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I've been reading this wiki page:
http://wiki.povray.org/content/HowTo:Fix_old_scenes_to_work_with_the_new_gamma_system
However, no matter what I try, if I want to reproduce 3.6 colors in 3.7 I *also*
have to use the gamma_color_adjust macro described on that page. The wording in
that article makes it seem like switching from color rgb to color srgb should be
enough. Can anyone else confirm this? Thanks.
Mike
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posfan12 <nomail@nomail> wrote:
> However, no matter what I try, if I want to reproduce 3.6 colors in 3.7 I *also*
> have to use the gamma_color_adjust macro described on that page. The wording in
> that article makes it seem like switching from color rgb to color srgb should be
> enough. Can anyone else confirm this? Thanks.
Anything that smoothly transitions from one color/shade to another
(such as in gradients or in the lighting of curved surfaces) will
look different depending on the assumed_gamma, regardless of whether
the specified colors look the same or not. (That's because they will
not look linear with assumed_gamma 1.0.)
Without going into the discussion of how accurate this is to reality,
the only way you can currently achieve the 3.6 results is by using
#version 3.6 or assumed_gamma 2.2.
(Ok, there's a third possibility, but it involves twiddling with the
finish parameters of all objects, and it's complicated.)
--
- Warp
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Am 15.07.2014 18:25, schrieb posfan12:
> I've been reading this wiki page:
>
>
http://wiki.povray.org/content/HowTo:Fix_old_scenes_to_work_with_the_new_gamma_system
>
> However, no matter what I try, if I want to reproduce 3.6 colors in 3.7 I *also*
> have to use the gamma_color_adjust macro described on that page. The wording in
> that article makes it seem like switching from color rgb to color srgb should be
> enough. Can anyone else confirm this? Thanks.
The article is intended for people wishing to migrate their scenes from
3.6- to 3.7-style gamma handling; in this process, it is virtually
/inevitable/ that you will need to:
"5. Toy around with overall brightness and/or brightness of individual
light sources, until you feel comfortable with the illumination. You may
also want to tweak some of the colours in your scene (both pigment and
light sources)."
If applying the gamma_color_adjust macro to all colours in the scene (in
addition to using the srgb keyword instead of srgb) happens to get you
exactly where you want to go, then that's perfectly ok; other scenes may
need other colour adjustments though.
If all you're after is making a 3.6 scene render the same in 3.7 as it
used to in 3.6, then by all means you should instead try to use
"#version 3.6" and "assumed_gamma 2.2"
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Am 15.07.2014 20:19, schrieb Warp:
> Anything that smoothly transitions from one color/shade to another
> (such as in gradients or in the lighting of curved surfaces) will
> look different depending on the assumed_gamma, regardless of whether
> the specified colors look the same or not. (That's because they will
> not look linear with assumed_gamma 1.0.)
>
> Without going into the discussion of how accurate this is to reality,
> the only way you can currently achieve the 3.6 results is by using
> #version 3.6 or assumed_gamma 2.2.
... which reminds me (thanks, Warp) that I once had this high up on my
agenda for stuff to address once the 3.7 release proper would be out,
but somehow lost it out of sight... must have run out of round tuits or
something.
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It's the wording of the article that confuses me.
For instance it says, "The title of this page and part of its contents are
somewhat outdated..." What is outdated in the article? Those are the steps you
have to take in POV 3.7. The article is meaningless if all you're using is POV
3.6.
Also, it says, "If you are still using version 3.6, or need more flexibility of
the gamma parameter:" Again, if all you're using is POV 3.6, then you shouldn't
be reading the article at all.
Lastly, the article says, "As of version 3.7.0.beta.41, POV-Ray natively
supports gamma-adjustment of color literals, provided they conform to the sRGB
standard..." But it does not provide any examples of the new technique.
Mike
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Also, is assumed_gamma now depracated? I was re-reading an old post and you said
it was in 3.7. It's an old post.
http://news.povray.org/4c6513b9%241%40news.povray.org
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Le 15/07/2014 21:26, posfan12 nous fit lire :
> Also, is assumed_gamma now depracated? I was re-reading an old post and you said
> it was in 3.7. It's an old post.
