Proof Beyond Reasonable Doubt 2008 - page 3

Mike McNamee revisits the topic after a five year gap
Why Should Photographers Care?

Only photographers who routinely send their work into a process printing environment (eg magazines, books, reports, brochures, catalogues and perhaps newspapers) need to worry in detail about proofing and even then, somebody downstream from them in the workflow is likely to proof a picture for an important job. This does not imply though that the photographer should be ignorant of proofing. At the simplest level the photographer should understand what they are being shown or what is being discussed if somebody telephones with a problem. The whole reason for proofing is the removal of doubt about what is likely to happen when the ink eventually hits the paper.

Perhaps a better concept for the photographer is a calibrated print, that is a print that is known to accurately portray the file from which it came. The word 'accurately' is key to this discussion – it is not good enough to indulge in a bit of hand waving and claim that the print 'looks OK off my printer', when standing before a defence lawyer, when a job has gone woefully wrong (they do, rarely, but it does happen). A contract proof must be demonstrably correct, with the ability to follow an audit trail back to known standards of accuracy. This is what the certification process is all about; FOGRA (for example) tells you how your proofer stacks up against the known standard and issues you with a paper document to confirm that finding.

A special case for proofing by the photographer is for material that is being sent to the local newspaper. Some of the repro is appalling and it is not always the fault of the printer. If you have compiled an advertisement for your photographic services for the local rag, you owe it to yourself to ensure that you are shown in a favourable light. At the very least you should soft proof your proposed artwork on screen to check that the disastrous loss of depth and contrast that inevitably occurs on newsprint does not destroy your message – don't try anything too subtle!

ABOVE: An advertisement cross-rendered to an ISO newspaper profile shows a reasonable match to the printed copy on the right. Note that by checking the 'show paper white' option, the white proofing paper has been matched to the darker, more yellow newsprint.

CONTRACT PROOFING

As we mentioned earlier this is the highest level of proofing and a contract proof is normally signed to confirm a binding contract between the printer and the client. Providing the final job matches the contract proof, all errors are down to the client from this stage forward. If he has failed to spot that an image is reversed or out of place, he carries the can! Today's contract proofs are so good that they are truly representative of the input colour, at error levels that cannot be reliably detected by the unaided eye. Two identical proofs, off machines on opposite sides of the world, should be just that, identical. One of the best examples is the IKEA catalogue. This is a 192 million copy publication made in centres all over the world and controlled by GMG proofers to known and certified standards in, we think, about 27 centres. The certification standards for contract proofing are provided by UGRA/FOGRA (for Europe) and IDEAlliance/GRACoL (in the USA). These standards are evolving and have recently been tightened yet further. To comply with the standards, the errors on a particular target have to be measured and reported on a label attached to the contract proof. The errors are tightly controlled as you will see later.

 

Paper Matters

Papers for proofing should be selected with care as some of them are intended merely to give an impression of what an image is going to look like ahead of committing to a large expensive piece of fine art paper. Others are specialised products made to exacting standards for contract proofing. A Google search for 'proofing paper for inkjet' returned more than 2 million hits!

Epson products such as Enhanced Matte Paper may be used for lower grades of proofing but for more specialised work there are four options as tabled below:

Paper has a profound influence on the outcome of the proofing process. The 'colour' of paper is a complex subject and has specifications and ISO Standards all to itself (as do teeth and dentures by the way!). The aim when choosing a paper is to closely match the paper that you are proofing towards, that is if you are printing to a bright-white, gloss paper you should choose a bright-white proofing paper. When a proofing paper has more brightness than the 'aim' paper, you can add ink (and colour) to match when using Absolute Colormetric rendering intent. If the paper is already too dull you cannot add any ink to make it whiter! The four Epson proofing products are compared with the paper used for printing Professional Imagemaker in the table opposite and also graphically.

ABOVE: Epson's premium quality 'Standard Proofing Paper' is certified by FOGRA and carries the FOGRA logo on its box, along with a copy of the certification document inside.

Above: The spectral traces for all the Epson proofing paper range are flat in the blue area, showing an absence of optical brightening agents. The paper used to print Professional Imagemaker is, by contrast, brightened, as shown by the lift at the left-hand side of the trace.

