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Re-separating Files to Reduce Printing Costs by Gordon Pritchard PRINTERS ARE CONSTANTLY CHALLENGED to find ways of reducing their manufacturing costs as well as dealing with a myriad of customer-supplied files that are typically from a colour separation point of view not optimized for the press. One solution rapidly gaining popularity with printers and publishers alike, that has the potential to achieve press optimization, is the re-separating of customer-supplied files through the application of Grey Component Replacement (GCR) techniques. Taking an inventory of your typical presswork CMY ink coverage can help you determine whether the ROI opportunity with re-separating files is high (illustrated above) or low (left image). GCR adoption is seen most predominantly within newspaper and magazine publishers, printers of inserts, flyers, directories and catalogues. The most-promoted reasoning behind re-separating customer-supplied files, certainly in terms of return on investment (ROI) justification, is that it allows a printing company to reduce ink usage. True ink savings using GCR is both content dependent and impacted by how the original images are separated. The average ink-usage reduction through this technique is understood to be around 15 to 25 percent in CMY inks, coupled with an increase of about six percent in K ink. If executed properly, this ink reduction occurs while maintaining the same visual appearance as the original art supplied. Calculating an ROI, therefore, is fairly straightforward. Ink ROI and beyond If, for example, you assume that the average ink consumption for a sheetfed printer to be about two percent of their gross earnings, then a printing company company generating about $10 million per year should spend around $200,000 annually on ink. If this same printer was to reduce their ink usage by 20 percent, they will save around $40,000 a year in ink costs alone. Theoretically, if the shop spent $10,000 on a re-separation solution then their payback time would be about three months and they will have saved $30,000 in the first year of implementation. The promoted savings, however, are typically based on ink reductions that result from converting an Under Colour Removal (UCR) separation into a heavy GCR separation, and then extending that savings to total annual ink usage. This is a method that does not typically reflect the actual print production experience, because the majority of separations are already done using GCR techniques since it is the default setup in popular separation profiles used by Adobe Photoshop. Another consideration is the amount of CMY used in daily production relative to the amount of black-only presswork. To get a better idea as to what your actual ink-savings ROI might be, a printing company should first consider examining separation techniques currently used in prepress, from a representative sampling of realworld jobs. The company might also look at their current presswork to determine the ratio of CMY ink usage (where the savings should occur) relative to black ink. So, even though your final ink mileage may vary from what is suggested by various suppliers, the economics of ink savings alone for the majority of print shops will usually justify the investment. Re-separating customer files by applying GCR techniques not only reduces ink consumption but also provides important benefits in the pressroom. Because a GCR separation uses a non-chromatic colour (black) throughout the tonal range and reduces the proportion of C, M, and Y in the mid-tones and quarter-tones, the colour in GCR separated images is much more stable, as solid C, M, and Y ink densities naturally vary through a pressrun. Note, however, that this is a double-edged sword since the added stability means less ability for the press operator to move colour if required. For many printers, the increased colour stability is a perfect compliment to the industry trend for a by-the-numbers manufacturing process. More direct pressroom benefits of re-separating files include: Reduced make-ready times/faster start-ups/less wastage; Harmonized separations enhance the printability of press forms; Optimized maximum ink coverage (TAC or TIC); reduced fan-out or web growth; Dramatic improvement of image appearance when slight press misregistration occurs; Reduced drying times; higher printing speeds; improved repeatability of print jobs; and Grey balance within images is more stable. RGB to CMYK The vast majority of images entering the print-production process begin in raster RGB mode. To be usable, they must first be converted from an RGB colour space into a print CMYK colour space. This conversion has two significant impacts: First, there is a compression and alteration of colours as the image is transformed from the original RGB gamut to the different gamut used for CMYK presswork and, secondly, there is a major impact in the printability of imagery in terms of colour stability, press performance/runnability, and ink usage (manufacturing cost). 22 PRINTACTION DECEMBER 2009
