[argyllcms] Re: Something is wrong
- From: Yves Gauvreau <gauvreau-yves@xxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Mon, 9 Dec 2019 11:13:09 -0500
Roger,
On 12/9/2019 7:22 AM, graxx@xxxxxxxxxxxx wrote:
Yves,
In general, to get the best results possible, should we just pruned out
these
outliers? Would taking multiple measures of the patches and use the
average
or the "median" be a good practice or just a waste of time?
You need to understand what you're doing. In the context that the
device (paper) is highly non-linear, *all* the patches are important
to build a model of the output.
Lut base profile are so sparse that it's impossible to capture the fine
details of this non-linearity you speak of. I don't know how the CMMs
compute their output when they need to interpolate between grid points
but I doubt it is in a non-linear fashion. I believe these Lut are in
PCS space, so gamma = 1.0 and I wouldn't be surprised if the
interpolation was basically linear as well.
Outliers are always a nuisance IMHO.
Is there a way you can start with a tiny patch set? Instead of the
full 1000+? That way, less chances of errors. I seem to remember, a
long time ago, that Argyll was able to make profiles from as low as 60
some patches. If that was still the case, you could make all the
measurements one at a time (if the software allows manual reading) and
analyze each patch. You need to better understand what you're
measuring to be able to tell if there is something wrong with the
generated profile. That's what I do. You have to understand the
underlying device behavior from the measurements. / Roger
Maybe I don't understand what you mean but I would believe a more robust
approach then a patch by patch one, would be to measure all the patches
several times and use "average(.exe)" to sort out which of these measure
we will actually use (average, median or a Geometric Median). This
should improve our chance of obtaining a measure that is closer to the
real thing. Your approach, sound nice, but choosing a measure just
because it's closer to the target isn't good practice IMHO, there is
nothing to say that this measure is the best one or the worst for that
matter. Maybe the printer is way off for this particular color or maybe
it's an out of gamut color and the "best" measure should be farther away
for this or that particular target.
Yves
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