對灰度圖像進行分塊取高頻，再重構

I=imread('circles.png');
[M,N]=size(I);
for i=1:8:M
    for j=1:8:N
        T1=wkeep(I,[8,8],[i,j]);
        T2=dct2(T1);
        m=mean2(abs(T2));
        for h=1:8
            for k=1:8
                if abs(T2(h,k))<m
                    T3(h,k)=0;
                else T3(h,k)=T2(h,k);
                end
            end
        end
        T4=idct(T3);
        for h=1:8
            for k=1:8
                J(i+h-1,j+k-1)=T4(h,k);
            end
        end
    end
end