Le 2019-11-03 à 06:14, Le_Forgeron a écrit :
> Le 03/11/2019 à 07:07, Greg Kennedy a écrit :
>> POV-Ray 3.7 gives this warning if you try to trace a scene without assumed_gamma
>> set:
>>
>>>   Possible Parse Error: assumed_gamma not specified in this POV-Ray 3.7 or later
>>>    scene. Future versions of POV-Ray may consider this a fatal error. To avoid
>>>    this warning, explicitly specify 'assumed_gamma 1.0' in the global_settings
>>>    section. See the documentation for more details.
>>
>> My question is: Why will this become a fatal error, instead of just defaulting
>> to 1.0?  It seems like most people would *want* there to be some sensible
>> default, instead of breaking and having to add additional keywords to their
>> scenes.  I know I would, anyway.
>>
> 
> Because... IIRC, scenes before modern era where rather with CRT gamma,
> varying from 1.8 to 2.7; And it was wrong, physically, but it was the
> usage and the design used that. So you cannot fix them automatically by
> applying a 1.0 instead, or even a 2.4 everywhere.
> 
> And there is no way to guess the correct value.
> 
> What the message states is: for version 3.7 or greater, you should have
> an assumed_gamma (and hopefully 1.0). Ulterior version of software might
> consider that a 3.7 file without assumed_gamma is faulty. That's all.
> Nothing more, nothing less.
> 
> It does not stop you from parsing 3.6, 3.5 or smaller version of a
> scene. And then gamma handling is historical (and painful).
> 
> So, for 3.7+ scenes, take right now the habit of having an explicit
> assumed_gamma, always.
> 

When rendering older scenes with gamma other than 1, setting it to 1 
don't detract, and often gives better results anyway.

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