How to apply an 9x9 average filter to image with some boundary options?

Hi! I know how to apply an average filter, but how to apply it with a certain boundary options?

For example: boundary option: X=0 or periodic?

Thank you in advance! I'm trying to learn Matlab by myself and this could be very useful for me!

Answer 1

[Image Analyst]

You can use imfilter() or conv2():

out = conv2(double(grayImage), ones(9)/81, 'same');

This assumes zeros outside the image. I can't think of any reason why you'd need a periodic situation.

[Lachezar Petkov]

I'm trying to solve a several questions from the textbook. It says to use imfilter. I read the help file, but I did not see where I put the boundaries?

The questions ask for: X=0, X=225, mirror-reflection, periodic, equal to nearest border value.

I thought if I understand the periodic and x=0 boundary with imfilter I could sort out the rest.

Answer 2

[Walter Roberson]

http://www.mathworks.com/help/images/ref/imfilter.html#input_argument_options

[Image Analyst]

Too bad it doesn't have a "mask-shrinking" option. I think that would be more like what people would want rather than symmetric.