MATLAB: How to measure the aspect ratio of a certain part of an image

aspect ratiomnist dataset

I am working with the mnist dataset and I am trying to calculate the aspect ratio of every number. The aspect ratio is defined as the minimum ractangular area that the number covers any idea how to do that?

Best Answer

Try this:
% im is the MNIST image
sum_row = sum(im, 2);
sum_col = sum(im, 1);
min_row = find(sum_row, 1);
max_row = find(sum_row, 1, 'last');
min_col = find(sum_col, 1);
max_col = find(sum_col, 1, 'last');
width = max_col-min_col+1;
height = max_row-min_row+1;
aspect_ratio = height/width;
This solution is also much faster then regionprops() and both give the same result as shown by following example
tic
sum_row = sum(im, 2);
sum_col = sum(im, 1);
min_row = find(sum_row, 1);
max_row = find(sum_row, 1, 'last');
min_col = find(sum_col, 1);
max_col = find(sum_col, 1, 'last');
width = max_col-min_col+1;
height = max_row-min_row+1;
aspect_ratio1 = height/width;
toc
tic
props = regionprops(imbinarize(im));
aspect_ratio2 = props.BoundingBox(4)/props.BoundingBox(3);
toc
Eq = isequal(aspect_ratio1, aspect_ratio2);
Result:
t1 =
   2.6254e-04
>> t2
t2 =
    0.0145
>> Eq
Eq =
  logical
   1
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