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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