Le 18-02-06 à 08:45, clipka a écrit :
> Am 06.02.2018 um 03:06 schrieb Mike Horvath:
>> Also, is there a way to speed this up? Right now it's stuck at 6% of the
>> mosaic phase for an hour. I don't recall UberPOV being this slow. :(
> 
> The example given in the knowledgebase article uses the so-called
> "macronormals" approach, as opposed to the "micronormals" approach that
> is only described in the text itself.
> 
> Blurred reflections always need oversampling, i.e. at some point the ray
> has to be split up into multiple rays that go into slightly different
> directions.
> 
> With the macronormals approach, that oversampling is done upon
> reflection: Wherever a ray is reflected at an object, the ray is split
> up into a fixed number of sub-rays. The drawback is that any sub-ray
> that also hits a blurred-reflective surface will be split up even
> further into the same number of sub-sub-rays. In a scene with many
> blurred-reflective surfaces, this causes render times to explode.
> 
> The micronormals approach can also be used in the same mode of operation
> (essentially just replacing "scale 1000" with e.g. "scale 0.001"), but
> alternatively it can be used with just one single texture (rather than
> the average of a high number of textures) and some means of effecting
> oversampling at the pixel level. This avoids the explosion of render
> time in blurred-reflection-heavy scenes. (The drawback is that it also
> increases render time for portions of the scene that have no blurred
> rteflections; however, this can be partially mitigated by employing an
> adaptive mechanism for the oversampling at the pixel level.)
> 
> The latter is essentially the mode of operation UberPOV uses. To effect
> oversampling at the pixel level, UberPOV provides a special
> anti-aliasing mode that shoots a number of rays randomly within each
> pixel, and uses stochastic analysis to adapt the number of rays shot per
> pixel to the image content.
> 
> In official POV-Ray, a very similar oversampling can be effected by
> using ever so slight focal blur; adaptive focal blur is recommended in
> that case.
> 
> 
> A completely different approach to avoid the explosion of tertiary rays
> is to provide two copies of each blurred-reflective object: One with
> blurred reflections using an average of many textures and the
> "no_reflection no_radiosity no_refraction" keyword, and one with just
> one plain texture (or a low-quality blurred reflection) and the
> "no_image" keyword. However, this approach breaks down if a
> blurred-reflective surface is to be visible in a perfect mirror.
> 
In that case, you can use the micronormals way.
If using mocronormals, you need to use antialiasing to get decent 
results. In some cases, you may need to increase the recursion depth by 
one or two notches : +r4 or +r5.

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