Resolution. (computer printers)
by William Harrel

Do you need 600-dpi resolution? It's all a question of image.

Just when you think an industry standard has been set, somebody moves the mark. All of the major manufacturers are championing low-cost 600-dpi printers.

There's nothing new about 600-dpi printers. High-end desktop publishers and graphics designers have used 600-, 800-, and 1200-dpi devices for a few years now. Until recently, high-resolution printers have been too expensive for personal use. Today you can buy one, such as the HP Laser-Jet 4, for less than $1,500 (if you shop around).

Why 600 dpi? Twice the resolution means twice the quality, right? Actually, 600-dpi resolution is four times higher than 300-dpi resolution.

In applications where the information is more important than the packaging, such as word processing and spreadsheets, 300 dpi is plenty of resolution. But newsletters, presentations, and sales proposals should look as slick as possible. This is especially true when you plan to reproduce them on a copy machine or at the print shop, where some quality invariably gets lost in the process.

Some 300-dpi printers don't handle large type well. Curved edges can print broken and uneven, and characters with diagonal legs, such as M, V, and W, print with jaggies (stairstepping). Small type can print with strokes (fine lines) broken up, or with circles (b, d, p) filled in. Higher resolution helps maintain fine lines and stroke weights in small text, and large text printed at higher resolution has smooth, sharp edges.

But where you'll really notice a difference is in graphical and gray-scale (photograph) images. Some graphics contain tight arcs and angular lines that 300-dpi printers can't print without jaggies. Jaggies result from dots too large to fill in--or smooth out--tight areas. The tighter dots of 600-dpi printers smooth out graphics much more effectively than the larger dots produced by 300-dpi printers.

Since laser printers simulate shades of gray by alternating black dots with white areas, 600-dpi printers have a significant advantage over 300-dpi printers. Photographs print more sharply at 600 dpi. You wind up with about four times the number of stimulated shades of gray as on a 300-dpi machine. Printers with 300-dpi resolution are capable of only 25 shades of gray; 600-dpi printers can simulate more than 100 shades of gray.

The 600-dpi printers also print tighter screens, or percentages of black, in device-dependent graphics, such as those created by Corel-DRAW!, Micrografx Works, and other draw programs. Screens create shading and other gray fills, such as Corel's graduating linear and radial fountain fills.

For many applications, 600-dpi resolution proves good enough for camera-ready art that is to be reproduced. Printers with 600-dpi resolution also make better proof printers. However, when you need perfect text and graphics, you'll still need to run your documents on an imagesetter at the neighborhood service bureau. Toner--what the printer uses to print--is still toner; it cannot produce fine lines and grays as well as imagesetters, even though today's toner is much finer than that of just a few years ago.

Not only do you get improved text and graphics from these new high-resolution printers, but they also print faster. New RISC processors and other innovations, such as improved parallel ports, halve the processing time. The Lexmark 4029's parallel port, for example, can accept two or three times more data per second than the ports of 300-dpi printers developed a few years ago. Several printers, such HP's LaserJet 4, are built around Intel's 20-MHz 80960 RISC processor, which processes data at breakneck speeds and requires less printer RAM, making the printers less expensive to produce and upgrade.

Other innovations, such as windows accelerators, also turn in record printing times. These combination software-hardware solutions use your computer's memory, TrueType fonts, and souped-up printer drivers for speeds as much as ten times faster than those of printers that do not support such solutions.