Graphics Programs Reference
In-Depth Information
away with small differences in deltaE, especially when the math used to produce the values is
undefined. This isn't to say that comparing groups of measured patches for evaluating differ-
ences isn't useful, it is. If these differences between the two Matchprints were over six, using
any of the deltaE calculations, I'd begin to worry. With all three reports, the two Matchprint
proofs are close (just a bit over three).
In the old days, CMYK files were separated into four pieces of film, one
for each color channel. The film would be used to burn plates for print-
ing on a press. Like the rest of the digital world, filmless systems are
becoming more common. Direct-to-press or direct-to-plate are newer
processes that take CMYK data and produce impressions (pits on a cylin-
der to hold ink) without film. Some contract proofing systems are
designed to proof film-based printing systems; others are designed for a
filmless process. The contract proofing system has to be compliant with
the type of print process being utilized. It's necessary that the printing
process be defined before a contract proof is made. A film-based proof
will serve little purposes if the eventual printing press is
Computer-to-Plate
(CTP). Film-based separations have one advantage—that being a print
shop can examine the film and provide feedback as to the effectiveness
of the separation. With filmless proofs, it is not always evident that the
correct CMYK parameters are ideal for the press conditions.
Profiling the Press
A user can output a target to a printing press and build an ICC profile of
the press. There are a number of reasons why this might present a
problem. First, getting a press up to density and running any job is expen-
sive. Finding a vendor to agree to run the targets necessary to build a
press profile isn't going to be easy unless the company running the press
really wants that profile. Often the targets can be printed on a part of a
press run that isn't being used, such as blank sheet that would be cut
away. For this press profiling process to be effective, the targets have to
be printed using the paper, inks, and press conditions as subsequent print
jobs. Changing ink or paper invalidates the press profile. Some print
shops have presses set up for a specific paper (often referred to as a
house
stock
) and run the same ink set. This press always runs the same condi-
tions so profiling this condition is quite effective, assuming the press can
be kept in a consistent behavior. Some printers have multiple presses and
may run a job on press #1 today and a job on press #2 tomorrow. A
printer might pull a job off a particular press at the last minute due to
scheduling or other issues like a malfunctioning press. What happens
now if the job you intended to go onto one press goes to a different press?
Are both presses behaving in a similar fashion? If not, the original press
profile and CMYK conversions might cause a problem for the pressman.
