Colour Adjustment - Part 7

Proof beyond reasonable doubt

Few problems cause as much grief in the press industry and those of us who feed into it as "proofing". In some part at least, money is the source of all the evils here. A mismatch between proof and final job usually involves money for remedial action or loss of business from a disgruntled client. Proofs of all kinds are representations (either on a monitor or on paper) of how a final rendering of a job will look. Proofing is all about the integrity of an image or document. Integrity can mean the words, the colours, the quality, the arrangement on the page or combinations of these. A job is scrapped if the picture is the wrong colour or if it is upside down - proofing is intended to spot either error, before the final job is run. In DTP, the very simplest proof is a copy of the text to ensure that the spelling is correct and that the words actually make sense. Other variants of proofs are more complex and fall into two categories, analogue and digital proofs.

Analogue Proofs usually use the same technology as the printing press and usually employ the same separation films and/or plates or both. Digital Proofs use a machine other than the press to mimic press behaviour, providing a cheaper but slightly less reliable method of predicting the outcome from the press. Over recent years the arrival of fast digital printers has enabled the proofs to be made in exactly the same way as the final job will be run. They have also allowed variable content printing in which successive "drops" of the press will print a different version of the artwork, for example with a specific name and address.

Analogue Proofing In analogue proofing, the same type of technology is used to create the proof as will be used to run the final job on a press. From the DTP layout, an Image Setter is used to create films with which to make the printing plates or to make the plates directly (in the so-called Computer to Plate, CtP, technology). To analogue proof, these same films or plates are used to make a proof. The two main methods are the Chromalin Method or WetProofing. The Chromalin system has been superseded by WetProof and both are Dupont products. In this process, the actual films are used to create a single proof in a process which takes about an hour (i.e. not cheap!). In traditional wet proofing the actual plates are used on a slow manual press, again taking lots of labour. Wet proofing is about as close as it is possible to get to running the real job as the same plates, inks and paper stock may be used. Progressive proofs can be made by this method which are 7 paper proofs showing

Yellow,
Yellow+Magenta,
Magenta,
Cyan,
Cyan+Magenta+Yellow,
Black.
4-colour

Progressives enable the press operator to check the output from each part of the process and compare it .

The main advantage of analogue proofing is that it reveals problems of moiré fringing which occur from the interaction between the pattern of half tone dots and the image structure. Obviously with a proofing method that does not exactly mimic the half tone structure no warning of moiré will be flagged. There are a number of proofers which accommodate the need to check the half tone structure, the most common of which is the IRIS proofer.

Contract proofs

A contract proof is one which is "signed off" as representing the final output, ahead of giving permission to run the whole job. The press operator retains the contract proof and the print run is matched to it. In the case of any dispute, the contract proof provides tangible evidence of what everybody signed up to, at the outset. Contract proofs tend only to be employed on high value, high prestige or large run jobs, mainly because of the cost of making them.

Scatter proofs

If a multi-page document contains a small number of randomly placed images these are sometimes gathered together on a single sheet and proofed on their own while the remainder of the document is proofed "for position only" i.e. to check text and that all the pictures are in the correct place and orientation. FPO's are often desktop laser prints.

Page proofs

Page proofs come in two kinds, "Reader Spreads" which show what the reader will see in the bound document and "Imposition Proofs". If you take the staples out of a magazine then the single sheet of paper (usually 2xA4 printed both sides) shows you what an imposition proof looks like. Thus you will find in Professional ImageMaker that page 15 is on the same proof as page 22. Seeing the imposition proof enables the press operator to allow for an image on one page "robbing" ink from the picture on the same imposed page. The "tracking" as it is called is tweaked to make the best optimisation of the two pages.

