- your image is grayscale and is called img;
- the central pixel is at column x and row y;
- the radius of the circle is r;
- you do not require weighting at the rim of the circle - that is, each pixel is either entirely inside or entirely outside the circle;
How can I get the values of a circular region around a particular pixel?
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How can I get the values of a circular region around a particular pixel?
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David Young
2014-11-3
Assuming:
then you can do something like this
[xgrid, ygrid] = meshgrid(1:size(img,2), 1:size(img,1));
mask = ((xgrid-x).^2 + (ygrid-y).^2) <= r.^2;
values = img(mask);
where values will have a column vector containing the values in the circular region.
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Jennifer Bernier
2018-11-7
I'm doing something similar but with 5000 unique circular ROIs on a single image, and I can't figure out how to scale this method without using a loop (which takes a long time). Does anyone have any suggestions?
Image Analyst
2018-11-8
5000 iterations of a for loop should take only a few microseconds Here is the timing on my system:
Elapsed time is 0.000010 seconds.
So, 10 microseconds. If yours is taking a lot longer, then there is something else that's taking the time, it's not the for loop itself.
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Image Analyst
2014-11-3
% Demo to have the user freehand draw an irregular shape over a gray scale image.
% Then it creates new images:
% (1) where the drawn region is all white inside the region and untouched outside the region,
% (2) where the drawn region is all black inside the region and untouched outside the region,
% (3) where the drawn region is untouched inside the region and all black outside the region.
% It also (4) calculates the mean intensity value of the image within that shape,
% (5) calculates the perimeter, centroid, and center of mass (weighted centroid), and
% (6) crops the drawn region to a new, smaller separate image.
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