function lab = XYZToLab(xyz,whiteXYZ) % lab = XYZToLab(xyz,whiteXYZ) % % xyz is a 3 x N matrix with xyz in columns % whiteXYZ is a length 3 vector with the white point. % lab is a 3 x N matrix of [Lstar;astar;bstar] % % Formulae are taken from Wyszecki and Stiles, page 167. % % xx/xx/xx baw Created. % xx/xx/xx dhb Made compatible with version 3.5 % 10/10/93 dhb Changed name to XYZToLab. % 5/9/02 dhb Improved help % Check xyz dimensions [m,n] = size(xyz); if ( m ~= 3 ) error('Array xyz must have three rows') end % Check white point dimensions [m,n] = size(whiteXYZ); if ( m ~= 3 || n ~= 1) error('Array white is not a three vector') end % Separate out the compontents X = xyz(1,:); Y = xyz(2,:); Z = xyz(3,:); Xn = whiteXYZ(1); Yn = whiteXYZ(2); Zn = whiteXYZ(3); % Allocate space [m,n] = size(xyz); lab = zeros(3,n); fX = zeros(1,n); fY = zeros(1,n); fZ = zeros(1,n); % Calculate fX lX = find( (X/Xn) < 0.008856 ); bX = find( (X/Xn) >= 0.008856); if (length(bX) ~= 0) fX(bX) = (X(bX)/Xn) .^(1/3); end if (length(lX) ~= 0) fX(lX) = 7.787*(X(lX)/Xn) + 16/116; end % Calculate L lY = find( (Y/Yn) < 0.008856 ); bY = find( (Y/Yn) >= 0.008856); if ( length(bY) ~= 0 ) lab(1,bY) = 116*(Y(bY)/Yn).^(1/3) - 16; fY(bY) = (Y(bY)/Yn) .^(1/3); end if ( length(lY) ~= 0 ) lab(1,lY) = 903.3 * (Y(lY)/Yn); fY(lY) = 7.787*(Y(lY)/Yn) + 16/116; end % Calculate fZ lZ = find( (Z/Zn) < 0.008856 ); bZ = find( (Z/Zn) >= 0.008856); if (length(bZ) ~= 0) fZ(bZ) = (Z(bZ)/Zn) .^(1/3); end if (length(lZ) ~= 0) fZ(lZ) = 7.787*(Z(lZ)/Zn) + 16/116; end % Compute a and b lab(2,:) = 500.0*(fX - fY); lab(3,:) = 200.0*(fY - fZ);