How to extract different (256,256) images from a (512,512) image and calculate the average of them?

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MAN
MAN 2022-6-6
评论： Carson Purnell 2022-6-9
Hi
I have an image (512,512) double. I want to extract different images with size of (256,256) with moving on image with pixel step equal to 16 and finally get an average from all of the extracted images. I think it needs 2 or 3 for loop for moving on the original image(512 and 512) and extract different images with size (256,256). Could you please help me in coding with MATLAB?
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MAN
MAN 2022-6-8
编辑：MAN 2022-6-8
Sorry if I did not explain well. I have an image(512,512) double. I need samples in size of 128*128 or 256*256. I just nead to "mean of the samples". I do not need to mean of each sample.
Carson Purnell
Carson Purnell 2022-6-9
If you want the mean of samples my code does exactly that. If you want the samples to each be stored, then just store them in a third dimension within the loop so you can look at them later with
store(:,:,count) = im(i:i+samplesiz-1,j:j+samplesiz-1)
on the inner loop after the count increment.

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采纳的回答

Carson Purnell
Carson Purnell 2022-6-6
Just loop through the step sizes and accumulate a sum, then divide by the count.
imsiz = 512;
im = rand(imsiz);
step = 16;
samplesiz = 256;
in = zeros(samplesiz); count =0;
for i=1:16:imsiz-samplesiz+1
for j=1:16:imsiz-samplesiz+1
in = in+im(i:i+samplesiz-1,j:j+samplesiz-1);
count = count+1;
end
end
imavg = in/count;
  2 个评论
Image Analyst
Image Analyst 2022-6-6
编辑：Image Analyst 2022-6-6
Ran in:
Except it doesn't do what I thought you wanted : get the mean at every window location as the window scans the image in jumps of 16, and then get the overall average of those 625 subimages.
imsiz = 512;
im = imresize(imread('cameraman.tif'), [512, 512]);
subplot(2, 1, 1);
imshow(im)
axis on;
step = 16;
samplesiz = 256;
in = zeros(samplesiz, class(im));
count =0;
for i=1:16:imsiz-samplesiz+1
for j=1:16:imsiz-samplesiz+1
in = in+im(i:i+samplesiz-1,j:j+samplesiz-1);
count = count+1;
end
end
imavg = in/count;
subplot(2, 1, 2);
imshow(imavg, []);
axis on;
See if my answer below is what you want.

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更多回答（1 个）

Image Analyst
Image Analyst 2022-6-6
编辑：Image Analyst 2022-6-6
Ran in:
You can do it with blockproc. Demo attached.
Or you can do it with a nested for loop where you move your window along and compute the mean inside each window.
% Create sample 512 x 512 image.
grayImage = imresize(imread('cameraman.tif'), [512, 512]);
subplot(2, 1, 1);
imshow(grayImage);
title('Original Image')
axis on
% Define parameters.
windowSize = 128; % or 256
stepSize = 16;
[rows, columns] = size(grayImage);
% Define where the windows will be located that we will take the mean inside.
startRows = 1 : stepSize : (rows - windowSize - stepSize)
startRows = 1×23
1 17 33 49 65 81 97 113 129 145 161 177 193 209 225 241 257 273 289 305 321 337 353
startCols = 1 : stepSize : (columns - windowSize - stepSize)
startCols = 1×23
1 17 33 49 65 81 97 113 129 145 161 177 193 209 225 241 257 273 289 305 321 337 353
outputImage = zeros(length(startRows), length(startCols));
outputRow = 1;
outputCol = 1;
% March the window over the image.
for row = 1 : length(startRows)
thisRow = startRows(row);
for col = 1 : length(startCols)
thisCol = startCols(col);
% Get sub-image.
subImage = grayImage(thisRow:thisRow+windowSize-1, thisCol:thisCol+windowSize - 1);
% Get its mean.
outputImage(outputRow, outputCol) = mean2(subImage);
outputCol = outputCol + 1;
end
% Increment to the next pixel in our output image.
outputCol = 1;
outputRow = outputRow + 1;
end
% Display the output image.
subplot(2, 1, 2);
imshow(outputImage, []);
axis on
title('Output Image')
% Get the overall average of all the subimages
overallAverage = mean2(outputImage)
overallAverage = 104.2951

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