Navigating digital color printing machine specifications can be daunting. Here is our review of specs.
Resolution
Digital printing quality is more than the numbers. Dots Per Inch only tells you laser addressability. If there is only one number, it means it is the same in both directions, 600x600, for example.
The dot size produced by the laser within the printer is about 10 to 42 microns in width. There is also the size of the actual particle of toner, and in most cases, it is smaller than the addressability.
With 25,400 microns to an inch, a simple conversion of DPI to microns shows:
600 dpi = 42.33 microns addressability but actual particle could be 6-8 microns
1200 dpi = 21.17 microns addressability but actual particle could be 3-5 microns
2400 dpi = 10.58 microns addressability but actual particle could be 2-3 microns
600 dpi is the threshold -- it usually means you will get good-looking type and line art, and anything over 600 dpi is great but perhaps not always visible to the eye. A grain of salt is about 60 microns and the eye can see particles to about 40 microns.
Color printing is handled in a variety of ways and every supplier has their own secret sauce. Bit depth could be a determinant but, it usually represents processing, not rendering. Digital printers do not use traditional halftone dots -- they all have secret and proprietary algorithms for rendering photographs. How do you evaluate print quality? Look at the samples, or do your own samples. Look for:
1. Gradients and tints
2. Solid colors
3. Skin tones
End users assume that the higher the numbers, the better the print quality, which is not necessarily the case. You could try to compare laser addressability, toner spot size, and other attributes of digital imaging and electrophotography, but your head might then explode.
Speed
We use a standard sheet with four toners to gauge speed. Suppliers present operating speed in simplex pages per minute or per hour. Over 80 percent of all printing is duplexed so the 2-sided speed is more important.
On sheetfed machines, duplexing means the sheet goes through the imaging engine twice so this cuts the simplex speed in half. Webfed printers have advantages in configuration so their duplex speed appears faster than the simplex speed. Xeikon uses a unique imaging system that images both sides of the web at virtually the same time and HP Indigo roll systems add additional engines inline.
Océ has a monochrome printer that has a special imaging system and Xerox has a new Nuvera with two imaging engines. High-speed monochrome printers for transaction printing use two engines in tandem with a turn bar to print both sides of the roll inline. Some of these approaches may be applied to future systems.
Some printers vary speed by the weight of the stock. Heavier stocks may run slower than lighter weight stocks. Over-sized sheets may run slower through the bypass feeder, but faster from the main drawers.
Because there are so many choices at so many price/performance levels, you need to determine your needs. Two slower machines or one high-speed machine? Many suppliers have tools to help you make this decision.
List Price
There are many configurations based on:
1. Number of paper decks or drawers
2. Extra color stations
3. RIP level
4. On-line finishing
5. Workflow
6. Special features
so the listed price is only a guide to get you in the ballpark. Suppliers may have multiple RIP levels, many based on EFI, and many proprietary. For high-end systems, the Creo RIP is popular. Pricing is also affected by trade-ins, trade-ups, special deals, and other discounts.
Colors
All digital color printers have four toners (CMYK). Kodak NexPress printers have a fifth station that can be either an extended gamut toner or a gloss unit. The HP Indigo line can be configured with CMYK and up to three spot colors, which can be mixed to order.
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