Colour Management: Developing a RIP-to-roll workflow

by all | 2 November 2017 10:41 am

By Sal Passanisi
The short runs—and even shorter lead times—of today’s wide-format printing market can pose quality challenges for the sign and display graphics industry. To meet these challenges without compromise, sign shops’ operations must evolve to support a completely colour-managed workflow, from raster image processor (RIP) software to digital inkjet printer to roll or rigid media.

Fortunately, achieving this goal is easier now than ever for both sign shops and commercial printing companies. The following are some of the insights they have gained from this experience over the past several years.

Begin at the beginning
Where possible, sign shops should ensure all of their image capture and display devices, including cameras and monitors, are correctly colour-profiled and calibrated, so as to ensure the printed cyan, magenta, yellow and key/black (CMYK) graphics match the originally captured and displayed colours as closely as possible. There are numerous tools available today for developing and implementing International Color Consortium (ICC) profiles and for calibrating devices.

Colour matching can be a weak link in the workflow process because many companies are still using colour profiles from offset printing, which follow offset plate curve principles. Today’s digital printers—from small-format inkjet proofers to grand-format presses—can achieve a much wider colour gamut than offset and flexographic printers and, thus, can achieve results that were previously constricted by technology.

It is particularly important to optimize the calibration of computer monitors, so what is seen on the screen reflects exactly how the output will appear when digitally printed with CMYK inks. By getting the right colour profiles in place from the start and implementing a quality control program, signmakers can minimize the need for additional work ‘down the line.’

Consider the substrates
A trade show booth is an excellent example of the complexity involved in today’s sign and graphics production environments, as it may involve the inkjet printing of graphics on a wide variety of substrates, from polyvinyl chloride (PVC) and other plastics for rigid components to paper and textiles for flexible signage. The white point of each base substrate can significantly affect the appearance of the printed output, so it is extremely important to take each material into account when developing and communicating colour specifications for a given project.

The most obvious examples where issues can arise are substrates that carry their own non-white base colour, such as brown kraft paper. Even backlit graphic substrates, however, may have varying white points.

Experts recommend establishing a digital master standard, assigning a spectral value for each colour. From there, other dependent standards can be created that reflect the spectral value differences for each given substrate. This way, sign shops can come as close to achieving the master standard as possible when targeting colours for various materials.

By taking each substrate into consideration during the graphic design and specification process, all colours can be aligned for an entire trade show booth, whether they are individually intended for digitally printed vinyl graphics, soft signage or even accompanying brochures.

A digital workflow
Beginning right at the design phase, a digital workflow has become preferable in today’s industry. While graphic designers love to not only see their work, but also touch and feel it, and there is still a need for physical standards in terms of colour guides, digital tools have become increasingly capable of allowing users to select colours and visualize them as they will appear on target substrates.

A designer can now measure a colour with a visualization tool before using a software plug-in like Adobe Illustrator’s to pull that colour into a graphic and finding the closest match for the intended substrate, all without having to wait for physical samples to be produced to see how far off-target the printed colours could be. Some visualization tools, for example, create a ‘soft proof’ that allows designers to check colours accurately on-screen. They even simulate the dot gain of the final printing process.

Designers also appreciate the opportunity to choose and add spot colours to their graphics, but they should be able to do so in a context that allows them to easily see (a) whether or not and, if so, (b) how those spot colours can be reproduced with CMYK inks on the substrate. The inks used in digital wide-format printers have a much higher pigment load than those used in offset or flexographic printing and, therefore, can achieve a higher percentage of colour matches.

Regardless of which model of printer will be used, everyone involved in the workflow should be able to know the optimal CMYK breakdown of
a spot colour for a specific substrate.

Ensuring print perfection
If all of the devices have been colour-profiled and calibrated accurately beforehand, then the design, pre-press and pre-media steps will all go more smoothly. This is important because today’s compressed production cycles do not allow for the production of numerous proofs, for samples to go back and forth with the client, for long setup times at the printer and then for the testing of materials to get tricky brand colours right.

