rgb2hsi.m

冈萨雷斯的经典教材数字图像处理的matlab版源代码

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);