Last Updated: 01/11/2016
prepress and print
colour management in prepress and print, is it helpful?
digital input, prepress, accepting images
In the printing industry, the transition to successful reproduction of digital images, those captured digitally and/or supplied electronically was, and for some still is, an uphill struggle.
Scanning transparencies, the standard for input for many years is largely in the past
When scanning, a final transparency film could be considered a definitive reference to the image originator or client’s intent. In many cases the transparency was first scanned, then output as a press-ready CMYK file using a traditionally set up scanner. The CMYK file was produced automatically with no place for ICC profiles.
Digital imagery needs quite a different approach and, plainly, a different expertise.
digital origination of images
During an images passage from originator to designer, retoucher and the pre-press room, various users may carry out colour and tonal correction – and in many cases the desired appearance is rather ambiguous since no accurate proof is done until far later in the process, it may even be viewed on an un-calibrated screen. When image viewing and correction relies on screens they all need to be set up right or issues can crop up with each alteration.
CMYK “recipes” for inks on paper
Why not just make "CMYK" like the old days and work by the numbers?
Like RGB, a CMYK recipe, in the form of a "CMYK setting" or, more ideally, an ICC CMYK profile is absolutely device specific. This means that it is made to suit a particular type of printing machinery and paper surface. For example, “sheet-fed coated”, “sheet-fed uncoated”, “ web offset coated” and “ web offset uncoated”. In order to achieve continuous appearance, these different paper categories and press types actually require quite different CMYK recipes (i.e. different mixtures of inks and, thus, quite different plates) to attain the same printed colour on paper!
This is because the papers and the press types have different qualities. The same original CMYK file made into a single set of plates and printed across those devices/papers listed above would provide quite a different printed appearance. If skin tones or neutrals are included, for example, this can cause quite an issue as errors of colour cast are really easy to spot on the final print. Same goes for product colour.
Unfortunately, as we know, even quite inexperienced users of ©Adobe Photoshop, perhaps designers or photographers, might feel they can "separate" RGB to make CMYK and this is most often done without any guidance, or knowledge of press destination and / or paper type. Perhaps even using Photoshop defaults.
This can mean that combining files from different originators on one set of plates might result in a mixed bag of CMYK recipes, all printed on a single press sheet.
So, as an example, the neutral grey areas on different images might contain different ink mixes. Plainly, this is a nightmare for the printer since a correction fixing one area would cause a problem in another area.
the future is here
Robust guidelines for print, proof and CMYK preparation are needed, to enable users to prepare CMYK files from RGB and to make proofs the right way, using the right CMYK “recipe”. Also to make the "right" plates. But, in order to provide universally useful guidelines, the printing process ideally needs more standardisation in practice.
So, what can be done? And can good practice help solve these problems?
click here for an article about my own work in this area with Gordon Baird at Christie's International media Division.
what is a “standards based workflow”?
In a standards based workflow the combination of CtP (or image–setter/film/plate) and press is run to an ISO standard, generally ISO 12647-2. All Proofs should include a standard, recognised, colour wedge, such as the Ugra / Fogra Media Wedge CMYK, which can be measured and checked for accuracy. CMYK ICC profiles which accurately reflect real press output are used when separating to CMYK also for soft–proofing and proofing. More below:
the major concerns in producing and handling data for print:
incoming file integrity
ability to view and, therefore, to assess colour accurately
separation of RGB to CMYK (which ICC profile, if any?)
proofing and proof control, checking proof quality
CtP (plate) curves
the press condition
the Press room
Historically, the printing industry has found that files from digital cameras can be somewhat difficult to deal with.
But why? - what's with digital images and their colour and tonal values:
When viewing, editing, proofing or converting a digital image within Photoshop (since v5, 1998), ICC profiles are always used. If ICC profiles are not properly specified for an image, (even with Colormanagement set to OFF) a profile has to be assumed by Adobe's colour management mechanism. So, setting colour management Policies to OFF does not really mean colour management is OFF, it just menas that changes may happen without the user knowing about them.
Unfortunately it's not widely known that, unless associated with an accurate ICC profile (such as AdobeRGB1998.icc), the digital numbers in an RGB file have no real meaning in defining colour and tone.
This means that if a digital image file is opened without using an ICC profile, (i.e an image without an embedded ICC profile, or if that profile is ignored) assumptions have to be made about the meaning of the RGB colour numbers and this can have some seriously undesirable results.
