Approved-By:  Public-Access Computer Systems Forum <LIBPACS@UHUPVM1.BITNET>
Newsgroups: bit.listserv.pacs-l
Date:         Fri, 9 Oct 1992 13:21:13 CDT
From:         Walt Crawford <BR.WCC@RLG.BITNET>
Subject:      Display resolution: summary and conclusions

----------------------------Original message----------------------------
Thanks to those who provided answers to my question about display
resolution. Since most answers actually went back to PACS-L, I
won't repeat them here.

To summarize what respondents said:
1. It's possible to increase *apparent* resolution using
   anti-aliasing techniques (varying color/gray scale in
   adjoining pixels). This does not increase *displayable*
   resolution, however, and is mostly a software solution.
   Incidentally, it's why U.S. television appears to have
   much higher resolution than it actually has: the color
   palette is nearly infinite, and the shadings increase
   apparent resolution.

2. Monitors can accept and process signals with more
   information than there are physical pixels on the screen.
   Thus, it's not *fraudulent* (i.e., legally actionable)
   to claim display capabilities greater than the physical
   resolution of the picture tube. However, such displays
   cannot be completely clear...the problems have been
   described as "glare" or "blurriness" or whatever, but
   come down to using the nearest available pixel...

Here, then, is what I think can usefully be said--and it's
very important if you're buying displays where you *need*
high resolution (or if you're designing software that will
*use* high resolution):

a. Many displays have a greater electrical resolution than
   physical resolution. Attempting to use the full electrical
   resolution will inherently result in less-than-clear displays,
   since the pixels aren't really there.

b. If you can find out the actual horizontal display area (excluding
   underscan) and the dot pitch, you can calculate the maximum
   *physical* resolution. For any real-world purposes, this should
   also be the maximum *useful* resolution. (The horizontal number
   is always the larger of the two, and almost all modern displays
   except page displays use a 4:3 hor:ver ratio.)

c. To do rough estimates, you can figure that most advertised
   display sizes are overstated by an inch or two (because part
   of the tube is masked off), and that the horizontal display
   size is roughly 0.85 of the diagonal size.

d. Given all of that, some rough assumptions should include:
   1. 1024x768 requires at least a 15" and probably a 16"
      display at 0.31mm pitch, at least a 14" and probably
      a 15" at 0.28mm pitch.
   2. 1280x960 requires at least an 18" display at 0.31,
      at least a 17" at 0.28, at least a 16" at 0.26mm.
   3. No 14" monitor with dot pitch greater than 0.31
      (which usually means 0.39 or 0.51) can clearly display
      800x600; at 0.51, even 640x480 can't be displayed clearly.

e. HOWEVER: for easy reading, for most people, given typical
   Windows/Macintosh text design, you really want text lines
   to be roughly 1/4" high, which means an effective 72dpi.
   That means that, for ease of use, appropriate figures might be:

   640x480: at least 10.4" diagonal (in other words, the best
     notebook LCD screens just barely make it)
   800x600: at least 13" true diagonal--which most 14" displays
     don't quite offer; a 15" display is probably advised
   1024x768: at least 16.7" true diagonal (probably an 18" display)
   1280x960: at least 21" *true* diagonal!

f. If someone claims 150 dpi screen resolution *in a color screen,*
   check it out very carefully! That requires 0.17mm dot pitch,
   which is far below any cost-effective manufacturing technique
   that I'm currently aware of. (Monochrome screens are an entirely
   different matter.)

My thanks to those who responded. Now, to get that 15" monitor
that *can* do 1024x768 correctly, but which really *should* run
at 800x600...

=Walt Crawford, br.wcc@rlg (BITNET), br.wcc@rlg.stanford.edu=
=Permission to forward or copy granted if signature retained=
=Usual disclaimers apply: my words, my opinions.=

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