clipka <ano### [at] anonymousorg> wrote:
> Am 01.01.2013 22:23, schrieb Mr:
> > Ive <ive### [at] lilysoftorg> wrote:
> >> The animation feature of POV-Ray can be used to make it a spectral
> >> render engine. The basic idea is to render a set of gray-scale images
> >>    - each representing a specific wavelength - and finally combine them
> >> using the CIE color match function.
> >> To simplify this task I have created a few POV-Ray SDL scripts and some
> >> examples.
> >> You'll find the download link, some images and more explanation here:
> >>
> >> http://www.lilysoft.org/CGI/SR/Spectral%20Render.htm
> >>
> >> -Ive
> >
> > Would this help POV to render caustics any faster?
> >
> > I ask this because I could not after all my attempts get POV-Ray to render some
> > caustics scene with chromatic dispersion as fast as Lux Render did (Lux uses
> > spectral rendering)other than that I would have been so happy to use POV because
> > of so many other features, but for this particular scene, the speed issue was
> > really too high of a bottleneck, preventing it to keep the same quality between
> > the two renderers.
>
> I'm not sure how Lux does it, but here's one optimization I could
> imagine, which POV-Ray currently doesn't do:
>
> When the generated photon map is evaluated for a dispersed (and hence
> monochromatic) ray from the camera, dispersed (and hence also
> monochromatic) photons with a different wavelength could theoretically
> be ignored (and those typically are a lot if you make ample use of
> high-quality dispersion).
>
> In POV-Ray, the fact that a photon was subject to dispersion (and hence
> is monochromatic) is forgotten in the stored photons map; such photons
> are instead stored just like normal non-dispersed colored photons. Thus,
> POV-Ray needs to evaluate each and every photon even for monochromatic rays.
>
> As Ive's approach only deals with one single wavelength per render
> anyway, it automatically gets that optimization for free. However, for
> non-dispersed rays and photons it loses a lot in terms of performance,
> as it needs to trace such rays and photons over and over again for each
> wavelength even though their trajectory is the same for all wavelengths.
>
> Hard-coding this optimization into POV-Ray should be no big deal; it
> doesn't even need full-fledged spectral color math to work. It would
> probably increase the photons map memory footprint by 20% though.


Thanks! Your explanation is so clear! I would vote for the speed optimization as
I have so much RAM, but I would understand if others disagree. In which case I
would never be able to finish that stupid render. It's not even pretty, just a
comparative test :-)

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