Instead, today’s inkjet printers offer digital front ends (DFEs) with ICC colour profiles. In most cases, these profiles can be fine-tuned within the RIP software for the production environment with the specific ink set and substrate in mind.

A standard set of master parameters will minimize the need for corrections and reduce errors, as well as save time and money. By using the appropriate tools and techniques at the beginning to ensure files are optimized for printing, a sign shop can implement an entire ‘RIP-to-roll’ production workflow, increasing its throughput and improving its profitability.

Measuring before managing
As business management consultant Peter F. Drucker famously put it, “you can’t manage what you don’t measure.” Instruments for colour measurement are critically important parts of a colour management workflow.

Using a properly calibrated spectrophotometer at various steps, from design through pre-press and production, will help ensure colour standards are being communicated and the desired results are achieved. And if multiple spectrophotometers are being used across the production environment or throughout the supply chain, then additional tools should be used to ensure they are aligned with each other.

That said, even when one user measures a colour via spectrophotometer and finds it within tolerance, while another does the same elsewhere, the results may still fall far apart within the colour spaces; this difference is known as Delta E. Visual evaluation alone can be even more subjective.

This is why the common practice is not necessarily the best practice when it comes to colour accuracy. Instead of producing a new, physical sample to work with at each step of the workflow, it is preferable to provide access to the original colour data—whether a master or dependent standard—to be measured against.

A digital workflow makes this possible, whereby the exact colour specified by the designer can be accessed and used at each stage of production, from proofing to printing. This is the best possible approach for improving colour consistency all the way down the line, for everything from trade show booths to packages on retail shelves.

This technique also offers simplicity and efficiency when tackling a complicated colour management project. By way of example, it was used in 2016 with wide-format graphics for the U.S. College Football Playoffs, which were produced using a broad variety of printing technologies and substrates. As everyone involved was able to work from the same set of master standards, they could quickly determine which colour effects could or could not be achieved. This was important because there would be very little time to specify colours based on the outcomes of the games along the way.

Let there be light
It is also worth noting the perception of colours changes depending on the lighting under which they are viewed. As such, controlled lighting should always be used whenever colours are visually evaluated throughout the process.

A light booth that features several different modes should allow for evaluation under all of the viewing conditions the graphics will experience in the field. One major example is light-emitting diode (LED) illumination, a final standard for which is currently in the final stages of development by the International Organization for Standardization (ISO).

Six keys for colour

As print service providers (PSPs) aim to implement colour-managed workflows to help reduce costs and cycle times, while improving output quality, they should keep the following key instructions in mind:

1. Make sure all image capture and viewing devices are profiled and calibrated. Do not depend on offset-centric techniques when working with digital inkjet or dye-sublimation printing.
2. Always consider target substrates early in the design process and establish both master and dependent digital standards against which to measure colours at each step of the workflow.
3. Use customized ICC profiles for output devices, fine-tuning them to take best advantage of each particular device, e.g. the expanded colour gamut of a digital wide-format inkjet printer.
4. Use spectrophotometers as the primary physical means of evaluating colours, supplemented by visual evaluation. Make sure all of these instruments are aligned with each other for consistency.
5. When visually evaluating colours, always do so under controlled lighting, replicating the various conditions under which the graphics will be displayed.
6. Above all, establish standard processes to ensure effective colour specification, communication, measurement and management across the entire supply chain.

The best way to think of the process is not so much as ‘colour management’ in the abstract, but instead as optimizing colours for substrates, based on the applicable printing system. This may seem like a minor shift in thinking, but it is an important one, because it specifically accommodates today’s production technologies and demanding conditions when optimizing a shop’s workflow.

Sal Passanisi is a regional sales manager for X-Rite Pantone, which develops colour measurement and management hardware, software and services for the sign and display graphics industry. For more information, visit www.xrite.com[5].

Source URL: https://www.signmedia.ca/colour-management-developing-rip-roll-workflow/

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