[argyllcms] Re: help with camera profile

  • From: Iliah Borg <ib@xxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 19 Jul 2012 09:41:28 -0400

On Jul 19, 2012, at 7:14 AM, Stephen T wrote:

> Hello,
> I have used ufraw, I have an IT8.7/2 and, after several attempts at camera 
> profiling, I don't use them anymore.
> 1. Ufraw is based on dcraw but it does some weird scaling of the linear TIFF 
> data.
> Output the same raw photo of the camera target as a linear TIFF in ufraw, 
> dcraw, DarkTable and in Raw Therapee.
> Compare the scanin results: ufraw is anomalous.
> Ufraw also lacks tools like RGB tone curves that are most useful for 
> rendering the output.

I agree that ufraw does not have an option for the output suitable for 
> 2. It is really difficult to control glare (flare) and get good uniformity of 
> REFLECTANCE when shooting in sunlight. An incident light meter is not 
> helpful. Check the average RGB around the edges of the target in ufraw. If 
> the variation is more than 2 or 3% then the profiling will likely have 
> problems.

To get raw values and to confirm the uniformity you can use RawDigger, 

> 3. The IT8.7/2 target has a good spread off patches but the Kodak paper has 
> flourescent whitening additives. The target white point will not be neutral 
> in direct sunlight (lots of UV).

Sensors have very low response to UV.

> 4. Digital cameras have good system linearity and a simple matrix profile 
> should be satisfactory.

The better is the camera the more linear is output, except, maybe, the last 
(brightest) stop. But the camera exposure meters are already calibrated to 
avoid using the brightest stop when possible.

Iliah Borg

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