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in news:3e9ae5d1@news.povray.org Will W wrote:
> So do you think they know what we know?
> I would hope so.
It may take some time, but in the end they will.
Though, sometimes I wonder why assumed_gamma is a Float and not a Bool.
Gamma_correction yes/no.
Ingo
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On 14 Apr 2003 14:11:34 -0400
ingo <ing### [at] tag povrayorg> wrote:
> Though, sometimes I wonder why assumed_gamma is a Float and not a
> Bool. Gamma_correction yes/no.
Because it is a correction value? IMHO, it is suposed to let you adapt
the image to the intended viewing conditions. I think I finally learned
how assumed_gamma is related to the typical "viewing gamma" on most
gamma tutorials like this one:
http://www.w3.org/TR/PNG-GammaAppendix.html)
If I'm not wrong, it works this way:
viewing_gamma = pov_output_gamma * display_gamma
where
pov_output_gamma = 1/(Display_Gamma_ini_setting/scene_assumed_gamma)
and display_gamma is the gamma corrections of your display.
So, with assumed_gamma 1.0 you end up with a viewing_gamma of 1.0,
suposing you have set properly your ini setting to the real gamma of
your monitor. The usual recommendation says you must use a "viewing
gamma" of 1.0 for bright environments, 1.25 for poorly light rooms, and
1.5 for really dark rooms.
Please, can someone confirm I'm not worng?
--
Jaime Vives Piqueres
La Persistencia de la Ignorancia
http://www.ignorancia.org
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in news:200### [at] ignoranciaorg Jaime Vives
Piqueres wrote:
> Please, can someone confirm I'm not worng?
>
You're not wrong.
There are two reasons why I sometimes wonder why there is no
"Gamma_correction yes/no" instead of assumed_gamma;
- assumed_gamma seems to generate a lot of confusion although the way it
works is technically correct.
- Working with POV-Ray is like working in a photo studio (even for outdoor
scenes) where you have full control over the lighting scheme and thus over
contrast range / distribution ('gamma').
Ingo
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"Gena" <obu### [at] mailcom> wrote in message
news:3E9AF410.968C320C@mail.com...
> 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.
I tend to leave assumed_gamma out. I should have learned enough about all
this by now but it's still a stumbling block for me. I'm not sure why it is
suggested, dare I say required, in every scene file made now. I'm all for
the value of 1.0 for new renders and the reasons behind it, but what stops
me all the time is that it has seemingly become a requirement and yet I
thought it was still just a suggestion. A person might expect their
Display_Gamma, set in the main povray.ini file, to be all that is needed.
Until, of course, a scene file is rendered from another computer and then
adjustments made to the gamma for that reason.
Anyway, this is always the subject of debate and yet it still goes on even
after the documentation tries to settle it once and for all. I don't see any
solution unless assumed_gamma becomes mandatory (error without it) and
people follow the advice given for its usage.
All that said, Christoph has shown it can be done, obviously. Looked fairly
good to me.
Sure hope someone is willing to mess with that jumble I put together for the
"facade" of the cathedral. It's starting to look quite repulsive now. :-)
I don't seem to get much effort into this project these days... or any other
for that matter.
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Will W wrote:
> 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).
Did you mean "set the display_gamma to 2.2" in that last sentance?
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"Edward Coffey" <eco### [at] alphalinkcomau> wrote in message
news:3E9### [at] alphalinkcomau...
> Will W wrote:
> > 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).
>
> Did you mean "set the display_gamma to 2.2" in that last sentance?
>
No, I meant what I said.
display_gamma only affects what POV sends to the screen. It's important to
have it right so you get the right feedback when you're developing textures.
Otherwise it would be like painting with watercolors under one of those
bright bluish streetlights. Your end product would only look good under the
same streetlight-- it would look garish and ugly in daylight or in a home.
Of course you won't notice anything is wrong unless you can see your work on
somebody else's monitor (that has a different gamma).
Once display_gamma is set, if assumed_gamma is 1 then POV knows how to
adjust the the colors in the jpgs and other images it produces for a
"neutral" appearance. But if you *assume* that your audience is using only
PCs (like, maybe you're sending your portfolio to Microsoft) then you can
adjust assumed_gamma to the best value for that audience.
I think that's right. I'm pretty sure, and others seem to be agreeing with
this.
--
Will Woodhull
Thornhenge, SW Oregon, USA
willl.at.thornhenge.net
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Will W wrote:
> "Edward Coffey" <eco### [at] alphalinkcomau> wrote in message
> news:3E9### [at] alphalinkcomau...
>
>>Will W wrote:
>>
>>>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).
>>
>>Did you mean "set the display_gamma to 2.2" in that last sentance?
>>
>
>
> No, I meant what I said.
>
> display_gamma only affects what POV sends to the screen. It's important to
> have it right so you get the right feedback when you're developing textures.
> Otherwise it would be like painting with watercolors under one of those
> bright bluish streetlights. Your end product would only look good under the
> same streetlight-- it would look garish and ugly in daylight or in a home.
>
> Of course you won't notice anything is wrong unless you can see your work on
> somebody else's monitor (that has a different gamma).
