How to create a new square matrix with entries of each middle point of each subsection of another larger square matrix?

I have a square matrix of size 611x611 in which I want to create a grid on of 47 rows and 47 collums (I believe I can do this with matt2cell command?). Then I want to construct a new square matrix of size 47x47, in which every entry is the middle or approximate middle entry (doesn't have to be exactly the middle one) of each grid square in the 611x611 square matrix. I hope it is clear what I am trying to ask!

PS: If doing it with the middle entry is very difficult or not possible, then every entry of the the 47x47 square matrix being the average of the values of the grids in the 611x611 square matrix is also fine!

Answer 1

[Rik]

The code below requires the Image Processing toolbox, although you can do it with loops and mat2cell as well.

A=imread('pears.png');A=A(1:400,1:400,:);A=imresize(A,[611 611]);imshow(A)

fun_pick_middle=@(block) block.data(round(end/2),round(end/2),:);
B = blockproc(A,[611/47 611/47],fun_pick_middle);
imshow(B)

[Borys Bulka]

Do you know how I could do it with mat2cell? Because I am using a university version and am not sure if I have this toolbox on here.

[Rik]

University licenses tend to include this toolbox, butI can write something when I'm back at a computer. Why don't you read the documentation in the meantime and see if you can find out how to split your image into cells?

[Borys Bulka]

Would very appreciate one with mat2cell if you have time and energy for it ofcourse! I would then be able to understand the process behind it much better. I will in the meantime twy to read the documentation on what you have already provided!

[Borys Bulka]

Aah I think it worked! However, it outputs me a 50x50 matrix instead of a 47x47 one.

[Borys Bulka]

My matrix is named B. When I type in size(B), then it gives me the following answer: 611 611 3. This I find strange cause I thought size only gives length and width. What does this third value of 3 stand for and mean? Is it perhaps thats why it gave me a 50x50 matrix instead of a 47x47 matrix?

[Rik]

The size function returns all dimensions, omitting higher dimensions only if they are not 1. The third dimension in the case of images is the color (RGB).

To do the same thing with mat2cell, you need to find the size of each block. The vectors you need to enter need to sum to the dimensions of the input image.

A=imread('pears.png');A=A(1:400,1:400,:);A=imresize(A,[611 611]);
B=mat2cell(A,...
    size(A,1)/47*ones(1,47),...
    size(A,2)/47*ones(1,47),...
    size(A,3));
for n=1:numel(B)
    B{n}=B{n}(round(end/2),round(end/2),:);
end
B=cell2mat(B);
imshow(B)

size(B)

ans = 1×3

47 47 3

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[Borys Bulka]

This makes much more sense now to me, thank you so much for your explenation it helped me a lot!

[Rik]

You're welcome. If I solved your question, please consider marking my answer as accepted answer. If not, feel free to post a comment with your remaining issues.