Matlab中RGB和HSI的相互转换

HSI----->>>RGB:

function rgb = hsi2rgb(hsi) %HSI2RGB Converts an HSI image to RGB. %   RGB = HSI2RGB(HSI) converts an HSI image to RGB, where HSI is %   assumed to be of class double with:   %     hsi(:, :, 1) = hue image, assumed to be in the range %                    [0, 1] by having been divided by 2*pi. %     hsi(:, :, 2) = saturation image, in the range [0, 1]. %     hsi(:, :, 3) = intensity image, in the range [0, 1]. % %   The components of the output image are: %     rgb(:, :, 1) = red. %     rgb(:, :, 2) = green. %     rgb(:, :, 3) = blue. %   Copyright 2002-2004 R. C. Gonzalez, R. E. Woods, & S. L. Eddins %   Digital Image Processing Using MATLAB, Prentice-Hall, 2004 %   $Revision: 1.5 $  $Date: 2003/10/13 01:01:06 $ % Extract the individual HSI component images. H = hsi(:, :, 1) * 2 * pi; S = hsi(:, :, 2); I = hsi(:, :, 3); % Implement the conversion equations. R = zeros(size(hsi, 1), size(hsi, 2)); G = zeros(size(hsi, 1), size(hsi, 2)); B = zeros(size(hsi, 1), size(hsi, 2)); % RG sector (0 <= H < 2*pi/3). idx = find( (0 <= H) & (H < 2*pi/3)); B(idx) = I(idx) .* (1 - S(idx)); R(idx) = I(idx) .* (1 + S(idx) .* cos(H(idx)) ./ cos(pi/3 - H(idx))); G(idx) = 3*I(idx) - (R(idx) + B(idx)); % BG sector (2*pi/3 <= H < 4*pi/3). idx = find( (2*pi/3 <= H) & (H < 4*pi/3) ); R(idx) = I(idx) .* (1 - S(idx)); G(idx) = I(idx) .* (1 + S(idx) .* cos(H(idx) - 2*pi/3) ./ cos(pi - H(idx))); B(idx) = 3*I(idx) - (R(idx) + G(idx)); % BR sector. idx = find( (4*pi/3 <= H) & (H <= 2*pi)); G(idx) = I(idx) .* (1 - S(idx)); B(idx) = I(idx) .* (1 + S(idx) .* cos(H(idx) - 4*pi/3) ./cos(5*pi/3 - H(idx))); R(idx) = 3*I(idx) - (G(idx) + B(idx)); % Combine all three results into an RGB image.  Clip to [0, 1] to % compensate for floating-point arithmetic rounding effects. rgb = cat(3, R, G, B); rgb = max(min(rgb, 1), 0); 

RGB---->>HSI

function hsi = rgb2hsi(rgb) %RGB2HSI Converts an RGB image to HSI. %   HSI = RGB2HSI(RGB) converts an RGB image to HSI. The input image %   is assumed to be of size M-by-N-by-3, where the third dimension %   accounts for three image planes: red, green, and blue, in that %   order. If all RGB component images are equal, the HSI conversion %   is undefined. The input image can be of class double (with values %   in the range [0, 1]), uint8, or uint16.  % %   The output image, HSI, is of class double, where: %     hsi(:, :, 1) = hue image normalized to the range [0, 1] by %                    dividing all angle values by 2*pi.  %     hsi(:, :, 2) = saturation image, in the range [0, 1]. %     hsi(:, :, 3) = intensity image, in the range [0, 1]. %   Copyright 2002-2004 R. C. Gonzalez, R. E. Woods, & S. L. Eddins %   Digital Image Processing Using MATLAB, Prentice-Hall, 2004 %   $Revision: 1.4 $  $Date: 2003/09/29 15:21:54 $ % Extract the individual component immages. rgb = im2double(rgb); r = rgb(:, :, 1); g = rgb(:, :, 2); b = rgb(:, :, 3); % Implement the conversion equations. num = 0.5*((r - g) + (r - b)); den = sqrt((r - g).^2 + (r - b).*(g - b)); theta = acos(num./(den + eps)); H = theta; H(b > g) = 2*pi - H(b > g); H = H/(2*pi); num = min(min(r, g), b); den = r + g + b; den(den == 0) = eps; S = 1 - 3.* num./den; H(S == 0) = 0; I = (r + g + b)/3; % Combine all three results into an hsi image. hsi = cat(3, H, S, I);