%HSI颜色不同于RGB，均衡化只需针对对亮度即可

Y1=rgb2hsi(X11);

H1=Y1(:,:,1);

S1=Y1(:,:,2);

X1=Y1(:,:,3);

g1=histeq(X1);

g2=histeq(S1);

g3=histeq(X1);

Y1=cat(3,H1,S1,g3);

f1=hsi2rgb(Y1);

figure

imshow(f1),title('HSI图像均衡化');

下面是两个颜色空间变换的函数

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);

function hsi=rgb2hsi(rgb)

rgb=im2double(rgb);

r=rgb(:,:,1);

g=rgb(:,:,2);

b=rgb(:,:,3);

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;

hsi=cat(3,H,S,I);