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 09:58:35 EDT (-0400)
  Re: weird white stain with beta povray v3.8.0 (not with povray v3.7.0)  
From: William F Pokorny
Date: 16 Jan 2022 13:46:53
Message: <61e4681d@news.povray.org>
On 1/14/22 6:06 AM, Warren wrote:
> Cousin Ricky <ric### [at] yahoocom> wrote:
>> On 2022-01-13 10:06 (-4), Warren wrote:
>>> Hi,
>>> I post a message here, because I get a weird render with povray 3.8.0 beta 1 of
>>> a scene with the following resolution : 1280x960 (see attached image with this
>>> message) , you can see a white stain that has the shape of a heart near the
>>> pentagram. When I render this same scene with stable v3.7.0 the white stain
>>> doesn't appear. And even weird, when I render this scene with povray "3.8.0
>>> beta1" but with the resolution of 640x480, I don't get this white stain in the
>>> final image.
>>
>> What I've found so far:
>>   - The artifact varies with the image size.  A 960x720 render leaves an
>>     oblong stain on the upper left vertex.
>>   - The artifact isn't completely absent with 640x480.  At 640x480, tiny
>>     white spots appear along the veins of the pentagram, but they are
>>     absent in a 3.7 render.  I presume that this means you did not put
>>     them there deliberately, and that they are related to the big heart-
>>     shaped stain.
>>   - 3.8 beta 2 does not solve the problem.
> 
> There are other things to consider:
> - First off, set the boolean 'PlaceWell' (line 19 of main pov file) to false, to
> get a faster rendering, the heart shape artifact being always there.
> - Changing the minimum_reuse value from '0.015' to '0.01' make the 'heart shaped
> artifact' to disappear, but the little white stains you talked about are there,
> it seems.
> 

The following might, or might not, be of help to you with official 
versions of POV-Ray.

I took a quick look at at this bug with my current povr branch and found 
along with some recent bounding code changes it got me to a more stable 
fail for a bug I've been chasing for years. Details posted in the v4.0 
group.

My povr branch is now considerably different than official POV-Ray 
offerings, but after translating the pentagram up by 2x the thread 
radius(a) I got away from the 'white regions.' I never saw the heart 
shaped one - no idea why not in povr. Image attached.

(a) - Media needs clean start and stop intervals. Near coincident 
shape/surfaces can cause confusion and leave intervals open - and with 
emission media this results in extremely bright regions.

Where you had media I moved from min, max samples and interval 
specifications to just 'samples 10'.

In many places you are using the srgb keyword with channel values 
outside the 0-1 range. My povr branch doesn't allow this because any 
'srgb calculation' outside the 0-1 range is wacky. See post elsewhere 
for details. If you need values outside 0-1, use rgb to exactly specify 
what you want for internal linear values.

includes/outdoorsLamp.inc -> debug statement line 218 uses LampZpos and 
it should be LampZPos.

Bill P.


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