rgb到xyz到lab色彩空间转换ppt.ppt

1、Realize the color space conversion CIERGB to CIEXYZ to CIELAB,Team members： 高雯菁 李佩佩 徐宁 李心雨,Colorimetry and its empirical foundations,Colorimetry is a scientific field in which the physical specifications of light stimuli that produce a given color sensation under restricted viewing conditions are st

2、udied.,In particular ,it seeks to represent the spectral power distribution of any incident light with a much reduced number of parameters .,It is mainly concerned with color matching and predicting small color differences when two stimuli do not match.,The receptor-level theory of color matching,On

3、e of the main goals of colorimetry is to derive a concise numerical representation of any given color stimulus from its spectral power distribution.,But , A spectral power distribution may take more than 40 numbers to specify.,Therefore, the main task of colorimetry is to determine the three cone re

4、sponse functions.,The bipartite field used in color matching experiments.,1.“” means color matching. 2. (C), (R), (G), and(B), represent color stimuli or lights. 3. R,G, and B, represent scalar multipliers, meaning the amounts of light.,Color matching experiments,chromaticity coordinates,Let R, G, a

5、nd B be the tristimulus values of a given color, then its chromaticity coordinates (r,g,b) are defined as:,Since r+g+b= 1 it is only necessary to specify any two of r , g, and b.,Transformation between two sets of primaries (RGB TO XYZ),Let(R)(G)(B) and(X)(Y)(Z) be two sets of primaries. A color sti

6、mulus(C) can be expressed by the following two color matching relations: (C) CR(R)+CG(G)+CB(B) (C) CX(X)+CY(Y)+CZ(Z).,If we determine the tristimulus values of(X),(Y), and(Z)using the primaries(R),(G), and (B), we have the following relations:,Let R, G, B be the tristimulus values for the (R), (G),

7、(B) primaries and X, Y, Z be the tristimulus values for the (X), (Y), (Z) primaries. Their chromaticity coordinates are denoted by r,g,b and x,y,z . As we have just shown, the transformation from R, G, B to X, Y, Z can be done by a 33 matrix, A:,the above equation can be expressed as,From the equati

8、on and the definition of chromaticity, we have X+Y+Z=(a11+a21+a31)R+(a12+a22+a32)G+(a13+a23+a33)B =(R+G+B)(a11+a21+a31)r+(a12+a22+a32)g+(a13+a23+a33)b,Substituting the above relation into the previous equation， we can have,Z can be computed as z= 1-x-y.,From the equation we have discussed ,We can ge

9、t the conclusion that: given four pairs of corresponding chromaticity coordinates in both spaces, the transformation can be uniquely determined by solving a system of linear equations in eight unknowns.,Let (x1,y1,z1), (x2,y2,z2), (x3,y3,z3), (x4,y4,z4) be four points in the chromaticity space of th

10、e primaries(X),(Y),(Z), and (r1,g1,b1), (r2,g2,b2), (r3,g3,b3), (r4,g4,b4)be their corresponding points in the chromaticity space of the primaries (R), (G), (B).,Then ,we can determine the parameters of matrix A.,Alternatively, we can solve the transformation by another Algorithm,Let (x1,y1,z1), (x2

11、,y2,z2), (x3,y3,z3), (x4,y4,z4) be four points in the chromaticity space of the primaries(X),(Y),(Z), and (r1,g1,b1), (r2,g2,b2), (r3,g3,b3), (r4,g4,b4)be their corresponding points in the chromaticity space of the primaries (R), (G), (B).,This algorithm is faster than the previous.,A =,CIELAB color space,(Xn,Yn,Zn) are the tristimulus values of the reference (neutral) white point.,Built