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That was great to read. Dang it all! So I've misinterpreted the
assumed_gamma and display_gamma meanings all this time!? I was going by
a assumed_gamma 2.2 being needed to equal the display_gamma, not a 1.0
multiplied by 2.2 kind of way (is that even right?). I know my monitor
gamma correction goes from light to dark based upon 1.0 is normal
setting, less than one is darker, more than one is lighter; so this
would be opposite that.
If I ever used assumed_gamma in a scene it has been 2.2 and then up or
down from there. I'll check this out and see how it all looks compared.
What's odd is that if no global_settings gamma is set at all then
shouldn't the image appear as if assumed_gamma were 1.0? I've never seen
a obvious lightened-up image if so.
Thanks for the good reference page.
"John M. Dlugosz" wrote:
>
> I've written a tutorial/explaination/guide to POV's Gamma issues and
> features. Initial draft and samples are up at
> http://www.dlugosz.com/POV/Gamma/ .
>
> Comments and corrections welcome.
>
> --John
--
omniVERSE: beyond the universe
http://members.aol.com/inversez/POVring.htm
mailto:inv### [at] aol com?PoV
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I'm not sure what really happens if Displayed_Gamma is not specified. The
source code
has a default value noted in the configuration header, but the docs indicate
that gamma correction
has to be "enabled" or it works like older versions.
If assumed_gamma equals Displayed_Gamma, which it is if Displayed_Gamma is
defaulting to 2.2 for you, then the gamma correction function does nothing.
Adjusting the value in the scene file shifts the response curves, the same
as if you post-processed the image in PhotoShop by dragging the middle
handle in Levels. And it's the =ratio= between the two numbers that
matters, unless you are saving the Displayed_Gamma in the output file.
If you trace with 1.0, you will indeed get different colors! The response
curve of your medum is different. So you will need to build your scene that
way from scratch, for new work, picking colors and lights to match this
situation. The advantage is that now your output references a standard
calebration, and can be adjusted to exactly counter the response curves of
any given display.
--John
Bob Hughes wrote in message <36E6E341.49DB2518@aol.com>...
>That was great to read. Dang it all! So I've misinterpreted the
>assumed_gamma and display_gamma meanings all this time!? I was going by
>a assumed_gamma 2.2 being needed to equal the display_gamma, not a 1.0
>multiplied by 2.2 kind of way (is that even right?). I know my monitor
>gamma correction goes from light to dark based upon 1.0 is normal
>setting, less than one is darker, more than one is lighter; so this
>would be opposite that.
>If I ever used assumed_gamma in a scene it has been 2.2 and then up or
>down from there. I'll check this out and see how it all looks compared.
>What's odd is that if no global_settings gamma is set at all then
>shouldn't the image appear as if assumed_gamma were 1.0? I've never seen
>a obvious lightened-up image if so.
>Thanks for the good reference page.
>
>"John M. Dlugosz" wrote:
>>
>> I've written a tutorial/explaination/guide to POV's Gamma issues and
>> features. Initial draft and samples are up at
>> http://www.dlugosz.com/POV/Gamma/ .
>>
>> Comments and corrections welcome.
>>
>> --John
>
>--
> omniVERSE: beyond the universe
> http://members.aol.com/inversez/POVring.htm
> mailto:inv### [at] aolcom?PoV
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