POV-Ray : Newsgroups : povray.advanced-users : Speeding up media : Re: Speeding up media Server Time
6 Jul 2022 18:50:21 EDT (-0400)
  Re: Speeding up media  
From: William F Pokorny
Date: 15 Feb 2021 06:00:30
Message: <602a544e$1@news.povray.org>
On 2/15/21 2:37 AM, Thomas de Groot wrote:
> Op 14/02/2021 om 20:38 schreef Ash Holsenback:
>> On 2/14/21 2:33 PM, Ash Holsenback wrote:
>>> On 2/14/21 12:32 PM, Alain Martel wrote:
>>>> Le 2021-02-14 à 11:02, Ash Holsenback a écrit :
...
> Give that man a beer!
> 
> Much better assuredly.
> 
> Pending more learned answers on your last question, I would be wary to 
> affirm this. The point being probably - if those are silently ignored by 
> method 3 as Alain states - that people will wring themselves into hoops 
> only to see some 'improvements' to their media, without any results 
> obviously. If, on the other hand, those are /not/ ignored, we need to be 
> dead sure about it. What does the code say, Mr Pokorny?
> 

Generally, I recommend we make the recommendation to use only media 3 
more strongly. Using the other methods with the current code base is 
potentially confusing given they won't get some of the normal defaults 
due how the flip to method 3 was done in the parsing phase.

I agree with Alain. The keywords: confidence, variance and ratio are 
used only with methods 1 and 2 (a). The use of the variance word in the 
method 3 wording is I suppose correct, but unfortunate. Another sample 
is taken between two existing, if the difference between the two end 
samples is > the aa_threshold.

(a) For the purposes of documentation see (a1) and ignore the rest of 
this footnote. Someone can set the intervals in method 3 to more than 1 
and if they do ratio does come into play with a lit and un-lit intervals 
scheme internally which 'probably' doesn't have much of an end effect 
for method 3, but... Always true, sometimes, almost never, never? Not 
sure... When using multiple medias with mixed sampling types, I know of 
some bleed through in the keyword settings between methods.

(a1) It would be good to somewhere add a note along the lines of: When 
using multiple medias, it's strongly recommend all use the same sampling 
method. With the current code there is some keyword setting bleed 
between methods.

Aside: The sentence about monte carlo.... only applies to methods 1 and 2.

Aside: FWIW. In povr I plan to at least make it appear methods 1 & 2 and 
their keywords do not exist at all (and I'll pull jitter from media 3). 
Ideally, I'll replace the whole of the current implementation with a new 
media 3 like one. There are standing issue with media 3 too with respect 
to speed, accuracy of result and when and if adaptive sampling actually 
kicks in. But, it's media - which is fuzzy. Most remaining issues don't 
matter much to an end result as I recall - so long as we sample enough 
that things look good. ;-)

Bill P.


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