SO how does gamma work in POV these days?

When I try to use global_settings {assumed_gamma ...} I get an error message
telling me that this will not work any more and directing me to the
documentation. The documentation, however, touts Display_gamma and [quote]"the
new assumed_gamma global setting"[end quote].

I can state confidently that the gamma that is actually put into my renders is
way too high -- every image I create is very bright with very little contrast.

None of the ini-files I can find has Display_gamma set so this should default to
2.2 (according to the documentation) which is about right judging from the
greyscale chart in the docs. I manually correct the images after-the-fact in a
graphics program (PhotoStudio 5.5 in case that matters) and they look about
right when I reduce gamma to about 50%.

(This is 3.7b29 - I've been following every beta since 3.6;
  Win2k3, but I get the same effect on my XP and S.08 boxes)

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Sven Geier <.sven.at.sgeier.dot.net.nospamplease> wrote:
> I can state confidently that the gamma that is actually put into my renders is
> way too high -- every image I create is very bright with very little contrast.

  This is actually something I would like to know as well. As far as
I remember all POV-Ray 3.7 betas have used by default a much brighter gamma
than POV-Ray 3.6 uses by default, and nowhere have I seen an explanation
for this. This means that all scenes will render very differently in 3.7
than they do in 3.6, unless you specifically go and specify an assumed_gamma
when rendering with 3.7.

  Why was the default gamma changed so drastically in 3.7 compared to 3.6?
Why can't the default gamma be the same in both? Having a drastically
different default is only going to cause problems, as scenes will render
very differently.

-- 
                                                          - Warp

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"Sven Geier" <.sven.at.sgeier.dot.net.nospamplease> wrote in message 
news:web.49089f15440ec5fc5b4449250@news.povray.org...
> SO how does gamma work in POV these days?

I can only comment about what works for me ....

The scene I'm working on right now has this in the globals block:

#if (version < 3.7)
    assumed_gamma 2.2
#end

with Display_Gamma=2.5 in quickres.ini  my scene renders the same in 3.6.1 
and 3.7 beta's

Jim

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I noticed this today.  I received an error about gamma when rendering an image
with the version set.  I turned off the version information and the the image
created was overexposed.

"Jim Holsenback" <jho### [at] hotmailcom> wrote:
> with Display_Gamma=2.5 in quickres.ini  my scene renders the same in 3.6.1
> and 3.7 beta's

Okay, I tried this, expect I put the Display_Gamma in povray.ini.  However, it
still was pretty bright.  I tried "Display_Gamma=1.0" instead and everything is
darker, more like what I expect.  I also tried 1.8 (MAC), 2.2 (Windows) and both
created an overexposed image.

Note that I'm using Vista.  I haven't tested with XP but I assume I'll get the
same results.

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"SafePit" <ste### [at] reids4funcom> wrote in message 
news:web.490e82ae66e3e89ea044b9730@news.povray.org...
>I noticed this today.  I received an error about gamma when rendering an 
>image
> with the version set.  I turned off the version information and the the 
> image
> created was overexposed.
>
> "Jim Holsenback" <jho### [at] hotmailcom> wrote:
>> with Display_Gamma=2.5 in quickres.ini  my scene renders the same in 
>> 3.6.1
>> and 3.7 beta's
>
> Okay, I tried this, expect I put the Display_Gamma in povray.ini. 
> However, it
> still was pretty bright.  I tried "Display_Gamma=1.0" instead and 
> everything is
> darker, more like what I expect.  I also tried 1.8 (MAC), 2.2 (Windows) 
> and both
> created an overexposed image.

I think you got it wrong!

There are two parts for this .....

The Display_Gamma=XX goes in the command line box, or in quickres.ini file. 
From the top toolbar select Tools/Edit resolution INI file.  The entry 
differes from display to display. My value is 2.5 yours may be the same or 
it may not. The other piece is in your scence source file ....

#if (version < 3.7)
    assumed_gamma 2.2
#end

Cheers Jim

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Sven Geier wrote:
> When I try to use global_settings {assumed_gamma ...} I get an error message
> telling me that this will not work any more and directing me to the

I think you mean a warning message? It should not be an error (errors halt
parsing).

The gamma changes are covered in the release notes. I've once summarized
them in message http://news.povray.org/4891a3cf$1@news.povray.org.

-- Chris

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"Jim Holsenback" <jho### [at] hotmailcom> wrote:

> There are two parts for this .....
>
> The Display_Gamma=XX goes in the command line box, or in quickres.ini file.

It also works in povray.ini which, for Windows, is read first for global
options.  Quickres.ini would override the defaults.

ust to make sure, I also tested on the command line with the same results.
Display_Gamma=1.0 looked good, 1.8/2.2/2.5 were all blown out.

> From the top toolbar select Tools/Edit resolution INI file.  The entry
> differes from display to display. My value is 2.5 yours may be the same or
> it may not. The other piece is in your scence source file ....
> #if (version < 3.7)
>     assumed_gamma 2.2
> #end
>

Yep, I did add that option, although it doesn't make any difference in 3.7.  :-)

Thanks for the help Jim, it got me where I needed!  Even if I needed a different
value.

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"SafePit" <ste### [at] reids4funcom> wrote in message 
news:web.490faa2766e3e89ea044b9730@news.povray.org...
>> #if (version < 3.7)
>>     assumed_gamma 2.2
>> #end
>>
>
> Yep, I did add that option, although it doesn't make any difference in 
> 3.7.  :-)

that's because assumed_gamma is not used in v3.7 anymore just Dispaly_Gamma 
.....

like chris said in his post, you should read release notes
http://news.povray.org/4891a3cf$1@news.povray.org

Cheers

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An easy way to fix this is to add these to the end of your master POVRAY.INI 
file

; Picture brightness
Display_Gamma=1
File_Gamma=1

For me the only setting that makes "normal" looking pictures is 1.0, higher 
values look to bright/washed out.

Sorry if you don't agree but it works best for me...

"Sven Geier" <.sven.at.sgeier.dot.net.nospamplease> wrote in message 
news:web.49089f15440ec5fc5b4449250@news.povray.org...
> SO how does gamma work in POV these days?
>
> When I try to use global_settings {assumed_gamma ...} I get an error 
> message
> telling me that this will not work any more and directing me to the
> documentation. The documentation, however, touts Display_gamma and 
> [quote]"the
> new assumed_gamma global setting"[end quote].
>
> I can state confidently that the gamma that is actually put into my 
> renders is
> way too high -- every image I create is very bright with very little 
> contrast.
>
> None of the ini-files I can find has Display_gamma set so this should 
> default to
> 2.2 (according to the documentation) which is about right judging from the
> greyscale chart in the docs. I manually correct the images after-the-fact 
> in a
> graphics program (PhotoStudio 5.5 in case that matters) and they look 
> about
> right when I reduce gamma to about 50%.
>
> (This is 3.7b29 - I've been following every beta since 3.6;
>  Win2k3, but I get the same effect on my XP and S.08 boxes)
>
>

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