Re: need help with inkjet proofs
Re: need help with inkjet proofs
- Subject: Re: need help with inkjet proofs
- From: Steve Upton <email@hidden>
- Date: Wed, 15 Nov 2000 00:04:37 -0800
At 2:55 PM -0500 11/6/00, email@hidden wrote:
In a message dated 11/5/00 8:48:50 PM, email@hidden writes:
>One thing I have found - after looking at device gamuts in 3D - is
>that most of the Epson ink jets do not produce the shadow colors that
>a press or proofing system will. This means that you will see very
>grey or otherwise thrashed shadow colors on the proof.
This is a tricky one, Steve. The first question is whether the press truely
has a wider dark gamut than the Epson, or whether the Epson is not being run
with rich blacks and maximal dark combinations, which will vary drasticly
with the profiling software, the settings, and the paper. If we are talking
about a profile for the RGB driver, then these capabilities are not even
available;
Yes, this is exactly what I was talking about; Epsons with the RGB
drivers (I failed to mention this point). I agree than with a RIP you
can open things up. My concern is that many are under the impression
that these printers (using RGB drivers) are large gamut.
Next we have the issue of how well the profile graphs actually represent the
device; two profiles that produce indistinguishable output for in-gamut files
can have drasticly different gamut maps in ColorThink, which is only
describing their outline, not how the contents of those outlines are
distributed.
Mostly agreed. Some graphs produced by ColorThink are what I would
call "gamut boundary" graphs. They plot the boundary of the gamut
using a 3D wire mesh. The important inner-gamut behavior of the
device (and the profile) is not depicted by this type of diagram.
ColorList information plotted in 3D can offer more insight into
profile differences however.
I don't totally agree that "indistinguishable" profiles produce
drastically different gamut graphs however. Most professional-level
profiling applications produce profiles - and gamut graphs in
ColorThink - for the same device that are similar. Popular (and
effective for output) scanner-based profiling applications may
produce gamut graphs that are quite different but I would venture
that this is because the proofing intents of the profiles are in fact
drastically different.
One of the often-overlooked limitations of scanner-built profiles is
that they do not build acceptable proofing transforms. Part of that
reason seems to stem from the fact that they do not accurately read
the white point of the media. Please correct me if I am wrong here
but that has been my findings. This also does not say that they
cannot or do not have the ability to produce acceptable profiles for
output.
Beyond that we have to decide if any difference that is actually
a difference between the press output and the proofer output (not the 3d
representations of their profiles) is visually significant. This is an area
where delta-e values, and graphed differences, can be deceptive, as they do
not necessarily translate into significantly different visual results. The
eye is not at its best distinguishing between one formula for rich black and
another.
I am not referring exclusively to graphed differences and delta-e.
The 3D gamut graphs are very useful for determining when a proofer
gamut does not match a press gamut. Ultimately I agree that the eye
is the final judge but I cannot tell you how many times I have
struggled with device proofing only to finally discover (after I
wrote the software to graph the profiles) that in many cases the
proofer did, in fact, not have the gamut required to make the proof.
Only by comparing an overlay of the profiles in 3D was I able to see
that the inkjet was missing tons of shadow colors or would never be
able to give me 100% press yellow or cyan. It is important to know
where the problems may lie in proofing so as to not waste time
chasing one's tail (speaking as one dizzy from experience)
Keep in mind that settings such as UCR, GCR, UCA, total ink and
total black will significantly change the shadow gamut of a profile.
Indeed, and this is why I suggest a RIP for inkjets so as to be able
to take advantage of the full device gamut.
I welcome more discussion around this topic.
Regards,
Steve Upton
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