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> ..., and perhaps some adjusting for the contrast
> is needed...
How? Colors with assumed_gamma = 1 look washed-out.
If there is a way to increase contrast using that value let us
know.
I usualy use default values (I guess it's 2.2). If normal value
for assumed_gamma is 1 why it's not a default value?
Gena.
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"Gena Obukhov" <obu### [at] mail com> wrote in message
news:3E9A2071.A34BDF4A@mail.com...
> > ..., and perhaps some adjusting for the contrast
> > is needed...
>
> How? Colors with assumed_gamma = 1 look washed-out.
> If there is a way to increase contrast using that value let us
> know.
>
> I usualy use default values (I guess it's 2.2). If normal value
> for assumed_gamma is 1 why it's not a default value?
Just stepping in briefly-- has everyone adjusted their monitors according to
POV's specs?
What I know from recent reading is that PCs generally need a gamma of around
2.2 while Macs generally need one of 1.6, and somehow the assumed_gamma is
supposed to even things up. I *think* that means that assumed_gamma 1 will
be right for anybody who has adjusted their monitor as suggested in the POV
docs-- http://www.povray.org/documentation/view/128/ -- section 5.2.2.2.2.2
I spent an hour or so a week ago noodling through all the POV stuff I could
find on gamma, and doing the monitor adjustment as shown above. Although I'm
running a Dell Windoze box, my best gamma setting was at 1.4 -- *way*
different from what my reading led me to expect. But then my monitor is an
add-on flat screen.
Changing my monitor settings according to the above link has made my world
brighter and more colorful. I think before a group settles on an
assumed_gamma setting, it would be good if everyone calibrated their
monitors.
--
Will Woodhull
Thornhenge, SW Oregon, USA
willl.at.thornhenge.net
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in news:3e9a4670@news.povray.org Will W wrote:
> POV docs-- http://www.povray.org/documentation/view/128/ -- section
> 5.2.2.2.2.2
>
> Although I'm running a Dell Windoze box, my best gamma setting was at
> 1.4 -- *way* different from what my reading led me to expect. But
> then my monitor is an add-on flat screen.
I think I should add a note to the above mentioned paragraph that explains
that flatscreens don't have the same gamma-curve as CRT's and that thus
the method won't work (although the result may look resonable).
If you want to use flatscreens for graphics work you need one that is
designed for it.
Ingo
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Will W wrote:
> supposed to even things up. I *think* that means that assumed_gamma 1 will
> be right for anybody who has adjusted their monitor as suggested in the POV
> docs-- http://www.povray.org/documentation/view/128/ -- section 5.2.2.2.2.2
You are talking about Display_gamma which works together with
assumed_gamma. That gamma stuff was always a 'terra incognita'
for me :)
I think the main confusing definition in assuming_gamma is that
it 'resolves the problem with brightness of images on different
platforms'. But it's actually not true unless you use format containning
gamma info (e.g. PNG). If you use JPG it will be normal on PC but still
bright on Macintosh. So IMHO for viewing final image in non-gamma format
it doesn't help.
It helps when you render image on different platforms. In this case you
can set assumed_gamma=1 and set different Display_Gamma on different
platforms, for example 2.2 on PC and 1.8 on Macintosh. In this case POV-Ray
will create image based on your Display_Gamma settings. So actual value
which you have to play with is Display_Gamma not assumed_gamma which
should be usually equal 1.
Please correct me if I'm wrong :)
Gena.
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Great models! Especially for completely hand-made models.
We have a family already :)
There are some visible artefacts but I think you are
aware of it.
Keep on good job Jim :)
Gena.
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Gena Obukhov wrote:
>
> I removed 'ambient' from all textures (except cathedral facade),
> reduced radiosity brightness to 0.6, reduced 'diffuse' to 0.6 and
> reduced sky brightness.
> You can see the result below. Let's decide which value for
> assumed_gamma we should use.
> IMHO we should use something from the middle 1.4-1.6 even
> though such value is not right from theoretical point of view :)
Attached is my adaptation of the scene for assumed_gamma 1 - i did not try
to modify the textures apart from removing the ambient since they are
provisonal anyway. I changed the light position to be fairly conforming
with the painting (although this is tricky since the painting does not
really have consistent lighting...)
The modified scene is in p.b.s-f. (only the main scene, the other
modifications are only the removing of ambient in finishes)
Concerning assumed_gamma: not specifying it results in a linear output,
just as if assumed_gamma and display_gamma have the same value. As Tim
explained most people are used to design their textures for assumed_gamma
1.
Christoph
--
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 28 Feb. 2003 _____./\/^>_*_<^\/\.______
Post a reply to this message
Attachments:
Download 'capriccio9a.jpg' (86 KB)
Preview of image 'capriccio9a.jpg'
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Christoph Hormann wrote:
> As Tim explained most people are used to design their textures for
> assumed_gamma 1.
Do you have any hard data to support that assumption? I would think that
most people would use the default 2.2. I know, I have never used
anything else.
/Ib
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Gena Obukhov wrote:
> You can see the result below. Let's decide which value for
> assumed_gamma we should use.
I'm for the default 2.2.
/Ib
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On Mon, 14 Apr 2003 11:27:00 +0200, Ib Rasmussen <ib### [at] ibrasdk> wrote:
> > You can see the result below. Let's decide which value for
> > assumed_gamma we should use.
>
> I'm for the default 2.2.
Quoting manual from http://www.povray.org/documentation/view/216/
"Recommended value for assumed_gamma is 1.". Since it is likely representative
work of POV possibilites I would suggest follow this recommendation.
ABX
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Ib Rasmussen wrote:
>
> > As Tim explained most people are used to design their textures for
>
> > assumed_gamma 1.
>
> Do you have any hard data to support that assumption? I would think that
> most people would use the default 2.2. I know, I have never used
> anything else.
I have not investigated this matter into depth, could be interesting to
see what is commonly used in the IRTC scenes where source is given. At
the risk of repeating myself, 'assumed_gamma' is not meant as a value to
adjust to personal preferences, in fact it is not really necessary because
for technically correct results you would either use a value of 1 (meaning
correct gamma correction being applied) or give no value (meaning the
render result is linear and needs to be gamma corrected afterwards).
As explained before the huge advantage of using correct gamma adjustment
is that you can achieve realistic results by using 'correct' settings.
You can surely also achieve realistic pictures with linear gamma but this
will require adjusting the values to fit well with each other until things
look good. This will be immensely tricky when several people are working
on a scene - one will change the sky/light/radiosity settings to gain some
effects and all others will cry because their part no more looks good.
Christoph
--
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 28 Feb. 2003 _____./\/^>_*_<^\/\.______
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