Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!ucsd!ucbvax!PMGVAX.WR.USGS.GOV!rex
From: rex@PMGVAX.WR.USGS.GOV (Rex Sanders)
Newsgroups: comp.laser-printers
Subject: re: compensating for distortion
Message-ID: <9007120320.AA28393@crayola.cs.UMD.EDU>
Date: 19 Jun 90 17:16:08 GMT
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> I tried to print a perfect square on an Apple LaserWriter II NT using
... (several lines of reasonable PostScript code deleted)
> But the square that I got was distorted. It is approximately 0.5 mm longer
> in the y direction (11" direction) and 0.5 mm shorter in the x direction
> (8.5" direction). It is essential for us to get an undistorted printout.

Various brands of laser printers I've played with for the last 6 years
have some kind of distortion like you describe.  You must remember that
most laser printers are basically copying machines with some fancy
electronics and lasers added.  Have you seen *any* copier that did not
distort your original?

The printing process used by laser printers & copiers is essentially
analog, with lots of belts, rollers, etc., that are subject to
slippage.  Try printing a 20 mm grid across the page, and measuring
each cell.  You will find the variance from cell to cell is as great as
the variance from "perfection"!

We do lots of maps on laser printers, and have warned users not to use the
maps for accurate measurements.  You can also measure the average distortion
across the page, and put fudge factors in your plotting software.  However,
the fudge factors will vary from printer to printer.

Laser printers are wonderful devices, but don't depend on them for
high-accuracy graphics.

-- Rex Sanders, US Geological Survey
   rex@pmgvax.wr.usgs.gov