Converting from RGB to CMYK is accomplished by passing the image through a 3-channel CIEL*a*b* profile where the RGB is converted to CMY and the black channel added according to the profile-defined parameters. When RGB colour images are converted into processcolour counterparts (cyan, magenta, and yellow) an achromatic black channel is added. This is done because, if the colour black in presswork is just made from CMY, it can often appear muddy or patchy. Also, making dark colours from the three chromatic process colours can lead to a high volume of ink on the press sheet causing drying and offset issues. Finally, compared with a grey made primarily of a single black ink, neutral colours made up of three process colours are more difficult to maintain on press. The net effect of introducing black ink in process printing is to optimize the printability of press forms. The conversion process from RGB to CMYK is done by taking the 3-channel RGB image, passing it through a 3-channel (device independent) CIEL*a*b* profile connection colour space where the RGB is converted to CMY and the black channel added and finally outputting the result as a 4-channel CMYK image. Since the colours in an image can be made up of a variety of different percentage combinations of process colours, while still delivering the same final visual appearance, there are a several ways to introduce the black component in a colour separation. The first separation method is typically referred to as Under Colour Removal (UCR). Whenever large percentages of three process inks are mixed together to form a colour, there will be a substantial neutral or grey component. That is to say, past a certain point, adding more of one of the C, M, or Y process colours simply darkens the result. So, instead of just adding more colour, the UCR formula uses black ink to replace a partial amount of the other process colours in the shadow areas and in neutral colours. In a screen tint build of 50 percent cyan, 40 percent magenta, and 45 percent yellow, for example, magenta acts as the greying component. So, the 40 percent magenta value indicates the largest potential amount of black that can be added in place of a percentage of some of the other colours. The second separation method is typically referred to as Grey Component Replacement (GCR), which is a specialized form of Under Colour Removal. GCR involves a more general replacement of chromatic inks not just the close to neutral ones, as with UCR. In a GCR separation, black is substituted for a partial amount of the process colours in all areas where the three chromatic colours are present even in lighter tones. That added range of colour, where CMY can be replaced with black, is the key to how GCR reduces CMY ink usage. Both UCR and GCR separation techniques use a defined parameter to limit the maximum amount of ink that will be used in the darkest part of the image. This maximum total dot percentage is referred to as either TIC (Total Ink Coverage) or TAC (Total Area Coverage) and is determined according to the type of presswork and substrate that the images will be used for. Incidentally, the difference in the range of the black channel makes it fairly easy to determine which method was used to create a particular CMYK separation. With a UCR separation, the black printer appears as a skeleton image that is typically missing tones around the zero to 30 percent range, while the CMY looks very colourful. In contrast, the black printer in a GCR separation looks more like a full-range greyscale image with the CMY appearing washed out. Pressroom concerns with GCR While there are many benefits with maximum GCR separations, this technique may also create problems on press depending on the type of work that you do. Here are eight major concerns to watch out for: 1. A GCR separation makes extensive use of black ink throughout the tonal range. This places a greater emphasis on the integrity of the black ink and press unit, particularly in a black first-down ink sequence. The impact on presswork will be greatly magnified with a GCR separation if there are issues of poor transfer, trapping, dot-gain instability, or ink/water challenges with the black printer. Also, because black is used throughout the tone range, there is potential for a slight increase in the visibility of rosettes in large, flat, screen tint builds. There can also be a greater risk of black ink traveling down from unit to unit and contaminating the next process ink. Lastly, because of the greater amount of black ink, there is a possibility of pastels and skin tones having a grainy appearance. 2. Re-separating images using heavy GCR can introduce subject moiré (black screen angle conflicting with dark pattern in the original) where there would be no moiré caused by the original separation. A UCR separation is distinguished by the C, M, and Y channels looking like full greyscale images, with the K channel appearing weak. With re-separations, images are converted from CMYK to CMYK using a Device Link Profile rather than a 3-channel CIEL*a*b* profile. This preserves the integrity of singleand 2-colour screen tint builds. 3. Ink savings can be quite dramatic with furniture and other dark imagery if the GCR program is too aggressive and removes all of the cyan. The furniture can simply go red on press. 4. Heavy GCR separations are problematic if the print buyer is the type that prefers to go to press runs and adjust colour rather than match the signed-off proof. Since there is little process colour to adjust, solid ink density moves to adjust colour will not have much impact. 5. Poorly implemented GCR algorithms may remove all of the colour near a natural trap line in an image effectively negating the trap. Then, if the press gets a little out of register, the re-separation process has created a press issue. 6. There is an increased disconnect between grey balance targets in the colour bar (CMY no K) and grey balance within the live image area (minimal CMY heavy K). This may cause issues with some closedloop press control systems. 7. In coldset newspaper printing, where yellow is often first down, there will be less yellow ink laid down and, hence, a reduced sealing effect of the paper prior to the other process inks being overprinted. This can lead to less saturated colour during image reproduction. Continued on page 24 A GCR separation is distinguished by the C, M, and Y channels looking like weak greyscale images, with the K channel appearing as a full greyscale. DECEMBER 2009 PRINTACTION 23
