Path: utzoo!attcan!uunet!nbires!pdj
From: pdj@nbires.nbi.com (Paul Jensen)
Newsgroups: comp.sys.mac
Subject: Re: 72 vs. 95 dpi large screens
Summary: Resolution independence will be great.
Message-ID: <136@nbires.nbi.com>
Date: 25 Jul 88 18:41:04 GMT
References: <5349@eagle.ukc.ac.uk>
Organization: NBI Inc., Boulder, CO.
Lines: 34

This discussion of screen resolution seems pretty bizarre at times, with high 
resolution screens getting the reputation of being terrible to look at.

I was developing a screen font for 6 point Helvetica on my usual non-Mac screen
which has a resolution of 120 dots per inch, when a colleague observed:

	"That's not Helvetica! See, look at the serifs on the lower case 'p'!"

Indeed, they were right - I had cloned a Times Roman face in hopes no one
would notice.  The charade was visible even at 5 points.

So how come I can easily read a 6 point font on my 120 dpi screen,
while the Mac 6 point font looks almost unusable on the same screen?

Well, the Mac treats _all_ screens as if they were 72 dpi - ie, one pixel
per point - so 6 points becomes 6/120'th of an inch on a 120 dpi screen 
rather than 6/72'nd of an inch.  That's a character cell 6 pixels high 
when it should be 10 pixels high.  

Or, said in other terms, the 6 point cell is displayed as an apparent
6/120 * 72 = 3.6 point cell.  Now that's tiny, even on a 300 dpi LaserWriter.*

Well, actually, I fibbed a bit since my usual system tries to present a screen 
which is about 11% larger than real life, and the actual screen resolution is 
actually 108 dpi.  Thus it treats the screen as if it were 120 dpi.

Resolution independence will eventually have to be part of QuickDraw's
definition to support outline fonts that can be scaled for the printer.
Maybe the screen representations will even encorporate a user controlled
aspect ratio.  Or perhaps Display PostScript will replace QuickDraw. 
________
* Curiously, a 4.32 point character can be sometimes be strikingly more legible
than a 4 point or even 5 point character on the LaserWriter.  Hint: think about 
the impact of 'units' - 1/18'th of a point.  Courtesy of Dick Dunn.