I=imread('cancer.bmp');
[y,x,z]=size(I);
myI=double(I);                  % 圖象的數據類型為無符號整型，必須轉換為雙精度實型才能計算
%%%%%%%%%%% RGB to HSI  %%%%%%%%
H=zeros(y,x);
S=H;
HS_I=H;
for i=1:x
    for j=1:y
        HS_I(j,i)=((myI(j,i,1)+myI(j,i,2)+myI(j,i,3))/3);
        S(j,i)=1-3*min(myI(j,i,:))/(myI(j,i,1)+myI(j,i,2)+myI(j,i,3));
        if ((myI(j,i,1)==myI(j,i,2))&(myI(j,i,2)==myI(j,i,3)))        % 三者相等，H計算式中分母為零，無法計算
            Hdegree=0;
        else    
            Hdegree=acos(0.5*(2*myI(j,i,1)-myI(j,i,2)-myI(j,i,3))/((myI(j,i,1)-myI(j,i,2))^2+(myI(j,i,1)-myI(j,i,3))*(myI(j,i,2)-myI(j,i,3)))^0.5);
        end    
        if (myI(j,i,2)>=myI(j,i,3))
            H(j,i)=Hdegree;                                     % G≥B, H 在[0,π]范圍內
        else
            H(j,i)=(2*pi-Hdegree);                              % G < B, H 在(π,2π]范圍內
        end     
    end 
end

%=====色度識別====%          % 色度識別需要依靠專家知識，此處僅舉一例說明

Hth1=0.9*2*pi; Hth2=0.1*2*pi;  % 檢測紅色，紅色的色度值在0或2π附近
Nred=0;                        % 記錄紅色或接近紅色的像素點個數
for i=1:x
    for j=1:y
        if ((H(j,i)>=Hth1)||(H(j,i)<=Hth2))
            Nred=Nred+1;       
        end
    end
end

Ratio=Nred/(x*y);            % 紅色像素點所占比例

if (Ratio>=0.6)              % 判別是否為紅色  
    Red=1
else
    Red=0
end    


HS_I=uint8(HS_I);                                                    % 實型轉換為整型才能作為圖象顯示

figure(1);
imshow(I);
figure(2);
imshow(HS_I);