[argyllcms] Re: Scaling of XYZ reference data for camera input profile
- From: Iliah Borg <ib@xxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Tue, 15 May 2012 12:26:38 -0400
On May 15, 2012, at 12:09 PM, Gerhard Fuernkranz wrote:
> Am 15.05.2012 16:27, schrieb Stephen:
>>
>> I have an idea to improve highlights for a camera input profile: can I scale
>> XYZ data linearly to match an increase in exposure?
>>
>> For example, +1 EV of exposure compensation = 2 x linear device RGB. Will
>> XYZ also increase by the same factor of two?
>
> XYZ is a linear light space, so the numbers are expected to scale linearly
> with intensity.
>
> I would wonder though, how accurate various cameras can realize the
> prescribed f-stops and shutter speeds, how well they are repeatable, and how
> uniform the steps between different adjacent f-stops and shutter speed are
> distributed in reality.
The biggest problem is flare in fact. The good profiling strategy is to shoot
in a way that prevents flare almost completely (but it is hard to achieve for
a casual user). Shoot a target, open RawDigger and check that the white patch
is close to saturation, about 90% of max value in raw. Once that is done, shoot
a series of images adjusting the exposure down 2 stops at a time, 3 times. That
allows to make a synthetic target covering 11 stops. More is rather useless as
flare is too strong.
--
Iliah Borg
ib@xxxxxxxxxxx
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