🚀 go-pugleaf

> Which brings up the question: exactly how is a line of resolution defined?
> Consider an alternating pattern of 640 white and dark lines (320 white,
> 320 dark) that my computer is displaying on a TV set.  I look closely and
> can see all of the white and dark lines (they don't merge).
> Am I seeing 640 lines of resolution, or only 320?  

Simple answer: you're seeing roughly _480_ TV lines of resolution.  You have
to multiply the full horizontal res by 3/4 (640x3/4 = 480) to get TV "lines."

The reason for this goes back to the original NTSC specs, which attempted
to give the same resolution in both the vertical and horizontal.  There are
about 483 visible vertical scanlines, but because of spot blooming and other
perception problems (known as the Kell factor), you really get ~330 lines.
So the horizontal resolution was also set up to be ~330 lines, but since
TV screens are rectangular, obviously that res had to apply to a horizontal
viewing distance equal to the vertical veiwing distance.  Ie: a square.
    ________________   _
   |            :   |   \
   |            :   |    \
   |            :   |     > 483 lines scanned, ~330 perceived
   |            :   |    /
   |____________:___|  _/
   ^ 330 lines  ^.......... For same size as vertical height (square)
   ^ 440 lines total^...... For full width of screen ( square res * 4/3)

As to how horz lines are actually measured in consumer items, sometimes it's
done electronically but often it's just done by eye using a line chart :-)

Again, this is very simplified and can be nitpicked, but the main points are:
 a) The horizontal resolution measurement is given for 3/4 screen width.
 b) In TV-speak, each black/white line pair = 2 TV lines.

kevin <kdarling@catt.ncsu.edu> <76703.4227@compuserve.com>