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Using device link profiles Re-separating CMYK makes it possible to optimize CMYK images targeted for one or more print conditions to work with the required single CMYK print condition. It further allows the changing of the maximum total ink area coverage, as well as the application of GCR separation techniques to maximize ink savings and on-press colour stability. Re-separating images also renders all separations in multi-page and multi-file source input projects, such as magazines and newspapers, to a common, optimized, colour separation format, which ultimately enhances the printability of the job. The re-separating of documents is typically done using a sophisticated Device Link profile (DVL), which may be embedded within the primary prepress workflow (RIP) or housed in a standalone system linked to the main prepress workflow. Unlike ordinary ICC profiles, DVL profiles do not describe a specific colour space, but instead define the conversion from a specific source colour space to a destination colour space. The basis for creating a DVL profile is always an ordinary ICC profile. The use of a DVL profile allows the integrity of the colour separations to be maintained so that pure C, M, Y, and K screen tones remain pure and that solid (100 percent) C, M, Y, and K values remain solid. As there are many re-separation solutions available in the marketplace, it is important to consider the following key issues (presented here in a Q&A format) around 1. Device Link profile creation/validation and 2. Re-separation implementation. Working through these issues should help any printer narrow down a list of technological requirements and features (and to understand their impact). These issues can also help to prepare a printer with questions for the various suppliers. In general, there is no right or wrong answer, but workflow factors should be prioritized to determine a best fit for your shop. 1) Device Link profile creation/validation Is the DVL profile created/supplied by the vendor, created by the customer, or supplied by a third party? In general, customer-created DVLs require greater customer sophistication, while supplied profiles equal greater simplicity. What is the DVL profile created from: Generic industry reference characterization data/profile (SNAP, GRACoL 7, SWOP) or customer-specific data? In general, customer-specific data provides the best potential for quality since industry data may not reflect actual shop conditions, even though the shop may be running to an industry standard. Industry derived DVL profiles provide a simpler but potentially less accurate implementation. Who supplies the customer-specific characterization data the customer themselves, the vendor, a third party who measures customer-supplied press sheets, or the vendor/third party doing on-site press runs? In general, customer-supplied characterization data is the least reliable, vendor or third party conducting on-site press tests the most reliable. How will the press run, that will be measured to provide the characterization data, be validated to ensure that it is operating within normal parameters and, hence, will provide reliable data? In general, it is worth having the press checked for mechanical and chemical condition by the vendor or third party prior to any characterization run. How will the DVL/or solution be evaluated in order for customer acceptance and sign-off? In general, there should be written specific performance criteria (e.g. maintain single colour colours, no contamination of solid colours, etc.) for customer acceptance. Will validation be based on a proof, press run or measured data (pre and post re-separation)? In general, a soft on-screen and hard physical proof (pre and post re-separation) are sufficient to show colour integrity and ink usage reduction. Can the re-separation parameters of the DVL profile be changed by the customer; or does this require vendor intervention? In general, allowing the customer to adjust the parameters makes for a more finely-tuned process that can be quickly adapted should press conditions change. However, it requires a degree of customer knowledge to be successful. If the vendor needs to be involved, then fine adjustments will take longer and likely be more expensive. However, it does place responsibility on an organization that likely has greater resources and knowledge which, in the end, may lead to a better final result.
BOOKBINDING 2) Re-separation implementation Is GCR re-separation done inside the main prepress workflow or is it run over a dedicated workstation? In general, GCR re-separation done inside the main prepress workflow provides a simpler, faster process. GCR re-separation done on a dedicated workstation provides a more customizable and updatable solution but also involves more computers and supporting infrastructure. Some vendors offer both, or allow the customer to scale from one to the other as circumstances change. Does re-separation occur during the initial PDF-refinement stage, after the PDF refine stage (perhaps at a dedicated workstation) or during the rendering of the files to plate? In general, early-stage re-separation means that print buyers can see that their files have been altered/optimized if they proof the files using remote proofing; or if they receive the files back from the printer either during the production process or afterward. This may, or may not, be a concern. Late re-separation at the rendering stage means that the altering/optimization would be hidden. Printers should also consider asking potential suppliers if their solution handles vector graphics separately from raster images; or if their solution handles documents containing a mix of RGB and CMYK images; or if their solution handles documents containing a mix of embedded profiles? Testing the tools Once you have narrowed down the solutions that will provide the best fit for your business, it is a good idea to run a test to see how closely supplier promises meet technological performance. To perform