How to automatically obtain upper-left pixel coordinates of one of the 4x4 blocks I obtained splitting an image?

Hello.

I managed to split a 224x224 image into 4x4 blocks with mat2cell.

For example: splittedImage is my 4x4 cell matrix with 56 pixel each cell, I need to obtain automatically from a cell of those the upper-left pixel coordinates in the original image.

How can I do it?

Thank you.

Answer 1

[Image Analyst]

Try indexing:

[rows, columns] = size(ca)
for col = 1 : columns
    for row = 1 : rows
        thisCellContents = ca{row, col};
        upperLeftPixelValue = thisCellContents(1,1);
        % Now do something with upperLeftPixelValue -- process it somehow.
    end
end

It looks like you never read the FAQ, so go here for a good description of how cell arrays work and when to use braces, brackets, or parentheses.

https://matlab.fandom.com/wiki/FAQ#What_is_a_cell_array.3F

[Claudio Eutizi]

Thank you for the answer.

I wrote the question wrong, i'm sorry.

I don't need the first pixel's value, but its coordinates in the entire image.

[Image Analyst]

I don't know off the top of my head. mat2cell is tricky so that's why I never use it. I'd recommend just dividing the number of rows and columns by the grid lengths to get the locations, something like

yourMatrix = ones(80, 120); % Whatever.
[rows, columns] = size(yourMatrix) % Get sizes along each dimension.
% Find out where each tile is divided along.
rowDividingLines = round(linspace(1, 0.75 * rows + 1, 4))
colDividingLines = round(linspace(1, 0.75 * columns + 1, 4))
% Get index of upper left pixel for each tile.
[R, C] = meshgrid(rowDividingLines, colDividingLines)