Pixel

A pixel (short for "picture element," also called a pel) is the smallest individually controllable point in a raster image. On a display, dot matrix printer, or in ASCII art, it is the tiniest unit whose output can be adjusted independently. The idea of a picture element goes back to the early days of electronic imaging: the German term *Bildpunkt* appeared in an 1888 patent, and the English phrase "picture element" was used in U.S. patents as early as 1911. The word *pixel* itself was first published in 1965.

Pixels are typically arranged in a regular two-dimensional grid. Each pixel stores one or more numerical values that represent a sample of an image. A higher sampling density can capture finer spatial detail, though the final result also depends on the optics, sensor, processing, and display. In color imaging, a pixel is often represented by components like red, green, and blue (RGB) or cyan, magenta, yellow, and black (CMYK). The term's meaning shifts by context: in camera sensors, a pixel may refer to a single scalar element (a photosite or sensel), while in medical imaging like MRI, it can mean a set of component intensities for a specific spatial location.

Early consumer computers rendered software at low resolutions, making individual pixels visible to the naked eye. Graphics created under those constraints are often called pixel art, especially in video games. Modern computers and displays can handle orders of magnitude more pixels, leading to measurements like the megapixel (one million pixels).

The word *pixel* combines "pix" (short for "pictures") and "el" (for "element"), similar to *voxel* (volume pixel) and *texel* (texture pixel). "Pix" appeared in *Variety* magazine headlines in 1932 as an abbreviation for movies, and by 1938 photojournalists used it for still pictures. Frederic C. Billingsley of JPL first published "pixel" in 1965 to describe picture elements from space-probe scans of the Moon and Mars. He learned the term from Keith E. McFarland at General Precision, who said it was already in use around 1963. The concept of a picture element dates to television's early days, with Paul Nipkow's 1888 German patent using *Bildpunkt*. The term "picture element" itself appeared in *Wireless World* magazine in 1927, though earlier U.S. patents used it from 1911. Some authors, as early as 1972, explained pixel as "picture cell." In graphics and video processing, *pel* is often used instead of *pixel*—IBM employed it in the original PC's technical reference. Note that *pixilation* (with a second *i*) is an unrelated filmmaking technique using stop-motion animation with live actors, popularized by Norman McLaren and Grant Munro.

Technically, a pixel can refer to a numerical sample in an image file, an element in a transmitted signal, a controllable point on a display, a printed sample, or a photosensitive element in a camera. Related terms like pel, sample, dot, photosite, and sensel are not interchangeable in every context. Pixel counts serve as measurements, such as 2,400 pixels per inch or 640 pixels per line. "Dots per inch" (dpi) and "pixels per inch" (ppi) are sometimes confused: ppi describes the sampling density of a digital image or display, while dpi describes the density of physical marks (like ink droplets). A printer may use multiple dots to reproduce one image pixel—for example, a 600 ppi image printed by a 1,200 dpi inkjet printer—so dpi cannot be directly compared with ppi as a measure of effective resolution. Increasing sample count preserves finer detail only if the source and imaging system contain that detail. Pixel count is often called "resolution," though that term can also refer to spatial resolving power or sampling density. A 640 × 480 VGA image contains 307,200 pixels (about 0.3 megapixels). The pixels in a digitized image (like a JPEG) may not correspond one-to-one with screen pixels, depending on how the computer displays it. An image made of pixels is called a bitmapped or raster image; the word *raster* comes from television scanning patterns and is also used for halftone printing and storage.

For convenience, pixels are normally arranged in a regular two-dimensional grid, allowing many common operations to be applied uniformly to each pixel. Other arrangements are possible.