In digital imaging, a pixel, or pel, (picture element) is a physical point in a raster image, or the smallest, addressable element in a display device; so it is the smallest, controllable element of a picture represented on the screen. The address of a pixel corresponds to its physical coordinates. LCD pixels are manufactured in a two-dimensional grid, and are often represented using dots or squares, but CRT pixels correspond to their timing mechanisms and sweep rates.

Each pixel is a sample of an original image; more samples typically provide more accurate representations of the original. The intensity of each pixel is variable. In color image systems, a color is typically represented by three or four component intensities such as red, green, and blue, or cyan, magenta, yellow, and black.

In some contexts (such as descriptions of camera sensors), the term ''pixel'' is used to refer to a single scalar element of a multi-component representation (more precisely called a ''photosite'' in the camera sensor context, although the neologism ''sensel'' is sometimes used to describe the elements of a digital camera's sensor), while in others the term may refer to the entire set of such component intensities for a spatial position. In color systems that use chroma subsampling, the multi-component concept of a pixel can become difficult to apply, since the intensity measures for the different color components correspond to different spatial areas in a such a representation.

The word ''pixel'' is based on a contraction of ''pix'' ("pictures") and ''el'' (for "element"); similar formations with ''el''  for "element" include the words voxel and texel.

Etymology

The word "pixel" was first published in 1965 by Frederic C. Billingsley of JPL, to describe the picture elements of video images from space probes to the Moon and Mars. However, Billingsley did not coin the term himself. Instead, he got the word "pixel" from Keith E. McFarland, at the Link Division of General Precision in Palo Alto, who did not know where the word originated. McFarland said simply it was "in use at the time" (circa 1963).

The word is a combination of ''picture'' and ''element'', via ''pix''. The word ''pix'' appeared in ''Variety'' magazine headlines in 1932, as an abbreviation for the word ''pictures'', in reference to movies. By 1938, "pix" was being used in reference to still pictures by photojournalists.

The concept of a "picture element" dates to the earliest days of television, for example as "''Bildpunkt''" (the German word for ''pixel'', literally 'picture point') in the 1888 German patent of Paul Nipkow. According to various etymologies, the earliest publication of the term ''picture element'' itself was in ''Wireless World'' magazine in 1927, though it had been used earlier in various U.S. patents filed as early as 1911.

Some authors explain ''pixel'' as ''picture cell,'' as early as 1972. In video processing, ''pel'' is often used instead of ''pixel''. For example, IBM used it in their Technical Reference for the original PC.

Words with similar etymologies

Texel (texture element) and luxel (lux element) are words used to describe a pixel when it is used in specific context (texturing and light mapping respectively)

A voxel is a ''volume element'', the 3D analogue of a 2D pixel.

Surfels (surface elements) have the same naming pattern as pixels, but share more similarities with shrunken triangles than expanded pixels.

A resel is a ''resolution element'', used to describe the discrete number of resolvable elements of a continuous signal (e.g. in optical imaging).

Technical

thought of as the smallest single component of a digital image. However, the definition is highly context-sensitive. For example, there can be "printed pixels" in a page, or pixels carried by electronic signals, or represented by digital values, or pixels on a display device, or pixels in a digital camera (photosensor elements). This list is not exhaustive, and depending on context, there are several terms that are synonymous in particular contexts, such as pel, sample, byte, bit, dot, spot, etc. The term "pixels" can be used in the abstract, or as a unit of measure, in particular when using pixels as a measure of resolution, such as: 2400 pixels per inch, 640 pixels per line, or spaced 10 pixels apart.

The measures dots per inch (dpi) and pixels per inch (ppi) are sometimes used interchangeably, but have distinct meanings, especially for printer devices, where dpi is a measure of the printer's density of dot (e.g. ink droplet) placement. For example, a high-quality photographic image may be printed with 600 ppi on a 1200 dpi inkjet printer. Even higher dpi numbers, such as the 4800 dpi quoted by printer manufacturers since 2002, do not mean much in terms of achievable resolution.

