如何加速圖像上代碼計算「每像素」的對比度（局部對比度）？

Question

我寫了一個Matlab函數來計算每個像素的對比度（即，窗口的中心像素（3x3）和窗口中所有像素的平均值之間的差異，以及所有像素的標準偏差窗口中的像素）。

該代碼運行非常緩慢的一個1024x1024灰度圖像。有沒有加快代碼的方法？謝謝！

function [ imContrast ] = LocalContrast(im) 
% [ imContrast ] = LocalContrast(im) 
% Compute the contrast between a center contrast and its neighbors. 
% 
% Equation: window_size = 3x3 
%    x_contrast = (x_center - mu)/std(pixels_in_window) 
%    mu: mean of the pixels' gray values in the window 
% 
% Input: 
%  im - original image in gray scale 
% 
% Output: 
%  imContrast - feature matrix of contrast, same size of im 

[rows, cols] = size(im); 
imContrast = double(zeros(size(im))); 

% Boundary - keep the gray values of those in im 
imContrast(1,:) = im(1,:)/255; 
imContrast(rows,:) = im(rows,:)/255; 
imContrast(:,1) = im(:,1)/255; 
imContrast(:,cols) = im(:,cols)/255; 

% Compute contrast for each pixel 
for x = 2:(rows-1) 
    for y = 2:(cols-1) 

     winPixels = [ im(x-1,y-1), im(x-1,y), im(x-1,y+1),... 
         im(x,y-1), im(x,y), im(x,y+1),... 
         im(x+1,y-1), im(x+1,y), im(x+1,y+1)]; 

     winPixels = double(winPixels); 

     mu = mean(winPixels); 
     stdWin = std(winPixels); 
     imContrast(x,y) = (double(im(x,y)) - mu)/stdWin; 
    end 
end 
end 

Answer 1

下面介紹一種使用圖像處理工具箱的方法。鑑於你的圖像被稱爲im，

平均差（MD）：

MD = im - imfilter(im,fspecial('average',[3 3]),'same'); 

標準偏差差（SDD）：

SDD = im - stdfilt(im, ones(3));