Intel ( i845G ) profiling

Matthias Hopf mhopf at
Wed Mar 12 05:20:31 PDT 2008

On Mar 12, 08 12:52:08 +0100, Simon Thum wrote:
> > Well, I implemented this, so I know that it does arbitrary FIR
> > filters. But maybe you know better from just reading the abstract...
> Sorry I didn't mean to offend you. I made a guess which wasn't properly 
> communicated.
> I meant 'linear' as in gamma-corrected or 'linear with luminance'. This 
> essentially means you need at least 10 bits of precision or tricky 
> lookups (or accept loss). I don't say thats infeasible or you/the 
> authors didn't do so, but usually this is mentioned. Though 
> 'High-quality' could refer to that, I don't know.

Ok, that makes sense. So far all filters have only been described to
work linearly in some color space (which typically R'G'B' is used, which
doesn't have a linear mapping to linear RGB). Yes, this is some aspect
many people do not understand or care.

Question is: in which space do you want to be linear? Perceptually,
R'G'B' is typically what you want, there are some exceptions, though
(e.g. antialiasing should be linear in RGB, thus modern cards do
gamma-corrected antialiasing in R'G'B' AFAIK).

If you want to be linear in RGB with an arbitrary filter, ATM I don't
see an alternative to the inverse-gamma, filter, gamma sequence - and
there you certainly run into quantization issues. 10bit might help, but
then you would like to have the better quantization anyway. This doesn't
tell, however, whether the filter can be done on GPUs or not. Most
probably, you can do it easily, and GPUs use IEEE floats internally for
computation anyway.



Matthias Hopf <mhopf at>      __        __   __
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