How to remove specific portions of a image?

Hey, I wish to remove circles from my image by specifying its center and the radius. Its a bw image and i wish to specifically remove few selected circles by specifying their centers and radii. I know strel can be used but i am not able to figure out how to use it for this purpose. Thanks.

[Steve Eddins]

See today's blog post for a little bit more on this question.

Answer 1

[Image Analyst]

Keeping in mind that an image must remain rectangular, what does "remove" mean to you? You can't really remove those pixels but you can replace them with something, such as another image, a texture, a uniform gray level, or smear the boundaries inwards with roifill(). What do you want to do?

[Image Analyst]

arjun's "Answer" moved here:

Hey Analyst, Sorry i meant the pixels i would want to transform would be white circles in a bw image ,i want to make them black, thats what i meant by remove. thanks.

[Image Analyst]

See the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_create_a_circle.3F to create a circle mask. Then use that to replace the image

grayImage(mask) = 0;

[Image Analyst]

If you just want to replace all pixels above some value, like 250, with 0, then do this

binaryImage = grayImage > 250; % or whatever.
grayImage(binaryImage) = 0; % Set to 0.