Convolution kernels

Posted by Knecht, David on Feb 26, 2009; 4:01pm
URL: http://imagej.273.s1.nabble.com/Convolution-kernels-tp3693561.html

I am trying to understand how a convolution like a 2x2 mean filter  
actually works.  I presume it always starts in the upper left of the  
image.  It would then calculate the average of those first 4 pixels.  
I thought that the sliding window of the convolution resets as it  
moves so that you are always calculating from the original values of  
the image matrix as opposed to using the new calculated value from  
applying the convolution.  I ran a test to confirm, and to my surprise  
it appears that the convolution is applied continuously. Is that  
right?  Is this described somewhere in the documentation?  I would  
imagine that you could filter either way and it is just how the  
algorithm is implemented.  Also, is it described somewhere how imageJ  
handle the edges?  Dave

Dr. David Knecht
Department of Molecular and Cell Biology
Co-head Flow Cytometry and Confocal Microscopy Facility
U-3125
91 N. Eagleville Rd.
University of Connecticut
Storrs, CT 06269
860-486-2200
860-486-4331 (fax)