Re: [Algorithms] Gaussian blur kernels

[Nicholas \Indy\ R. <ar...@gm...>]

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.

> Similarly, what about running the 5x5 (or whatever size) N times in
> succession over the same texture? Is there a mapping that comes into play
> here, like, "X successive passes with a kernel of NxN is approximately
> equal to 1 pass with kernel of MxM"?

I think the computation goes like this:

Running two successive Gaussian blurs is equal to one Gaussian blur,
who's distance is equal to the square root of the sum of the squares
of the two blurs.

Thus, for two 5x5 blurs: sqrt(5^2 + 5^2) ~= 7. Or two 5x5 blurs is
about equal to a 7x7 blur.

Nicholas "Indy" Ray