Dot pitch (sometimes called line pitch, stripe pitch, or phosphor pitch) is a specification for a computer display, computer printer, image scanner, or other pixel-based device that describes the distance, for example, between dots (sub-pixels) on a display screen. In the case of an RGB color display, the derived unit of pixel pitch is a measure of the size of a triad plus the distance between triads.
Dot pitch may be measured in linear units (with smaller numbers meaning better resolution), usually millimeters (mm), or as a rate, for example dots per inch (with a larger number meaning higher resolution). Closer spacing produces a sharper image (as there are more dots in a given area). However, other factors may affect image quality, including:
- Undocumented or inadequately documented measurement method, complicated by ignorance of the existence of different methods
- Confusion of pixels and subpixels
- Element spacing varying across screen area (e.g., widening in corners compared to center)
- Differing pixel geometries
- Differing image and pixel aspect ratios
- Miscellanea such as Kell factor or interlaced video
Traditionally, dot pitch in displays has been measured on the diagonal, as this gives the most accurate representation of image quality. 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.
The exact difference between horizontal and diagonal dot pitch varies with the design of the monitor (see pixel geometry and widescreen), 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 has a horizontal pitch of 0.22 mm.
The above dot pitch measurement does not apply to aperture grille displays. Such monitors use continuous vertical phosphors band on the screen, so the vertical distance between scan lines is limited only by video input signal's vertical resolution and the thickness of electron beam, so there is no vertical 'dot pitch' on such devices. Aperture grille only has horizontal 'dot pitch', or otherwise known as 'stripe pitch'.