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Hi there,
I wonder if anyone could explain why the same pov script produces
different looking images between 3.6 and 3.7 beta ? The images are :
http://www.piritipany.com/spiralramp.jpg 3.6 version
http://www.piritipany.com/spiralramp_v7.jpg 3.7beta version
The render settings are exactly the same.
The 3.6 version is better IMHO.
Any help would be appreciated
Cheers
Rob Richards
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Rob Richards <ari### [at] btinternet com> wrote:
> Hi there,
>
> I wonder if anyone could explain why the same pov script produces
> different looking images between 3.6 and 3.7 beta ? The images are :
>
> http://www.piritipany.com/spiralramp.jpg 3.6 version
>
> http://www.piritipany.com/spiralramp_v7.jpg 3.7beta version
>
> The render settings are exactly the same.
>
> The 3.6 version is better IMHO.
>
> Any help would be appreciated
>
> Cheers
> Rob Richards
assumed_gamma?
--
Carlo
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Doh!
I should have checked the release notes! latest beta has gamma
correction on by default. That was the reason
Cheers
Rob
On Sat, 17 Jan 2009 14:04:17 +0000, Rob Richards
<ari### [at] btinternetcom> wrote:
>Hi there,
>
>I wonder if anyone could explain why the same pov script produces
>different looking images between 3.6 and 3.7 beta ? The images are :
>
>http://www.piritipany.com/spiralramp.jpg 3.6 version
>
>http://www.piritipany.com/spiralramp_v7.jpg 3.7beta version
>
>The render settings are exactly the same.
>
>The 3.6 version is better IMHO.
>
>Any help would be appreciated
>
>Cheers
>Rob Richards
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Rob Richards <ari### [at] btinternetcom> wrote:
> http://www.piritipany.com/spiralramp.jpg 3.6 version
> http://www.piritipany.com/spiralramp_v7.jpg 3.7beta version
First thing I notice is the significant difference in brightness. First thing
that comes to my mind is "gamma".
Comparing your images, it looks like your 3.6 image is gamma-corrected for a
typical PC display gamma (something like 2.2), while your 3.7 image has no
gamma correction applied.
3.7 sees a stronger separation between render engine and "frontend", and in this
context gamma correction has been revised to get it completely out of the
engine.
I think the current mechanism is still far from intuitive. Try setting
assumed_gamma to 2.2, and maybe add a "version 3.6;" statement; pay attention
to the warning messages output by POV-Ray regarding these settings (you don't
have to heed them, but they may give you hints).
The other issue I see in the 3.7 shot are dark bands on the background, but I
guess these are just reflections that are not as prominent in the 3.6 shot due
to the gamma correction stuff.
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Rob Richards wrote:
> Doh!
>
> I should have checked the release notes! latest beta has gamma
> correction on by default. That was the reason
>
> Cheers
> Rob
>
the docs need to be updated to reflect this, I think:
http://www.povray.org/documentation/view/3.6.1/260/
Yet clearly in my scenes the Display_Gamma has an effect.
Display_Gamma=2.2 : scene renders bright
Display_Gamma=1.0 : scene renders darker (like 3.6 without assumed_gamma)
Display_Gamma=0.45: scene renders quite dark
"For scene files that do not contain an assumed_gamma global setting the INI file
option Display_Gamma will not have any affect on the preview output of POV-Ray or for
most output file formats. However, the Display_Gamma value is used when creating PNG
format output files, and also when rendering the POV-Ray example files (because they
have an assumed_gamma), so it should still be correctly set for your system to ensure
proper results. "
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Dan Connelly wrote:
> the docs need to be updated to reflect this, I think:
> http://www.povray.org/documentation/view/3.6.1/260/
Why would you update the 3.6.1 docs to reflect 3.7 beta behavior? ;-)
It has been said multiple times in these groups that the release notes are
what you should be looking at for 3.7 *beta*. The download page also tells
you to read the release notes. Please do!
Thorsten
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Thorsten Froehlich wrote:
> It has been said multiple times in these groups that the release notes
> are what you should be looking at for 3.7 *beta*. The download page also
> tells you to read the release notes. Please do!
>
> Thorsten
Whoops! I was redirected to the 3.6.1 docs from:
http://www.povray.org/beta/documentation
I should have caught that...
From the beta 10 change list:
o If the scene language version is set to 3.7 (or not set at all), then
gamma correction will default to ON, with the value used being set by
the 'display_gamma' INI file setting. Note that in previous versions of
POV-Ray gamma correction was OFF by default but otherwise this is the
same.
o If the scene language version is set to earlier than 3.7, then gamma
will be OFF by default.
o Notwithstanding the above, if the keyword 'assumed_gamma' is present
in the scene's global_settings, then POV will take one of the following
actions:
a) if "assumed_gamma 2.2" is present, gamma correction will be turned
OFF and a warning issued. the same thing will happen if the value
specified is not 2.2 but happens to be the default for the platform
setting given to POV-Ray when it was compiled (e.g. Windows is 2.2).
b) if "assumed_gamma 1.0" is present, gamma correction will be turned
ON (if it's not already on) and in any case a warning will be issued.
c) if a value other than the above is specified, it is ignored and a
'possible error' message is issued.
You will note from the above that therefore it is no longer possible to
adjust the amount of gamma correction from a scene file. This is as
designed since scene files should be as much as possible be platform
independent, and the gamma of particular display hardware does not belong
in the scene file. If you really need to specify 'assumed_gamma' you can
do so in an INI file or on the command-line; however in those cases you
may as well just use 'display_gamma' in its place.
When writing file formats that support gamma specification, the inverse
of the assumed_gamma value will be embedded in the file headers, so that
an appropriately equipped display program can 'undo' the gamma correction
if it is so desired. This is as per previous versions of POV-Ray.
