POV-Ray: Newsgroups: povray.general: difference in lighting between 3.6 and 3.7

POV-Ray : Newsgroups : povray.general : difference in lighting between 3.6 and 3.7		Server Time 29 Jul 2024 18:27:08 EDT (-0400)

From: stevenvh
Subject: difference in lighting between 3.6 and 3.7
Date: 8 Nov 2010 08:40:01
Message: <web.4cd7fcd96a6f79bac0721a1d0@news.povray.org>

With the betas of v3.7 I sometimes have noticable differences in lighting
compared to images rendered with v3.6. Will all betas for 3.7 behave in the same
way, and the final version too?
TIA
Steven

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From: Alain
Subject: Re: difference in lighting between 3.6 and 3.7
Date: 8 Nov 2010 11:33:24
Message: <4cd82654@news.povray.org>


> With the betas of v3.7 I sometimes have noticable differences in lighting
> compared to images rendered with v3.6. Will all betas for 3.7 behave in the same
> way, and the final version too?
> TIA
> Steven
>
>

Short: Yes.

Long: It's due to the way of handeling gamma. 3.7 computes colours in a 
linear space, then apply the gamma to the output file and preview. If 
the gamma is not set properly in the ini file(s), then the output gets 
bright or dark.
If you output to PNG, the file is writen using a linear space end gets a 
gamma chunk with the proper gamma information.

Do NOT use assumed_gamma when using 3.7.
It have very limited support, only 2 values are recognised, and will be 
completely droped in some future.


Alain

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From: stevenvh
Subject: Re: difference in lighting between 3.6 and 3.7
Date: 8 Nov 2010 11:45:00
Message: <web.4cd82843c4c1d86cc0721a1d0@news.povray.org>

Thanks for clarifying, Alain.

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From: clipka
Subject: Re: difference in lighting between 3.6 and 3.7
Date: 19 Nov 2010 12:45:33
Message: <4ce6b7bd$1@news.povray.org>

Am 08.11.2010 17:33, schrieb Alain:

> If you output to PNG, the file is writen using a linear space end gets a
> gamma chunk with the proper gamma information.

That's not really true; in 3.7, PNG is written with gamma encoding by 
default, too (depending on an ini file setting)- but you won't see any 
difference in brightness compared to linear encoding in most image 
viewers, because indeed gamma information is written to the file header.

BTW it's not even a good idea to use linear encoding for PNG, as it is 
more prone to banding artifacts (unless you use an unconventionally high 
bit depth), and may also look different than intended with a few image 
viewers that ignore the gamma information in the PNG header.

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From: SharkD
Subject: Re: difference in lighting between 3.6 and 3.7
Date: 14 Jan 2011 13:30:01
Message: <web.4d3095f5c4c1d86cd70fe6f50@news.povray.org>

"stevenvh" <nomail@nomail> wrote:
> Thanks for clarifying, Alain.

A few limited-case workarounds are listed here:

http://wiki.povray.org/content/HowTo:Fix_old_scenes_to_work_with_the_new_gamma_system

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