Will W wrote:
> "Edward Coffey" <eco### [at] alphalinkcomau> wrote in message
> news:3E9### [at] alphalinkcomau...
> 
>>Will W wrote:
>>
>>
>>>That sounds like an alternate approach that could work. However it isn't
>>
> the
> 
>>> one that's implemented in POV-Ray.
>>
>>I maintain that it is.
>>
> 
> <snip good example>
> 
> Yes, you can force POV to do it this way. But it is not the way the gamma
> tools were desigend to work.
> 
> Here's a counter example: Roll the clock forward about two years. In 2005
> you do up some wallpaper on your trusty old Mac with its gamma of 1.8 and
> send it tou your friend who is still using her trusty old PC with its gamma
> of 2.2. She emails you an immediate response saying that she's delighted,
> the colors are so vibrant! Neither of you think about gamma.
> 
> Why is this? Where has the gamma problem gone to?
> 
> It went into history. Although neither you nor your friend have updated your
> hardware in quite a while, you are both staying current with software and
> recent trends. So naturally you sent her the image in a lossless compression
> ..png file, which is so much better than the lossy old jpg files everybody
> used to use. The png file also carries the gamma information so it can tell
> whatever machine it ends up on how to best display itself. No problems.
> 
> *That* is what POV's gamma system is designed for. Eternal universality--
> what a concept.

You are quite correct that with file fomats that record the gamma of the 
stored image this problem disappears altogether, you can render at a 
gamma of 1.8, your friend's software sees that the image has a recorded 
gamma of 1.8 and does the necessary conversions to display it properly 
on their gamma 2.2 system. Of course, using such gamma aware software 
will result in correct display of all the PNG images I make using the 
procedures I have described here. These procedures are not 'forcing' POV 
to work in any weird and unnatural way, they are simply using the 
features to do the job they were designed for - to get around the 
limitations of non gamma-aware formats while not causing any detriment 
when using gamma-aware formats. I am curious to see a concrete example 
of how you believe the gamma controls should be used *today*, since the 
only suggestion I've seen is changing assumed_gamma from 1 to 2.2 when 
changing the target from a gamma 1.8 system to a gamma 2.2 system, which 
results in effects opposite to those which are desired.

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"Edward Coffey" <eco### [at] alphalinkcomau> wrote in message
news:3E9### [at] alphalinkcomau...

<snip to chase>

> I am curious to see a concrete example
> of how you believe the gamma controls should be used *today*, since the
> only suggestion I've seen is changing assumed_gamma from 1 to 2.2 when
> changing the target from a gamma 1.8 system to a gamma 2.2 system, which
> results in effects opposite to those which are desired.

First, that was not the suggestion. Check out the POV docs-- they are good
reading. Combined with earlier messages in this thread, they do an excellent
job of describing the hows and whys of POV's approach to gamma.

Second, your curiosity will have to wait quite a long while. See my response
to Christoph Hormann. Basically I feel everything that needs to be said
about the subject has been said  quite adequately-- people have what's
needed to make informed decisions.

Thank you for the conversation.


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

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Will W wrote:
...
> Basically I feel everything that needs to be said
> about the subject has been said  quite adequately-- people have what's
> needed to make informed decisions.
...

I couldn't agree more.

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Gena wrote:
> 
> 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.

Attached is a rendering I did with assumed_gamma 1 and Christoph's 
latest version.  I used the chart in the POV docs and decided that my 
monitor's gamma is 2.6.  So I set this as the display gamma in my master 
ini.  I rendered to a png file and that is what is attached.  Now this 
rendering looks overexposed on my monitor.  Presumably it looks good on 
yours?

To get a rendering that looks nice and saturated and contrasty I need to 
set my display gamma at more like 1.6.  So I am still not clear on 
whether the textures are wrong or if my display gamma value does not 
match the gamma value for my monitor.

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Attachments:
Download 'v016.png' (390 KB)

Preview of image 'v016.png'

Jim Charter wrote:
> Attached is a rendering I did with assumed_gamma 1 and Christoph's 
> latest version.  I used the chart in the POV docs and decided that my 
> monitor's gamma is 2.6.  So I set this as the display gamma in my master 
> ini.  I rendered to a png file and that is what is attached.  Now this 
> rendering looks overexposed on my monitor.  Presumably it looks good on 
> yours?

