Volume 8: Color Proofing Technologies
Color Proofing
Proofing is the critical link between the graphic production process and printing. A proof is the visual contract between the printer and their client. It is the closest thing to ink on paper, short of firing up the printing press.
As defined by several online print-provider websites, ‘a color proof is used to simulate how the printed piece will look. Because of differences in equipment, paper, inks, and other conditions between color proofing and production pressroom operations, a reasonable variation in color between color proofs and the completed job is to be expected. When variations of this kind occur, it will be considered acceptable performance and the proof becomes a contract between the client and supplier.’
The three leading proofing technologies are digital halftone, inkjet, and monitor proofing. These represent the predominate technologies in most graphic production departments. They also represent the majority of SWOP-certified solutions currently on the market.
Some readers may argue that toner-based systems should be included on this list. Although toner-based technology offers excellent results, it is not widely considered to be of high enough quality to be used as a contract proof. Color laser proofs are commonly used as an intermediate proof to review content and composition.
Measuring Quality
One of the most respected venues for evaluating proof quality is the IPA Color Proofing RoundUP, conducted annually at the IPA Technical Conference. The conference’s organizers evaluated nearly 30 color proofing systems this year, based on the following criteria:
- Visual match to the GRACoL press sheet
- Colorimetric match (Delta E) to the press sheet using a IT8.7/4 color target. Monitor-based systems matched the L*a*b* SWOP calibration test
- Ability to accurately reproduce multi-channel images accompanied by a multi-channel ICC source profile
- Match to specific Pantone solids and Pantone tints
- Costs of the system and media
Digital Halftone
Digital halftone is the Ferrari of the three proofing technologies. Digital halftone systems can cost several times that of other systems. Likewise, digital halftone proofs cost many times that of other types of proofs. However, like the Ferrari, you get what you pay for.
Most digital halftone devices use laser thermal imaging to produce a proof. A laser beam strikes a color-coated donor sheet causing the colorant to be transferred to a receiver. The receiver is often a transfer sheet, or carrier. The image is then transferred from the carrier to the actual printing stock or other substrate using a combination of heat and pressure. Donor materials are coated with pigment-based colorant that closely simulates the color characteristics of printing inks.
Digital halftone proofs replicate the halftone screening method used for offset printing: screen ruling, dot shape, dot gain, and screen angle. Therefore, digital halftone proofs provide a better indication of printed detail and the possibility of moiré patterns.
Another major advantage of digital halftone proofs is their ability to be produced on the same substrate as the actual printed piece. This is a significant advantage over inkjet proofs, which are limited to specially coated stocks, and as a result must simulate the actual paper color by altering the overall color of the proof.
In addition to screening and choice of substrates, digital halftone devices offer other unique features such as the ability to produce true metallic colors and print with opaque white for use on clear and other specialized substrates.
Inkjet
Inkjet has become a reliable and widely accepted alternative to digital halftone proofing. Not too long ago most printers would have balked at being asked to match an inkjet proof on press. However, over the past five years, advances in inkjet technology and color management software have made inkjet a worthy alternative to digital halftone technology. In fact, many printers now provide them to their customers as a contract proof.
Unlike a digital halftone proof, inkjet proofs do not reproduce the halftone dots. Tiny droplets of ink are sprayed from a print head through a series of small nozzles onto specially coated paper, which dries immediately. Advances in inkjet technology allow for near-continuous tone proofs with dot sizes of 2 picoliters or less.
While digital halftone devices require highly-specialized lasers, costly pigmented donors, and proprietary software, inkjet devices rely on commercially available color management and RIP technology to achieve color fidelity. Using ICC color profiles, inkjet devices can be ‘tuned’ to accurately simulate varying printing technologies and substrate characteristics. For a further explanation of color management and its application to proofing, please read the second edition of The Digital Edge, available on our website.
Monitor Proofing
Often referred to as soft-proofing because of the lack of a physical or ‘hard’ proof, true contract-quality monitor proofing only emerged on the scene about four years ago. ICS’s Remote Director(TM) became the first SWOP-certified monitor-based proofing system in January 2003. Today SWOP has almost 20 certified monitor-based systems listed on their website. This year’s IPA Color Proofing RoundUP featured seven monitor-based proofing solutions. Three years ago, only one monitor-based system participated in the annual event.
Running on commercially available hardware, monitor-based systems rely on advanced color management software to approximate the brightness, color, and contrast of a printed piece. This is no small challenge, matching the characteristics of transmitted light on a monitor to reflected light from a printed piece. Monitor-based proofing systems rely on tightly controlled room lighting and viewing booth conditions for accurate color evaluation between screen and printed piece.
Monitor-based proofing systems have the ability to provide added features such as real-time remote viewing, collaborative review, mark-up, and digital sign-off.
The Future of Proofing
Recent technologies such as PDF, CTP, and digital printing have dramatically changed the graphic arts industry, which includes proofing technologies.
A few years ago the list of proofing technologies would have included analog technologies such as Cromalin®, Color Key(TM), and MatchPrint(TM). These were used to proof color-separated films. Similarly, in a few years this list may not include any digital ‘hard’ proofing technologies.
Take for example digital printing, where it is common to print a single piece for a customer’s approval as opposed to generating a proof. Printing one piece with a digital press is much more cost effective than with a commercial press. There are no films, no plates, no make-ready, no time wasted getting the press ‘up to speed’, and no wash-up afterwards.
Tighter deadline, shorter budgets, global print procurement, and falling flat-screen monitor prices will continue to increase the use of monitor-based proofing for all types of printing. Standard technologies such as PDF, JDF, and ICC color management will ensure end-to-end quality and consistency. Lastly and most significantly, newcomers to the industry, more comfortable with digital media then their ‘analog’ predecessors, will readily accept monitor-based proofing. -gs
