POV-Ray : Newsgroups : povray.documentation.inbuilt : User:clipka assumed_gamma Server Time: 18 Jan 2019 00:59:49 GMT
  User:clipka assumed_gamma (Message 1 to 8 of 8)  
From: dick balaska
Subject: User:clipka assumed_gamma
Date: 20 Nov 2017 20:30:37
Message: <5a133b6d$1@news.povray.org>
Not an inbuilt, per se, but:

The bottom of this page
http://wiki.povray.org/content/User:Clipka/Gamma
says
" Change #version to 3.7.
Remove the assumed_gamma statement. "

When I do that, povray 3.7.2-alpha (github/master) says
" 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."

These statements conflict, yes?
-- 
dik


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From: clipka
Subject: Re: User:clipka assumed_gamma
Date: 20 Nov 2017 23:12:05
Message: <5a136145$1@news.povray.org>
Am 20.11.2017 um 21:30 schrieb dick balaska:
> Not an inbuilt, per se, but:
> 
> The bottom of this page
> http://wiki.povray.org/content/User:Clipka/Gamma
> says
> " Change #version to 3.7.
> Remove the assumed_gamma statement. "
> 
> When I do that, povray 3.7.2-alpha (github/master) says
> " 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."
> 
> These statements conflict, yes?

Um... er...

... well, it /does/ work (despite the warnings), doesn't it, and
besides, the section carries a note saying "Under Construction"... I was
just about to...

... ah, dang it - you got me there.

The section was written at a time before modern gamma handling was truly
finalized. I'm a bit surprised you didn't spot more errors ;)


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From: dick balaska
Subject: Re: User:clipka assumed_gamma
Date: 21 Nov 2017 00:22:00
Message: <5a1371a8$1@news.povray.org>
Am 11/20/2017 06:12 PM, also sprach clipka:

 > carries a note saying "Under Construction"

With a little work, I think you could get that in an even smaller font. ;)

> I'm a bit surprised you didn't spot more errors ;)
> 

Well I didn't actually *read* it.
I was trying to shut up the warning, couldn't remember the exact syntax, 
and thought it might be faster to google "povray assumed_gamma" than 
look at one of my own source files. ;)

But nowhere did you actually print
global_settings{assumed_gamma 1.0}
:)

-- 
dik


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From: Kenneth
Subject: Re: User:clipka assumed_gamma
Date: 21 Nov 2017 00:50:00
Message: <web.5a13778e72941d1089df8d30@news.povray.org>
I hadn't seen that otherwise-excellent page before, but I agree about the
strange "Remove assumed_gamma" statement. I have two theories about this: 1) The
statement may be outdated, from a time before v3.7x became more 'astute' about
handling legacy scenes. 2) Possibly it's CORRECT (?)-- maybe older v3.6 scenes
ARE just so out-of-whack re: 3.7x that *any* assumed_gamma would be wrong. But
that causes the 'no assumed_gamma' error, so *something's* not correct there.

Mention is made that older scenes will probably require lots of work of various
kinds anyway, to bring them fully up to date. That being the case, it would seem
logical to start with assumed_gamma 1.0 as the first 'fix.'

Something else I noticed...

-----
'Gamma Settings:'
 POV-Ray's gamma handling is governed by the following parameters:

 The 'gamma' scene file keyword applied to color values, which forces POV-Ray to
apply gamma decoding to individual colors.
-----
(No mention is made  of using 3.7x's 'srgb' colors-- as of version
3.7.0.beta.41-- instead of adding the 'gamma' keyword)

And in...

-----
'Getting Individual Colors Right:'
If you frequently pick colors, or feel more at home with defining colors by
pixel values rather than physical brightness levels, you can use the gamma
keyword to have POV-Ray do the computations automatically for you, e.g.:

#local MyColor = color rgb <255,128,0>/255 gamma 2.2;

This syntax also allows for using the sRGB transfer function; as the sRGB color
space has become quite widespread through the influence of the World Wide Web,
where it is the official standard, it is probably an even better bet than a
power-law function with a gamma of 2.2:

#local MyColor = color rgb <255,128,0>/255 gamma srgb;
-----

(These examples likewise don't mention 3.7x 's 'srgb' colors, so should another
example be included? Like so...)

