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A proof for all reasons
By Andy McCourt

Proofing and colour management may sound dry topics but, like the glistening demonstration car in the showroom, proofs need to represent what is delivered to the customer. Andy McCourt was part of the complex digital proofing revolution that hit Australia in the late 1990s but deals with it in an easy-to-read way.

If you were seduced into ordering a cherry-red Monaro HSV with antelope leather seats and beige trim; would you accept delivery of a maroon model with velour fabric and brown interior trim?

Of course not, and this is what proofing is all about – matching what the customer sees and approves to the final printed output. Unfortunately, proofing and colour management in the graphic arts is infinitely more complex than manufacturing cars.

There are two fundamental kinds of proof – content and contract. We can quickly deal with content proofs since they need only represent the correct text, in the correct position with the correct illustrations. Printers do use another kind of proof known as an imposition proof which shows the fall of pages on, say, an 8-up press sheet but this is really an advanced form of content proof. Content proofs can be laser copies, magazine ‘dummies’ or just quick plots at low resolution on a wide format printer. Essentially, they need reading, marking up, commenting upon and offering instructions to the designer to change the file and make another content proof for re-checking.

“The role of contract proofing is to render a hard copy facsimile of colour images that squeeze ten million colours into four or five thousand. It’s a bit like the 300 Spartan soldiers that held off an army of one million Persians under Xerxes at the Battle of Thermopylae in 480BC. Sometimes the results are the same.” 

Content proofs are not judged for colour so, more and more, we are seeing them sent electronically as PDFs and either printed out by the customer, or marked-up on screen using the annotation option in Adobe’s Acrobat or more advanced applications such as Kodak’s RealTimeProof or Proofitonline.com. These applications track changes and versions and some can manage the approval process remotely via the internet.

THE SOFT MACHINE
Monitor-based or ‘soft’ proofing would seem to be the best method for both content and contract (colour-accurate) proofs at first glance and it is - in a totally managed and profiled environment. However, digital cameras, Macs and PC monitors work in RGB and printing works in CMYK. Wide format printing can work in up to 12 colours and this presents issues of matching what is seen on the monitor to what comes out of the printer. Added to this are fluctuations in monitor colour – the ‘drift,’ differences from brand-to-brand, the viewing light conditions and subjective opinion. It is no wonder the most common complaint in digital reproduction is “the colours don’t match the monitor.”

The professional digital reproducer invests in better-than-average monitors such as the Apple cinema screen, Eizo or Quato calibratable monitors; and a monitor profiling devices such as Colorvision SpyderPRO or EyeOne Display and Huey from GretagMacbeth (now part of X-Rite.) When you consider the low cost of profiling tools these days – as little as $155 for a ColorVision Spyder2Express – it is sheer madness and masochism to attempt commercial digital reproduction without them. About $1,275 would buy you a complete Colorvision PrintFIX  PRO Suite that will create both monitor and printer profiles with amazing accuracy when you consider colour measuring instruments and profiling software can cost $7,000-$20,000 and more.

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What calibrating and profiling monitors to printers means is that the monitor can deliver a soft proof of the intended end result, but a word of warning – emailing the PDF to Mr or Ms Client for approval will only be accurate if their monitor is profiled to the same curves as yours – and viewed in similar light. Have you ever stood in front of a bank of plasma, LCD and CRT televisions in a big electrical store? The colours are all different. This is what to expect – times 100 – if you expect colour to look the same on uncalibrated monitors.

HARD COPY PROOFS
So we come to hard copy proofs – the ones a client will sign off on. A more contentious area of the graphic arts would be hard to find. Firms and individuals have ended up slogging it out in Court over huge unpaid print bills because the ‘colours weren’t right.’

Proofs come in many varieties dependent upon the intended reproduction method. Photographic proofs of a wedding shoot will need to faithfully render the hue of the bridesmaid’s dresses, floral bouquets, pure blacks and virginal whites. Wide format posters and POS displays of brand merchandise and corporate colours – Coke Red, Foster’s Blue, Cadbury Purple and so forth – need to render much wider gamuts of colour than mere offset print reproduction, such as this magazine.

Ironically, it is more difficult to produce a proof that accurately predicts the printed result  in fewer colours than the full visible spectrum. How many colours are on a typical advertising page of this magazine? One thousand? Four thousand?

Actually, there are only four; three if you don’t call black a colour. Cyan, Magenta, Yellow and Black. These four colours are arraigned in tiny dots to present the grand optical illusion that is printed colour. A feat of conjuring that presents a gamut of approximately 4,000 achievable colours to represent the ten million or so that the human eye can perceive.

