Monitor Dot Pitch- Daniel
Knight, December 1, 1999
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 640x480
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): dot pitch 0.28 0.27 0.26 0.25
horizontal 0.22 0.22 0.21 0.20
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.  Recent articles on Online Tech Journal
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