POV-Ray : Newsgroups : povray.binaries.images : Oscilloscope : Re: Oscilloscope Server Time
27 May 2024 09:23:00 EDT (-0400)
  Re: Oscilloscope  
From: William F Pokorny
Date: 5 Feb 2023 16:41:59
Message: <63e022a7$1@news.povray.org>
On 2/5/23 05:42, m@b wrote:
>>    texture { uv_mapping
>>     pigment {
>>      image_map {
>>       hdr "FILENAME.hdr"
>>       gamma 1.5
>>       map_type 0
>>       interpolate 2
>>       once
>>      }
>>     }
>>    finish {emission 1}
>>    }
>>   interior { ior 1.0 }
>>   }
>>   no_shadow
>> }
>>
>> object { Environment scale 1000} // might have to adjust  😉
>>
> 
> Thanks for that. I am getting a patchy illumination, when I animate it 
> there is inconsistency between frames. Any thoughts?
> 
> The only change I made was to reduce the Environment gamma to 1, the 
> scene was over-illuminated at 1.5.

Bill W. - Is there a reason for using uv_mapping with map_type 0 over 
map_type 1 only in the image_map block? I think what you have OK, but 
it's not how I would have coded the mapping. :-)

Random thoughts / questions.
---------------------------

- With .exr and .hdr images the file gamma should always be left at 1.0. 
These files have values in both the [0,1) range and [1,1+]. This means 
any gamma other than 1.0 creates adjustments which move in opposite 
directions depending upon whether particular color channel values at a 
given pixel <1 or >=1. It 'should be' any .hdr, .exr file one finds out 
and about was written at a gamma of 1.0. IIRC, POV-Ray itself cannot 
write .hdr / .exr files at other than 1.0.

- With .exr and .hdr images, interpolation is I believe iffy. The image 
interpolation code was written for [0,1] ranges. I usually use no 
interpolation with high dynamic range images and move to higher 
resolution environment maps if need be. However, I've not 'really' 
looked at how the different interpolation options work with typical .exr 
and .hdr images.

- With respect to blotchiness frame to frame, remember, v3.7 introduced 
the radiosity high reproducibility option. Use High_Reproducibility / 
+HR on the command line or in the ini file. An more reliable alternative 
is to use single threads for each frame (+wt1). This, though, might lead 
one to manually break up the rendering of frames into buckets to make 
use of all your cores / threads.

- Puzzling to me - some of the dark grid lines on the screen flicker in 
and out of existence during the render...? Unsure why this would happen 
unless perhaps using method 3 anti aliasing? If using method 3 remember 
you need to specify the seed used (can't recall the ini/command line 
option +ss maybe?) to keep results consistent render to render.

Bill P.


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