I=imread('greens.jpg');
if isgrb(I)
    [M N R]=size(I);
    data1=zeros(M,N);
    data2=zeros(M,N);
    data3=zeros(M,N);
    for i=1:M
        for j=1:N
            data1(i,j)=I(i,j,1);
            data2(i,j)=I(i,j,2);
            data3(i,j)=I(i,j,3);
        end
    end
I=double(I);
[M,N]=size(I);
Y=zeros(M,N);
f=zeros(M,N);
u=3.9;
q=rand(1);
for t=1:2
for i=1:M
    for j=1:N
    x=i;
    y=j;
    temp=data1(i,j);
%     temp=data2(i,j);
%     temp=data3(i,j);
    x1=mod(x+y,M)+1;
    y1=mod(x+2*y,N)+1;
    Y(x1,y1)=temp;
    Y(i,j)=I(x1,y1);
    f(i,j)=round(((I(i,j)+1)*255)/2);
        str1=dec2base(f(i,j),2,8);
        str2=dec2base(I(i,j),2,8);
        for k=1:8
            str3(k)=xor(str2num(str1(k)),str2num(str2(k)));
        end
        I2(i,j,t)=bin2dec(num2str(str3));
        q=q*(1-q)*u;
    end
    end
end
T=zeros(M,N,3);
for i=1:M
    for j=1:N
    T(i,j,1)=data1(i,j);
    T(i,j,2)=data2(i,j);
    T(i,j,3)=data3(i,j);
    end
end
figure(1)
subplot(2,2,1),imshow(unit8(I));
title('原始圖象')
subplot(2,2,2),imshow(unit8(Y));
title('cat變換后的圖象')
subplot(2,2,3),imshow(unit8(I2));
title('本文加密算法2次后的圖象')