The data from the spectrophotometer shows that none of the proofing media has any optical brightening agents in them but that the actual magazine does. This is typical and generally desirable; OBAs in a proofing paper are likely only to cause confusion during accurate assessment when they affect the visual appearance but (depending the actual magazine, however, add that little bit of bite, zing, or pop (whatever you wish to call it!) to the final output.

Above: Each cluster of points shows 15 reading around an large sheet to demonstrate both measurement and paper consistency. Epson Standard Proofing Paper is whiter and brighter than the commercial grades but not as cool as the stock used to print Professional Imagemaker.

To assess the spread in real-life printing we analysed an advert provided by Canon. For this we had the original file to give the base data, two proofs and then actual magazines and two newspaper adverts for what came off the press. The results are pretty much as would be expected. The proofs are the most accurate, followed by Professional Imagemaker, The British Journal of Photography, then The Guardian newspaper. This is the expected order because the proofs were calibrated, our own magazine rendering was onto the laminated inside front cover, on high-quality paper from a sheet-fed press, BJP is coated stock (probably off a web press) and The Guardian is newsprint. The data are tabled and shown graphically. Although a camera shot of all the subject artwork is shown there is more variability in the lighting and the gloss of the paper for this to be meaningful. However, the dullness of the newsprint is easy to spot, the poorer of the two seems to be a particularly grubby piece of printing even by newspaper standards! A proof cross-rendered to an ISO Newsprint profile was a good mimic of how the advertisement reproduced in The Guardian of July 08, with an error of just 3.7ΔE in the red of the photographer's top.

The data above only tell part of the story. The GMG proof of the Canon advert was measured and found to have an error of just 1.6 Lab ΔE. This is better than we can achieve at Professional Imagemaker as we do not have a GMG RIP; the best we do is around an average of 3.8, inside the old FOGRA standard but outside the latest one. To achieve this level of accuracy requires really stringent controls of every part of the process including temperature and humidity. The data are shown below.

Avg All 1.6
Max Value 3.3
Min Value 0.6
Primary 1.8
We are hoping to investigate some RIPs at a later date.

Papers

All the Epson papers proved to be capable, in line with Epson's claims. For a photographer wishing to create a proof for a quality magazine, the Standard Proofing Paper, or Semimatte White will cover the job very well. For lower grade paper simulation both the Publication and Commercial grades will suffice, but neither would be recommended for creating a good impression outside of a printing environment, accurate they may be, but they do lack the extra 'zing' of their companions. There has been a tendency for design houses to proof on brightened stock simply to create a more favourable impression, but this is not contract proofing!

Epson ColorBase

As part of our striving to achieve greater accuracy we employed the free utility, Epson ColorBase to linearise the test 4800 printer. This had no effect on the overall accuracy of our results although we started with a seemingly welllinearised printer. However, Colorbase would prove useful for owners of the less well specified Epson models such as the Stylus Pro 2400. These are not factory linearised and the benefits of using Colorbase are that you can pick up some high-quality profiles from the web and use them in your printing.

RIPs

There are many RIP solutions around, some much less impressive than others. If the evidence of advertisements provided with contract proofs to Professional Imagemaker are anything to go by, the GMG seems to reign. Although GMG provide RIPs for Epson, Canon and HP wide-format printers, we see mainly Epson-based proofs. Most of the RIP suppliers also provide a proof verification module, frequently as an add-on. The industry is used to selling into the press market and prices will seem high to photographic sole-operators; this is the difference between controlling a desktop inkjet and an £8 million press!

Above: While the GMG RIP seems to rule the roost in the proofing market an effective and far less expensive RIP is available from ColorBurst. They make strong claims for their colour precision as demonstrated by this graph of a number of Epson printers, tested at the PMA shootout.

ABOVE: Some things have not changed! You still need an accurate, controlled viewing environment for assessing proofs. D50 is the standard viewing colour temperature in the print industry (ie 5000°K) and you need a rendering index of at least 95 to comply with ISO standards. Perversely, the most common screen set-up for photographers is D65 with a gamma of 2.2. An accurate screen is as important as your viewing booth and instrumental screen calibration is essential.

OVERALL

The improvements in the accuracy of the proofing process and its relative ease of use are quite outstanding over the five years since we last looked at the topic. This is almost exclusively due to the progress that has been made in inkjet technology in providing a high gamut, stable output onto well-controlled paper stock. In a well-managed environment the photographer should never get a shock when they open the publication they have supplied – sadly they still do on occasion, but that is not the fault of the proofing workflow!

Page 1: Page 2