Prepress (and Printing)

Is Colourmanagement needed, is it helpful?

digital input:
In the printing industry, the transition to successful reproduction of digital images which are supplied electronically has been an uphill struggle.
scanning transparencies:
Whilst transparency film could be viewed as definitive reference to the originator’s intent, then scanned and automatically converted to press-ready CMYK using a well set up scanner, digital imagery needs quite a different treatment.
Origination:
Image originators often carry out colour correction before data even reaches the designer, retoucher or prepress operator – and the communication of colour is often ambiguous since no accurate proof is done until far later in the process.
CMYK “recipes”:
Like RGB, CMYK is device specific, it is made to suit a particular type of printing. Think “sheet-fed coated”, “sheet-fed un-coated”, “ web offset coated”, “ web offset un-coated&rdquo. However, as we know, even inexperienced users of ©Adobe Photoshop might separate RGB to CMYK and this is often done without any guidance, or knowledge of press destination and can even result in a mixed bag of CMYK recipes on a single press sheet. Plainly, this is a nightmare for the printer.
the future:
Robust guidelines are apparently needed, to enable users to prepare CMYK files the right way, to the right CMYK “recipe”. But, in order to provide universally useful guidelines, printing ideally needs standardisation.

So, what can be done? And can good practice help solve these problems?

click here to download a pdf about our work at Christie's International media Division. (.zip file 3.1MB)

What is a “standards based workflow”?

The combination of CtP (or image–setter/film/plate) and press is run to an ISO standard, normally ISO 12647-2, 2004. All Proofs include a standard, recognised colour wedge and are able to be measured and checked against standard press data. ICC profiles which accurately reflect real press output are used for separation, soft–proofing and proofing.

Major concerns in producing and handling data for print:

A: incoming file integrity
B: ability to view and, therefore, to assess colour accurately
C: separation of RGB to CMYK (which ICC profile, if any?)
D: proofing and proof control, checking proof quality
E: CtP (plate) curves
F: The press condition

A: Incoming files: -
what we are about to receive: -

Digital Capture:

As is well known in the design and printing industry, digital camera capture can be somewhat difficult to deal with.
But why?

Digital images, colour and tonal values:
When viewing, editing, proofing or converting digital image data within or from Photoshop (since v5), ICC profiles are always used. If ICC profiles are not specified for an image, (even with Colormanagement OFF) profiles are, by necessity, assumed.

Unless well aligned by the camera manufacturer to the tonal and colour values anticipated within a Photoshop WorkingSpace profile, a digital camera output file generally contains only ambiguous information as to colour and tone.

This means that when an image capture file is opened, assumptions have to be made about the meaning of the RGB colour numbers and this can have undesirable results.

RGB ambiguity:
It is, unfortunately, not widely known that, until associated with an accurate ICC profile, the digital numbers in an RGB file have only ambiguous meaning as to colour and tone.
This is an issue which can bite quite hard when viewing, editing and converting RGB image files. Many RGB files are passed around the industry without embedded profiles. Providing an RGB file without an embedded profile is akin to tearing the cover and title pages off a book and then trying to work out what the book is!

The ICC profile:

The accurate ICC profile can be used to provide the information needed to translate the ambiguous RGB file values to a universal reference, a reference which is both unambiguous and which is directly related to human visual perception. (this reference colourspace is the L*a*b* colourspace – it is at the centre of colourmanagement. It is not necessary, however, to deal with L*a*b* numbers manually, Photoshop interprets the colour for viewing, editing and conversion.

When digital camera files are received without an ICC profile which properly relates to the RGB numbers, images can require quite considerable image processing to align the digital colour to the colour and tone of the original object.
Of course, an accurate ICC profile provides the information to carry out this alignment automatically

In some cases a simple adjustment to workflow can move the file a long way towards accuracy, however, assumptions about the originator’s intent (i.e. the desired appearance) will have to be made.

Of course, this situation applies to scanner files too. Unfortunately, many scanners are used in a way that destroys tonal and colour detail at the outset and this can often be much improved by adjustment to workflow and the introduction of a good ICC profile to characterise the scanner’s behaviour.

Responsibilities of the image originator:

It is of utmost importance that image originators take good care when producing files, since bad or non-existent colourmanagement at image origination or during initial edits often leads to misunderstandings between photographer, art director and/or retoucher about “real appearance” and, thus, disappointment ensues when the print is completed.

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B: Ability to assess colour accurately
C: Separation of RGB to CMYK

Viewing, assessing & optimising output and RGB to CMYK file separation:-

Receiving files, checks in prepress or image processing
Provided that a properly Calibrated and Profiled Display System is available, and armed with the right knowledge, there are robust procedures for taking in image files from originators who may operate without good colour control.
In many cases, these protocols can fairly simply make up for errors in colourmanagement earlier in the workflow, but, of course, not for misguided colour and tonal edits.
Plainly there is no substitute for a well colour managed Display System and sensible colour settings in use at the time of origination and initial editing and image sign off.

Viewing:

When viewing a digital image on a Monitor Display it is imperative that the visual appearance is closely related to final appearance in print. To achieve this, two things are required, an accurate (i.e. well calibrated & profiled) Display System and, ideally, even when viewing RGB files, a CMYK press profile which truly anticipates on-press colour.

CMYK separation
(the “ink recipe”):

If the destination printing press is run in standard condition, then the relevant ∗standards based CMYK profile can be selected for soft-proofing (i.e. on-screen proofing) to assist operator assessment of just how the image in question can be expected to reproduce in print.
Of course, each CMYK press type or condition (paper, ink type etc.) needs different colour recipes, so that the CMYK numbers change dependent on destination (e.g. coated, un–coated, sheet-fed, web).
Good ICC profiles simply deal with this.
The same (perhaps *standards based) CMYK profiles are used to convert, or separate, RGB to CMYK in a way which provides a file to the printer which actually suits his normal printing condition well.

