Re: [Algorithms] Gaussian blur kernels

[Jon W. <jw...@gm...>]

Nicholas "Indy" Ray wrote:
> On Wed, Jul 15, 2009 at 4:46 PM, Joe Meenaghan<jo...@ga...> wrote:
>   
>> Would the 5x5 over the lower res texture be approximately equivalent to a
>> 9x9 at the higher res for example, or perhaps something along these lines?
>>     
>
> No... That isn't how it works; A downsample shares very little in
> common with a blur.
>
>   

Actually, they are both low-pass filters, so 
downsampling-plus-upsampling is a form of blur. However, box filtering 
(the traditional downsampling function) isn't actually all that great at 
low-pass filtering, so it can generate aliasing, which a Gaussian filter 
does not. (AFAICR, the Gaussian filter kernel shares some properties 
with a sinc reconstruction kernel, and thus is "optimal" under certain 
conditions/assumptions, but details are hazy).

Sincerely,

jw



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