Digital proofs

Have you ever noticed that when you are walking about the busy city streets all the motorists are fools and when you get into you car, the pedestrians suddenly all become fools? With apologies to the pure of mind who don't think that way, the same analogy applies to photographers and printers. The photographers claim that the idiot press operator has screwed up their beautiful blue sky which looks nothing like their monitor and the press operator berates the fool photographer for presenting him with an impossibly out of gamut image that he will never ever be able to print accurately. As with drivers and pedestrians the truth lies somewhere in the middle but it is certainly true that high quality ink jet printers have fuelled this frank exchange of views. You have to realise at the outset that your inkjet/printing press/laboratory prints all have their own colour capabilities and that they are inevitably different. An exact match is an impossibility and a close one is only achieved with skill on the part of the provider and acceptance on the part of the client. However with a little goodwill on all sides a satisfactory compromise is usually achievable. If it is not there is a case for either training up the deficient party or parting company.

The problems listed above have caused some magazines and pres-press bureaus to refuse to handle anything other than original transparencies (not even negatives are accepted). Their argument is that the transparency acts as its own proof - all you need do is hold it up to a light box and use the scanner operator's experience to get the correct digital file from it.

The option remains therefore for the creation of an accurate digital proof, which is trusted by the art director, the photographer and the printer. Such is the quality of today's desktop inkjet printers that such a quest is achievable providing the correct precautions are taken

Proofing from Adobe Products

The common colour architecture of the Adobe product range means that an image printed from Photoshop will match that same image printed from Illustrator, InDesign or Acrobat. However, to do so, the colour must be managed in an identical way from all applications.

A note of caution: please note that we are referring here to the creation of proofs which mimic press behaviour. This is NOT the same thing as printing pictures for a client’s wedding album! For that you should print directly to your inkjet printer from an RGB file in the way you know and trust.

Application Set-up

For printing in the UK you should set-up your colour to use Europe Prepress Defaults (in Photoshop; Edit>Color Settings>Settings>Europe Prepress Defaults). This will give you Adobe RGB (1998) as your RGB colour working space and deliver better separations to CMYK, especially in the cyan part of the gamut. If you want or need the full low down on this see Martin Evening's Book on Photoshop 7 page 92 (available from HO at £29.99).

Next you should have available, profiles for your own printers and for the press you are trying to simulate. If you have neither, you can obtain profiles for your printer/paper combination from the manufacturers’ web sites or pay to have then made as bespoke profiles for your own set-up. The latter course is the most accurate by some way. Your press people may be, as yet, unspecified or may not have profiles. Either way, you should talk to somebody ahead of deciding, even if it is only to a more experienced colleague! There are arguments for not profiling a CMYK press, but to provide average conditions and to this end, using the Photoshop SWOP or Euro Prepress defaults is OK for many jobs. Specifying a generic profile or even no profile for a CMYK job is less risky than not providing a profile with an RGB image. In the former you will still get close, in the latter anything can happen and frequently does! When choosing your CMYK settings you should decide between "coated" and "uncoated" paper stocks. This magazine is printed on coated stock, weekly magazines are often printed to lower quality, coated stock and newspapers are printed on uncoated stock. The quality degrades in the same order.

On Screen- Soft proofing

This is a relatively new feature, introduced in Photoshop 6 and onwards. Assuming that the relevant profile is available in the "color" folder, Photoshop can access it and present, on screen, a quite accurate impression of how an image will print with that profile/ink/paper combination. It is turned on by clicking View>Proof Colors>Custom; then select the profile from the drop down menu. If your CMYK working space is, for example, Euro Press and you wish to soft proof to that standard then clicking Proof Working CMYK or simply Ctrl-Y will produce the result. You may even compare different options for output by clicking Window>Document>New Window. This opens a new view of the current image, which can be soft proofed with a different profile.

Perfect representation of an output is not possible because screens and paper are distinctly different ways of displaying images. It is nevertheless possible to obtain an accurate idea of how an image will behave when it is printed. This assumes that your screen is calibrated and is displaying at the same colour temperature as your viewing area. Prepress standard is D50 (i.e. 5000°K) but other standards use D65 (6500°K). If you do not adjust your monitor, it is quite likely to be running at 9500°K and will be very blue. Until your eyes get used to it, D50 will look quite yellow compared to D65. Of greater importance to viewing is actually the illumination level. Screens are quite dark (think about how poorly a monitor lights a room on its own) and a transparency to be matched should be lit to the same level. On the other hand ISO standards for “proof viewing” call for very high illumination levels (1,500 to 2,500 lux compared to normal office lighting levels of 200 lux). At the same time the standard calls for near darkness when adjusting on-screen images (32 lux). You certainly can't maintain both in the same room as the proofing level will flood light everywhere! Some experts recommend that you do not place a transparency viewer and monitor side by side but force the user to turn away by 90° to make the comparison.