>
> Once display_gamma is set, if assumed_gamma is 1 then POV knows how to
> adjust the the colors in the jpgs and other images it produces for a
> "neutral" appearance. But if you *assume* that your audience is using only
> PCs (like, maybe you're sending your portfolio to Microsoft) then you can
> adjust assumed_gamma to the best value for that audience.
>
> I think that's right. I'm pretty sure, and others seem to be agreeing with
> this.
display_gamma does not only affect what POV sends to the screen, it also
affects what it sends to the saved image file. I believe the connection
between 'assuming' your audience uses a certain gamma and the
'assumed'_gamma setting is completely unintended and misleading. When
rendering (not while doing the lighting and texturing on your system,
only during the final render) for an audience you believe to have a
certain display gamma, you set display_gamma to match it.
The way I understand it is you set assumed_gamma to 1 and leave it
alone, as others have said, it may be less confusing if it were a
boolean option to select whether gamma correction is applied to the
output. You develop your scene using display_gamma set to 1.8, and do
any renders designed to be viewed on similar systems the same way. When
you do a render designed to be viewed on systems with display systems
having a gamma value nearer 2.2, you change the display_gamma value to
2.2 for the final render. It looks bright on your monitor, but you send
it off to a PC user and it looks spot on when they view it on their
gamma 2.2 system.
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"Edward Coffey" <eco### [at] alphalinkcomau> wrote in message
news:3E9### [at] alphalinkcomau...
> display_gamma does not only affect what POV sends to the screen, it also
> affects what it sends to the saved image file.
Well yes, sort of. *If* assumed_gamma is used, then the display_gamma is one
of the factors used in determining the actual rgb values. I thought I had
said that, but it is hard to be clear. If assumed_gamma is turned off, then
display_gamma doesn't matter-- the file will be built with no gamma
correction at all. [see footnote]
> I believe
the connection
> between 'assuming' your audience uses a certain gamma and the
> 'assumed'_gamma setting is completely unintended and misleading.
Well, you are reading much more into something I intended as a useful
mnemonic than I thought would happen.
>
When
> rendering (not while doing the lighting and texturing on your system,
> only during the final render) for an audience you believe to have a
> certain display gamma, you set display_gamma to match it.
Yes, that seems to be what the dang thing is there for.
> The way I understand it is you set assumed_gamma to 1 and leave it
> alone, as others have said, it may be less confusing if it were a
> boolean option to select whether gamma correction is applied to the
> output. You develop your scene using display_gamma set to 1.8, and do
> any renders designed to be viewed on similar systems the same way. When
> you do a render designed to be viewed on systems with display systems
> having a gamma value nearer 2.2, you change the display_gamma value to
> 2.2 for the final render. It looks bright on your monitor, but you send
> it off to a PC user and it looks spot on when they view it on their
> gamma 2.2 system.
That sounds like an alternate approach that could work. However it isn't the
one that's implemented in POV-Ray.
There is another piece of this that isn't getting enough emphasis. The
design used in POV-Ray fits very well with image file formats like .png that
enable the client software to do the final adjustments. This isn't very
widely supported as yet, but browsers and image editors that use the png
gamma information are coming. POV-Ray is just ahead of the curve on this
one-- its method of handling gamma will make more sense as newer software is
adopted.
Yet another thing is that assuming that all PCs are 2.2 and all Macs are 1.8
is increasingly in error as time goes by. I'm not the only PC user with a
newfangled flatscreen whose gamma is now around 1.6 - 1.8.
[note] It occurred to me as I was rereading this that if I'm using POV to
prepare an image for a heightfield, I probably need to set assumed_gamma at
zero or the heightfield will be distorted. That might explain why some of my
experiments have been less than successful... hmmm.
--
Will Woodhull
Thornhenge, SW Oregon, USA
willl.at.thornhenge.net
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On Tue, 15 Apr 2003 00:38:37 -0700
"Will W" <wil### [at] NOSPAMwizzardsnet> wrote:
> [note] It occurred to me as I was rereading this that if I'm using POV
> to prepare an image for a heightfield, I probably need to set
> assumed_gamma at zero or the heightfield will be distorted.
This will give you a blank image! :)
--
Jaime Vives Piqueres
La Persistencia de la Ignorancia
http://www.ignorancia.org
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On 14 Apr 2003 16:53:33 -0400
ingo <ing### [at] tagpovrayorg> wrote:
> There are two reasons why I sometimes wonder why there is no
> "Gamma_correction yes/no" instead of assumed_gamma;
>
> - assumed_gamma seems to generate a lot of confusion although the way
> it works is technically correct.
Yes, but gamma in general generates a lot of confusion, isn't? ;)
> - Working with POV-Ray is like working in a photo studio (even for
> outdoor scenes) where you have full control over the lighting scheme
> and thus over contrast range / distribution ('gamma').
That's true, but I think you must have a way to adjust the image for
the viewing conditions (once the scene is finished), without having to
change all the lighting and texturing setup. Also, we need a standard
way to "syncronize" our viewing gammas when sharing code. The float
assumed_gamma give us this all, IMHO.
--
Jaime Vives Piqueres
La Persistencia de la Ignorancia
http://www.ignorancia.org
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