Page 45 - Print21 July-Aug 2018 Magazine

This is not to imply it is easy: diligence and regular measurement, calibration and reporting are needed, but, for those printers with the
desire and disciplines, it is totally achievable. For the purposes of
this report, we are concentrating
on ‘proper’ spectrophotometric measurement in the print process. Colorimeters used to profile monitors are not covered – any designer in the graphics sphere should be profiling and calibrating their monitors.
Speaking of measurement, like all process control systems, you cannot control what you have not measured, and almost nothing is as demanding as measuring spectral colour. Ink density measuring
is also very useful, which is why manufacturers have stuck with some spectro-densitometers but spectrophotometers measure
real CIE L*a*b* colour and some inkjet proofers even have built-in spectrophotometers. The colour management journey always begins – and ends – with correct measurement, which is why you need reliable instruments that are regularly checked and calibrated.
Ask the Doctor
One of Australia’s leading colour management authorities is David Crowther of Techkon and Printflow distributor Colour Graphic Services, aka ‘The Colour Doctor.’ His opinion on ICC profiles is revealing: “We often get asked to fix ‘our colour management,’ but technically colour management is really only about
“Just making a new ICC print profile will not fix bad colour – a systematic and methodical approach is required.”
using ICC profiles,” he said. “Just making a new ICC print profile will not fix bad colour – a systematic and methodical approach is required. An ICC profile is merely capturing the device behaviour based on the device calibration, where all the hard work is done.”
He continues: “Analysing and controlling colour quality across the many types of print is more about measurement and then how the data is used. What is the visual colour appearance like? Digital print and contract proofing is an interesting case in point.”
Almost all of these systems use ICC profiles in some way for their colour management, but Crowther notes:
“It is also possible to verify the colour output by measuring a multi-patch step wedge. The subsequent report
can be based on ISO 12647-7 or 8 tolerances – a green tick means the print is passed. But does that mean
the print colour is perfect? Right in
the middle of the tolerances? Does
the print have a warm reddish look,
or too yellow, too blue or too green? What is the grey balance like? You need to delve deeper to find out about the visual colour appearance. The summary report will show you possibly low ΔE (delta E) values within the tolerances, but does it explain or provide with information about which way the colour appearance is leaning to?”
Watch out for the grey areas
When dealing with solid process or spot colours, ΔE measurements are fine, but Crowther maintains that, where there is critical tone work, you will need to look at the TVI (dot gain) and grey balance (CMY). “This is where any issues with colour appearance can be measured, identified and remedial action taken,” he says.
“When measuring for visual colour appearance, a check of the print and/ or proof should be made under ISO
3664 lighting. Unfortunately, many print companies fall short in this area – it is often the easiest thing to fix and the expense is not too high.
Basically, if you are performing ‘correct’ colour measurement, the measured results should align with what you are seeing, under ISO 3664 viewing conditions,” he says.
‘Correct’ colour measurement means following a structured SOP (standard operating procedure) that defines instrument care, calibration, settings and how exactly the measurements are to be completed.
Colour crucial in packaging
Crowther highlights the importance of an SOP in packaging. “Printers
in the critical brand packaging sector are under cost pressures, with reduced time-to-market for new products, maintaining prices for repeat product print runs and offshore competition.”
With online ‘Cloud’ methods to check and compare colour print quality performance, using this type of approach eliminates the need for on-site press checks or couriering hard copy proofs around. A web- based analytics model enables job and print company colour quality performance to be checked in real time, from laptops or iPads.
Colour management
Above:
X-Rite’s new eXact spectro- densitometer
Opposite:
X-Rite’s Intellitrax2 press-
side bar scanning spectro- photometer for closed- loop colour when
used with Rutherford software
Print21 JULY/AUGUST 2018 45