Cross Rendering for CMYK proofing It is quite common for a prepress provider or printer to ask for an RGB image so that they can control the conversion to CMYK to their common standard. In these circumstances it is still imperative that a hard copy goes with the job so that everyone knows what they are looking at. One way is to cross render the image into a proof which takes the RGB data, converts it to a CMYK simulation and then uses the inkjet’s RGB based profile to ensure the accuracy of delivery of the CMYK mimic. Photoshop may be set up to do that (see the call out boxes) and even mimics the off-white base-tone of the standardised print stock. When you soft proof or the cross render do not leave white margins on screen or on the paper proof. If you do it will look a dull beast in comparison to its RGB cousin- that is a fact of life, we are making a simulation of the eventual output which is never going to be as bright as an inkjet!

Epson printer

Above: The latest Epson Stylus Pro 4000-PS has all the facilities for proofing at high precision and speed. See the review in this issue.

x-Rite

ABOVE: Professional Imagemaker’s main design work station and proofing area. Our monitors are calibrated with an X-Rite Screen Optimiser and we use the X-Rite Digital Swatchbook to check both the input and outputs. The viewing booth on the left is equipped with D50, D65, Tungsten and Ultraviolet lighting.

Cross Rendering

Paper Matters

Paper has a profound influence on the outcome of the proofing process. The “colour” of paper is a complex subject and has specifiactions and ISO Standards all to itself (as do teeth and dentures by the way!).

The paper stock for Professional Imagemaker has a Brightness of 95% and a colour represented by 0.9, -2.3 on the Lab scale; that is blue towards magenta, which is typical of a stock with a moderate amount of optical brightening agent. Epson Premium Lustre has the same brightness but the colour is more blue at 0.2; - 4.0. Tetenal Duo print, a high OBA material has brightness that is actually 0.5% less but looks brighter because of the OBA. This also pushes its tone to a deeper blue at 3.5; - 8.0. Epson Dupont Commercial Matte proofing paper, a high premium material specifically designed for the job has a brightness of 95.8% and is slightly warm cream at 0.3; 3.0. Proofs on these papers are all affected by their base colour. The Epson Premium Lustre and Epson Dupont profile in more accurately and deliver more precision in the final output. The Tetenal produces a brighter print but is actually less accurate in absolute colour terms. These variations in profile accuracy are due to the distorions in the colour measurement influenced by the ultra violet component of the paper coating.

For Epson users, we can make the decision easy for you, use the Proofing paper Semi-Matte; in our tests to date it holds the record for most accurate delivered proof.

Artists Proofs & Printers

Proofs It is arguable whether this topic should be included here. However for completeness, in the world of Fine Art and Limited Edition printing they have their own terms and meanings for proofs. A printer's proof is retained by the printing service provider, for reference when additional limited edition prints are called up, the so-called "print on demand". The printer's proofs may also include the prints made while the image is being adjusted to the satisfaction of the artist. The final proof (i.e. the one which is accepted as the final version) is called a BAT from the French bon à tirer or "good to pull or print". This proof can be an inkjet print, a giclée, Iris or Silk Screen. An artist's proof is one of a small number retained by the artist, which are not included in the count of the limited edition. Artists proofs are not normally sold but should the artist become very famous the cache of having something which is different can inflate the value of the proof - a bit like the pencil sketches of the revered and the famous really! Printers such as the Epson 4000, 7600 and 9600 will proof and create fine art output.

To RIP or Not To RIP?

