how to avoid for loops or faster way for compute 3x3 avarage value of an image

1 次查看(过去 30 天)
I have a few pixels in an image and I want to calculate the average values ​​of a 3x3 window centred on those pixels in Matlab. It should be noted that not all over the image, just a few desired pixels.
I tried this code and it works but I prefer to avoid using for loops. Is there another way for doing that?
clc
clear
close all
img = imread('cameraman.tif');
x= [10,15,20];
y= [15,25,35];
m=-1;
n=-1;
window = zeros(3,3);
Avg = zeros(max(size(x)),1)
for k=1:max(size(x))
for i = 1:3
for j=1:3
window(i,j) = img(x(k)+m,y(k)+n);
n=n+1;
end
n=-1;
m=m+1;
end
Avg(k) = mean(window,'all')
end

采纳的回答

Image Analyst
Image Analyst 2020-10-19
编辑:Image Analyst 2020-10-19
If you're only doing it at 3 locations, don't worry about using for loops. It will be fast.
If you insist on using built-in functions to process the whole image, then...
Use imfilter():
kernel = ones(3)/9;
outputImage = imfilter(grayImage, kernel);
Or you can use conv2():
kernel = ones(3)/9;
outputImage = conv2(double(grayImage), kernel, 'same');
then you can reference outputImage(row, col) for the desired locations. Just be aware that y comes first, not x, so it's outputImage(y(1), x(1)), NOT outputImage(x(1), y(1)).
  4 个评论
ali eskandari
ali eskandari 2020-10-19
编辑:ali eskandari 2020-10-19
Thank you for your answer, the problem is that I have around 100 images and I want to apply this method on all of them and honestly there are more than three locations. Besides, I should add this code to other computations so the speed of computation is so important for me, that is why I am looking for a faster way. I just applyed it on one image to see how does it work.
Image Analyst
Image Analyst 2020-10-19
编辑:Image Analyst 2020-10-19
Try this:
grayImage = imread('cameraman.tif');
x = [10, 15, 20];
y = [15, 25, 35];
windowWidth = 3;
halfWidth = floor(windowWidth/2)
Avg = zeros(length(x), 1);
for k = 1 : length(x)
% Convert x and y into row and column.
row = y(k);
col = x(k);
% Get subimage centered about the (x, y) location.
window = grayImage(row - halfWidth : row + halfWidth, col - halfWidth : col + halfWidth);
% Compute the mean of that subimage.
Avg(k) = mean(window,'all')
end
If you have more than a few thousand points in the images to inspect, then it's best to just filter the whole image with conv2() or imfilter() like I originally said, and pluck out the locations you want.
To process a sequence of images, see the FAQ.

请先登录,再进行评论。

更多回答(0 个)

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by