an evaluation requires running a test form through the solution and examining and comparing the results to your existing workflow. This suggested press test form, which includes test elements, or targets, (labeled here as number q to number 1*) can be used to perform an objective evaluation of any solution s performance. Targets q, w, e, r and 1* are designed to test the ability of the technology to maintain the integrity of pure singleand 2-colour builds. These elements should be butted together and then trapped to see how trapping is affected. q CMY grey balance vignette and step wedge; w CMY brown balance (CMY have the same tone values) vignette and step wedge; e C, M, Y, K vignette and step wedges should remain single colour with tone values preserved; r B (C/M), R (M/Y), G (C/Y) vignette and step wedges should remain two colour only; 1* Maximum TIC/TAC targets, ranging from too low (e.g. 230 percent) to too high (e.g. 400 percent), to see how the solution brings TIC/TAC to a common requested value. The following test elements are for subjective visual evaluation: u Grey balance image separated GCR using Photoshop defaults; i Grey balance image separated UCR using Photoshop defaults; (Note: targets u and i are intended to test preservation of grey balance through re-separation) o Saturated and deep skin tone colours, should be separated according to your existing standard; 1) PDF file to test ability of solution to handle mix of images and text; 1! GCR (medium) separation using black limit 100 percent and maximum ink 320 percent; 1@ GCR (medium) separation using black limit 90 percent and maximum ink 280 percent; 1# UCR separation using black limit 100 percent and maximum ink 320 percent; 1$ UCR separation using black limit 90 percent and maximum ink 280 percent; Continued on page 26 The test form should contain both objective and subjective test elements. Imposing the re-separated file above, and inline with the original, allows for direct comparison in proof and on press. DECEMBER 2009 PRINTACTION 25
TRADE PRINTING Gordon Pritchard Continued from page 25 (Note: targets 1! to 1$ are intended to reveal how different types of separations are brought to a common setting through reseparation and whether any colour appears distorted as a result.) 1% Deep colour with lots of black using UCR with a black limit 100 percent and maximum ink 320 percent. This target is intended to show any loss of richness or any colour shift in deep shadows, as well as artifacts in the transition to shadow tones; 1^ High key pastel original, which means it was originally separated using UCR with a black limit 100 percent and maximum ink 320 percent. This is intended to show how pastels with heavy black GCR perform on press: and 1& Vector (Illustrator) graphic, to see how, and if, vector graphics are affected by reseparation. If you have any unusual image requirements, such as graphics that overlay spot colours on top of CMYK, or process-colour images that include a 5th or 6th spot-colour channel, be sure to include those as well. Once the test elements are returned by the prospective vendor, they should be imposed in line with the original test elements. Add elements: t Grey balance bars which go the width of the press sheet; and y Your preferred colour bar. The top half contains the test images/files as supplied by you to the vendor. The bottom half are the same images processed by the vendor s GCR re-separation solution. Two proofs from one imposed form Once a proof is output from these test forms, cut that proof in half so that you have two pieces; one that contains the original images and the other containing the processed images. Take the proof of the processed images and cut it into strips through the center of the images. Then lay the strips on top of the proof of the original art. The images should fuse together looking no different where they cross over. Examine the objective elements q to r to determine whether they have maintained their integrity; and 1* to determine how the different TIC/TACs have been handled. The next step is to validate the increased colour stability on press by going on press with the imposed form. The press operator should be instructed to run to the appropriate Solid Ink Densities (SIDs) trying to even them out across the width of the sheet. The proof should not be available, as the press sheet should simply be run to the numbers. Once the SIDs have been reached, pull out several sheets for evaluation later. Then raise the magenta SIDs by 10 points (for example, 1.35 M becomes 1.45 M) and pull some sheets. Then raise the magenta SIDs by a further 10 points (to 1.55 M) and pull another few sheets. Then perform the same increase, but with the cyan SIDs. Again, pull sheets at the appropriate increased SIDs. Because the images are inline with each other, the increase in SIDs gets applied to both conventional and re-separated images. By cutting the form in half and comparing strips of the images, as was done with the proof, you should be able to see the difference in colour stability between the processed images and their originals. Once you ve evaluated the workflow aspect of the proposed solution and completed a press test to confirm its performance integrity and functionality, the fun part begins negotiating a mutually agreeable price with your supplier of choice. About Gordon Pritchard: Formerly Print Quality Marketing Manager for eight years at Creo and three years at Kodak, Pritchard has presented at print technical conferences trained printers and buyers regarding print quality issues in Europe, North America, and Asia. His print quality blog is here: http:// qualityinprint.blogspot.com/ and he can be reached at: pritchardgordon@gmail.com. There should not be a visible difference if the re-separated presswork is cut and placed over the press sheet that was not re-separated. 26 PRINTACTION DECEMBER 2009