On 2017-01-05 11:58 PM, clipka wrote:
> Am 06.01.2017 um 04:48 schrieb David Buck:
>
>> It may not be related (media was after my time with the product), but in
>> the early days of POVRay we'd often get "speckles" on objects.  They
>> were usually black pixels.  The problem was floating point precision and
>> was corrected by adjusting the epsilon factor to determine how far away
>> from one intersection point counts as a separate hit versus the same
>> hit. For example, if a ray hits a sphere, and we trace another ray back
>> to the light source to determine if we're in a shadow, it's possible
>> that the first ray's intersection point was slightly inside the sphere
>> and the ray back to the light source hits the same sphere on the way
>> out.  This would count as a shadow and would make a dark pixel.
>>
>> This bug in media feels very much the same to me.  I wouldn't be
>> surprised if it's a problem with precision - especially seeing that
>> scaling the scene eliminates the problem.
>
> Actually it's pretty much the opposite: These media speckles are
> essentially a side effect of the very mechanism by which those dark
> pixels are avoided.
>

Interesting.  Ray tracing is always more tricky than it first appears.

David

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