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 millimetres, a smaller number generally means a sharper image, and vice versa, as there are more dots in an area of any given size. Note, however, that a monitor with a smaller dot pitch usually has a better-quality image, 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 attempting to judge picture quality
- tightness of electron beam focus and aim
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 horizontal dot pitch of 0.25 mm has four dots per linear millimetre, and a 0.20 mm dot pitch display has five dots per linear millimetre.
The exact difference between horizontal and diagonal dot pitch varies with the design of the monitor (see Pixel geometry), but a typical entry-level 0.28 mm (diagonal) monitor has a horizontal pitch of 0.24 or 0.25 mm, a good quality 0.26 mm (diagonal) unit a horizontal pitch of 0.22 mm.
Some modern 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, while 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.
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