[argyllcms] Re: Problem chartread: "Need reflection spot, strip.......instrument doesn't support it"

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 03 Mar 2015 10:58:37 +1100

Per Nordlund wrote:

> I used -f D50M2 as
> FWA compensation. Is there any difference using only M2?

    FWA compensation works by adjusting your profile measurements
to match your viewing conditions, so by choosing an M2 condition,
you are assuming that your viewing environment is UV poor.

There shouldn't be a difference between -f D50M2 and -f M2,
but note that neither of these options are accurate in
calculating a good visual result - they are just there to allow
comparison to other measurements made under M2 conditions.
This is because the measurements are D50M2 but the XYZ
calculation uses D50, a situation not perfectly consistent with
the real world.

If your viewing environment is UV poor, then it is better
to use -f -i D50M2, so that both the measurement and XYZ
calculation use the same illuminant.

In practice I guess there may not be a huge difference between
-f M2 and -f -i M2, but they are different.

Graeme Gill.

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