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Dan Connelly <djc### [at] yahoocom> wrote:
> Thorsten Froehlich wrote:
> > It has been said multiple times in these groups that the release notes
> > are what you should be looking at for 3.7 *beta*. The download page also
> > tells you to read the release notes. Please do!
> >
> > Thorsten
>
>
> a) if "assumed_gamma 2.2" is present, gamma correction will be turned
> OFF and a warning issued. the same thing will happen if the value
> specified is not 2.2 but happens to be the default for the platform
> setting given to POV-Ray when it was compiled (e.g. Windows is 2.2).
Sorry for the trivial question but
- I've tried ot used assumed_gamma 2.2 in the pov file
- I've tried ot used Display_Gamma=2.2 in the pov file
- I've tried to add it to the povray command-line "Display_Gamma=2.2"
- I've tried to add it to the povray command-line "Display_Gamma=2.2
File_Gamma=2.2" (like in scenes/incdemo/glasses/glass.pov)
Without any luck.
I've also searched the source code for it but so far i'm not expert in using the
defaults, but the changelog mentions "Added "File_Gamma" INI option" which i
have not found at the moment.
Any hint?
Thanks a lot in advance.
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> Sorry for the trivial question but
> - I've tried ot used assumed_gamma 2.2 in the pov file
> - I've tried ot used Display_Gamma=2.2 in the pov file
> - I've tried to add it to the povray command-line "Display_Gamma=2.2"
> - I've tried to add it to the povray command-line "Display_Gamma=2.2
> File_Gamma=2.2" (like in scenes/incdemo/glasses/glass.pov)
>
> Without any luck.
Please be more specific:
(1) What is your actual problem?
(2) Are we talking about preview, or file output?
(3) If file output, what file type?
All these play a role; (1) because it determines what your gamma settings should
be; (2) because it determines which INI option to use; and (3) because the
actual output file gamma handling is done in the file-format-specific modules,
so problems may be specific to the file type you choose.
In addition, the behavior depends on which "#version" you choose in the scene
file.
> I've also searched the source code for it but so far i'm not expert in using the
> defaults, but the changelog mentions "Added "File_Gamma" INI option" which i
> have not found at the moment.
>
> Any hint?
All command line / INI options are defined in "processrenderoptions.cpp"; you
will find "Display_Gamma" there between "Display" and "Draw_Vistas", and
"File_Gamma" between "Field_Render" and "Final_Clock".
The values are read in using a framework; you will find references to the
"kPOVAttrib_XYZ" identifiers - e.g. "kPOVAttrib_DisplayGamma" and
"kPOVAttrib_FileGamma" - in the code actually evaluating these (in this case a
template in "renderfrontend.h"); from there, dig up the road to modules such as
png.cpp...
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"clipka" <nomail@nomail> wrote:
> > Sorry for the trivial question but
> > - I've tried ot used assumed_gamma 2.2 in the pov file
> > - I've tried ot used Display_Gamma=2.2 in the pov file
> > - I've tried to add it to the povray command-line "Display_Gamma=2.2"
> > - I've tried to add it to the povray command-line "Display_Gamma=2.2
> > File_Gamma=2.2" (like in scenes/incdemo/glasses/glass.pov)
> >
> > Without any luck.
>
> Please be more specific:
> (1) What is your actual problem?
I would like to render a file (generated using VMD ->
http://www.ks.uiuc.edu/Research/vmd/) and get the same rendering with 3.6 and
3.7 for comparison (i've used transparency on it and i cannot be sure where the
difference in rendering comes from Gamma or else).
> (2) Are we talking about preview, or file output?
Both, but preferably file output.
> (3) If file output, what file type?
targa (.tga).
> In addition, the behavior depends on which "#version" you choose in the scene
> file.
There is no define, only a header stating:
// POV 3.x input script : plot.pov
// try povray +W1590 +H1066 -Iplot.pov -Oplot.pov.tga +P +X +A +FT +C
#if (version < 3.5)
#error "POV3DisplayDevice has been compiled for POV-Ray 3.5 or above.\nPlease
upgrade POV-Ray or recompile VMD."
#end
> > I've also searched the source code for it but so far i'm not expert in using the
> > defaults, but the changelog mentions "Added "File_Gamma" INI option" which i
> > have not found at the moment.
> >
> > Any hint?
>
> All command line / INI options are defined in "processrenderoptions.cpp"; you
> will find "Display_Gamma" there between "Display" and "Draw_Vistas", and
> "File_Gamma" between "Field_Render" and "Final_Clock".
>
> The values are read in using a framework; you will find references to the
> "kPOVAttrib_XYZ" identifiers - e.g. "kPOVAttrib_DisplayGamma" and
> "kPOVAttrib_FileGamma" - in the code actually evaluating these (in this case a
> template in "renderfrontend.h"); from there, dig up the road to modules such as
> png.cpp...
ok, found them, but in fact i was not clear. I would like to keep the code as it
is, but how can i alter on the command line the behaviour ?
I would like to do:
(1) povray3.7 plot.pov ... -> 3.7 rendering with new gamma correction
(2) povray3.7 GammaParameter=2.2 -> 3.7 rendering with no gamma correction
This is in order to see if the differences i'm seing between 3.7 and 3.6
rendering comes only from the Gamma processing, or from something else (that i
should report in the forum and/or upstream to the VMD developper).
I could attach some files but each of them is around 18MB (uncompressed), so
before going to this, i'll prefer asking the simple point here:
- is it possible to tweak povray3.7beta to mimic the 3.6 behaviour (concerning
the gamma rendering, of course), with a command line or specicif .ini?
Thanks a lot for your work, patience and dedication (i'm using povray + vmd for
more than 8 years now, but i'm just starting contributing...).
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