Near letter-quality (NLQ) printing is a process where dot matrix printers produce high-quality text by using multiple passes to produce higher dot density. The tradeoff for the improved print quality is reduced printing speed. Software can also be used to produce this effect. The term was coined in the 1980's to distinguish NLQ printing from true letter-quality printing, as produced by a printer based on traditional typewriter technology such as a daisy wheel, or by a laser printer.
In 1985 The New York Times described the marketing of printers with the terms "near letter-quality, or N.L.Q." as "just a neat little bit of hype", but acknowledged that they "really show their stuff in the area of fonts, print enhancements and graphics".
Video Near letter-quality printing
Technology overview
Near letter-quality is a form of impact dot matrix printing. What The New York Times calls "dot-matrix impact printing", was deemed almost good enough to be used in a business letter
Reviews in the later 1980s ranged from "good but not great" to "endowed with a simulated typewriter-like quality".
By using multiple passes of the carriage, and higher dot density, the printer could increase the effective resolution. For example, the Epson FX-86 could achieve a theoretical addressable dot-grid of 240 by 216 dots/inch using a print head with a vertical dot density of only 72 dots/inch, by making multiple passes of the print head for each line. For 240 by 144 dots/inch, the print head would make one pass, printing 240 by 72 dots/inch, then the printer would advance the paper by half of the vertical dot pitch (1/144 inch), then the print head would make a second pass. For 240 by 216 dots/inch, the print head would make three passes with smaller paper movement (1/3 vertical dot pitch, or 1/216 inch) between the passes. To cut hardware costs, some manufacturers merely used a double strike (doubly printing each line) to increase the printed text's boldness, resulting in bolder but still jagged text. In all cases, NLQ mode incurred a severe speed penalty.
Because of the slow speed of NLQ printing, all NLQ printers have at least one "draft mode", in which the same fonts are used, but with only one pass of the print head per line. This produces lower-resolution printing, but at higher speed.
Expensive NLQ printers had multiple fonts built-in, and some had a slot where a font cartridge could be inserted to add more fonts. Printer utility software could be used to print with multiple fonts on less-expensive printers. Not all of these utilities worked with all printers and applications, however.
Maps Near letter-quality printing
Hardware/software control
Okidata's dot matrix printers had three print modes:
- High Speed Draft or Utility printing for drafts and other documents
- NLQ (near letter-quality) printing: "crisper and more like the characters produced by a typewriter"
- LQ (letter quality): "most like typewriter printing for final drafts and documents where appearance matters"
Market penetration
NLQ became a standard feature on all dot-matrix printers. While NLQ was well received in the IBM PC market, the Apple Macintosh market did not use NLQ mode at all, as it did not rely on the printer's own fonts. Mac word-processing applications used fonts stored in the computer. For non-PostScript (raster) printers, the final raster image was produced by the computer and sent to the printer, which meant dot-matrix printers on the Mac platform exclusively used raster ("graphics") printing mode. For near letter-quality output, the Mac would simply double the resolution used by the printer, to 144 dpi, and use a screen font twice the point size desired. Since the Mac's screen resolution (72 dpi) was exactly half of the ImageWriter's maximum, this worked perfectly, creating text at exactly the desired size.
Tradeoffs
Due to the extremely precise alignment required for dot alignment between NLQ passes, typically the paper needed to be held somewhat taut in the tractor feed sprockets, and the continuous paper stack must be perfectly aligned behind or below the printer. Loosely held paper or skewed supply paper could cause misalignments between passes, rendering the NLQ text illegible.
References
Source of the article : Wikipedia
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