变换读取

a=imread('c:\boat.png');
b=a(:);
[k,l]=size(a);
[y0,i0]=sort(b);
m=k*l;

for i=1:m
y1(i0(i))=y0(i);
end

w=1;
for i=1:256
for j=1:256
c(j,i)=y1(w);
w=w+1;
end
end

figure;
imshow(c,[]);