On Sat, 28 Apr 2007 18:42:50 +0200, Jasper Schalken  

> Isn't it possible for the code to simply disregard pixels outside the
> image? That is, instead of  pretending they actually exist and have a
> colour (if it works as I described above, that colour being the
> average of all the other pixel's colours), just don't include them in
> the blur at all. Only blur with pixels that do exist.
>  But someone should have a look at the code before I take my
> assumptions/theories too far. I will have another look and see if I
> can understand what it is doing.

You could have a look at the matrix convolution filter code. (Be warned  
there are some minor bugs concerning edge effects IIRC) but it will serve  
as an introduction to the different ways of treating edge data.

Many algorithms , from the various interpolation methods to the many  
filters based on matrix convolution of which blur is an example, can  
require data outside the image to function upto the edge.

This has quite simply to be made up by one means or another. There are  
several strategies whose suitabilities generally depend on the image  

So in short , no, they cant just be ignored.

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