In article <ericp06-385ADD.06454128052006@newsclstr02.news.prodigy.com>,
"Eric P." <ericp06@sbcglobal.net> writes:
>
> It is my understanding that the human eye can't distinguish much
> above 72 or perhaps 75 dpi, ...

The resolving power of the human eye varies greatly from person
to person, especially at close distances, but a typical value for
a young person with good vision would be in the neighborhood of
150 to 250 lines per inch. And a line requires at least two pixels.

--

Warren S. Sarle       SAS Institute Inc.   The opinions expressed here
saswss@unx.sas.com    SAS Campus Drive     are mine and not necessarily
(919) 677-8000        Cary, NC 27513, USA  those of SAS Institute.

"Warren Sarle" <saswss@unx.sas.com> wrote in message
news:e5d47c$2ho$1@foggy.unx.sas.com...
|
| In article <ericp06-385ADD.06454128052006@newsclstr02.news.prodigy.com>,
| "Eric P." <ericp06@sbcglobal.net> writes:
| >
| > It is my understanding that the human eye can't distinguish much
| > above 72 or perhaps 75 dpi, ...
|
| The resolving power of the human eye varies greatly from person
| to person, especially at close distances, but a typical value for
| a young person with good vision would be in the neighborhood of
| 150 to 250 lines per inch. And a line requires at least two pixels.
|

A simple empirical test is to take a ruler with fine divisions and see if
you can resolve them.  I have no trouble (with my glasses on) seeing either
1/64" or 1/100".  That's at least a lower limit of 100 lpi.  If you have a
good printer and a decent graphics program you can make your own charts.

Norm