Everyone who is familiar with the prepress proofing aspect of the printing business has probably heard a tale of the print salesperson who meets his client in the local adult-beverage lounge. Happy hour is a good time to relax and get to know your client outside the work environment. And by the way, he brings along the latest contract proof of a packaging job for the client to approve and sign. The client has a seat in the subdued lighting of the lounge, they discuss the job, the salesperson shows him the proof, the client looks at it from a few different angles, says "Yeah, that's looking really good" and signs off on it.
A week or so later, the client receives his printed product and the color reproduction is not even close to what the client thinks he signed off on in the bar.
And so the story goes. The nature of color reproduction requires consistency, predictability, and repeatability. This begins with viewing color in lighting similar to the environment in which the final printed piece will be displayed for sale, and carries through to setting standards for ink, substrate, and so on. So although this story is a bit farfetched, the contract proof, by its very definition has been a debatable target, especially in the flexo arena.
The default explanation for the variability of color in the flexo process is typically stated as, "Well, we don't have standards such as SWOP, Gracol, Euro, etc., and the press configurations and ink delivery systems have many variables, so each printer is different and standardization is a nice concept but not practical." Well, the standardization is an ongoing process and is in development with such industry supported approaches as FIRST, Flexographic Image Reproduction Specifications and Tolerances. This approach is designed to provide guidelines, however, not standards like SWOP for offset. But flexo is certainly moving in the right direction.
As we watched the evolution of computer-to-plate (CTP) adoption in the offset industry, the one facet of the process, which slowed this adoption initially, was the lack of a solid digital proofing method. Over time the proofing technology moved ahead, and once it was implemented we saw a renewed interest and a more rapid pace in the onslaught of CTP in the commercial offset market.
We can learn from this history as we make our way toward a digital flexo platemaking implementation. Most successful adopters of digital flexo thus far, whether using photopolymer mask ablation or direct laser engraving, have taken the step of stabilizing their new digital proofing process prior to installing the flexo imager in the plate room. This has enabled them to establish the relationship between the press and the proofing system output and verify that the digital prepress system can match the output of the press. Because after all, the objective of any proofing system is to faithfully represent what the output of the printing machine will be.
Over the course of time, and driven by the adoption of CTP technologies initially in the offset sector and now more recently in the flexo segment, a variety of technologies have been and will continue to be utilized by printers and prepress providers to present color to their clients.
Our purpose here is to convey the attributes of one technological approach, digital halftone proofing. We will review this process in general terms, illustrate the technology with one manufacturer's approach, and follow this up with a more in-depth look at alternative proofing methods in future articles.
By definition, the contract proof sets the print buyer's expectation of what the printer will deliver as finished goods from a graphical reproduction standpoint.
What should a contract proof do? A proof should accomplish three things:
1. Contract: It is the agreement between the budget holder and the print provider;
2. Communication: It communicates the desired result to those responsible for its creation; and
3. Risk reduction: The proof serves to reduce the risk to all participants in the process.
To illustrate this approach, we will use the Prediction Digital Halftone Proofing System from Latran Technologies. Additionally, Kodak and Creo have digital halftone proofing offerings that deliver similar halftone proofs utilizing slightly different imaging technologies and proofing media. Time and space does not allow for complete description of each system available. Specific information can be provided to the reader by the author if needed.
There are three components to the Prediction system: the RIP, the imager and the finisher/laminator.
The system will accept 1-bit TIFF data from most major prepress system vendors, such as Esko-Graphics, Creo, Rip-It, AGFA, Artwork Systems, and more.
With its ability to output at 2400 or 2540 dpi resolution, the system will match the output of the leading plate setting systems.
The Prediction system is available in two basic formats: 1420 (13.5" x 19.3") and 2230 (22" x 29"). Fully automated systems and semiautomatic versions are available. Because of the nature of the packaging business with the plethora of spot color requirements, most flexo applications will utilize a semi automatic approach.
Once a press profile has been completed, illustrating the typical range within which the press prints routinely, a set of pigmented ink sheets is matched to those color parameters. The available ink sheets are based on the following industry standards: SWOP, GRAcol, Eurocolor, Publication, and Pantone Hexachrome. Additionally, specialty spot colors and metallics are available. Software development is being finalized as I write on a soon-to-be-released product known as Dalmatian. Dalmatian expands the available proofing gamut for spot colors and will accurately predict the color of the spot utilizing Prediction's extended gamut CMYK set plus red, green, blue, orange and purple. Spot colors are imaged with process colors, and a density dial enables a consistent digital adjustment for solid color densities.
Spot color reproduction continues to be the most sought-after characteristic of a contract proof. Although all spots are not 100 percent achievable with any system, much work is being done to close the gap by all manufacturers involved in the digital halftone proofing arena.
Appropriate color tables and ICC profiles can either be sent with the file to the imager or can reside on the system as standard parameters.