∗standards based CMYK profile = an ICC profile built from data collected from a press run to a standard, perhaps an ISO, or other industry accepted standard.

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D: proofing, and proof control checking proof quality:

Proofing the output:

As long as the process of making printed proofs is controlled by good colour management and with settings that truly relate to actual press output, then proofs will provide an accurate preview of standard press output. Of course proofing equipment will require a regular re-calibration, again, to a standard condition.

It has been said that "There is no proof without an Ugra/FOGRA MediaWedge." That is a pretty powerful statement, but if a proof purports to represent press potential (and we believe that it must), then that must be able to be proven. The addition of an internationally standardised control wedge, e.g. an Ugra/FOGRA MediaWedge, to any proof allows a user to easily read the strip into diagnostic software and assess proof accuracy.

The Ugra/FOGRA MediaWedge

Print appearance optimised up front, the advantages:

Users can now both soft (screen) and hard-proof files in the secure knowledge that content seen on screen and on proofing stock is truly achievable on press. This means that fine tuning of images can be brought forward in the process and that, potentially, on–press Make-Ready time and paper wastage is much reduced. It’s always a positive to save time and money whilst increasing quality and predictability. If the relationship between pre-press and print is well controlled a better financial relationship is fostered also.

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E: CtP (plate) compensation curves
+ optimising the press condition:-

In a quest for consistency of output and better proof matching, many client’s and print management companies require their printing jobs to be run to ISO standards. In the UK it seems that the bulk of general sheet-fed commercial work is now commissioned by those who want to see printing done to relevant ISO standards.

Adjustments to the process: -
CtP (or film/plate) process and press settings have an inseparable relationship and should be thought of as almost a single process.

In the past, many Image–Setter, CtP and on-press processes have, by necessity, been adjusted either to compensate for badly separated CMYK or to match badly made proofs, or perhaps both. When this is the case and the process has been adapted by moving the print process away from a standard condition, the supply of well-separated CMYK, although a step in the right direction, is somewhat futile.

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Why do the work?

Once CtP (or film/plate) process and press settings have been optimised to enable printed output to reach a standard (like ISO 12647-2, 2004), then, to take advantage of the improvements, incoming data should be properly controlled. Working to a standard is ideally a complete workflow process so that image and page data suppliers need to take proper control of both RGB to CMYK conversion and of expectations of printed appearance, by viewing/proofing accurately. Running to a standard means that this can be attained with relative simplicity.

When printing doesn’t work, the proof and the print job:
The loudest complaint that I heard from a large group of press plant owners and press operators at the GATF (Graphic Arts Technical Foundation) conference, Phoenix 2004, was that, often, supplied proofs do not match supplied digital data.
This would mean that when run on press at standard weights, the print is way off from the client’s desired appearance as seen on the supplied proof. When a job is supplied like that, digital data can be a real pain to print as the client’s expectations are often unreasonable when based on signing off an inaccurate proof.

Until we work in an industry where CMYK separation, proofing and print are all carried out to a proper standard, this will always be a “chicken and egg” situation: –

– Who should pay for the adjustments, especially if the job has to be pulled and plates must be remade?

– Which section of the industry should be the first to move to using standards based working methods.

What’s happening?
Currently, adoption seems to be operating on a piecemeal basis, with the standardisation snowball gradually picking up speed. Advantages are becoming increasingly apparent as momentum in the industry increases.

So, the biggest commissioners want standards based working methods, and are looking for better predictability and, inevitably, associated cost savings. It has been said that the ISO standard steamroller is on the move, better jump aboard, or become part of the road.

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The Press, at the heart of the process:

It is our belief that the printing press should be thought of as the heart of the colour reproduction system and that, once CtP and press are run in an optimum state, as defined by a proper standard (like ISO 12647-2, 2004), the press should be the target for CMYK separation. Any CMYK separation profile produced from measurement of a proof can be a poor second choice since press must then be pushed to match that proof.

It is far from ideal for the press condition to be adjusted, beyond basic running adjustments, on a job to job basis and at great cost to Make Ready times. Properly targeted separations make this a much less frequent necessity.

In practice, this adjustment process is often an unwelcome requirement, made in order to match proofs which have perhaps been made from CMYK data which has been separated badly, perhaps using an ICC profile which was made from a proof or perhaps even to a CMYK setting which someone made in Photoshop’s Custom CMYK dialogue.

Services:

We can offer many services, ranging from training to implementation of colour management, CtP adaptation and press optimisation.

click here to download a pdf about our work at Christies International media Division. (.zip file 3.1MB)

One client comments:

Gordon Baird
Managing Director
Christie's International Media Division
Global Head of Christie's Fine Art Photography

"Following the introduction of end-to-end process colour management procedures and controls,  our Fine Art Auction Catalogues have never looked better.   This has been achieved by developing subject specific digital image capture profiles,  establishing CTP tone reproduction curves from internal press measurement data,  profiling our proofing devices to the press condition and creating a bespoke RGB to CMYK conversion profile.   The latter provides for accurate retention of the original subject matter's integrity in terms of colour,  detail and dynamic range."

"I can't shower sufficient praise on Neil Barstow for his professional guidance,  diligent involvement,  and support given to the production team,  in achieving this end.   We would unreservedly recommend his services to anyone wishing,  seriously,  to implement robust colour management practice within their organisation."

March ’06

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