Path: utzoo!attcan!uunet!husc6!bloom-beacon!bu-cs!purdue!decwrl!adobe!ondine!greid
From: greid@ondine.COM (Glenn Reid)
Newsgroups: comp.lang.postscript
Subject: Re: PostScript scaling off?
Message-ID: <3931@adobe.COM>
Date: 20 May 88 19:53:49 GMT
References: <313@elan.UUCP> <752@mplvax.nosc.MIL>
Sender: news@adobe.COM
Reply-To: greid@ondine.UUCP (Glenn Reid)
Organization: Adobe Systems Incorporated, Mountain View
Lines: 27


In article <313@elan.UUCP> jlo@elan.UUCP (Jeff Lo) writes:
. . . postscript code deleted . . .
>>From this I would expect to get a 5 inch long horizontal line. However, it
>>is actually about 1/32 inch too long. Is it too much to expect better than
>>1/32 inch (~10 pixels or ~0.5%) accuracy, or is this known to be what happens
>>in a LaserWriter Plus and perhaps other printers as well?
>
>It seems that the average Canon printer engine is only nominally 300 dots
>per inch.  All the ones I have seen with Imagen labels have been more
>like 297 x 302.  The ones with Apple labels have been something else, I
>forget what.  But only within +/- 1% or so.  One would like to believe
>that this is adjustable, somewhere in the hardware.

I believe that this is actually due simply to the mechanical difficulty
of feeding paper at a precise rate.  Even different thicknesses of paper
can make minute differences as the paper is being fed through the marking
engine.

It is not that the "resolution" is 297 dots per inch.  It is the
process of transfer, I believe.  The PostScript interpreter has a 300
dpi frame buffer which it happily feeds to the marking engine.  The
bits in the frame buffer are, indeed, 5 inches long.  Beyond that, it
is probably just mechanical "noise".

Glenn Reid
Adobe Systems