Last Updated: 30/03/2016
the printing press
the heart of the image reproduction process
It is my belief that the printing press should be thought of as the very heart of the colour reproduction system and, that once CtP and press are run and maintained in an optimum state, i.e. in accordance with a proper press standard (like ISO 12647-2), the press should become the target for CMYK separation.
ICC CMYK profiles are incredibly important , as you read above, it's the ICC profile that provides the ink mixing recipes when transforming (separating) RGB files to CMYK.
This means that the CMYK separation ICC profiles must be produced from actual press data. A range of ICC profiles produced from standard press data are available for free download at eci.org.
Any CMYK ICC separation profile produced from measurement of a proof is quite a poor second choice (unfortunately, many "press profiles" have traditionally been made from proofs, for example Adobe's Euroscale Coated v1) - This is bad, because using such profiles makes for unsuitable plates and means that the press must daily be pushed away from it's ideal state.
It is far from ideal for the press to be adjusted, beyond basic running adjustments, on a job to job basis because of the great cost to make ready times. Properly targeted separations mean good plates, making this a much less frequent necessity - when running those separations through a well set-up CtP and a press run to the right ink weights, that is.
In summary, I have seen that day to day, large press adjustments are an unwelcome requirement and are in most cases made by necessity in order to match poor proofs. These proofs can be poor for many reasons, they may simply be from a poorly set up proof printer, or may have been produced using badly separated CMYK data.
Maybe those CMYK separations were made as mentioned above, using an ICC profile generated by measuring a proof - or perhaps even using a Photoshop "CMYK setting" which someone made using Photoshop’s Custom CMYK dialogue (this option is a legacy from Photoshop 4 and a very poor substitute for a "real" ICC press profile).
Working with calibrated displays in suitable lighting and properly matching the CMYK separation and proof to the standardised press, all falls into place.
much more here here on the prepress page
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