For those of us who cut our teeth with 8-bit computers in the late 1970s, 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 CRT Screen Size, Resolution, and Sharpness 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 – 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 the Mac’s displays and later the VGA standard on the PC side was square pixels (only at 640 x 480 for VGA, and SVGA later added 800 x 600 with 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 on the PC side. Henceforth, pixels were generally 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):

regular dot pitch     0.28  0.27  0.26  0.25
horizontal dot pitch  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 that 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 “CRT Screen Size, Resolution, and 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 “regular” dot pitch and horizontal dot pitch.

Keywords: #dotpitch #resolution

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