This is an issue which can bite quite hard when viewing, editing and converting RGB image files. Historically, many RGB files have been passed around the industry either without embedded ICC profiles or, even, in some cases with an incorrect profile embedded. In summary, an RGB file must have a correctly embedded ICC profile to be of any real use.
The embedded ICC profile, what is it doing:
The ICC profile is able to provide the information needed to translate RGB file values to universal reference numbers, the numbers in a reference colour space are both unambiguous and directly related to human vision.
The reference colour space sits quietly at the centre of colour management.
If digital camera files are received without an ICC profile which properly relates to the RGB contents, those files can require quite considerable image processing to achieve correct appearance - to match the colour and tone of the original subject or the image creators intent.
An accurate ICC profile provides the information to carry out this alignment automatically, appearance will be correct on screen, given that well calibrated display systems are in use throughout.
In some cases a simple adjustment to the protocols for receiving files can move image appearance a long way towards accuracy. However, if there is no ICC profile, or with an incorrect one, assumptions about the originator’s intent (i.e. the desired appearance) will have to be made.
Of course, this situation applies to digital scanner files too. In addition to this, unfortunately, many scanners are set up from the factory in a way that automates a superficially attractive appearance, but this may often destroy tonal and colour detail. This situation can often be much improved by 1: adjustment to settings - and - 2: the production of a good ICC scanner profile to characterise and define the scanner’s behaviour. Then files can be taken and viewed and appearance will be reliable.
Responsibilities of the image originator:
It is of utmost importance that image originators such as photographers and designers take good care of their working methods when producing files, since bad or non-existent colour management during image origination or during initial edits often leads to misunderstandings between photographer, art director, designer and/or retoucher about “real appearance” and, thus, disappointment often ensues when print is eventually viewed.
ability to assess and fix colour accurately,
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, even from originators who may operate without good colour control.
In many cases, these protocols can fairly simply make up for errors in colour management earlier in the workflow.
When viewing a digital image on a monitor display it is important that the visual appearance is closely related to final appearance in print. To achieve this, three things are required, 1: an accurate (i.e. good quality well calibrated & profiled) display system), 2: decent viewing conditions (subdued neutral light, no bright coloured walls etc.) and, for viewing RGB files, 3: a CMYK press profile (for soft-proofing) which truly anticipates on-press colour for the process in mind.
When adjusting files, corrections to colour and tone must be based on calibrated screen appearance and correct viewing conditions. Soft-proofing adds a further level of sophistication to this process in that printed results can be better anticipated. It's plainly futile to correct colour and tone on a system which may differ in appearance from another system down the line or which misleads as to printed results. Of course the ability to produce an accuaret printed proof further aids this process of optimisation - see proofing, below.
Using the “ink recipe”
If the printing press to be used on the job is run in standardised condition, then the relevant ISO standards based* CMYK ICC profile can be selected for soft-proofing (i.e. on-screen proofing), this will really help the operator to see just how the image in question can be expected to reproduce in print.
As discussed above, to achieve accurate printed colour, within paper capabilities, each CMYK press type or press condition (paper, ink type etc.) needs different ink recipes. In summary, the correct CMYK ink value numbers change, dependent on destination (e.g. coated, un–coated, sheet-fed, web etc.). There must be no such thing as "just give me CMYK" in an accurate working environment.
Good ICC profiles deal simply with this situation by providing accurate ink recipes. The *standards based ones are available for free.
In an ideal world, good (normally *standards based) CMYK profiles are used to convert, or "separate", RGB to CMYK in a way which provides a file to the printer and thus a plate which actually suits his normal printing condition well.
*standards based CMYK ICC profile = this is a profile built from data collected from a press run which was optimised, well controlled and according to the relevant ISO, or other industry accepted standard.
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 a very accurate prediction of standard press output. Of course proofing equipment will require a regular re-calibration to keep it in standard condition.
"There is no proof without an Ugra/Fogra Media Wedge." A pretty powerful statement - but, if a proof purports to represent press potential (and I believe that it must, rather than "doing it's own thing, like the old Cromalin), then that match must be able to be proven. The addition of an internationally standardised control wedge like the Ugra/Fogra Media Wedge below, allows a user to easily read the strip into proof control software to assess proof accuracy.