We have been struggling for some time now to get to grips with some RIPs. Raster Image Processors have a number of advantages for proofing and for photographic printing. They are often hosted on a separate computer so that you simply move your files into a watched folder and let the RIP get on with things while you work un-hindered on your own machine. They also often come with the ability to "nest" the files to provide the best utilisation of paper. If the RIP is the same one as will create the films or Computer to Plate (CtP) units then you should be more secure with your output. Vendors like Ilford supply a turnkey Studio printing solution which includes, the RIP, PC, Printer, calibration and training. If you detect a note of doubt in the first sentence it is because to date we have achieved higher precision without a RIP than with, a subject we will come back to.

Photoshop

ABOVE: Follow the sequence. The dialogue boxes are very daunting at first. The screen grabs assembled alongside should help. You can make your own as you proceed through the set-up by Alt-Clicking the Print Screen button then pasting successive pane views into Word or a new Photoshop document. Tidy them up and print then out for future reference. The sequence flows to the pane marked 10. At this point you have to go back to the tab at #7 and click on paper if you require a special paper size or a size change. When everything is to your requirements you keep clicking Ok until you get back to the Print pane #11. Here, if you hold down the Alt key you may click the Remember Button (red lined in #11) and Photoshop will do just that for your settings.

How Good is That?

We keep a close eye on our proofing at Professional Imagemaker and have the ability to collect data each time we go to print. Life is not always straightforward and we do make mistakes such as sending RGB files to press, where they turn out woefully dull and light. However, our results show that carefully controlled Epson inkjet printers easily perform as well as Iris machines costing hundreds of times more money; indeed, in our latest trials the Epson was almost twice as accurate. For proofing work, pigmented inks are preferred especially when instrumental measurements are going to be made. Epson UltraChrome inks “dry down” within an hour to within 1 delta E compared to almost 3-days for some dye ink/paper combinations. In a busy pre-press environment they tend to use Epson 9600’s simply to get the throughput and for the same reason the proofer version of the new Epson 4000 is able to run 4-colours only with 8 cartridges , exploiting the extra nozzles to get the ink onto the page even faster!

Professional Imagemaker

Pre-Flighting Pre-Flighting is an essential part of the proofing process, especially from a DTP application. If you need further proof go and take a look at page 23 of the March/April issue of Professional Imagemaker or more recently page 10 of May/June. In both cases an RGB file had slipped through the system and been converted to CMYK by the image setter's RIP with disastrous consequences. We had (incorrectly) assumed that such errors would be either discovered at pre-flight or would stall the RIP, neither occurred and so you were presented with a very poor reproduction of the images. Both InDesign and Acrobat 6 Pro have first rate preflighting and the preflight is followed by an offer to pacakge your layout ready to send to the printer. This assembles a new folder containing all your linked files, the required fonts, the InDesign layout document and a template for a text file in which you can add your name, telephone number and any special instructions for the printer. It really does take the strain out of sending documents away especiallyif it is something that you rarely do or you are new to business.

In-Design

ABOVE TOP: The digital proof, Iris proof and actual cover are measured up to provide reference data for future use. ABOVE: Adobe InDesign and Acrobat 6.0 both have pre-flighting capability. In the example shown we deliberately added an RGB image to last issue’s cover. This is flagged up with the yellow triangles to warn that all is not well. Preflighting flags up missing linked files, profiles, fonts so that they can be attended to by the photographer or graphic designer before they become a problem at pre-press.

Professional Imagemaker

ABOVE: This issue’s cover proof ready to go off with the CD’s and page proofs. The photographer always gets a copy of this proof as a memento - they look posh on the studio wall!

Folder

ABOVE: The “Package” command for InDesign makes a set of folders containing the fonts, documents and images to complete the job. The text file (right) contains listings of the files as well as instructions and contact telephone numbers.

Colour Proof correction

ABOVE: Sadly, no longer in print, Colour Proof Correction revealed all the secrets of taking a long hard look at a proof and improving the output. The one-time presence of this 150 page tome reflects the complexity of the subject.

Photo Quote: Everyone has talent. What is rare is the courage to follow the talent to the dark place where it leads. - Erica Jong