[argyllcms] Re: Gamut of output profiles
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 14 Sep 2007 00:32:08 +1000
Lars Tore Gustavsen wrote:
I have played a lot with the different gamut tools from argyll recently.
I was little shocked when found out that the printer profile I had
with largest gamut for my Epson R2400, was one produced with eye-one
match "easy rgb 1.2" chart. That is a small 45 patch chart.
Output from iccgam -v is
Total volume of gamut is 764113.519232 cubic colorspace units
The one produced by Epson for the same Premium Luster paper is
749007
A typical 1000 patch rgb profile that I have created myself is
723600
And if I process the "easy rgb" target in Argyll I end up with
595777
And a similar sized target (45 patches) created in Argyll gives me
612517
Question is :
Can I trust these values?
The volume calculated depends on a number of factors, but they are
reasonable given the way they are derived. Factors include:
1) Which intent (table) you chose. The most literal gamut volume
is the absolute colorimetric one (ie. iccgamut -ff -ia).
2) The colorspace. The default is D50 L*a*b*, but CIECAM02 Jab can
also be chosen.
3) The accuracy of the profile. This depends on the instrument, the
instrument setup (ie. illuminant, observer, UV filter etc.) and
the way the profile was created. A profile created from few
test points is likely to be less accurate, since there is lots
of space between the point to interpolate.
4) The ink limit. This may not be applicable for an RGB driven printer
(although it will appear indirectly as an effect of the drivers
paper type setting), but has a very direct bearing for CMYK devices.
5) The exact printing conditions. Maybe the manufacturer had a different
batch of paper, ink, or the printer they used was in a slightly
different condition (ie. production batch, wear etc.).
6) Whether the profiling package applies some sort of gamut mapping
in the A2B tables. Profilers are not meant to do this for the
colorimetric tables, but who knows ?
7) The algorithm used to interpolate and smooth the test points.
Argyll uses one that balances fit and smoothness. Others may
fit exactly, without regard to smoothness, resulting in a different
profile and gamut.
I have made a wrml file showing the easy target processed in eye-one
match against the same measurement file processed in Argyll here.
http://www.mulebakken.net/div/small-argyll-match.wrl
Argyll is the color one.
This looks like a maximum density issue. If the two profiles are derived
from the same source points, and it is the colorimetric A2B table we're
looking at, how do the respective fit errors compare (ie. profcheck output) ?
Graeme Gill.
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