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what would cause this


Preston Earle <PEarle@...>
 

Chris writes:
So the explanations for why the proof isn't predicting this might be:

2.) Perhaps printing K first is factor contributing to excessive black
ink gain compared to what the proof is predicting.

Preston responds:

I don't believe the order of the ink laydown will have a significant effect
on dot gain. It could well have an effect on ink trapping, which could
effect the final print appearance. Normally, black is printed as the first
down color because it is usually the lightest form and thus gives fewer
problems with wet-ink trap.

3.) A laminate proof allows 400% ink and can still retain detail; unlike
a press. The shadow area needs to be lightened in order to reproduce
effectively on press.
As to the laminate proof, what kind of proof is it? Was it made from film
(Matchprint, Color-art, Waterproof)? In that case, it should have the same
dot characteristics as the image on the plate: Total ink limit, maximum
black, etc. The problems in not matching the proof would be in the press
or platemaking. If the proof was a digital proof (Iris, Approval, etc.),
wouldn't it have been made from the same CMYK file as the film/plate, such
that it showed the same separation characteristics as the printing
film/plate? The fact that it might show more detail for a 400%TAC file is
not relevant since the file from which it was made should have the same dot
values as the printing film/plate.

If the proof was from some other proofer, perhaps one that used an RGB
file, then certainly the color separation issues of RGB > CMYK could cause
the printed image not to match the proof, but wouldn't this simply indicate
that the "proof" wasn't really a "Proof", but rather a different
representation of the same image?

So this is one of those examples of the limitations
of these kinds of proofs. Interaction between inks (such as tack and
print sequence) is not predicted with pretty much any kind of proof
except a press proof.
Pre-press proofs should predict the interaction of the various elements
under "standard conditions". It's when the conditions fall outside
standard that a press proof might be required.

This isn't to say that the solution to making the printed image better
isn't in the RGB>CMYK conversion. As Dan points out, different images may
need different set-ups. However, if you adjust the conversion to take into
account the abnormal dot-gain due the particular print conditions, then the
proof won't match the original, but that's a different problem.



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