The more pixels used to represent an image, the closer the result can resemble the original. The number of pixels in an image is sometimes called the resolution, though resolution has a more specific definition. Pixel counts can be expressed as a single number, as in a "three-megapixel" digital camera, which has a nominal three million pixels, or as a pair of numbers, as in a "640 by 480 display", which has 640 pixels from side to side and 480 from top to bottom (as in a VGA display), and therefore has a total number of 640 × 480 = 307,200 pixels or 0.3 megapixels.

The pixels, or color samples, that form a digitized image (such as a JPEG file used on a web page) may or may not be in one-to-one correspondence with screen pixels, depending on how a computer displays an image. In computing, an image composed of pixels is known as a ''bitmapped image'' or a ''raster image''. The word ''raster'' originates from television scanning patterns, and has been widely used to describe similar halftone printing and storage techniques.

Sampling patterns

For convenience, pixels are normally arranged in a regular two-dimensional grid. By using this arrangement, many common operations can be implemented by uniformly applying the same operation to each pixel independently. Other arrangements of pixels are possible, with some sampling patterns even changing the shape (or kernel) of each pixel across the image. For this reason, care must be taken when acquiring an image on one device and displaying it on another, or when converting image data from one pixel format to another.

For example:

LCD screens typically use a staggered grid, where the red, green, and blue components are sampled at slightly different locations. Subpixel rendering is a technology which takes advantage of these differences to improve the rendering of text on LCD screens.

The vast majority of color digital cameras use a Bayer filter, resulting in a regular grid of pixels where the ''color'' of each pixel depends on its position on the grid.

A clipmap uses a hierarchical sampling pattern, where the size of the support of each pixel depends on its location within the hierarchy.

Warped grids are used when the underlying geometry is non-planar, such as images of the earth from space. The use of non-uniform grids is an active research area, attempting to bypass the traditional Nyquist limit.

Pixels on computer monitors are normally "square" (this is, having equal horizontal and vertical sampling pitch); pixels in other systems are often "rectangular" (that is, having unequal horizontal and vertical sampling pitch – oblong in shape), as are digital video formats with diverse aspect ratios, such as the anamorphic widescreen formats of the Rec. 601 digital video standard.

Resolution of computer monitors

Computers can use pixels to display an image, often an abstract image that represents a GUI. The resolution of this image is called the display resolution and is determined by the video card of the computer. LCD monitors also use pixels to display an image, and have a native resolution. Each pixel is made up of triads, with the number of these triads determining the native resolution. On some CRT monitors, the beam sweep rate may be fixed, resulting in a fixed native resolution. Most CRT monitors do not have a fixed beam sweep rate, meaning they do not have a native resolution at all - instead they have a set of resolutions that are equally well supported. To produce the sharpest images possible on an LCD, the user must ensure the display resolution of the computer matches the native resolution of the monitor.

Bits per pixel

The number of distinct colors that can be represented by a pixel depends on the number of bits per pixel (bpp). A 1 bpp image uses 1-bit for each pixel, so each pixel can be either on or off. Each additional bit doubles the number of colors available, so a 2 bpp image can have 4 colors, and a 3 bpp image can have 8 colors: ::* 1 bpp, 2¹ = 2 colors (monochrome) ::* 2 bpp, 2² = 4 colors ::* 3 bpp, 2³ = 8 colors :: ... ::* 8 bpp, 2⁸ = 256 colors ::* 16 bpp, 2¹⁶ = 65,536 colors ("Highcolor" ) ::* 24 bpp, 2²⁴ ≈ 16.8 million colors ("Truecolor")

For color depths of 15 or more bits per pixel, the depth is normally the sum of the bits allocated to each of the red, green, and blue components. Highcolor, usually meaning 16 bpp, normally has five bits for red and blue, and six bits for green, as the human eye is more sensitive to errors in green than in the other two primary colors. For applications involving transparency, the 16 bits may be divided into five bits each of red, green, and blue, with one bit left for transparency. A 24-bit depth allows 8 bits per component. On some systems, 32-bit depth is available: this means that each 24-bit pixel has an extra 8 bits to describe its opacity (for purposes of combining with another image).

