function [L,a,b] = RGB2Lab(R,G,B) % function [L, a, b] = RGB2Lab(R, G, B) % RGB2Lab takes matrices corresponding to Red, Green, and Blue, and % transforms them into CIELab. This transform is based on ITU-R % Recommendation BT.709 using the D65 white point reference. % The error in transforming RGB -> Lab -> RGB is approximately % 10^-5. RGB values can be either between 0 and 1 or between 0 and 255. % By Mark Ruzon from C code by Yossi Rubner, 23 September 1997. % Updated for MATLAB 5 28 January 1998. if (nargin == 1) B = double(R(:,:,3)); G = double(R(:,:,2)); R = double(R(:,:,1)); end if ((max(max(R)) > 1.0) | (max(max(G)) > 1.0) | (max(max(B)) > 1.0)) R = R/255; G = G/255; B = B/255; end [M, N] = size(R); s = M*N; % Set a threshold T = 0.008856; RGB = [reshape(R,1,s); reshape(G,1,s); reshape(B,1,s)]; % RGB to XYZ MAT = [0.412453 0.357580 0.180423; 0.212671 0.715160 0.072169; 0.019334 0.119193 0.950227]; XYZ = MAT * RGB; X = XYZ(1,:) / 0.950456; Y = XYZ(2,:); Z = XYZ(3,:) / 1.088754; XT = X > T; YT = Y > T; ZT = Z > T; fX = XT .* X.^(1/3) + (~XT) .* (7.787 .* X + 16/116); % Compute L Y3 = Y.^(1/3); fY = YT .* Y3 + (~YT) .* (7.787 .* Y + 16/116); L = YT .* (116 * Y3 - 16.0) + (~YT) .* (903.3 * Y); fZ = ZT .* Z.^(1/3) + (~ZT) .* (7.787 .* Z + 16/116); % Compute a and b a = 500 * (fX - fY); b = 200 * (fY - fZ); L = reshape(L, M, N); a = reshape(a, M, N); b = reshape(b, M, N); if ((nargout == 1) | (nargout == 0)) L = cat(3,L,a,b); end