Open image, read block of pixels, average the intensity of the block, display average intensity matrix

How would one open an image, block image in say, 20x20 pixel blocks and then get the average of each 20x20 pixel block's intensity? Is the conversion of RGB to Grayscale required, or just good practice? I then would like to generate a matrix with those averages. Still learning MatLab so any help would be greatly appreciated.

Answer 1

[KALYAN ACHARJYA]

Considering Gray Image, if not convert to grayscale then perform

im=imread('Image.jpg'); 
%.................^^ Change as per image name
[rows colm]=size(im);
block1=im(1:20,1:20);
%..here ^^ you can choose the block acccordingly
avg=mean(block1(:));
disp(avg);

[Don Simon]

This looks to produce a matrix of 20 numbers as columns? Is a 20x20 block of pixels averaged the same as a "column 1" in this list? What I am trying to do is average the first 20x20 pixels as a block and average those 400 pixels' intensities and display that number. Then grab the same for the next 20x20 block of pixels, and so on.

[KALYAN ACHARJYA]

grayscale image is just 2-D matrix, do whatever as you want. You can check for pad array here.

Also read this thread.

[Don Simon]

Yes, I got that, thanks. Is the number generated for 'Column 1' an average for the first 20x20 pixels? Is 'Column 2' number an average of the next block (pixels 21-41horiz x 20vert)? That is what I am trying to attain.

[KALYAN ACHARJYA]

How you move the 20x20 window? You can as you want, just undestand the issue.

Block Operation, mask operation, window movement read all terms-

[KALYAN ACHARJYA]

%This code is just for undestand how to move the window (20x20) over image

% Not recomended for multiple use of for loops, look other approaches of block operation

im=imread('Image.jpg'); 
%.................^^ Change as per image name
[rows colm]=size(im);
k=1;
for i=1:20:rows-20
for j=1:20:colm-20
block(k)=im(i:i+19,j:19);
current_block=block(k);
avg=mean(current_block(:));
fprintf('The Block Number %d and Avg is: %f',k,avg);
k=k+1;
end
end

Try with 10x10 matrices as an example, you will get the idea.

[Don Simon]

Thank you. I am getting a column average for A1-A20, then column 2 average is B1-B20, etc. instead of the full average from the A1-T20 block of 20 cells. I'll keep at it.