Re: [Algorithms] Gaussian blur kernels

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

Fabian Giesen wrote:
> However, all of this is a non-issue in graphics. Pixel shaders give you 
> cheap pointwise evaluations at no cost. If you want only every second 
> pixel, then render a quad half the size in each direction.
>
>   

But that cheap sample is using a pretty crappy box area filter for its 
sampling, so it is not aliasing free.

> In short, the optimal "polyphase" implementation of a 5x5 Gaussian 
> followed by a 2:1 downsample in both directions is just to render to the 
> smaller rendertarget directly with the 5x5 Gaussian Pixel shader and the 
> correct texture coordinates.
>
>   

But originally the problem wasn't just downsampling -- it was using some 
combination of downsampling, filtering and upsampling to approximate the 
result of a bigger Gaussian blur, but making it faster.

Sincerely,

jw




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