pixels inside circle

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.

Answer 1

[Image Analyst]

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.

[thoraya]

thank you for the fast answer.

I will try to adapt this code to meet my needs

[Shaban Sikander]

How to find the black pixels inside a specific circle?

[Image Analyst]

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.