This example shows an image with a portion greatly enlarged, in which the individual pixels are rendered as little squares and can easily be seen.

In digital imaging, a pixel (picture element^[1]) is the smallest piece of information in an image. Digital imaging or digital image acquisition is the creation of Digital images typically from a physical object Pixels are normally arranged in a regular 2-dimensional grid, and are often represented using dots or squares. Each pixel is a sample of an original image, where more samples typically provide a more accurate representation of the original. In Signal processing, sampling is the reduction of a Continuous signal to a Discrete signal. The intensity of each pixel is variable; in color systems, each pixel has typically three or four components such as red, green, and blue, or cyan, magenta, yellow, and black. In Physics, intensity is a measure of the time-averaged Energy Flux. CMYK (short for '''c'''yan, '''m'''agenta, '''y'''ellow, and k ey ( Black) and often referred to as process color

The word pixel is based on the abbreviation "pix" for "pictures"; similar back-formations include voxel, luxel, and texel. A voxel (a Portmanteau of the words Volumetric and Pixel) is a volume element representing a value on a Regular grid in

Technical

A 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 an image. The definition is highly context sensitive; for example, we can speak of 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, e. g. pel, sample, byte, bit, dot, spot, etc. We can also speak of pixels in the abstract, or as a unit of measure, in particular when using pixels as a measure of resolution, e. g. 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 in the printer field, where dpi is a measure of the printer's resolution of dot printing (e. Dots per inch ( DPI) is a measure of spatial Printing or Video dot density in particular the number of individual dots that can be placed within the span g. ink droplet density). For example, a high-quality inkjet image may be printed with 200 ppi on a 720 dpi printer.

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. Image resolution describes the detail an Image holds The term applies equally to Digital images film images and other types of images 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. Many compact digital still cameras can record Sound and moving Video as well as still Photograph. The term Video Graphics Array ( VGA) refers specifically to the display hardware first introduced with the IBM PS/2 line of computers in 1987, but through its widespread 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. In Computer graphics, a bitmap or pixmap is a type of memory organization or Image file format used to store Digital images The In Computer graphics, a raster graphics image or bitmap, is a Data structure representing a generally rectangular grid of Pixels The word raster originates from television scanning patterns, and has been widely used to describe similar halftone printing and storage techniques. A Raster scan, or raster scanning, is the pattern of image detection and reconstruction in television and is the pattern of image storage and transmission used in most computer Halftone is the Reprographic technique that simulates Continuous tone imagery through the use of equally spaced dots of varying size

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 also possible, with some sampling patterns even changing the shape (or kernel) of each pixel across the image. In Mathematics and in particular Functional analysis, convolution is a mathematical operation on two functions f and

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. Cleartype is a technology which takes advantage of these differences to improve the rendering of text on LCD screens. ClearType is the Microsoft implementation of Subpixel rendering technology aiming to improve the appearance of text on certain types of Computer display
• Some 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. Explanation Bryce Bayer's patent called the green photosensors luminance-sensitive elements and the red and blue ones chrominance-sensitive elements.
• A clipmap uses a hierarchical sampling pattern, where the size of the support of each pixel depends on its location within the hierarchy. Clipmapping is a method of clipping a Mipmap to a subset of data pertinent to the geometry being displayed In Mathematics, the support of a function is the set of points where the function is not zero or the closure of that set
• Warped grids are used when the underlying geometry is non-planar, such as images of the earth from space. ^[2]
• The use of non-uniform grids is an active research area, attempting to bypass the traditional Nyquist limit. In Signal processing, the Nyquist rate is two times the bandwidth of a Bandlimited signal or a bandlimited channel ^[3]
• Pixels on computer monitors are normally square, but some digital video formats have non-square aspect ratios, such as the anamorphic widescreen formats of the CCIR 601 digital video standard. Digital video is a type of Video recording system that works by using a Digital rather than an analog video signal Pixel aspect ratio (PAR in Computer graphics terminology is a mathematical Ratio that describes how the horizontal length of a Pixel in an imaging Anamorphic widescreen is a videographic technique utilising rectangular (wide pixels to store a Widescreen image to standard 43 aspect ratio. ITU-R Recommendation BT601, more commonly know by the abbreviations Rec

Display resolution vs. native resolution in computer monitors

Modern computer monitors use pixels to display images, often representing an abstract image such as a GUI. The resolution of this image is called the display resolution and is determined by the video card of the computer. A video card, also known as a graphics accelerator card, display adapter, or graphics card, is a hardware component whose function is to

Modern computer monitors also have a native resolution. In the case of an LCD monitor, each pixel is made up of individual triads, and the number of these triads will determine the native resolution. In CRT or Computer terminology a triad is a group of three Phosphor dots coloured red green and blue on the inside of the CRT display of a On some CRT monitors, the beam sweep rate may be fixed, resulting in a fixed native resolution. The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or

To produce the sharpest images possible, the user must ensure the display resolution of the computer matches the native resolution of the monitor.

