Re: maclife.de
Re: maclife.de
- Subject: Re: maclife.de
- From: Graeme Gill <email@hidden>
- Date: Sat, 16 Aug 2008 11:45:27 +1000
Uli Zappe wrote:
Just FYI, SilverFast, OTOH, does not expand luminosity at all in the
perceptual intent (in fact, there simply is no different perceptual
intent in these profiles), making the images always look dim, but they
never clip. So SilverFast was also deducted 0.5 points for the opposite
reason, or else it would have been on par with the Logo profiles. The
Logo profiles seem to hit the sweet spot in between.
You can choose whether to create an "always absolute intent" profile
using the -u flag in Argyll, rather than the default relative colorimetric
intent table, the former having the benefit of more L*a*b* PCS headroom for
clipping. See <http://www.argyllcms.com/doc/colprof.html#u>
The delta E values of the Monaco profiles and Argyll are certainly not
bad, it's just that the Logo profiles are better.
Self fit error is not a good measure of ultimate quality, since it assumes
that the data set is a perfect representation of the device behavior,
which it is not, since it is sparsely sampled and contains measurement
uncertainty (noise).
A more rigorous measure would be to use a much higher
resolution test chart (say 5 to 10 x as many test points) as the
reference, removing from it the test points used to create the
profile. The test set is then an independent test that
gives a better measure of how well the profile represents the
underlying device characteristics. Even this approach has its
drawbacks, since the reference points also contain a lot of noise,
making evaluation indistinct.
Note that (paradoxically) a profile that has a poorer self fit
measure may in fact be a better fit to the underlying device
characteristic, because it has smoothed out some of the noise
in the measurement values, and conversely, a profile that has
a very low self fit error may be a worse match to the underlying
device, since it is slavishly following noise in the measurement
set, and may not be applying a reasonable model in between these
points to generate the interpolated values.
Graeme Gill.
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