Subpixels

Many display and image-acquisition systems are, for various reasons, not capable of displaying or sensing the different color channels at the same site. Therefore, the pixel grid is divided into single-color regions that contribute to the displayed or sensed color when viewed at a distance. In some displays, such as LCD, LED, and plasma displays, these single-color regions are separately addressable elements, which have come to be known as ''subpixels''. For example, LCDs typically divide each pixel horizontally into three subpixels. When the square pixel is divided into three subpixels, each subpixel is necessarily rectangular. In the display industry terminology, subpixels are often referred to as ''pixels'', as they are the basic addressable elements in a viewpoint of hardware, and they call ''pixel circuits'' rather than ''subpixel circuits''.

Most digital camera image sensors use single-color sensor regions, for example using the Bayer filter pattern, and in the camera industry these are known as ''pixels'' just like in the display industry, not ''subpixels''.

For systems with subpixels, two different approaches can be taken:

The subpixels can be ignored, with full-color pixels being treated as the smallest addressable imaging element; or

The subpixels can be included in rendering calculations, which requires more analysis and processing time, but can produce apparently superior images in some cases.

This latter approach, referred to as subpixel rendering, uses knowledge of pixel geometry to manipulate the three colored subpixels separately, producing a slight increase in the apparent resolution of color displays. While CRT displays use red-green-blue-masked phosphor areas, dictated by a mesh grid called the shadow mask, it would require a difficult calibration step to be aligned with the displayed pixel raster, and so CRTs do not currently use subpixel rendering.

The concept of subpixels is related to samples.

== Megapixel ==

A megapixel (MP or Mpx) is one million pixels, and is a term used not only for the number of pixels in an image, but to express the number of image sensor elements of digital cameras or the number of display elements of digital displays. For example, a camera that makes a 2048 × 1536 pixel image typically uses a few extra rows and columns of sensor elements and is commonly said to have "3.2 megapixels" or "3.3 megapixels", depending on whether the number reported is the "effective" or the "total" pixel count (as opposed to the 2048 × 1536 = 3,145,728 finished image pixels).

Digital cameras use photosensitive electronics, either charge-coupled device (CCD) or complementary metal–oxide–semiconductor (CMOS) image sensors, consisting of a large number of single sensor elements, each of which records a measured intensity level. In most digital cameras, the sensor array is covered with a patterned color filter mosaic having red, green, and blue regions in the Bayer filter arrangement, so that each sensor element can record the intensity of a single primary color of light. The camera interpolates the color information of neighboring sensor elements, through a process called demosaicing, to create the final image. These sensor elements are often called "pixels", even though they only record 1 channel (only red, or green, or blue) of the final color image. Thus, two of the three color channels for each sensor must be interpolated and a so-called ''N-megapixel'' camera that produces an N-megapixel image provides only one-third of the information that an image of the same size could get from a scanner. Thus, certain color contrasts may look fuzzier than others, depending on the allocation of the primary colors (green has twice as many elements as red or blue in the Bayer arrangement).

Display resolution

The display resolution of a display device (such as a digital television) is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resolution is controlled by different factors in cathode ray tube (CRT) and flat panel or projection displays using fixed-element arrays.

See also

Computer display standard

Dexel

Gigapixel image

Intrapixel and Interpixel processing

LCD crosstalk

Pixel advertising

Pixel art

Pixel art scaling algorithms

Pixel aspect ratio

Point (typography)

Rasterisation

Vector graphics

Voxel

References

External links

A Pixel Is Not A Little Square: Microsoft Memo by computer graphics pioneer Alvy Ray Smith.

Pixels and Me: Video of a history talk at the Computer History Museum.

Square and non-Square Pixels: Technical info on pixel aspect ratios of modern video standards (480i,576i,1080i,720p), plus software implications.

120 Megapixel is here now: A lot of information about MegaPixel and Gigapixel.

Category:Computer graphics data structures Category:Image processing Category:Digital geometry Category:Digital imaging Category:Digital photography Category:Television technology

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name	Tadhg Kelly
birthname	Joseph Tadhg Kelly
birth date	October 03, 1988
birth place	Chicago, Illinois, U.S.
occupation	Actor/Producer
years active	2001–present
website	}}

Tadhg Kelly (; born October 3, 1988) is an American actor and film producer. He is best known for playing Ben Singer on Nickelodeon's ''Unfabulous''. He is set to star in ''S.P. Untitled'' with Malese Jow, and recorded his debut album in 2008.

