Re: A discussion on accurate color ...
Re: A discussion on accurate color ...
- Subject: Re: A discussion on accurate color ...
- From: José Ángel Bueno García <email@hidden>
- Date: Wed, 25 May 2011 12:57:45 +0000
El día 24 de mayo de 2011 17:51, Eric Chan <email@hidden> escribió:
> Hi Jose,
>
> No, L*a*b* is not the ACR internal working space. (*)
Well, it was a doubt I have had in two last months.
>
> ACR's primary internal representation uses the ProPhoto/RIMM/ROMM RGB primaries. Exposure and brightness are based on the traditional logarithmic base 2 formulation (i.e., in stops). So boosting Exposure to +1, for example, means doubling the linear scene-referred values (i.e., increasing exposure by 1 stop). The white balance math (color temperature and tint) simply associates user-chosen white points (e.g., tungsten) to corresponding camera whites, by means of a profile's color matrix or matrices. More details (for developers) can be found in public DNG SDK on the Adobe site.
I had thought that linear values were compensated by Black, Brightness
and Contrast the way gamma correction do to simulate the non linear
response of human eye. Works fine as initial adjustment but I usually
letf those values to cero in scene-refered if adopt the ICC workflow
proposal.
>
> Cheers,
> Eric
>
> (*) ACR does use L*a*b* for some internal color difference estimates, e.g., for auto-calculated masks.
Then, are there color intenal color conversions or is something that
have mean in the interaction with camera profiles from DNG Profile
Editor.
Thanks, and excuse my ignorance about the tool I use everyday.
Jose Bueno
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