[argyllcms] Re: dispcal -a, when is viewing condition adjustment appropriate?

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 10 Nov 2010 03:49:07 +1100

Vallo Kallaste wrote:
I have never used the dispcal -a switch before and would like to
know when is it appropriate to use it? It certainly does something
and the results are not what I would call pleasant. Thus I'd like to
know if anybody is actually using it, when and why.
Also, is it right to assume that usage is constrained to sRGB, REC
709 and SMPTE 240M only? I.e. the usage is not appropriate when
calibrating to, say L* TRC?

If used at al, it needs to be used with some understanding of
what's going on in a wider sense. It makes use of a color appearance
transformation, which tries to preserve the appearance between
different viewing conditions. Exactly like using device profiles,
there needs to be some concept of source and destination viewing
conditions to be able to create a transform. To simplify things,
dispcal hides the source viewing conditions, and instead makes
some assumptions based on the target curve selected.
The assumption for REC 709 for instance, is that the source
is captured in a high brightness studio situation, while
your display may well be much dimmer, in a dim surround, therefore
calling for extra contrast (ie. effectively a higher gamma).

If the assumptions are incorrect, then the results will not
be reasonable. In a real color managed situation, this
will not be very relevant, since a display profile takes into
account the display calibration (effectively nullifying it),
and appearance preservation over viewing conditions is obtained
in creating perceptual gamut mappings.

Graeme Gill

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