[argyllcms] Re: help with camera profile

  • From: Iliah Borg <ib@xxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 25 Jul 2012 11:29:36 -0400

Dear Graeme,

Thank you for your response.

>> only digital cameras, but scanning negatives as well. For negatives I obtain 
>> an L* -> L* table
>> by measuring the densities on the film shot of the Kodak N2 target, and the 
>> reference L* values
>> of the target are also known (and measured). The profile composed by refine 
>> is correct if used
>> as a stand-alone.
> Hmm. Note that calibration in the above context is a device space table (ie.
> it is to linearise the device values before mapping them to CIE using
> a matrix or cLUT).

Working with film, the calibration can be done against density (or L*, or Y); 
because the values can be measured directly from the film and compared to the 
target. I usually have a characteristic curve that I apply "manually" to the 
scan results before profiling. That takes a lot of stress from working with 
colour film, and solves b/w film completely - no profile is needed for b/w film 
anymore, refine works the trick in a very decent manner. I understand that I'm 
in a small niche here, most of the users do not have access to film recorders, 
and pre-exposed control strips are not readily available these days.

With digital there is no simple way to get density or L* values, and 
linearization in RGGB domain does not work too well. This seems to call for 
calibration after converting for CIE (by applying a matrix). However G1 channel 
is always closely enough related to Y, and linearization for just G1 (or, at 
least, G) takes care of light un-evenness, flare, and such.

Iliah Borg

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