[argyllcms] Re: [argyllcms] Re: how many patches, profiling Epson printers

> --- Ursprüngliche Nachricht ---
> Von: Roger Breton <graxx@xxxxxxxxxxxx>

> My experience with FWA is that it invariably translates to
> shifts into the grayscale, from L=100 to L=TIL. It's as though
> the calculated gray axis, when I measure it after converting
> from Lab to Paper profile, is twisted towards the midtones,
> with b* values as high as -3.
> In fact, all the profiler's I tried so far (including argyll?)
> have never given me a complete and uniform neutral scale.

Roger,

the influence of FWAs on the color of blank paper can be indeed as large as
a couple of dE units (depending on the light source spectrum).

However, if you say that you *measured* the printed grayscale (I presume,
with the *same* colorimeter which you also used to measure the profile
target) and see a significant deviation from the CIELAB values which you
transleted by the profile (using absolute intent) to device space in order
to print the gray ramp, then I rather see profile accuracy, the
reproducibility of the printer, and/or the accuracy of the measurements as
possible reasons, but rather not fluorescense or metamerism.

Due to fluorescense, the instrument will indeed "see" the colors different
than they would look under a "true" D50 spectrum, but why should the same
instrument see see a difference, a) when you measured the taget, and b) when
you measure the printed gray ramp? In both cases the error should be the
same, thus the instrument readings should be the same as well.

If, on the other hand, measuring the grayscale would show good accuracy,
while visual inspection shows a significant deviation, then I would rather
make metamerism (viewing light != D50 spectrum) and/or fluorescense
responsible for that.


Btw, my experience is the same as Jan-Peter's, that a strong black
generation ("profile -kx ...") for CMYK profiles usually results in
significantly better grays with less color casts (at the cost of other other
deficiencies), than printing gray with high amounts of CMY ink and less
black ink.


Regards,
Gerhard

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