RGB to HSI
I=(R+G+B)/3;
S=1-3*min(R,G,B)/(R+G+B);
H = cos^(-1)((0.5*((R-G)+(R-B))) / ((R-G)^2 + (R-B)*(G-B))^(0.5))
If S = 0; H =0 ;
If B > G; H=360-H;
HSI to RGB
If 0 < H <= 120 then
B = 1/3(1-S)
R = 1/3(1+ ((S cos H) / (cos(60 -H))))
G = 1 -(B+R)
If 120 < H <= 240 then
H = H – 120
R = 1/3(1-S)
G = 1/3(1+ ((S cos H) / (cos(60 -H))))
B = 1 -(R+G)
If 240 < H <=360 then
H = H – 240
G = 1/3(1-S)
B = 1/3(1+ ((S cos H) / (cos(60 -H))))
R = 1 -(G+B)
算法参考来源： 冈萨雷斯 《数字图像处理》
function [H,S,I]=RgbToHsi(Image_Input)
Image_Input=double(Image_Input)/255;
R_Input=Image_Input(:,:,1);
G_Input=Image_Input(:,:,2);
B_Input=Image_Input(:,:,3);
I = (R_Input+G_Input+B_Input)/3.0;
[heigth,width]=size(R_Input);
S(1:heigth,1:width)=0;
H(1:heigth,1:width)=0;
for i=1:heigth
for j=1:width
temp=[R_Input(i,j),G_Input(i,j),B_Input(i,j)];
S(i,j)=1-3*min(temp)/sum(temp);
X=R_Input(i,j);
Y=G_Input(i,j);
Z=B_Input(i,j);
temp_1=((X-Y)+(X-Z)+1e-6)/(2*sqrt((X-Y).^2+(X-Z)*(Y-Z))+1e-6);
Sigma=acos(temp_1);
if(Z<=Y)
H(i,j)=Sigma/(2*pi);
else
H(i,j)=(2*pi-Sigma)/(2*pi);
end
end
end
function Image_out=HsiToRgb(H,S,I)
H_angle=H*360;
[heigth,width]=size(H);
R(1:heigth,1:width)=0;
G(1:heigth,1:width)=0;
B(1:heigth,1:width)=0;
for i=1:heigth
for j=1:width
if(S(i,j)<1e-6)
R(i,j)=I(i,j);
G(i,j)=I(i,j);
B(i,j)=I(i,j);
else
if(H_angle(i,j)>=0 && H_angle(i,j)<=120)
B(i,j)=(1-S(i,j))*I(i,j);
sigma=(H_angle(i,j)-60)*pi/180;
temp=tan(sigma)/sqrt(3);
G(i,j)=(1.5+1.5*temp)*I(i,j)-(0.5+1.5*temp)*B(i,j);
R(i,j)=3*I(i,j)-G(i,j)-B(i,j);
else
if(H_angle(i,j)>=120 && H_angle(i,j)<=240)
R(i,j)=(1-S(i,j))*I(i,j);
sigma=(H_angle(i,j)-180)*pi/180;
temp=tan(sigma)/sqrt(3);
B(i,j)=(1.5+1.5*temp)*I(i,j)-(0.5+1.5*temp)*R(i,j);
G(i,j)=3*I(i,j)-R(i,j)-B(i,j);
else
G(i,j)=(1-S(i,j))*I(i,j);
sigma=(H_angle(i,j)-300)*pi/180;
temp=(tan(sigma))/sqrt(3);
R(i,j)=(1.5+1.5*temp)*I(i,j)-(0.5+1.5*temp)*G(i,j);
B(i,j)=3*I(i,j)-R(i,j)-G(i,j);
end
end
end
end
end
Image_out(:,:,1)=R;
Image_out(:,:,2)=G;
Image_out(:,:,3)=B;