S B _S β (2). Here, (R ₀ , G ₀ , B ₀ ) 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.
(R _S , G _S , B _S ) are the three components of the specularly reflected light and are equal to the color of the light source, so they will be referred to hereinafter as "light source colors" in this specification. α and β indicate the degree of contribution of diffuse reflected light and specular reflected light to the amount of emitted light,
It is related to the surface material, direction, etc. This differs for each pixel, so the pixel position within the pixel is (x, y)
Then, R (x, y) G (x, y) B (x, y) = R ₀ G ₀ B ₀ a (x, y) + R _S G _S B _S β (x, y) (3) written. Such models are used in computer graphics, e.g.
According to Phon's model, R G B = [d+(1-d)・cosθ]・R ₀ G ₀ B ₀ + [W(θ)(cosα) ⁿ ]+R _S G _S B _S (4) 13th Image Engineering Conference, 1982
(2010, pp. 55-58).

Here, θ is the angle between the surface normal and the direction of the light source, α is the angle between the specular reflection direction and the camera direction,
d is a constant indicating the degree of intensity of diffusely reflected light and surroundings;
w(θ) is also a term indicating the degree of specular reflection light versus diffuse reflection light.

When the surface of a certain object is expressed by equation (3), if the objects are made of the same material but have different colors, only the object color is expressed as (R ₀ ′,
G ₀ ′, B ₀ ′), each pixel value can be calculated as shown in equation (5).

R′ (x, y) G′ (x, y) B′ (x, y) = R ₀ ′ G ₀ ′ B ₀ ′ α (x, y) + R _S G _S B _S β (x, y) ( 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, color distribution 200 in one color area in a color image.
is the origin O and the object color in the R, G, B color space.
C ₀ is included in the plane that creates the light source color C _S . and,
The color of each pixel is determined by the coordinate axis α connecting O and C0, and the coordinate axis α connecting O and _C0 .
It can be expressed by a coordinate axis β connecting C _S. This color distribution becomes as shown in FIG. 7 if the two coordinate axes α and β are viewed 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 by keeping the color distribution unchanged, a natural color change can be obtained.

To achieve this, it is necessary to determine C ₀ and C _S for the color region of a given color image, and to find the α and β values of each pixel. Actually, α=
Since there is no color with 0 or β=0, from the image
Although it is not possible to accurately determine C ₀ and C _S , it is not possible to accurately determine C 0 and C S , but the part of the image that is most likely to be the color of that color region (for example,
For a car with a red body, it is sufficient for practical purposes to read the image value of the part that looks very red and set it as C ₀ , and read the image value of the part that shines pure white due to specular reflection and set it as C _S.

For convenience, C ₀ and C _S are used to calculate α and β of each pixel.
Let the third chromatic belt C _d perpendicular to , for example C ₀ and
The vector product (cross product) of C _S is defined as C _d = C ₀ ×C _S (6). Express this C _d in R, G, B space.
When expressed as (7), C _d = R _d G _d B _d (7) The color (R, G, B) of each pixel in the image is expressed as R (x, y) G by introducing γ. (x, y) B(x, y)=R ₀ R _S R _d G ₀ G _S G _d B ₀ B _S B _d α(x, y) β(x, y) γ(x, y) (8 ) can be written. Here, γ is O of each color,
It corresponds to the distance from the plane created by C _S and C ₀ and is considered to be a noise component for pixels in the target color area.

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

α (x, y) β (x, y) γ (x, y) = R ₀ R _S R _d G ₀ G _S G _d B ₀ B _S B _d ^-1 R (x, y) G (x, y ) B(x,y) (9) In this way, α and β are found for each pixel. Convert the image part that had the object color C ₀ to C ₀ ′, and convert the other parts of this color area accordingly,
As mentioned earlier, formula (5) can be used to convert naturally.

Note that if there is no part that is considered to be specular reflection in the target area of the color image, the C _S should be assigned a value that is normally considered white in the display device (for example, 8 bits each for R, G, and B). For display devices with R _S = G _S = B _S =
255), there is no practical problem.

