MATLAB自定义函数：RGB与HSI颜色空间互换

看了冈萨雷斯的《数字图像处理（MATLAB版）》一本。其中提供了RGB与HSI颜色空间之间的相互转变函数。已在matlab7.0中测试成功。不敢独享，贴出来供大家参考，也当是我的备忘吧。
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. Ths input

% image can be of class double (with values in the rang[0,1]), uint8, or

% uint16.

% The output image, HSI, is of class double, where:

% hsi(:,:,1)= hue image normalized values 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].

%Extract the individual component images.

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);

function rgb=hsi2rgb(hsi)

%HSI2RGB Converts an HSI image to RGB.

% HSI2RGB Converts an HSI image to RGB, where HSI is assumed to be of

% class double with:

% hsi(:,:,1)= hue image normalized values 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].

% The components of the output image are:

% rgb(:,:,1)=red;

% rgb(:,:,2)=green.

% rgb(:,:,3)=blue.

%Extract the individaul 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);
希望用这个为基础可以写个叶面积计算的东西呵呵，应该没问题吧？拭目以待啊
PS：eps在matlab中指最小的不等于0的正数，是matlab uint16数中最接近0的数，或者可以理解为可以使（1＋eps）>1为真的最小数。加eps也就是为了在尽可能不影响计算结果的前提下避免0/0的情况出现的方法！
PS2:此处提供的rgb转成hsi的程序，结果提供的是double类型的结果，既用图像的double类型的数据计算的结果。如果要转成我们在书上见到的那种（H指角度范围在0到360度之间，S指色度值在0到1之间，I指亮度值在0到1之间）形式，可以在现有的H值上乘以360换算。