If these resolutions are different, the image may appear squashed or stretched, or the monitor may resample the image, resulting in a blurry or jagged appearance. Resampling is the digital process of changing the Sample rate or dimensions of digital imagery or audio by temporally or areally analysing and sampling the original data

Bits per pixel

Main article: Color depth

The number of distinct colors that can be represented by a pixel depends on the number of bits per pixel (bpp). Color depth. or bit depth, is a Computer graphics term describing the number of Bits used to represent the Color of a single Pixel 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
• 15 bpp, 2¹⁵ ≈ 32 thousand colors ("Highcolor" )
• 24 bpp, 2²⁴ ≈ 16. Highcolor graphics (variously spelled Hicolor, Hicolour, and Highcolour, and known as Thousands of colors on a Macintosh) is a method 7 million colors ("Truecolor")

For color depths of 15bpp (HighColor) and larger, the depth is normally the sum of the bits allocated to each of the three RGB (red, green and blue) components. See also True Colors (disambiguation. Truecolor is a method of representing and storing graphical image information (especially in computer 16bpp normally has five bits for red and blue, and six bits for green, as the human eye is more sensitive to green than 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). Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation especially visible Light.

Images with 256 colors or fewer (8bpp and less) are stored in the computer's video memory in either packed pixel (chunky) format, or planar format. Video memory is a term generally used in Computers to describe some form of writable memory usually RAM, dedicated to the purpose of holding the information necessary In packed pixel or chunky Frame buffer organization the bits defining each pixel are grouped together In Computer graphics, planar is the method of representing pixel colours with several bitplanes of RAM. In an indexed image, the pixel's value is an index into a list of colors called a palette. In computing indexed color is a technique to manage Digital images colors in a limited fashion in order to save computer's memory and file storage In Computer graphics, a palette is either a given finite set of Colors for the management of Digital images (that is a color palette) or Changing the colors in the palette produces a type of animation effect with a well known examples being the the startup logos of Windows 95 and Windows 98. Windows 95 is a consumer-oriented Graphical user interface -based Operating system. Windows 98 ( codenamed Memphis) is a graphical Operating system released on 25 June 1998 by Microsoft and the successor to Windows 95

Subpixels

Phosphor dots in a color CRT display bear no relation to pixels or subpixels

Pixel geometry of various CRT and LCD displays. A phosphor is a substance that exhibits the phenomenon of Phosphorescence (sustained glowing after exposure to energized particles such as Electrons The components of the Pixels ( Primary colors red green and blue in an Image Sensor or display can be ordered in different Patterns

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.

Most digital camera image sensors also use single-color sensor regions, for example using the Bayer filter pattern, but in the case of cameras these are known as pixels, not subpixels. Many compact digital still cameras can record Sound and moving Video as well as still Photograph. An image sensor is a device that converts an optical image to an electric signal Explanation Bryce Bayer's patent called the green photosensors luminance-sensitive elements and the red and blue ones chrominance-sensitive elements.

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.

The latter approach has been used to increase the apparent resolution of color displays. The technique, referred to as subpixel rendering, uses knowledge of pixel geometry to manipulate the three colored subpixels separately and produce a better displayed image. Subpixel rendering is a way to increase the apparent resolution of a computer's Liquid crystal display (LCD by rendering pixels to take account the screen type's physical properties The components of the Pixels ( Primary colors red green and blue in an Image Sensor or display can be ordered in different Patterns

While CRT displays also use red-green-blue masked phosphor areas, dictated by a mesh grid called the shadow mask, these can not be aligned with the displayed pixel raster, and therefore can not be utilised for subpixel rendering. The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or

