[argyllcms] Re: Camera matrix profile, adding ti3 perfect white data set

  • From: Elle Stone <l.elle.stone@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 22 Jan 2010 12:46:13 -0500

On 1/22/10, Klaus Karcher <lists@xxxxxxxxxxxxxxxxx> wrote:

>> Also, what might not be so
>> obvious, is that the profile made with the artificial data sets is
>> color-balanced, meaning r=g=b=neutral gray.
>
> Yes, but this might be misleading if the actual device response is
> different (e.g. due to offset or white balance errors).
>

>
> Klaus
>
With regard to device response, aren't camera sensors generally linear
in response? Mine seems to be. I did a couple of tests on my camera (a
Canon 400D/Rebel xti - not the greatest, not the worst digital
camera), taking a series of shots of a gray card, keeping light and
f-stop constant and successively reducing exposure time. As far as I
can tell, my camera response is linear across its usable dynamic
range. Indeed a problem I've had with the argyll profiles is that
colprof insists on concluding that the profile needs a gamma of 1.05
(for a linear raw shot). If I apply the argyll profile to the dynamic
range series, I have to apply an exactly opposite counter-corrective
gamma to get the shots to all line up as 256 128 64 32 16 etc. as they
should in a linear working space. So I use argyll to get the primaries
and then alter the profile TRC from gamma 1.05 to gamma 1.00.

Elle

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