Colour accuracy checks and proofing

Introduction

This page has been written specifically for designers interested in colour accuracy, working in-house or remotely. If you’re looking to setup your computer with the correct settings, please read the colour management page on this site.

Monitors

The bedrock of any colour managed workflow and system is an accurately calibrated colour monitor, especially if you are working out of the office. The position of the monitor in relation to ambient light is important and can affect your perception of colour. At Embassy Gardens we have calibrated monitors specifically used for colour sensitive work. More on this in the assessing colour section below.

Daylight is very changeable so:

• Choose a low level light room with little colour change
• Have neutral surroundings
• Avoid placing the monitor by a window if possible
• Calibrate your screen

Proofing

The main reason for proofing, whether on screen (soft proofing) or on paper (hard proofing) is to have a simulation of how colours will be reproduced by a printer running to international printing standards (ISO). Non-profiled images will display, proof and print unpredictably. The only way to prove how these images will print is for us to proof, after being viewed/converted to our working colour profile by our colour management system.

As colour perception and printing technology varies, colour standards have in-built colour tolerances (or margins) for passing or failing accuracy.

Colour difference can be measured using the term ΔE (Delta E) using a spectrophotometer. A score of around 2ΔE or less between separated swatches would be imperceptible, and 3 to 6ΔE would be considered a single ‘step’ in colour change. For comparison purposes, we have used ‘grey balance’ ΔE measurements and listed below the accuracy of each output device.

1. Typical ‘Digi’ proofs are calibrated, and outputs checked, to a tolerance from prepress ISO standards of 1.5ΔE. Above this level and the machine would be re-calibrated till it passed.
2. Our in-house colour room monitors are calibrated to prepress ISO standards of 2ΔE and are checked quarterly.
3. Press sheets can be measured for colour accuracy using PressSign software at our print suppliers, and have a tolerance of 2ΔE, although in some cases we can accept colour slightly beyond this tolerance level.
4. Laser printers are not accurate and must not be used for assessing colour. Significant colour changes have been found across consecutive outputs, and across calibrations.

Assessing colour

Our colour rooms are areas where ambient light and colour are controlled to reduce inconsistency in the representation of colour on monitors. This is useful for the accurate assessment and adjustment of layouts and PDFs ready for production. We use hi-spec monitors which are far more accurate than standard to display our material. A light box in the colour room can also be used to compare proofs and press sheets and if necessary. Adjustments using software can then be made on screen.

Soft proof (screen proof)

Soft proofing is the action of using a screen or monitor to judge the quality and accuracy of digital images. You must use a calibrated screen and software that has Colour Management enabled and set correctly.

For design and production

We recommend monitor colour temperature should be set to 6500k and gamma 2.2 (or set by your calibration software). Brightness set to between 80% and 100% of maximum (or set by your calibration software). Allow 15 minutes for your monitor to warm up, for accurate display of colour. In Photoshop view images at no less than 100% for accuracy when retouching, and in Acrobat, view PDFs at approximately 400% for genuine assessment of layouts and with separations switched on in Output Preview.

For printers

Quality Print Supplier who print to the ISO 12647-2 press conditions and apply the FOGRA press characterizations print our files without any manual adjustments on press. This means that files that have been approved on screen for colour are sent directly to the press and printed.

Whilst the press is running consistently to the required press conditions there is no need for hard copy proofs. This method is not yet suitable for all Suppliers and only those who have had prior discussion and agreement with Penguin Group (UK) technical production staff will be asked to work in this manner.

Plotter proof (lo-res digital proof)

For design and production

For all new printings, including Co-Edition language versions, we require a colour plotter proof for final approval which includes colour and text. These are not for colour checking, but are used to check the pagination, imposition, the combination of Co_Edition Base CMYK and Translation PDFs and the subsequent flattening.

For printers

• All quoted costs are to include 2 sets of plotter proofs per language and inclusive of courier costs.
• All plotters are to be supplied as an imposed booklet, gathered into the correct sequence and trimmed to show trim marks and bleed.
• Plotter Proofs must be rendered using the same RIP used for final plate-making to avoid discrepancies between plotter proofs and final plates.
• On all titles, plotters are to be supplied in one batch, regardless of the extent unless otherwise agreed.
• On co-edition printings, the Supplier must supply complete plotters of each language as files become available. The Supplier must not hold up the production of plotters, waiting for all edition files within the co-edition production to be available.
• For reprints, the printer must provide plotters of the cover, jacket if applicable and imprint page for approval.

On-Screen plotter proofs

Penguin Group (UK) is actively encouraging the supply of on-screen plotter proofs, either as PDFs via FTP or soft proofs via a pre-press system e.g. Kodak’s InSite.

As with the hard copy plotters, On-Screen Plotter Proofs must be rendered using the same RIP used for final plate-making to avoid discrepancies between plotter proofs and final plates.

The decision to use on screen plotter proofs should be agreed in advance with the Production Controller.

Digital proof (contract proof)

Digital proofs, also known as ‘Epsons’ and named after the manufacturer, are physical paper prints that vary in inkjet printing technology from traditional printing presses but will render files very accurately.

For production

All digital proofs are output to the specified FOGRA output intent and with the FOGRA CMYK Media Wedge which is measured to certify that they are accurate. See Colour Management for more detail.

We expect our printers to match the colour on press sheets to the contract proof if provided, if this is not achievable Production should be informed immediately.

For older titles and reprints where contract proofs are not available we may supply a previously printed book as a guide. If colours cannot be matched when printing in accordance to ISO12647-2 tolerances please discuss with your Production.

We require Suppliers to keep contract proofs for 6 months after the RAP date (if supplied).

Wet proof (press proof)

Wet proofs are press printed sheets intended for colour assessment or colour matching on press, and should be printed in accordance to ISO 12647-2.

With colour management in place, we now use calibrated screens and certified digital proofs for colour accuracy.

Wet Proofs should only to be used if the paper stock, inks or finishes are ‘out of the ordinary’, or the print supplier is struggling to achieve the required colour standards.

Please only supply wet proofs if requested by Production.

If you are wet proofing at Clays, a PressSign sheet should be supplied by Clays with the accompanying sheets to confirm colour accuracy. If this has not been supplied, please contact Clays immediately to obtain one.