Where Publishing Gets Practical(sm)
When setting up a file for color POD, you must consider the capabilities of the digital press your printer will be using. Following is a table of various color digital presses using electrostatic imaging technology currently in use:
|Company||Product||Max. Image Area (In.)||Max. Optical Resolution||Duplex Speed (A4)|
12.1" x 35' (feet)
18.7" x 35'
35 ppm (Note 1)
|Canon||CLC 1000||11 x 17||
|IBM||InfoColor 70||12 x 109.1||
|35 ppm (Note 1)|
|11.6 x 17.2||
|Scitex||Spontane||11.69 x 17.72||
|20 ppm (Note 2)|
12.08 x 36' (feet)
12.08 x 36'
18.7 x 26'
35 ppm (Note 1)
|Xerox||DocuColor 40||11.69 x 17.72||
|20 ppm (Note 2)|
Note 2: The Scitex Spontane and Xerox DocuColor 40 use the same imaging engine (developed by Xerox). The Scitex model (somewhat more expensive) has different control software than the Xerox unit. The output from each of these digital presses, however, is quite similar.
Not listed are the "digital" presses from Heidleberg. Those presses are based on traditional offset presses but have plate imaging devices mounted on the press. Plates are mounted, then imaged. The presses frequently use waterless offset printing with soy based inks. Early models may have somewhat lower resolution than traditional offset presses. While similar to standard offset presses, the Heidleburg DI presses use 'waterless' printing and the plates have somewhat different characteristics than standard offset printing plates. Much of the advice directed toward toner-based digital presses also applies to the Heidleburg DI presses.
The toner-based digital presses in the table essentially offer the same cost per unit for each copy in the run. There may be some "economy of scale" reflecting setup and riping cost after the first copy is produced. The Heidleberg DI presses, offer the same economics as traditional offset press... the first copies are expensive (to cover the plate imaging and make ready) while the subsequent copies become less and less expensive. Generally the toner-based digital presses are economic for runs of 1 to 500 (or so) copies; while the Heidleberg DI presses are economic from 400 copies on up.
A consideration for the book publisher is that the toner-based machines produce books on the press in collated order, while the digital-offset press requires that the pages be collated after printing is finished, which may involve some greater cost.
Digital presses are not the same as offset presses. They create their images using wet or dry toners rather than ink and the image is formed with static electricity instead of printing plates. As a result, many "standard" ways of creating artwork for offset presses does not give the expected result with a digital press. While the Heidleberg DI presses use the same basic printing process as normal offset, there are differences in the plate material (and the waterless printing process) that make them more like the digital toner-based presses for the preparation of artwork.
The most prevalent printing problem in toner-based devices is the inability to print large areas of solid color. Toner-based machines tend to leave streaks and bands of uneven color in flat-color areas due to the tendency of the electrostatic charge to vary in strength across the sheet due to variations in the paper and the characteristics of static electric charges. To avoid this problem, create 'noise' in the flat areas by using Photoshop or other software. The result will be a texture or 'flecking' in the flat-color areas.
With black, it may not be easy to avoid large solids. Many digital press operators suggest using a 'rich' black made up of varying percentages of Cyan, Magenta, Yellow, and blacK. There doesn't seem to be any particular consensus for a formula, so work with your selected printer to adjust to their preference. For example, one shop uses a 60C40M40Y100K; while another shop uses 40C20M20Y100K. Although the formula varies, it is important to notice that you use all the four colors, not just a 'kicker' of cyan as commonly used in offset printing.
It should be obvious, but please understand that digital printers can not print spot colors (with some limited exceptions for the Indigo E-Print). Use the Pantone Spot to CMYK color charts to find the CMYK equivalents. Although you can't 'reach' every PMS spot color, you can generate passable substitutions for about 98% of the PMS spot colors.
Since you can't do spot colors, metalic inks are a particular challenge. A heavy coverage of toner, however, often takes on a shiny, glossy look that may simulate a metalic ink. Some print-providers have developed 'formulas' to generate passable gold and silver looks; however, it's really best to just avoid metalic-looks in toner-based output.
Digital printers generally have operating resolutions of 400-600 'dots' per inch. Half-tone 'spots' are simulated by creating grids of the dots--since there are relatively few dots to begin with, the grids are limited in size by the 'half tone line ruling' (lpi) chosen and by the number of 'dots' available. The result is that only a rather limited number of shades are available making it unlikely to create smooth transitions throughout a gradation. If you must use a gradation, then add noise (in Photoshop) to allow the natural variations of the digital printing device less noticable. Simply avoid gradations from very dark to very light colors, since the range will likely exceed the capability of the machine and banding will result.
Remember that images on the monitor are able to show far more subtlety than a digital printer. Also, proofing devices, such as dye-sub or ink jet printers are often of much higher resolution than is the digital printer. (For example, an Epson ink jet prints at 720 or 1440 dpi, while most production digital printing devices are in the 400-600 dpi range.) To eliminate surprises, try to make proof copies on the actual machine to be used for the production run. At the very least, create a set of color swatches from your document and run them on the production printer to enable you to more accurately judge your likely result.
