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Re: A discussion on accurate color ...
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Re: A discussion on accurate color ...


  • Subject: Re: A discussion on accurate color ...
  • From: Eric Chan <email@hidden>
  • Date: Tue, 24 May 2011 13:51:57 -0400

Hi Jose,

No, L*a*b* is not the ACR internal working space. (*)

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.

Cheers,
Eric

(*) ACR does use L*a*b* for some internal color difference estimates, e.g., for auto-calculated masks.


On May 23, 2011, at 5:51 PM, José Ángel Bueno García wrote:

> Hi Barry, Hi Tom:
>
> The procedure at institution is avoid .tif or .jpg and shot raw from
> DSLR camera. Of course the raw is .dng.
>
> "I always ask the question: "What is the intended use of the data
> after acquisition?" can be the site of the institution, inkjet print
> or offset, so the DNG raw serves with the software tools that most of
> us have access: DNG Converter, DNG Profile Editor, PS CS,...
>
> Are you saying that GaMapICC isn't usefull? Or RoughProfiler. You can
> make conversions having the source of light for visualization in
> account.
>
> For what I know, lights at exposure spaces are "something near" D50
> (halogen tungsten), or the manufacturers try to get it. And what about
> the fast chromatic adaptation of human eyes?
>
> I reproduce art and photographic artifacs with flash, not with an
> almost monochromatic light as anyone can see in a SPD graph, and
> because is the less spiky light source (flash) that I know.
>
> In the other hand, is not L*a*b* the ACR working space?. L* for the
> exposure and brightness, a* for the color temperature and b* for the
> hue/shade (I think my translator don't works fine here).
>
> For me the less usefull illuminant is D65 that is high latitudes
> daylight most of the time, far away from 4950ºK in subtropical
> environments.
>
> Salud
>
> Jose Bueno
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  • Follow-Ups:
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      • From: José Ángel Bueno García <email@hidden>
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References: 
 >A discussion on accurate color ... (From: "Wheeler, Barry" <email@hidden>)
 >Re: A discussion on accurate color ... (From: Tom Lianza <email@hidden>)
 >Re: A discussion on accurate color ... (From: José Ángel Bueno García <email@hidden>)

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