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.

Post a reply to this message