pixels inside circle

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thoraya
thoraya on 21 May 2012
Commented: Image Analyst on 4 May 2018
hi; i need to find pixel coordinates inside a given circle C which is defined by its center position (x , y ) and its radius r. then i need also to find pixel coordinates located at the border of this circle knowing that the width of border is set at 1 or 2 pixels.

Answers (1)

Image Analyst
Image Analyst on 21 May 2012
Have you tried the code in the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_create_a_circle.3F It should be just slight modifications, if any, to get what you want.
  3 Comments
Image Analyst
Image Analyst on 4 May 2018
What does "find" mean to you?
To get a binary image with the black pixels indicated as "true", do
blackPixelMask = grayImage == 0; % Map of all black pixels.
blackPixelMask = blackPixelMask & circleMask; % Erase those outside the circle mask.
To count the number of black pixels, do this:
Make a circle mask, like the FAQ shows you. Then count the black pixels:
pixelsInCircleMask = grayImage(circleMask);
numBlackPixels = sum(pixelsInCircleMask)
Otherwise you'll have to give a precise definition of what the word "find" means to you in this context, because it's ambiguous. I don't know what it means to you.

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