The notoriety of this particular system comes from the ability to image directly to a broad range of typical substrates and the capability to transfer to even more. The limiting factors in direct imaging tend to be surface treatment for film substrates, and the ability to vacuum-hold a heavier board stock, for example, onto the imaging drum during imaging.
In these cases, the ink sheets are imaged to an intermediary stock known as ERM - extended range media. In this case, the pigment from the ink sheet is transferred to the ERM color by color as in normal imaging procedures. Once the entire job has been imaged to the ERM, it is combined with the substrate and fed through a laminating device wherein the pigment is transferred to the substrate. There is no laminated sheet left behind on the substrate surface, just the ink pigment. Options are available to transfer a matte or gloss finish over this for matching this requirement as it arises.
The Prediction uses laser ablation transfer technology, pigmented ink sheets and a transfer lamination process (in the event that the substrate properties preclude imaging directly to it). (See accompanying image.)
The process goes like this:
The operator sends the screened file to the Prediction workstation. Press dot gain is either applied in the prepress system then sent over as a 1-bit TIFF, or alternatively an uncompensated file is sent over and the press gain curve is applied there. The Prediction RIP accepts PS, EPS, TIFF-IT, PDF, 1-bit TIFF input.
The operator selects the appropriate ink sheets determined by spectrophotometer analysis of the printer's ink drawdowns. In the case of imaging directly to the substrate, the substrate is located on the vacuum drum. In cases where the image needs transferring to the substrate after imaging, the ERM is located on the vacuum drum.
The individual ink sheets are located over the top of the substrate/ERM and the individual digital images are fired by the laser imaging head at the ink sheet. The imaging spot size is 10 microns with this system. Other digital halftone proofers are typically in the 21 to 27 micron range. This reaction causes the ink pigment to be transferred from the ink sheet to the surface of the substrate - as is done on the printing press. The process is repeated for all colors. In the case of imaging to the ERM then transferring to the substrate, the pigment is transferred from the ERM to the substrate and the ERM carrier is removed. This process accounts for low optical dot gain values associated with the system. Therefore when dot gain curves are similar in the proofing stage to what is experienced on press, makeready times can be significantly reduced.
The pigment thickness on the proof is 3 microns and the registration is within 10 microns.
So how has this proofing method been accepted in the market place? The best source of information about any technology is the end user.
Following are excerpts of testimonials (supplied by Latran) extolling the benefits of digital halftone proofing:
What were your selection criteria for adding digital proofing?
"We opted for this system for several reasons. First, it produces a dot proof. Second, because we print on several different substrates, it allows us to transfer our images to the specific substrate that is being used for the job, so we can color-correct to the substrate. Third, we like the idea of being able to use ink sheets that closely match our inks and densities on press. Fourth, the system was recommended to us by a commercial offset printer who has had great success with it." (Andre Michaud, graphics director, Dow Industries, Wilmington, MA, USA)
How has the digital halftone proof been received by your major clients?
"After working for so many years with the guesswork of analog proofing, the biggest challenge has been to get our customers to understand that the four color process they see on the proof is what they can expect to see on press. When they sign off on their contract proofs from this system on the actual substrates we're going to run on, they know that's what we will deliver on press. It definitively saves them the time and expense of on-press approvals." (Mark Howard, VP of graphic services, Syracuse Label, Syracuse, NY, USA)
How was your proofing criteria met by digital halftone proofing?
"We investigated high end proofing systems for three years before making a decision. We were looking for technology that would enhance what we needed in our operations. We were looking for price points that would fit into our channel, and we were looking for proofing media that was easy to work with. This system is extremely accurate and is consistent from day to day. We calibrated it when it was installed and it has not deviated from that calibration since." (Paul Harstrom, composition manager, Discount Labels, New Albany, IN, USA)
So digital halftone proofing has had a significant impact on contract proofing, having been the standard in the offset CTP sector for many years. Now similar trends are being seen in the flexo CTP world. With the ability to image to the substrate being printed, using the same halftone screening as is used in plate imaging or engraving, with repeatable color fidelity, digital halftone proofing holds an edge over the emerging ink jet methods. However, the gap closes a bit every year.
The key to success is the delivery of accurate contract proofs to the print buyer, which can consistently represent the eventual printed piece. This predictability will drive cost out of all phases of the print production process. The print buyer and the printer can reach a point where press approvals are relegated to critical new product launches and not a necessity for each line extension.
The process can be controlled but the system is only as good as its weakest contributor. Process control is a team sport that includes the print buyer, the designer, the prepress provider and the printer/converter. Each player pays an integral role in maintaining the discipline of controlling the individual variables that impact the process.
We'll have more next time on the opportunities available with other types of contract proofing methods.
Patrick J. O'Brien is President of Premier Sales Ltd., in Peacedale, RI, USA. In addition to consultation services, Pat calls on nearly 30 years experience in the flexographic printing and converting industry to assist clients with sourcing technology and equipment systems from a worldwide network of manufacturers. He can be reached at 401-783-0817 or via e-mail at email@example.com.