Note that because this is a PNG file, and PNG stores gamma information, 
if the recipient's newsreader/image-viewer handles gamma correctly and 
everything is properly configured, they should see the image exactly as 
you see it on your monitor.

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Jim Charter wrote:

> Attached is a rendering I did with assumed_gamma 1 and Christoph's
> latest version.  I used the chart in the POV docs and decided that my
> monitor's gamma is 2.6.  So I set this as the display gamma in my master
> ini.  I rendered to a png file and that is what is attached.  Now this
> rendering looks overexposed on my monitor.  Presumably it looks good on
> yours?

It doesn't. I think I see the same as you - overexposed image.
I don't have that clever PNG viewer yet :( It makes sense to use
PNG only if people have gamma-aware viewers. I doubt if anybody
has it.

First of all we have to tune fog. It's too thick right now. The fog
is one of the components in that problem. If you'll render image
without fog it won't be so overexposed.

> To get a rendering that looks nice and saturated and contrasty I need to
> set my display gamma at more like 1.6.  So I am still not clear on
> whether the textures are wrong or if my display gamma value does not
> match the gamma value for my monitor.

That was also confusing to me. Eventually I decided don't use that table
from POV docs but rely completely on my feeelings :) As a result I defined
Display_Gamma as 1.8 instead of 2.2 from that table.

So just use Display_Gamma which suits fine to your feelings :) That's all I
can recommend for now.

Gena.

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"Jim Charter" <jrc### [at] aolcom> schrieb im Newsbeitrag
news:3e9cceec@news.povray.org...
> Gena wrote:
> >
> > 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.
>
> Attached is a rendering I did with assumed_gamma 1 and Christoph's
> latest version.  I used the chart in the POV docs and decided that my
> monitor's gamma is 2.6.  So I set this as the display gamma in my master
> ini.  I rendered to a png file and that is what is attached.  Now this
> rendering looks overexposed on my monitor.  Presumably it looks good on
> yours?
>
> To get a rendering that looks nice and saturated and contrasty I need to
> set my display gamma at more like 1.6.  So I am still not clear on
> whether the textures are wrong or if my display gamma value does not
> match the gamma value for my monitor.
>
>

sorry, I do not want to disturb 'cause I really don't have the time to join your
project (but I really liked the idea) and I think all important things about gamma
are already mentioned and I do also completely agree with Christoph about
the importance of assumed_gamma 1.0, BUT it seems there is still confusion.
So I have simply done a search'n'replace on ALL files to remove EVERY
ambient statement, did rise the radiosity brightness to 0.85 and did render
it with display gamma of 2.2 (and Jim, do not trust that poor test so much,
2.2 is the typical value for a crt monitor and for a tft and a mac it is usually
lower). Oh, one more thing, note that the texture include files have (for
historical reasons, I guess) also - sometimes quite high - ambient values, so
it is not a good idea to use them directly, so I have also changed the
T_Gold3C used for the cross.
I think with a little tuning of some diffuse values this is the way to go.

The changed files are Stpaul.inc, entrance.inc and ManOnSlip.inc. I guess you
can apply those small changes very quickly but if I should post them I can do.

Just a final note on the png file format: the ability of png to store a gamma chunk
does not mean that every png file contains gamma information. PoV adds the
gamma chunk but e.g. the program Jim did use to create the texture of his pretty
little figure does not.

so long
-Ive

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Attachments:
Download 'capriccio.png' (242 KB)

Preview of image 'capriccio.png'

Jim Charter wrote:
> 
> [...]
> 
> Attached is a rendering I did with assumed_gamma 1 and Christoph's
> latest version. 

No.  My version does not contain fog and removes all ambient finishes from
the textures.  Apart from that you also seem to use a different light
source than i set up (the area light is too large).

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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Hi
Well that's taking shape.
I just found what was disturbing me about that image: the boat is tilted.
I checked on original painting and I don't feel that.
I'm living in a harbour and I see a lot of boats.
That tilting make me think of a leaking and slowly sinking boat.

Marc

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Hi all.
Here is a new boat.
I've also made some adjustments to boat 1
(translations and scaling).
Boat_2.inc and the modified capriccio.pov
posted in p.s.b-f.
Bye.

Txemi Jendrix
http://www.txemijendrix.com

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Attachments:
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