SPARTANS OF DIGITAL REPRODUCTION
The role of contract proofing is to render a hard copy facsimile of colour images that squeeze ten million colours into four or five thousand. It’s a bit like the 300 Spartan soldiers that held off an army of one million Persians under Xerxes at the Battle of Thermopylae in 480BC. Sometimes the results are the same.

Once, contact proofs were produced chemically by skilled tradespeople. Names such as Cromalin, Colorart, Matchprint, Konsensus and Chromaproof were familiar to all in graphic arts. Today names like Epson, Canon, Hewlett Packard and the software RIPs that drive these digital machines such as GMG, Oris, BlackMagic, EFI-Best, Kodak Digital Matchprint, Agfa Colortune, Proof2Go – dominate contract proofing for printed reproduction.

Such software, together with colour measuring instruments (spectrophotometers, densitometers and colorimiters), are capable of profiling a wide format printer, running the appropriate ink and paper, and turning it into a very accurate contract proofing system. The secret is all in the profiling and in order to profile you must know how the end result will be printed. A glossy catalogue printed offset on a ten-colour Heidelberg will require a different output profile to a carton printed flexographically, or to the billboard printed on a grand format solvent printer.

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Printing presses all behave differently and, like people, they can be ‘fingerprinted’ for the ultimate proof-to-press accuracy. Heidelberg offers such a fingerprinting service to its press and workflow customers.

ICC THE LIGHT
Profiles can be ICC flavoured (International Colour Consortium) or otherwise but whatever they are they are a set of instructions to the device on how to render colour and must cover all the variable stages of production – a ‘closed loop’ colour-managed workflow where the proof is the most important part. Ideally, these are the devices that would be profiled:
• The digital camera
• The computer monitor
• The inkjet printer with inkset
• The proofing paper/s
• The printing press
• Any variation on the press, e.g. different inks, coated or uncoated paper etc.

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Across all of the above is one important issue relating to proofing and that is viewing conditions. Colour is light and vice-versa, as demonstrated by Sir Isaac Newton when he split white light into prismatic colours. For the scientifically minded, visible light covers wavelengths on the electromagnetic spectrum of between 400nm (nanometers) and 700nm. The ‘warm’ end is 700nm and beyond this we have infra-red rays, microwaves and radar. The ‘cool’ end is 400nm and beyond this we have ultra-violet, X-rays and Gamma rays.

Light sources vary in the mixture of these wavelengths and also in intensity. Colour temperature (or degrees Kelvin) is a measure of this. A tungsten household globe has a colour temperature of around 2,500° K – yellowish; while a clear blue sky can be 12,000 to 27,000° K. Colours will look markedly different when viewed under each of these light sources or anything in-between.

To overcome this, the graphic arts industry has standardised on the colour temperature of light sources used to view and assess proofs. The International Standards Organisation ISO 3664:2000 ‘Viewing conditions – graphic technology & photography’ specifies 5,000° K as the colour temperature standard. Such precise light sources are available from manufacturers such as GTI (Kayell Australia) and Just (DES) and are available in a variety of booth sizes and adjustability. Viewing and colour temperature are actually a little more complicated because a couple of weasels called spectral response and metamersim come into play but I think I’ve jammed enough arid colour science into this piece already! Suffice to say, if proofs are critical, view them under a consistent light source and make sure the client and printer also view them under the same kind of lightsource.

PROOFING BY NUMBERS
A final word on ‘proofing by numbers.’ This is where control strips – typically ten to thirty colour patches – are measured using a spectrophotometer. The data is recorded in the software. If another proof is made – e.g. remotely at the printer’s or client’s site; the same control strip is measured and if the data matches within acceptable Delta E tolerance, the proofs are deemed to be identical – even ‘certified.’

In a well-controlled process disciplined environment, the mathematical method does work. It even extends to soft proofing with ‘virtual’ densitometers controlled by the click of a mouse. But with complex multi-tiered processes where disparate parties network with each other to see a job through, variables and subjective analysis can compromise the numbers game. You can measure colour patches all you like and say to a client ‘they’re the same!’ but if she insist ‘the brown is too red’ you’ve lost the match.

Better to use your client’s eyes as the ultimate spectrophometer, involved them in the approval process and get their heads nodding when they see fantastic colour matched from proof to press or wide-format printer.

Andy McCourt is a regular contributor to Digital Reproduction