(Example) An example of the present invention will be described with reference to FIGS. 1 and 2. In the color image memory 1, for example, a full color image including an object whose color is to be changed is stored.
Each of R, G, and B is stored in 8-bit gradation.
This content is transferred to the CRT via D/A converter 2.
3 is displayed as a color image. The mask image memory 4 stores a color area to be changed in this image and a mask in one bit for each pixel.
This relationship is shown in FIG. The color image memory 1 also includes other backgrounds of the car. The mask image memory 4 has a mask image in which the value is "1" only for the part of the car body that is the object of the internal color change, and the value is "0" for the other parts. It is assumed that the mask image has already been created using a known technique such as observing a color image on a CRT and then using a pointing device to outline and fill in the inside.

The color specifying means 5 in FIG.
Using the CRT 3 and pointing device 6, the object color C ₀ and the light source color C _S are picked up from the image, and the first object color storage means 7 and
It is stored in the light source color storage means 8 and can be realized by a microcomputer or the like. Intermediate image calculation means 9
scans each pixel in the mask image memory 4, and scans the color image memory 1 for pixels whose value is "1".
(α, β) are calculated from (R, G, B) stored in , according to equation (9), and the α and β values are written into the intermediate image memory 10 as two image data. Once the intermediate image is completed, preparations for color changes are complete.

To actually change the color, the user first changes the object color using the pointing device 6 or keyboard 11, for example.
The R, G, and B values (R ₀ ', G ₀ ', B ₀ ') of the new object color C _{0 '} instead of C 0 are given to the color specifying means 5, and these are stored in the second object color storage means 12. It is started by The modified image calculation means 13 also scans each pixel of the mask image memory 4, and for pixels whose value is "1", the intermediate pixel memory 10
From (α, β) obtained from (α, β) and C _S , C ₀ ′, new R, G, B values (R′, G′, B′) are obtained by equation (5).
is calculated and written to the color image memory 1. When this is completed for all pixels, the color of the portion of the color image mask in the color image memory 1 where "1" stands in the mask image has been naturally rewritten to 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. The present invention allows the colors of a design to 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 the drawing]

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 5 is an explanatory diagram of the principle of the conventional device, 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 color space, and FIG. An explanatory diagram shown in the coordinate system of
FIG. 8 is an explanatory diagram showing a color distribution in a 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, 10... Intermediate image memory, 11... Keyboard, 12... second object color storage means, 13... changed image calculation means.

Claims (1)

[Claims] 1. The three primary color values of each pixel in the color change target area, which is a constant color part of the object surface in a color image, are calculated by calculating the three primary color values of black, object color, and light source color in a three-dimensional color space. The object color and the light source color are projected onto a plane, regarded as one point on the plane, and converted into two parameter values indicating the mixing ratio of the object color and the light source color.Then, the above two parameter values are converted to the newly given A color characterized in that the color of the color change target area is changed to a different color by calculating new three primary color values of each pixel using the second object color and the light source color as a mixing ratio. How to change the color of an image. 2. Color image storage means for storing a color image, first object color storage means for storing an object color of a color change target area that is a constant color portion of an object surface in the color image, and a light source in the color image. A light source color storage means for storing colors, and a plane in which the three primary colors of black, the object color, and the light source color extend in a three-dimensional color space, and the three primary color values of each pixel in the color change target area of the color image are stored in a three-dimensional color space. intermediate image calculation means for projecting onto the plane, treating it as one point on the plane, and converting it into two parameter values indicating a mixing ratio of the object color and the light source color; and pixels obtained by the intermediate image calculation means. intermediate image storage means for storing a value as an image; second object color storage means for storing a second object color after the color change of the color change target area;
mixing the two parameter values stored in the intermediate image storage means with the second object color stored in the object color storage means and the light source color stored in the light source color storage means; a changed image calculating means for calculating a new three primary color value for each pixel as a ratio and writing it into the color image storage means, and changing the color of the color change target area of the color image to a different color. Image color changing device.