"JimT" <nomail@nomail> wrote:
> Alain Martel <kua### [at] videotronca> wrote:
> > 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.
> > >>
> ..
> ..
> ..
> > When rendering older scenes with gamma other than 1, setting it to 1
> > don't detract, and often gives better results anyway.
>
> CRTs used respond non-linearly to electron beam intensity with, IIRC, low
> electron beam intensities stimulating the phosphors too little. Old operating
> systems/graphics display cards didn't add any correction factor so the only way
> to view images (on a CRT) in true colour was to increase the RGB values of dark
> colours using a gamma value of something like 2.4, when they were rendered. But
> the precise value depended on your monitor. Rendering an image to send to a
> printer might use a different gamma, maybe 1.0 (no correction). Though back
> then, colour printers were rather poor quality.
>
> For a short while, you could set a gamma value in Windows to suit your CRT
> monitor, then all images displayed on the monitor would display correctly -
> UNLESS they had already been gamma corrected, when dark colours would appear too
> bright.
>
> Thus, if you have old images that you rendered with a non-unit gamma, you should
> expect them to have dark colours that don't look dark enough on modern monitors,
> and if you re-render them with gamma = 1.0, they SHOULD appear more realistic.
> In other words, using old files, even if you specify an old POV-Ray version, you
> should probably re-set gamma to 1.0. I think this is why Clipka will give you a
> warning if you don't specify an assumed gamma.

See, I understand the reasoning behind having the assumed_gamma parameter, at
least for older scenes.  But what I don't get is, why is POV-Ray 3.7+ warn that
it will be a "Fatal error" in the future?

It seems to me that if you have
#version 3.7

(or higher)... then you should *by default* get assumed_gamma 1.0, and the
*only* reason POV-Ray should require this statement is if the user wants
something non-1.0 - for porting old pre-3.7 scenes, or special uses or whatever.

In my testing 1.0 does seem to be the default anyway, so, why force people to
include a command that sets the value to the default?

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