POV-Ray : Newsgroups : povray.beta-test : weird white stain with beta povray v3.8.0 (not with povray v3.7.0) : Re: weird white stain with beta povray v3.8.0 (not with povray v3.7.0) Server Time
10 Aug 2022 09:52:36 EDT (-0400)
  Re: weird white stain with beta povray v3.8.0 (not with povray v3.7.0)  
From: Kenneth
Date: 18 Jan 2022 01:00:00
Message: <web.61e65633c82cc78e4cef624e6e066e29@news.povray.org>
"Kenneth" <kdw### [at] gmailcom> wrote:
> Strange as it seems, if I simply eliminate your  +bs8  on the command line, I
> never see the artifact at 1280X960...well, not in 15 render attempts,
> anyway. I have no idea why that would matter.

Forget that; it's probably of no real consequence...because I think I've solved
at least part of the problem (the large heart-shaped artifact).
> ...I am seeing inconsistent results from
> render to render, even at the problematic 1280X960 render size. Sometimes the
> heart-shaped stain is there, sometimes not.

That's because of the scene's radiosity settings. I noticed that there was no
maximum_reuse value given, which means that it defaults to 0.2-- which is quite
large and can result in large splotchy artifacts-- the heart shape, for example.

My image examples are from an animation test. I changed minimum_reuse to 0.09...
and I now see LOTS of such artifacts. The reason why my earlier tests seemed
inconsistent is because of the random nature of such 'splotches' from render to
render, given the values used; and it just happened that the scene's rad
settings were sometimes producing only ONE *major* artifact...or none. The sizes
of such splotches vary according to the 'spread' between the minimum_reuse and
maximum_reuse values.

I also did a test with these rad values:
minimum_reuse 0.03
maximum_reuse 0.031

This produces even more splotches, all of the same (smaller) size.

It's obvious that these super-bright artifacts are showing up along the 'lines'
of the pentagram. The remainder of the problem must be that some of its srgb
colors are 'greater than 1.0' as was mentioned earlier, and are interacting
weirdly with radiosity; or that the scene's lights and fade_powers are somehow
too bright.

Apparently, radiosity is picking up a super-bright color from *somewhere*, and
using it in its calculations.

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