For those of us who cut our teeth with 8-bit computers in the late
70s, dot pitch wasn't an issue. A monitor might display 320 dots
horizontally by 200 vertically. On a 13" monitor (the norm back then)
with 12" viewable, you'd have about 9.5" horizontally. That's 0.75 mm
per pixel, so a horizontal dot pitch of 0.50 was more than enough. (See
Screen Size and Resolution for more
details on this calculation.)
As display resolution improved to 640 pixels (Apple's first color
monitor, IBM's EGA and VGA specs), dot pitch started to become an
issue. To display a sharp 640 x 480 image, the horizontal dot pitch on
a typical 13" screen would have to be 0.25 or 4 pixels per mm.
Of course, they didn't rate monitors by horizontal dot pitch (or AG,
for Aperture Grill) until a few years back, when someone determined
that 0.22 mm dot pitch sounded much better than the competition's 0.27
or 0.28.
The big breakthrough of Apple's displays and the VGA standard on the
PC side was square pixels. Until then, pixels were either taller than
they were wide - or vice versa. That pretty much came to an end in 1987
with VGA and the first Mac color display. Henceforth, pixels were
square.
That makes it easy to compare "regular" dot pitch, which is measured
on an angle, with horizontal dot pitch, which is measured across the
long dimension of the screen.
A little application of the Pythagorean Theorem (the square of the
hypotenuse equals the sum of the squares of the other two sides) and a
calculator let us quickly generate the following comparison
(approximate, with number rounded to two digits):
Most monitors today claim a dot pitch of 0.27-0.28 or a horizontal
dot pitch of about 0.22. In short, a little math shows they offer
virtually the same sharpness.
Today, most manufacturers have gone to the better sounding AG or
horizontal dot pitch, which makes it much easier to do the calculations
in our recent article on Screen Size and
Resolution.
But next time you're looking at monitors, do be sure you're
comparing the same measurement of dot pitch. If not, use the small
table above to translate old fashioned dot pitch with horizontal dot
pitch.
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