Dot pitch (sometimes called line pitch) is a specification for a computer display that describes the distance between phosphor dots (sub-pixels) or LCD cells of the same color on the inside of a display screen. Thus, dot pitch is a measure of the size of a triad.
Measured in millimeters, a smaller number generally means a sharper image, as there are more dots in an area of any given size. Note, however, that image quality is determined by multiple factors: a monitor with a smaller dot pitch is usually better, but by no means always, due to a number of factors, including:
- measurement method not documented, complicated by general ignorance of the existence of multiple methods
- differing pixel geometries
- differing screen resolutions when atempting to judge picture quality
Traditionally, dot pitch was always measured on the diagonal, as this gives the most accurate representation of the monitor. Starting about the mid-1990s, however, some companies introduced a horizontal dot pitch as a marketing ploy. By measuring only the horizontal component of the dot pitch and ignoring the vertical component, even a cheap, low-quality monitor could be awarded a small-seeming dot pitch. A display with a horizntal dot pitch of 0.24 mm has four dots per linear millimeter, and a 0.20mm dot pitch display has five dots per linear millimeter.
The exact difference between horizontal and diagonal dot pitch varies with the design of the monitor, but a typical entry-level 0.28mm (diagonal) monitor has a horizontal pitch of 0.24 or 0.25mm, a good quality 0.26mm (diagonal) unit a horizontal pitch of 0.22mm.
Some present-day manufacturers quote dot pitch measurements made on the horizontal, others on the diagonal, and many use both. In general, low-end manufacturers tend to quote a horizontal measurement, quality manufacturers tend to use the diagonal method, but there are many exceptions. A similar distinction can be made in the audio equipment field, where low-end makers tend to cite PMPO Watts while quality makers end to measure their outputs in RMS Watts.