Tek <tek### [at] evilsuperbraincom> wrote in message 40043c50@news.povray.org:
>> You can't really answer this from looking how it works in real life -
>> when you take a photograph of a star the ideal camera outside the
>> earth atmosphere in ideal empty space will only show an infinitely
>> small point.
>
> Well I was thinking of a digital camera, which works by having a grid
> of colour sensors that effectively just add together the brightness
> due to all photons falling upon that pixel. Surely with that a very
> small point would always be 1 pixel in size and have a brightness
> proportional to it's brightness multiplied by how much of the area of
> the pixel it covers.
>
> I'm not sure how all that corresponds to gamma ramps and such, but
> digital cameras tend to get sharp images without aliasing, so surely
> that can be used as a model for an anti-aliasing technique?
>

There seems to be many arguments on what's right in this thread but I (who
normaly just reads this group) want to give you all my view on the topic.
I'm not saying that this is more "right" or something like that, all is
IMHO.
I have for several years planned making my own raytracer and have though
long about the antialias problem (having had the clipping before/after aa
problem with pov). I have come to the conclusion that the super sampling
should be done on unclipped values on the argument that it is really an
approximisation to an intergral over the pixel. This gives the expected
result for small bright objects such as stars. The problem is that edges of
very bright object get alias problems, and that's not the expected result.
With a digital camera such an edge will look soft (at least partly) because
imperfections in the lenses and the air will make the bright light "bleed".
My plan is to simulate this bleeding in a post process step before the
clipping/gamma/whatever (the plan is to output the image with raw floating
point color values and do any transforms when saving to ex. png). That
should solve that problem too.

My planned raytracer is probably never going to be implemented, so don't ask
for it. I just enjoy thinking about features for it :)

-- 
Daniel Nilsson

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