Megapixel

A megapixel is 1 million pixels, and is a term used not only for the number of pixels in an image, but also to express the number of image sensor elements of digital cameras or the number of display elements of digital displays. An image sensor is a device that converts an optical image to an electric signal Many compact digital still cameras can record Sound and moving Video as well as still Photograph. A visual display unit, often called simply a monitor or display, is a piece of Electrical equipment which displays images generated from the Video For example, a camera with an array of 2048×1536 sensor elements is commonly said to have "3. 1 megapixels" (2048 × 1536 = 3,145,728). The neologism sensel is sometimes used to describe the elements of a digital camera's sensor, since these are picture-detecting rather than picture-producing elements. ^[4]

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. A charge-coupled device ( CCD) is an analog Shift register, that enables the transportation of analog signals (electric charges through successive stages (capacitors Complementary metal–oxide–semiconductor ( CMOS) (pronounced "see-moss" siːmɔːs ˈsiːmɒs is a major class of Integrated circuits CMOS technology An image sensor is a device that converts an optical image to an electric signal 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. Explanation Bryce Bayer's patent called the green photosensors luminance-sensitive elements and the red and blue ones chrominance-sensitive elements. The camera interpolates the color information of neighboring sensor elements, through a process called demosaicing, to create the final image. A demosaicing Algorithm is a digital image process used to interpolate a complete image from the partial raw data received from the color-filtered 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).

In contrast to conventional image sensors, the Foveon X3 sensor uses three layers of sensor elements, so that it detects red, green, and blue intensity at each array location. The Foveon X3 sensor is a CMOS Image sensor for digital cameras designed by Foveon Inc This structure eliminates the need for de-mosaicing and eliminates the associated image artifacts, such as color blurring around sharp edges. Citing the precedent established by mosaic sensors, Foveon counts each single-color sensor element as a pixel, even though the native output file size has only one pixel per three camera pixels. [1] With this method of counting, an N-megapixel Foveon X3 sensor therefore captures the same amount of information as an N-megapixel Bayer-mosaic sensor, though it packs the information into fewer image pixels, without any interpolation.

Standard display resolutions

Main article: display resolution

Display standards comparison

Selected standard display resolutions include:

Similar concepts

Several other types of objects derived from the idea of the pixel, such as the voxel (volume element), texel (texture element) and surfel (surface element), have been created for other computer graphics and image processing uses. A voxel (a Portmanteau of the words Volumetric and Pixel) is a volume element representing a value on a Regular grid in A texel, or tex ture el ement (also tex ture pi' xel) is the fundamental unit of texture space used in Computer graphics Surfel is an abbreviation of " surf ace el ement" In 3D computer graphics, the use of surfels is an alternative to Polygonal modeling Computer graphics are Graphics created by Computers and more generally the Representation and Manipulation of Pictorial Data Image processing is any form of Signal processing for which the input is an image such as photographs or frames of video the output of image processing can be either an image

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; but he did not coin the term himself, and the person he got it from (Keith E. Frederic Crockett Billingsley (23 July 1921 – 31 May 2002 was an American engineer who spent most of his career developing techniques for Digital image processing in support McFarland at the Link Division of General Precision in Palo Alto) does not know where he got it, but says it was "in use at the time" (circa 1963).

The word is a combination of picture and element, via pix. Pix was first coined in 1932 in a Variety Magazine headline, as an abbreviation for the word pictures, in reference to movies; by 1938 pix was being used in reference to still pictures by photojournalists. Variety is a weekly entertainment trade newspaper founded in New York in 1905 by Sime Silverman

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. Paul Julius Gottlieb Nipkow ( 22 August 1860 &ndash 24 August 1940) was a German Technician and Inventor. According to various etymologies, the earliest publication of the term picture element itself was in Wireless World magazine in 1927,^[5]though it had been used earlier in various U. S. patents filed as early as 1911. [2]

Some authors explain pixel as picture cell, as early as 1972. ^[6]

A detailed history of pixel and picture element, with references, is linked below.

See also

References

External links

• A Pixel Is Not A Little Square: Microsoft Memo by computer graphics pioneer Alvy Ray Smith.
• A Brief History of 'Pixel': More than you need to know about the history of pixel, pel, and picture element.
• Pixels and Me: Video of a history talk at the Computer History Museum. The Computer History Museum is a Museum established in 1996 in Mountain View California, when The Computer Museum (TCM in Boston)
• Square and non-Square Pixels: Technical info on pixel aspect ratios of modern video standards (480i,576i,1080i,720p), plus software implications.