The greatest strength of the digital presses is their handling of photos. Make the maximum use of photos in your project to maximize their impact. Color digital presses can approach fine magazine quality in reproducing photos. Of course the printer can't do any better than the original, so be sure you start with good quality photos and scan them at sufficeintly high resolution. (Generally 300 dpi on a good quality scanner will give acceptable results.)
The software you use will have a tremendous impact on the quality of the digital printer output. Use Quark Xpress or Pagemaker for the layout with other artwork created in Adobe Photoshop, Macromedia FreeHand, and/or Adobe Illustrator. Be sure to convert all artwork to the CMYK color space and make adjustments to the color balance as necessary.
Stay away from word processors and RGB graphics programs like Microsoft PowerPoint. (The word processors tend to only work in the RGB color space.) The 'rip' will need to translate the RGB colors 'on the fly' and may not give you the result you anticipate. (Often, the colors will appear dark and muddy--or the RIP will simply crash--or it may not output the images.) These programs are meant to create overheads and slides, not production graphics.
Even when using the suggested programs, some care must be taken to ensure proper colors. Quark, PageMaker, Photoshop, FreeHand, and Illustrator all have slightly different color rendering 'engines' in the software. (You'd think that the Adobe products would all use the same 'color engine.' ...You'd think! --but, alas, it's not the case as yet.) If you create items with the same color in Illustrator, FreeHand, and Photoshop then import them all into PageMaker or Xpress, the colors of the three elements simply won't match. Ensure that matching items are all created in the same software.
Like any project that goes through a 'service bureau' be sure to include all fonts and linked graphics files (don't 'embed' graphics). Save your files in the proper format (as requested by the printer). Typically, digital printing companies will prefer you use PostScript type one fonts and that you set trapping to none. You may be able to give your job to the printer as an Adobe Acrobat PDF. Discuss this posibillity with the printer. (See my article discussing Adobe Acrobat workflow.)
Output from digital printers can create problems when you get to the bindery phase of the project. Toner, unlike ink, sits on top of the paper--none of it is absorbed. This is particularly a problem with folding, since the toner will tend to 'crack' on the crease. It's best to avoid a design with printing across folds, but, if necessary, minimize any potential problem by using light coverage in fold areas.
To minimize cracking problems avoid saddle-stitched bindings--use perfect binding instead (two 90 degree folds instead of one 180 degree fold). If possible, have the cover laminated before folding. The toner will still crack, but it will be 'contained' by the lamination sheet. Also, lamination will make the toner look brighter and protect it from scuffing damage.
On the sheet-fed digital printers, registration can be a problem. Images may not line up across folds or 'signatures.' Simply avoid the problem by keeping images to a single page. The Heidleburg DI and the Indigo E-print suffer from 'wagging' on the tail end of 11 x 17 sheets, so the output is less precise (at that edge) than from larger sheetfed presses or the web-fed digital presses. Avoid tight registration, allow for a variation of up to 1/8 inch.
If using heavier stocks, be sure that the scores and folds are with the paper grain, not across the grain. This will minimize cracking of the paper and the toner. If you are planning to have items hole punched (3-hole binders or comb/spiral binding), keep toner away from the punch sites as the toner will crack around the holes.
Find out about the paper that the targeted machine can use before you create your design. Especially find out about bleeds, since they may require a larger (more expensive) sheet size. (Can you design for 8 x 10 1/2 instead of 8 1/2 x 11?)
"Tail wag" is a consideration with the Heidleberg DI and Indigo E-Print. Fine registration may be 'off' for images opposite from the 'gripper edge.' Keep the design and tight registration elements as close as possible to the gripper edge for these machines. Also, be aware of the 'auto-duplexing' feature of the particular machine--test duplexed items to ensure acceptable results. You may need to use a Xeikon machine (which prints both sides at the same time) to get good front to back registration if that is a critical consideration.
Digital presses generally can not run all the same papers as 'regular' offset presses. The Indigo E-Print requires special pre-treatment of all papers (otherwise the ink just 'rubs off'). Xeikon-based machines use roll paper that is not available in all types and finishes.
In general, a smooth premium white paper is the best choice for digital printing. Some ivory stocks will also give good results. (The paper color will affect the image colors.) Avoid recycled 'confetti' stocks and those with especially heavy textures. Toner won't stick evenly and/or may be rubbed off the high spots on these stocks before going through the fuser--resulting in really ugly output. Talk with your printer about the 'best' stocks for the target machine. Some colors print better on some stocks; matte and gloss stocks can give enormous differences in result. Heavier papers tend to give better results.
Moisture content can also wreak havoc with the color reproduction. Be sure that the printer has the paper in the shop (right by the machine) for at least 24 hours before your job is run. Paper should never be stored directly on concrete floors as it can pick up moisture from the concrete. Your printer should be aware of these issues, it's better to let the job wait for a day rather than rush it with 'unseasoned' paper--let the printer know you're willing to wait if paper availability is a problem.
Printers (the people) are still learning about their digital presses and they get better dealing with the quality issues all the time. (Try to) work with the same printer on several projects to give you both the chance to become experienced with the type of jobs you run and the strengths (and weaknesses) of the particular machine being used. If you always go to different shops, you may find that you can never 'get it right' since each printer may be set up differently or using different output devices.
To contact Aeonix Publishing group, send an e-mail to Info@Aeonix.com
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