I = imread('E:\matlab\work\lenna.bmp');  
[height,width] = size(I);  
figure  
subplot(221)  
imshow(I)%显示原始图像  
subplot(222)  
imhist(I)%显示原始图像直方图  
  
%进行像素灰度统计;  
s = zeros(1,256);%统计各灰度数目，共256个灰度级  
for i = 1:height  
    for j = 1: width  
        s(I(i,j) + 1) = s(I(i,j) + 1) + 1;%对应灰度值像素点数量增加一  
    end  
end  
%计算灰度分布密度  
p = zeros(1,256);  
for i = 1:256  
    p(i) = s(i) / (height * width * 1.0);  
end  
%计算累计直方图分布  
c = zeros(1,256);  
c(1) = p(1);
for i = 2:256   
        c(i) = c(i - 1) + p(i);  
end  
%累计分布取整,将其数值归一化为1~256 
c = uint8(255 .* c + 0.5);  
%对图像进行均衡化
for i = 1:height  
    for j = 1: width  
        I(i,j) = c(I(i,j)+1);  
    end  
end  
subplot(223)  
imshow(I)%显示均衡化后的图像
subplot(224)  
imhist(I)%显显示均衡化后的图像的直方图