Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.text
Subject: Re: Difference (among engines) -> fonts too thin
Message-ID: <6861@utzoo.UUCP>
Date: Tue, 24-Jun-86 19:51:06 EDT
Article-I.D.: utzoo.6861
Posted: Tue Jun 24 19:51:06 1986
Date-Received: Tue, 24-Jun-86 19:51:06 EDT
References: <756@imag.UUCP>, <429@opus.nbires.UUCP>
Organization: U of Toronto Zoology
Lines: 46

> ...I'm told that these two printers differ in one being "write
> black", the other "write white," and that this makes the difference in the
> appearance of fonts...

In theory, bits in memory define where the black/white edges on the paper
should go.  The laser reproduces that pattern of edges on the drum, which
picks up toner in that pattern and transfers it to the paper.  "Write
white" systems pick up toner in areas which were dark, "write black"
picks up toner in areas which were illuminated.  In principle, this should
not make a difference.  Except that it's not that simple.

(1) The electronics feeding the laser won't turn on and off instantly,
and neither will the laser.  Probably not significant, it's fast enough.

(2) The spot the laser traces on the drum is not square.  It's round.

(3) The spot the laser traces on the drum does not have perfectly sharp
edges, because the light won't focus infinitely well.  More serious.

(4) The drum's response to light isn't perfect, in particular on the
fuzzy edges of spots where only partial illumination is received.

(5) Light doesn't always go exactly where you put it, because the drum
material will reflect and diffuse it a bit.  It tends to spread.  Which
means that write-black machines tend to widen strokes and write-white
ones tend to narrow them.

(6) The pattern of light on the drum isn't perfectly reflected in the
pattern of charge on the drum when it reaches the toner, because charge
leaks off and wanders around a bit on its own.

(7) The toner itself won't necessarily stick to the edge of a charged
area as well as it sticks to the middle.

(8) The later processes, like transferring toner to the paper and fusing
it on, may also rearrange the toner a bit.  It might tend to spread or
contract.


In short...  "The amazing thing about a dancing bear is not how well it
dances, but that it dances at all."  To get optimal results, a font needs
to be custom-tuned for a particular print engine.
-- 
Usenet(n): AT&T scheme to earn
revenue from otherwise-unused	Henry Spencer @ U of Toronto Zoology
late-night phone capacity.	{allegra,ihnp4,decvax,pyramid}!utzoo!henry