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Anatomy of Colour - I

23 August 2017

Are you colour challenged about your ISO and Pantone?

Rahul Kumar confabulates with colour consultants and colour scientists to the puzzle of the jargons. Hopefully this will help you in your day-to-day printing

colour

Question: What is this thing called ICC Profiles?
Answer:
Well, it is at the heart of most colour management systems. In 1993, it was developed by the multi-vendor International Color Consortium. 

Question: Sounds impressive. But what does it do?
Answer:
Well, the ICC profile system (ISO 15076-1) uses tiny files that let you transmit colour characteristic data from camera files and design software, to monitors, printer drivers, RIPs and controllers. It’s also used to predict the final printed appearance on-screen or printed proofing systems. 

Question: You have ducked my question. What DOES it do, brother?
Answer:
It allows device-independent colour conversion – any input file with an ICC profile can go out to any monitor/output file with an ICC profile. You don’t need to know what the combinations will be in advance. 

Question: Ok, got it. What is this thing called CIELAB?
Answer:
ICC profiles work through a standard colour reference space. This is called CIELAB.

Question: In what way does CIELAB benefit me?
Answer:
For instance, a digital camera image in a page layout can be converted through the reference space and out, for example, to both a desktop Epson photo printer and a Heidelberg XL offset press, with their respective profiles ensuring that the appearance is broadly the same.

Question: Who provides these profiles?
Answer:
Generic profiles are often supplied by manufacturers with devices and software.

Question: My guru Kiran Prayagi insists on creating his own profiles. Why so?
Answer:
For greater accuracy. Colour gurus like Kiran Prayagi could create or modify profiles of your own individual devices, using a range of measurement instruments together with input targets or output patches and profile-generating software. X-Rite dominates the market, but other important instrument makers include Techkon and Barbieri. 

Question: Why is the reference space in ICC profiles considered a drawback?
Answer:
Aha. First sensible question that you have posed.

Question. Then answer it, brother.
Answer:
 The reference space of ICC profiles can be a drawback if there are colours that must be preserved unchanged – say a Pantone brand colour or carefully tuned CMYK images with under colour removal (UCR) or grey component replacement (GCR). These may be lost when they go through the reference space and out the other side.

Question: Sounds confusing. Any solution?
Answer:
There are ways to get around this by telling the system to detect and ignore Pantone numbers in the file, or to preserve the original black settings. 

Question: I have seen a pre-press firm try this, and fail.
Answer:
The alternative is to use Device Link Profiles.

Question: What's that now?
Answer:
These are pairs of profiles that convert directly from one colour set to another by using a unique look-up table (LUT) with no intermediates. Alwan Color Expertise, for instance, supplies LinkProfiler 5 software to set these up. 

rk
Rahul Kumar, PrintWeek India

Thank you Simon Eccles, freelance printing industry journalist and PrintWeek UK for the colour inputs.

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