The Ugra/FOGRA Media Wedge
Print appearance optimised up front, the advantages:
With properly accurate proofing, users can now both soft-proof (on-screen) and produce printed proofs of files in the secure knowledge that content seen on screen and on the proofing stock is truly achievable on press. This means that the process of fine tuning of images to suit reproduction can be brought forward in the process. Corrections can be made before plates are produced, long before ink hits paper on press. With good proofs and good procedure, on–press Make-Ready time and paper wastage is much reduced since plates are optimal so major adjustments to appearance at press side are no longer necessary. It’s always a positive step to save time and money whilst increasing quality and predictability.
If the relationship between image originator, retoucher, prepress and print is well controlled, better quality and a better financial relationship is fostered.
In a quest for consistency of output and better proof matching, many clients and print management companies now require their printing jobs to be run to ISO standards. The UK seems to be moving towards a situation where the bulk of general sheet-fed commercial work is commissioned by those who want to see printing done in compliance with the 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.
Historically, many plate production and on-press processes have, by necessity, been adjusted either to compensate for badly separated CMYK or to try match consistently badly made proofs, or both. It can get very tangled.
Where 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.
The target has been moved.
why do the work?
Once the plate making process and press settings have been optimised to enable printed output to reach a standard (e.g. ISO 12647-2), then, to take advantage of the improvements, incoming data can be properly controlled.
Working to a standard is ideally a complete workflow process so that image and page data suppliers take proper control of both RGB to CMYK conversion and of expectations of printed appearance, by viewing/proofing accurately. Running to a standard and god calibration protocols means that all of this can be attained with relative simplicity.
When printing doesn’t work, the proof and the print job:
The complaint that I heard most universally from a large group of press plant owners and press operators when I presented at a US Graphic Arts Technical Foundation conference, was that, far too often, supplied proofs do not match supplied digital data. This means that proofs look OK, but image file data is "wrong".
If the proofs were re-made on an accurate proofer, the appearance was significantly different to sign-off expectations. The client wanted a match to the "wrong" proof which they had signed off. That's hard to achieve and it's an unfortunately familiar situation.
In this scenario, when the unaltered job is run on press at standard weights, the print is way off from the client’s desired appearance. When a job is supplied like that, digital data can be a real pain to print as the client’s expectations are plainly unreasonable. What's happening here is that the proof actually looks good only because the content has been adjusted to suit the proof - despite the fact that the "proof" does not properly represent press output of the CMYK data supplied to be printed. It's not really a 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 remade?
– Which section of the industry should be the first to move to using standards based working methods.
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.
The biggest commissioners of print want standards based working methods, and are looking for better predictability and, inevitably, for the associated cost savings.
The print standards steamroller is on the move, better jump aboard, or become part of the road.
It is my belief that the printing press should be thought of as the very heart of the colour reproduction system and, that once CtP and press are run and maintained in an optimum state, i.e. in accordance with a proper press standard (like ISO 12647-2), the press should become the target for CMYK separation.
ICC CMYK profiles are incredibly important , as you read above, it's the ICC profile that provides the ink mixing recipes when transforming (separating) RGB files to CMYK.
This means that the CMYK separation ICC profiles must be produced from actual press data. A range of ICC profiles produced from standard press data are available for free download at eci.org.
Any CMYK ICC separation profile produced from measurement of a proof is quite a poor second choice (unfortunately, many "press profiles" have traditionally been made from proofs, for example Adobe's Euroscale Coated v1) - This is bad, because using such profiles makes for unsuitable plates and means that the press must daily be pushed away from it's ideal state.
It is far from ideal for the press to be adjusted, beyond basic running adjustments, on a job to job basis because of the great cost to make ready times. Properly targeted separations mean good plates, making this a much less frequent necessity - when running those separations through a well set-up CtP and a press run to the right ink weights, that is.
In summary, I have seen that day to day, large press adjustments are an unwelcome requirement and are in most cases made by necessity in order to match poor proofs. These proofs can be poor for many reasons, they may simply be from a poorly set up proof printer, or may have been produced using badly separated CMYK data.
Maybe those CMYK separations were made as mentioned above, using an ICC profile generated by measuring a proof - or perhaps even using a Photoshop "CMYK setting" which someone made using Photoshop’s Custom CMYK dialogue (this option is a legacy from Photoshop 4 and a very poor substitute for a "real" ICC press profile).
Working with calibrated displays in suitable lighting and properly matching the CMYK separation and proof to the standardised press, all falls into place
I can offer many services, ranging from training to implementation of colour management, CtP adaptation and press optimisation.
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. I would unreservedly recommend his services to anyone wishing, seriously, to implement robust colour management practice within their organisation."
click here to read an article about my work with Gordon Baird at Christie's International media Division.
click here for Christie’s website
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