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Monitor and Dot Pitch
For those of us who started 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):
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DOT PITCH
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Diagonal
.28 .27 .26 .25
horizontal .22 .22
.21 .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.
But next time you're looking at monitors, 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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