the basecurve is applied before the input color profile. that means you'll
distort the values with at least a matrix transform after mapping through
the curve. you'll do the same again for the output profile, then rgb
values will be measured by the color picker. quite possible that there will
be some computation errors piling up (are you using a lot of lut profiles?).
-jo
On Wed, Jul 17, 2013 at 1:36 PM, Torsten Bronger <
[email protected]> wrote:
> Hallöchen!
>
> Marie-Noëlle Augendre writes:
>
> > [...]
> >
> > Currently, I'm obliged to deactivate the basic curve as all my
> > images seem to picture lobsters instead of tennis players (or
> > whatever people I'm shooting): all the skin tones are very, very
> > red.
>
> For my camera, the enhanced colour matrix intensifies reds, too,
> compared to the standard matrix. But my own measurements confirmed
> this. Well, they make deep reds darker. But skin tones are
> practically untouched.
>
> And yes, the basecurve intensifies some already intensive colours
> even more. Sometimes, removing the leftmost point of the basecurve
> helps -- just drag it out of the plot to the left.
>
> But:
>
> I played around with it now, and find the basecurve's behaviour a
> little bit suspicious. I don't know whether this is intended
> behaviour though. Steps to reproduce:
>
> 1. Download
> https://bob.ipv.kfa-juelich.de/bronger/nex7_calibration/DSC02310.ARW
>
> 2. Import this RAW in DT.
>
> 3. Set up colour picker areas on patches L17 (red) and GS23 (black).
> Use the "RGB" mode to display values.
>
> 4. Now switch on and off basecurve and see how the green channel
> value is mapped from similar values to totally different values
> by the basecurve.
>
> Now, this may simply mean that I have not understood what basecurve
> actually does. I thought it was applied as a tone curve to the RGB
> channels separately. But this clearly is here not the case.
>
> Interestingly enough, there are three ways to eliminate this odd
> mapping:
>
> * You may switch the input profile from any matrix (standard or
> enhanced) to linear RGB.
>
> * You may switch the display profile from sRGB to linear.
>
> * You may remove the lowest control point of the basecurve.
>
> The latter two make me think that it is some sort of rounding
> error. The green value is clipped to zero, and the sRGB gamma
> cannot recover it anymore.
>
> So, is it a bug?
>
> Tschö,
> Torsten.
>
> --
> Torsten Bronger Jabber ID: [email protected]
> or http://bronger-jmp.appspot.com
>
>
>
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