Biography

Early life

Tadhg Kelly (aka Tadhg, pronounced "tayg") was born Joseph Tadhg Kelly in Chicago, Illinois to hotel industry executive Albert Kelly and life coach Marta Chausee. Kelly is the youngest of four children. He won his first piano competition in the first grade. At the same time, Kelly acted in his first dramatic lead role. He won a city-wide art contest in the third grade for his portrait of Mexican painter Diego Rivera. He and his family relocated to Claremont, California in 1996, where he eventually appeared in various TV shows and feature films.

Career

Kelly played Ben Singer on Nickelodeon’s television series ''Unfabulous.'' He is the big brother of Addie Singer (Emma Roberts). The siblings are portrayed as polar opposites. Ben is a prankster who enjoys causing trouble, though it usually ends with a moral lesson being learned by either himself or the target of his pranks.

Kelly's latest role is that of Johnny Sweet, a lovable musician in a new comedy co-starring Malese Jow. The series, to have been released in April 2008, was tentatively titled ''S.P.: Untitled'', and would allow fans to direct the subsequent filming. The untitled comedy is a coming of age story about a brother and sister who set out to make it in the LA entertainment scene. Previously, Kelly and Jow worked together on ''Unfabulous''. Kelly is also in the indie film ''Garden Party''.

Kelly prefers playing the guitar to the piano and was recording his first album in 2008, which was to be mainly acoustic with a touch of blues.

Filmography

Title ''Unfabulous'' ''S.P. Project''

Year	|	Role	Other notes
rowspan="1"	2004	|	Ben Singer	Television series (2005–2008)
rowspan="2"	2008	|	Johnny Sweet
''Garden Party''	John

External links

Category:1988 births Category:Actors from Illinois Category:American child actors Category:American film actors Category:American television actors Category:Living people Category:People from Chicago, Illinois

de:Tadhg Kelly pt:Tadhg Kelly fi:Tadhg Kelly tr:Tadhg Kelly

Theodore Lockard Thomas (born 1920) is an American chemical engineer and attorney who wrote more than 50 science fiction short stories, published between the early 1950s to the late 1970s. He also collaborated on two novels with Kate Wilhelm, as well as producing stories under the pseudonyms of Leonard Lockard and Cogswell Thomas, and has been nominated for a Nebula award and a Hugo Award.

Bibliography

Collaborations with Kate Wilhelm

''The Clone'' (1965, expanded from his 1959 short story of the same name)

''The Year of the Cloud'' (1970)

Short stories

"The Far Look", in ''Astounding'', August 1956

"Ceramic Incident", in ''Astounding'', October 1956

"The Innocents’ Refuge", in ''Science Fiction Stories'', May 1957

"Satellite Passage", in ''If'', Dec 1958, and available in ''The Best of the Best Part One''

"Day of Succession", in ''Astounding'', August 1959

"The Clone", in ''Fantastic'', Dec 1959

"December 28th", in ''Playboy'', Dec 1959

"The Intruder", in ''Fantasy and Science Fiction'', Feb 1961

"Test", in ''Fantasy and Science Fiction'', April 1962

"The Lonely Man", in ''Galaxy'', April 1963

"The Ice Ages", in ''Fantasy and Science Fiction'', April 1965

"Science Springboard, The: Smog", article in ''Fantasy and Science Fiction'', Jan 1966

"The Doctor", in ''Orbit 2'', 1967

"The Weather on the Sun", in ''Orbit 8'', 1970 (Also available in ''The Science Fictional Solar System'')

"Early Bird (Cogswell)", in ''Astounding'', 1973 (Also available in ''The John W Campbell Memorial Anthology'')

Ker-Plop, in Asimov's Science Fiction, 1979

"The Splice", in ''Fantasy and Science Fiction'', March 1981

As Cogswell Thomas

"Paradise Regained", in ''Saving Worlds'', 1973

As Leonard Lockard

"The Lagging Profession" (1961)

"Improbable Profession" (1952), in ''Astounding'', September 1952 (co-written with Charles L. Harness)

External links

Theodore L. Thomas Short Story Guide

Discussion of Thomas and the accuracy of his predictions

Category:American science fiction writers Category:Living people Category:1920 births

it:Theodore Lockard Thomas