Fspecial Disk Filter Shape

What is the actual shape of the pre-defined disk filter in MATLAB? Obviously it can't be exactly circular but what shape would it have with say a radius of 5. For example, the center row I'm guessing would have 9 pixels including the pixel of interest but I'm not sure... What about the other rows? Thanks.

Answer 1

[Image Analyst]

Just type it out and see:

>>theFilter = fspecial('disk', 5)

[B]

Thanks alot. How is the weighting determined? I was under the impression that each pixel was evenly weighted.

[Image Analyst]

Good question. I would tend to agree with you. The values in the center are the same but the values at the edge of the disk are somewhat different. I would guess it has something to do with the shape of the jaggies at the outer boundary. You can make them all the same if you want, then pass it into conv2() to do a averaging filter with uniform weights.

out = out > 0.5*max(out(:)); % Threshold.
out = out / sum(out(:)); % Normalize.
filteredImage = conv2(double(inputImage), out, 'same');