>
> http://news.povray.org/4c6513b9%241%40news.povray.org
>
>
Not at all, and quite the opposite: assumed_gamma when version is 3.7 is
rather mandatory (but should be assumed_gamma 1.0), otherwise there is a
warning.
--
IQ of crossposters with FU: 100 / (number of groups)
IQ of crossposters without FU: 100 / (1 + number of groups)
IQ of multiposters: 100 / ( (number of groups) * (number of groups))
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Am 15.07.2014 21:20, schrieb posfan12:
> It's the wording of the article that confuses me.
>
> For instance it says, "The title of this page and part of its contents are
> somewhat outdated..." What is outdated in the article? Those are the steps you
> have to take in POV 3.7. The article is meaningless if all you're using is POV
> 3.6.
For instance, the article suggests to "wait for the next beta" for the
"srgb" family of keywords, which has already appeared years ago.
It also suggests to "use '#version 3.7', and remove any 'assumed_gamma'"
statement, which will provoke a warning by now; you should instead
explicitly specify "assumed_gamma 1.0".
> Also, it says, "If you are still using version 3.6, or need more flexibility of
> the gamma parameter:" Again, if all you're using is POV 3.6, then you shouldn't
> be reading the article at all.
You indeed shouldn't use 3.6 any longer. However, some parts of the 3.7
gamma handling were already available in 3.6, by settig "assumed_gamma
1.0" - and using the gamma_color_adjust macro mentioned in the article
instead of the "srgb" family of keywords. The "only" problem back then
was that this gamma handling was implemented only half-heartedly,
apparently under the (utterly wrong) presumtion that this would be the
one and only gamma handling model used in the entire ecosystem in which
POV-Ray would be living. As a result, nobody actually really understood
how this gamma 1.0 mode worked (let alone how it was /supposed/ to
work), and using it was a pain in the ass. Especially when using 3rd
party input images for textures, people realized that /something/ was
wrong about the mode; it was probably then when many people started to
seriously dislike and even distrust this gamma mode, some even to this day.
"All" that 3.7 did was to establish a clear notion of how the gamma 1.0
model was supposed to work internally; what gamma models were used in
the outside world; draw a clear-cut line between POV-Ray's "inner world"
and the outside ecosystem (even where the outside ecosystem might happen
to use the same gamma model); and last not least implement conversion
algorithms right at those very borders, with optional tweakables where
appropriate.
Oh, and then, of course, identify (and in most cases address) stuff that
just /happened/ to be working better with the old gamma 2.2 (or 1.8 or
whatever) model, such as deciding /when/ to do anti-alias oversampling
(solved), or interpolating pigment gradients with strong brightness
contrast (still pending, as just reminded by Warp). Other - even closely
related - stuff turned out to be working better with the gamma 1.0 model
instead, such as actually /computing/ anti-aliasing, or interpolating
pigment gradients with strong colour contrast.
> Lastly, the article says, "As of version 3.7.0.beta.41, POV-Ray natively
> supports gamma-adjustment of color literals, provided they conform to the sRGB
> standard..." But it does not provide any examples of the new technique.
It does, in the code block right after the colon after that sentence.
It's what the "srgb" family of keywords does: They auto-convert the
specified sRGB colour components to whatever internal working gamma is
specified via "assumed_gamma". (When using "rgb" instead, it is assumed
that the colour components are already specified in accordance with the
assumed_gamma setting, and no conversion is applied whatsoever).
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Am 15.07.2014 21:26, schrieb posfan12:
> Also, is assumed_gamma now depracated? I was re-reading an old post and you said
> it was in 3.7. It's an old post.
>
> http://news.povray.org/4c6513b9%241%40news.povray.org
It is an old post indeed, and gamma handling in 3.7 pre-releases has
gone through various phases. Warp did a lot of - well, let's call it
"vocal criticism" ;-) - that did a lot good to shape and re-shape the
gamma handling as it is now.
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I did some further testing, and switching to srgb colors is fine and works just
as well as using the gamma_color_adjust macro. I don't know where I got the idea
that they produced differing results. Sorry for the trouble.
Mike
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