#local MyColor = color srgb <255,128,0>/255 ; // As of version 3.7.0.beta.41


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From: clipka
Subject: Re: User:clipka assumed_gamma
Date: 21 Nov 2017 00:58:28
Message: <5a137a34$1@news.povray.org>
Am 21.11.2017 um 01:47 schrieb Kenneth:

> Something else I noticed...

... was already outdated by the time you pressed the "send" button ;)


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From: clipka
Subject: Re: User:clipka assumed_gamma
Date: 21 Nov 2017 01:05:08
Message: <5a137bc4$1@news.povray.org>
Am 21.11.2017 um 01:58 schrieb clipka:
> Am 21.11.2017 um 01:47 schrieb Kenneth:
> 
>> Something else I noticed...
> 
> .... was already outdated by the time you pressed the "send" button ;)

(Your post, that is. The Wiki article was /no longer/ outdated by that
time ;))


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From: Kenneth
Subject: Re: User:clipka assumed_gamma
Date: 21 Nov 2017 07:25:01
Message: <web.5a13d3a872941d1089df8d30@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:
> Am 21.11.2017 um 01:58 schrieb clipka:
> > Am 21.11.2017 um 01:47 schrieb Kenneth:
> >
> >> Something else I noticed...
> >
> > .... was already outdated by the time you pressed the "send" button ;)
>
> (Your post, that is. The Wiki article was /no longer/ outdated by that
> time ;))

So I see!! Hey, that's a good magic trick ;-)

Thanks for taking the time to write such an understandable and all-inclusive
gamma   primer for POV-Ray.

The *only* small addition I can think of that might be useful would be to
mention that most image-viewer apps-- even modern ones-- may not be showing the
*actual* embedded gamma of a PNG image. (I'm thinking of our discussions re:
I've's IC/Lilysoft app, which *does* show the proper embedded gamma, especially
when that gamma is wrong.) I would imagine that many POV-Ray users might jump to
the opposite conclusion (uh, like I did)-- that most apps are 'correct' and that
IC (or some other likewise-correct app) is actually at fault when a PNG's
embedded gamma is plain wrong.

I admit that this is probably a 'special case' scenario, one that most users
would almost never run into. But as a general note about PNG and the current
state of modern viewing apps, it seems appropriate.


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From: clipka
Subject: Re: User:clipka assumed_gamma
Date: 21 Nov 2017 14:44:48
Message: <5a143be0$1@news.povray.org>
Am 21.11.2017 um 08:21 schrieb Kenneth:

> The *only* small addition I can think of that might be useful would be to
> mention that most image-viewer apps-- even modern ones-- may not be showing the
> *actual* embedded gamma of a PNG image. (I'm thinking of our discussions re:
> I've's IC/Lilysoft app, which *does* show the proper embedded gamma, especially
> when that gamma is wrong.) I would imagine that many POV-Ray users might jump to
> the opposite conclusion (uh, like I did)-- that most apps are 'correct' and that
> IC (or some other likewise-correct app) is actually at fault when a PNG's
> embedded gamma is plain wrong.

I already added a hint about this in
http://wiki.povray.org/content/User:Clipka/Gamma#Getting_The_Output_Image_File_Right:

"The PNG file format (+FN) provides a means to inform reading
applications (e.g. file viewers) about the encoding gamma used, so
software may display the output image virtually identical regardless of
the encoding gamma you choose; however, this mechanism seems to be
falling out of favour."

Not the most explicit mention of that issue, I concede, but right now my
focus is on other stuff, so I'll leave it as is for now.


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