[argyllcms] Re: Question about DeltaE from printread and one about iccexamin/profcheck

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 11 Sep 2007 17:20:11 +1000

Kai-Uwe Behrmann wrote:
Indeed, I looked at some available samples from other profiling packages, like PM and L-Prof, and found, the RGB 0...255 range where used for obvious reasons.

Sorry, I don't find the reasons obvious. Many CMYK devices
also use 8 bits, but you won't find a CGATS file having CMYK
values of 0-255. There is also the possibility of driving devices
with 12 or 16 bits/component, so for consistency these should
be 0-4095, and 0-65535 ? I don't think so.
The CGATS standard has always allowed for real values, so
this can't be a factor either.

> As well the #17 draft speaks explicitely about that range
for RGB.

This may be so, but it was added after I created the .ti3 format,
and ANSI standards are not easily come by as an individual (ie.
they are not generally available for download, only for a fee).
It seems that they have merely adopted the de facto usage of
other packages, without regard to the logic of it.

I think it's a bad recommendation for the reasons mentioned above.

> Did you run a different profiling package with argyll's
measurements, for instance L-Prof?

Argyll's measurements are labelled as .ti3 for the specific reason
that they are setup for Argyll. Importing other measurement
sets into Argyll using (say) logo2cgats takes care of these scaling
issues. Argyll has from it's inception kept the device values in
the same file as the measurement values, unlike many other profiling
packages in which require tracking several files, so I've never
regarded such things as freely interchangeable.

Graeme Gill.

Other related posts: