用Arnold置乱变换做图像加密,程序写出来了但是结果却不对,经过周期变换后不能恢复原图,下面是程序,请大家帮我看看那里有问题了~~


function embedimage=arnold1(embedimage,N)
[m,n]=size(embedimage);
a=double(embedimage)/255;
for k=1:N
    for i=1:m
        for j=1:n
            x=i+j;
            y=i+2*j;
            if x>m
                x=mod(x,m);
            end;
            if y>m
                y=mod(y,m);
            end;
            if x==0
                x=m;
            end;
            if y==0
                y=m;
            end;
            a1(x,y)=a(i,j);
        end
    end
    embedimage1=a1;
end
imshow(embedimage1)

还有就是怎么样才能对彩色的图像进行8*8的DCT变换?????