Ib Rasmussen wrote:
> 
> 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.

I think the majority of people simply go with the default of 2.2. I know,
I do.

-- 
Ken Tyler

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Ib Rasmussen wrote:
> 
> 
> 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.

It would depend on how many people have read the part of the manual that 
says "For new scenes, you should use an assumed gamma value of 1.0 as 
this models how light appears in the real world more realistically.". I 
have, so I use assumed_gamma 1.

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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 :)

What was the monitor_gamma used for creating these images? Unless 
everyone viewing them has monitors of that gamma value they are useless 
for comparison. Surely an assumed_gamma value should be chosen such that 
when someone renders the scene on their computer with the monitor_gamma 
set for their monitor, a ray calculated to have a color of <0.5, 0.5, 
0.5> is displayed as a grey perceived to have 50% of the monitor's full 
intensity. That value is 1.

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3E9### [at] ibrasdk...
> I'm for the default 2.2.

For what it's worth, I had until last year used the default 2.2, but after
having to switch monitors (CRT and flat) and running into gamma trouble, I'm
now all for assumed_gamma 1 and I don't regret it. Of course, textures and
lighting must be changed accordingly if they had been designed with
assumed_gamma 2.2 in mind.

G.


--

**********************
http://www.oyonale.com
**********************
- Graphic experiments
- POV-Ray and Poser computer images
- Posters

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"ingo" <ing### [at] tagpovrayorg> wrote in message
news:Xns### [at] povrayorg...
> in news:3e9a4670@news.povray.org Will W wrote:

> 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

Exactly so.

> and that thus
> the method won't work (although the result may look resonable).

No.

First you are contradicting yourself. If the results of the display_gamma
adjustment look more reasonable than they did before, then the system is in
better adjustment for your situation than it had been. Which is all that one
can hope to achieve no matter what type of display you've got.

It is true that the procedure given in the POV docs was designed to take
advantage of side effects of CRT technology-- on  a flat screen you don't
get the necessary blurring of raster lines that analog CRT phosphors
provide. That isn't a problem for me-- I just take off my glasses. Or you
can unfocus your vision to get the requisite blurring.

It is also true that the rate of change in brightness as one approaches the
extremes is different for flatscreens and CRTs, but that doesn't invalidate
the procedure. The procedure adjusts the central value of medium gray--
whether your whites are whiter and your blacks are blacker than someone
else's is a different thing entirely. And it doesn't even touch color
balance. (Paint Shop Pro has a color gamma calibration procedure that can
help with that).

> If you want to use flatscreens for graphics work you need one that is
> designed for it.

If I had everything I wanted, I'd be riding a powerful horse rather than
trudging along this muddy rut :-)

Thanks for your input.


--
Will Woodhull
Thornhenge, SW Oregon, USA
willl.at.thornhenge.net

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in news:3e9ac173@news.povray.org Will W wrote:

>> and that thus
>> the method won't work (although the result may look resonable).
> 
> No.

You're right, what I wrote is rather inaccurate, yet from your awnser I 
understand that you understood exactly what I meant. Guess I'll have to 
grow them pointy ears first, before I write that bit for the docs :)


Ingo

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Thanks very much, Gena! By jumping back and forth between what you've
written and the POV-Ray docs, I've learned a bit.

I've got my display_gamma set to 1.8, which is appropriate for my system,
which means that I've got POV's equivalent of an artist's studio with large
north-facing windows: a neutral environment for selecting colors and
brightness levels. When I use assumed_gamma 1, POV will use my display_gamma
without any further adjustment to correct the pixels it writes to the image
file. The result will be the best I can hope for in terms of viewabiltiy on
other systems. If I want to tune my jpgs to look their best on PC systems,
then I should set the assumed_gamma to 2.2 (and accept that fact that Mac
users will see a poorer image).

If I have chosen the .png format, POV will also write the appropriate gamma
correction factor into the image file. Then anybody who is using viewing
software that is smart about .png gamma corrections and correctly set up on
their system will see my image precisely the way I intended. But other than
in this situation, my work is going to be distorted on some other systems.

It seems to me that in a cooperative creation process, the people doing the
textures need to have their display_gamma settings correctly tuned for their
systems, and use assumed_gamma 1 in their output.

It also seems to me that in a cooperative situation, decisions on the
assumed_gamma level cannot be based on how jpgs look, since Macs and PCs and
other systems will always distort jpgs in different ways. The decisions need
to be made either on the basis of .png files displayed through a smart
viewer that is correctly configured for the individual system, or by sending
out .pov files that each contributor would render on their own (assuming
they have their display_gamma set correctly). Sending out sample .pov files
shouldn't be too difficult.

Does this sound right to you?



--
Will Woodhull
Thornhenge, SW Oregon, USA
willl.at.thornhenge.net

"Gena Obukhov" <obu### [at] mailcom> wrote in message
news:3E9A5D93.B10D1E84@mail.com...
> 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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"ingo" <ing### [at] tagpovrayorg> wrote in message
news:Xns### [at] povrayorg...
>
> You're right, what I wrote is rather inaccurate, yet from your awnser I
> understand that you understood exactly what I meant.

Uh, well... *now* I know that you know what I was talking about is so, yet
when I wrote that last message I wasn't sure that was the case.

But there are several people who have voiced an opinion about where to set
the assumed_gamma for a joint project. Including some who may be thinking
that the default value in one system-specific POV-Ray implementation is the
POV-Ray default used in all implementations on every platform.

So do you think they know what we know?
I would hope so.
But I feel I have cause to wonder about it.


--
Will Woodhull
Thornhenge, SW Oregon, USA
willl.at.thornhenge.net

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> What was the monitor_gamma used for creating these images? Unless

It was default value. I guess on my PC it's 2.2

So let's recap the discussion :)
From all those posts and POV-Ray doc we could make conclusion
that recommended assumed_gamma is 1. So let's use it.

If you feel that image looks too bright or too dark on your monitor
with assumed_gamma=1 try to adjust Display_Gamma parameter
which is monitor specific (I specified 1.8 for my monitor). Because
that parameter is placed in command line we don't have to have
gamma-specific sources for each platform.

Please, correct me if I'm wrong :)

Gena.

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Will W wrote:

> ...Does this sound right to you?

Totally agree :)
Let's use assumed_gamma=1 and adjust Display_Gamma
according to our monitors. Let's don't make any brightness
decisions on JPEG images let's render it on your platform
instead with your Display_Gamma settings.

Gena.

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