A=imread('nv.png');

[i,j]=size(A);  %图像的行和列

count = zeros(1,256);

for r=1:256

    count(r)=length(find(A == (r-1)));  %建立直方图

end

count=count./(i*j);    %各灰度的概率

A2=A;  %新建空图像

func=zeros(1,256);

counts_sum=0;

for k=1:256

    counts_sum=counts_sum + count(k);%各阶段概率之和

    func(k)=(256-1)*counts_sum;%量化

end

func2=round(func);%取整

for h = 1:i

    for w = 1:j

        for k = 1:256

            if A(h,w) == k-1

                A2(h,w) = func(k);   %在同一坐标位置上重新赋值

                break;%防止重复赋值

            end

        end

    end

end

subplot(121),imshow(A);

subplot(122),imshow(A2);