Add-on circuit card boosts Windows performance of old HP LaserJet printers


January 11, 1993|By MICHAEL J. HIMOWITZ

Three years ago I bought a Hewlett-Packard LaserJet II printer. I plugged it in and put it to work, and it has been turning out beautiful documents ever since. It's the best piece of computer equipment I've ever owned.

A couple million other people have done the same thing, and w have a problem now. While there are newer printers with higher resolution and fancier features, it's hard to justify spending the money on one when the old LaserJet is still working perfectly. And given HP's industrial-strength design, the old LaserJet is likely to keep chugging away for years.

Not surprisingly, hardware manufacturers have come up with variety of add-ons to increase the performance of older LaserJets for far less money than the cost of buying a new one.

The doubleRes IV from Laser Printer Accessories Corp. (LPAC) is one of the lowest-cost solutions. This circuit board, which plugs into the auxiliary input port of HP LaserJet II and III models, increases the printer's resolution from 300 dots per inch to 600 dots under Microsoft Windows. At the same time, it speeds up Windows printing considerably, which is quite a trick considering how much more data the board is handling.

Unlike more expensive LaserJet add-ons, the doubleRes doesn't provide the latest version of Hewlett-Packard's Printer Control Language (PCL-5), and it won't provide the built-in fonts found in LaserJet III and 4 models.

But for users of Windows, who have access to virtually unlimited software-based fonts, these are marginal issues compared to the higher resolution and better image quality that newer 600-dot printers such as HP's LaserJet 4 provide.

NB What's the difference between a 300-dot printer and a 600-dot

printer? Consider how laser printers form their images and how your eye perceives them.

Laser printers use imaging devices such as lasers or light-emitting diodes to record dots on a photosensitive drum, much like the drum in an office copier. The image is then transferred to paper using toner.

Smaller dots, precisely positioned and close together, produce images that appear smoother and more polished to the eye than larger dots spaced further apart.

A 300-dot-per-inch laser printer produces 90,000 dots per square inch. A 600-dot printer produces 360,000 dots per inch, which is four times the resolution.

The difference shows up in typefaces that are very small, which lose detail with coarser dot patterns, and with large typefaces or graphics with diagonals or curves, which can appear jagged even at 300 dots per inch.

The doubleRes works its magic by directing the printer's laser controller to produce smaller dots and space them closer together. This usually produces a much more pleasing image.

OC Installing the doubleRes was a snap, thanks to HP's thoughtful

design, which includes a connector for an additional printer control board behind a panel on the back of the machine. It took about four minutes to install the circuit card and attach the standard printer cable to it (some other LaserJet enhancers use circuit cards that must be installed in the computer).

Once the card is installed, you tell the LaserJet to accept input from the auxiliary port by pushing buttons on the control panel on the front of the printer. The doubleRes manual explains how to do this clearly.

The third step is to install the doubleRes software printer driver in Windows, which takes about two minutes. When you print, you can choose the doubleRes driver, which produces 600 dots, or the standard LaserJet driver at 300 dots. If your printer has a PostScript cartridge installed, you can use it without a problem, but you'll get only 300-dot resolution. Printing from non-Windows applications is also at the LaserJet's standard 300-dot resolution.

For the most part, doubleRes worked beautifully. I tried it with a half-dozen Windows applications, and it produced sharper, crisper text than before with Windows True Type fonts and PostScript fonts accessed with Adobe Type Manager.

The results with graphics were mixed but generally favorable. Lines were sharper and crisper, with no noticeable "jaggies" on diagonals and curves. Gradient fill patterns, which move gradually from dark to light, were also smoother. Scanned photographic images reproduced as halftones were also more detailed and pleasing.

But some straight fill patterns -- the finer patterns in particular - produced muddier results than I expected. The folks at LPAC said this was the result of "toner mashing," which means the grains of standard HP toner aren't fine enough to produce the very smallest dots.

To solve this problem, you can buy microfine toner cartridges from LPAC at $140 apiece. These provide about 25 percent more toner but cost 75 percent more than standard HP toner cartridges.

I also ran into a problem using Calendar Creator Plus for Windows. When I printed calendars, doubleRes sometimes produced black where white should be and refused to print the tops of boxes.

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