Attentive readers of the industry media may have noticed that editorials devoted specifically to colour proofing do not appear as frequently as they used to.  This isn’t because proofing is less of a ‘hot’ topic than before; rather it’s because proofing is now perceived as one component – albeit an important one – of the digital workflow.  For every feature dedicated to proofing, there are maybe half a dozen on managing colour within a digital workflow.

So it’s a question of terminology, and certainly not a case of a diminished role for proofing.  Quite the opposite:  printers who have expanded from offset into digital print and multimedia output have found that as the number of output technologies increase, colour accuracy and consistency become a greater challenge.  As a result, the demands made on the proofing solution are more various, and the need for flexible configurations becomes greater.

However, there is a danger that in subsuming proofing into the larger subject of workflow, we overlook just how fundamental a part of the production process it is.  The proof is the glue that binds together the workflow from design to press – and increasingly, beyond the press.  It’s the linchpin between the colour space of the digital files and the colour space – hard or soft – of the final output.  It’s also crucial to the commercial transaction, because it’s the contract between the buyer and the service provider, communicating the end result to those who have to create it, and reducing the risk to everyone involved in the process.

This is quite a job description, and as workflows become more varied and complex, proofing has to perform a wider range of tasks, from providing simple content and positional checks to tracking and managing inputs in collaborative working models spanning continents.  Choosing the right proofing solution is vital, and it helps to understand the range of solutions available, the technologies they are based on, and what each brings to the workflow table.  In other words, don’t forget the proofing basics.

It helps to start by looking at different proofing scenarios.  As noted above, the simplest proofing tasks are content and positional checks – is everything there that should be, and is it in the right place?  This category can also include imposition proofing – essential in a CTP workflow.  In these applications, accurate colour is not essential – after all, you can check content and position on a mono proof.

The question of which imaging technology to use arises as soon as you have to proof the colour component of a job, and the choice becomes steadily more important as it becomes more critical that the final print matches the proof.  At one end of the spectrum are applications where an approximation of the printed colour is enough – a holiday brochure, for example; at the other end are jobs where reproducing an exact colour is fundamental to the success of the outcome – matching the corporate colour of a premium brand, for example, or the precise shade of clothing in a catalogue, or a fine art print.  In these applications, the requirement is for a contract proof – one that demonstrates not only accurate colours, but also renders the halftone screen precisely so that you can identify subject moiré or screening moiré problems.  Achieving these levels of certainty may well also involve replicating the contribution made by the stock the job is printed on, and the inks that are used.

Finally there are the distributed proofing scenarios represented by hardcopy remote and ‘virtual’ proofing.  In the former, proofs are output at one or more remote locations – at a client’s head and regional offices, for example – with the knowledge that every proof will be identical.  In virtual proofing, the proofs are viewed in ‘soft copy’ form on computer monitors.  Hardcopy, remote and virtual proofing are becoming more popular with the increased adoption of collaborative creative and production models where a number of people need to be involved in the approval cycle.

Of course, none of the above scenarios is mutually exclusive – in many cases a single job will involve employing a variety of solutions to meet a range of requirements, from content checking to producing contract proofs in remote locations.  Applying efficient, cost-effective proofing at each stage of the cycle depends on choosing between the available solutions, which in turn depends on appreciating the technologies involved.

The proofing ‘pyramid’

The range of proofing technologies and solutions can be visualised as a pyramid, with lower-cost, higher-volume systems at the base and a progression towards more expensive options for specialised applications at the apex, featuring more complex feature sets.

But this simple model needs to be qualified a little in the light of inkjet’s position as far and away the most widely used proofing process.  This is testimony to its versatility as a process that can meet almost all proofing requirements:  for example, the inkjet printer supplied with your PC is perfectly adequate for basic content and positional checks, but with the simple addition of a special-purpose RIP such as the KODAK MATCHPRINT Inkjet Proofer the same printer can introduce predictable colour output at an early stage of the production process.  Climbing further towards the apex of the pyramid, inkjet also drives a high-end proofing solution such as the KODAK VERIS Digital Proofer, which produces consistent, repeatable four-up contract proofs.

At some point along the quality curve an important technology frontier is crossed.  It comes at that point, noted above; when it is critical that the colour being proofed is the colour that will be printed and the question is whether or not you need to exactly reproduce the individual dots by using a ‘dot-for-dot’ proofing solution.

When tolerances are tight and there’s no room for error, inkjet is not an option.  Although most inkjet proofing suppliers offer a ‘halftone simulation’ feature, this needs to be understood for what it is – a compromise, on several levels.  There is the question of resolution, for example:  while inkjet devices may offer resolutions of 720 x 720 dpi, or perhaps 1440 x 720 dpi, a CTP system typically has a resolution of 2400 or 2540 dpi.  Proofing high-resolution files on lower-resolution devices requires resampling, which may, in some cases, introduce unwanted moiré.  Then there is the issue of spot size:  the smallest inkjet spot is 42 microns, while a CTP can render spots of just 10 microns.  This causes practical problems if, for example, you have to emulate light tints – some of the spots will have to be ‘dropped’ to match the colour. Fine screens, such as 80 lines per cm or higher cannot be authentically proofed.

Inks are another issue. Because inkjet inks have different hues than offset inks, producing a colour match on a halftone simulated proof requires adding contaminants to the CMYK separations to produce the correct hue of the offset inks:  for example, the inkjet proofer may have to add a small amount of magenta to the pure cyan to get the correct colour.

Inkjet halftone simulation cannot reproduce the exact screening rosette as it appears in the final print - so don’t confuse it with dot-for-dot proofing.  Instead, choose a digital halftone solution such as the KODAK APPROVAL Digital Color Proofing System, which employs thermal laser technology to reproduce the same screening structure used by our CTP devices for making plates.  Such solutions are powerful – they call for resolutions of at least 2440 dpi multi-density donors, and can use the same stock as the press – and accordingly carry a price premium, but they deliver the ultimate in proofing security.