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Answer 1

n digital imaging, a pixel, or pel[1], (picture element[2]) is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled.

Each pixel has its own address. The address of a pixel corresponds to its coordinates. Pixels are normally arranged in a two-dimensional grid, and are often represented using dots or squares. Each pixel is a sampleof 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),[3] while in others the term may refer to the entire set of such component intensities for a spatial position. In color systems that usechroma 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[4]and texel.[4]

Contents[hide]

• 1 Etymology
  • 1.1 Words with similar etymologies
• 2 Technical
  • 2.1 Sampling patterns
  • 2.2 Resolution of computer monitors
  • 2.3 Bits per pixel
  • 2.4 Subpixels
• 3 Megapixel
• 4 Display resolution
• 5 See also
• 6 References
• 7 External links

[edit]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).[5]

The word is a combination of picture and element, via pix. The word pix appeared in Varietymagazine headlines in 1932, as an abbreviation for the word pictures, in reference to movies.[6]By 1938, "pix" was being used in reference to still pictures by photojournalists.[5]

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 inWireless World magazine in 1927,[7]though it had been used earlier in various U.S. patents filed as early as 1911.[8]

Some authors explain pixel as picture cell, as early as 1972.[9] In video processing, pel is often used instead of pixel.[10] For example, IBM used it in their Technical Reference for the original PC.

[edit]Words with similar etymologies

• Texel (texture element) and luxel (luxelement) are words used to describe a pixel when it is used in specific context (texturing and light mapping respectively)
• A voxelis 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 reselis a resolution element, used to describe the discrete number of resolvable elements of a continuous signal (e.g. in optical imaging).

[edit]TechnicalA pixel does not need to be rendered as a small square. This image shows alternative ways of reconstructing an image from a set of pixel values, using dots, lines, or smooth filtering.

A pixel is generally 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.[11] For example, a high-quality photographic image may be printed with 600 ppi on a 1200 dpi inkjet printer.[12]Even higher dpi numbers, such as the 4800 dpi quoted by printer manufacturers since 2002, do not mean much in terms of achievable resolution.[13]

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 VGAdisplay), 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 scanningpatterns, and has been widely used to describe similar halftone printing and storage techniques.

[edit]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:

Text rendered using ClearType

• 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.[14]
• The use of non-uniform grids is an active research area, attempting to bypass the traditional Nyquist limit.[15]
• 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 videoformats with diverse aspect ratios, such as the anamorphic widescreen formats of the Rec. 601 digital video standard.

[edit]Resolution of computer monitors