Digital image
From Wikipedia, the free encyclopedia
A digital image is a representation of a two-dimensional image using ones and zeros (binary). Depending on whether or not the image resolution is fixed, it may be of vector or raster type. Without qualifications, the term "digital image" usually refers to raster images also called bitmap images.
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[edit] Raster
Raster images have a finite set of digital values, called picture elements or pixels. The digital image contains a fixed number of rows and columns of pixels. Pixels are the smallest individual element in an image, holding quantized values that represent the brightness of a given color at any specific point.
Typically, the pixels are stored in computer memory as a raster image or raster map, a two-dimensional array of small integers. These values are often transmitted or stored in a compressed form.
Raster images can be created by a variety of input devices and techniques, such as digital cameras, scanners, coordinate-measuring machines, seismographic profiling, airborne radar, and more. They can also be synthesized from arbitrary non-image data, such as mathematical functions or three-dimensional geometric models; the latter being a major sub-area of computer graphics. The field of digital image processing is the study of algorithms for their transformation.
[edit] Raster image types
Each pixel of a raster image is typically associated to a specific 'position' in some 2D region, and has a value consisting of one or more quantities (samples) related to that position. Digital images can be classified according to the number and nature of those samples:
The term digital image is also applied to data associated to points scattered over a three-dimensional region, such as produced by tomographic equipment. In that case, each datum is called a voxel.
[edit] Raster file formats
Most users come into contact with raster images through digital cameras. Some digital cameras give access to almost all the data captured by the camera, using the RAW file format. The Universal Photographic Imaging Guidelines (UPDIG) suggests this format be used when possible since RAW files produce the best quality images. This file format allows the photographer and the processing agent the greatest level of control and accuracy for output. Unfortunately, there is an issue of proprietary information [trade secrets] for some camera makers, but organizations are attempting to influence the manufacturers of them to avail these records publicly. An alternative may be a Digital Negative (DNG) an Adobe product described as “the public, archival format for digital camera raw data”.[1] Although this format is not yet universally accepted, support for the product is growing and archival confidence is building.[2]
[edit] Vector
Vector images may be created from scratch with illustration software, or by converting a raster image to vector form.
Often, both raster and vector elements will be combined in one image, for example, in the case of a billboard with text (vector) and photographs (raster).
[edit] Image viewing
The user can utilize different program to see the image. The GIF, JPEG and PNG images can be seen simply using a web browser because they are the standard internet image formats. The SVG format is more and more used in the web and is a standard W3C format.
Some viewers offer a slideshow utility, to see the images in a certain folder one after the other automatically.
[edit] History
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Images have existed since pre-history, but the electrical transmission and storage of images date from the 19th and 20th century, respectively. Photography and film also date to this era.
Images have been transmitted electrically since the 19th century, with the 1865 pantelegraph as the earliest fax machine, and in various forms as discussed in the history of television. Rasterization was developed in the 1884 Nipkow disk, and the earliest television recording were 1927 phonovision discs, using phonograph records to record a television signal. Television signals through most of the 20th century were analog, however.
Early electrical storage of images include the monoscope, a cathode ray tube used for image generation, which was replaced by test cards. Electrical storage of video developed with videotapes, first commercialized in the 1956 Quadruplex videotape. However, these were all analog formats.
Digital images were developed with digital computers in the 1950s and 1960s, particularly in the context of video games, using cathode ray tubes and in some cases panels of lights; see history of video games and first video game for details. The first use of a raster display (instead of a vector display) for video games was by Ralph Baer and associate in May 1967, which may be considered among the earliest digital raster images.
[edit] See also
[edit] References
- ^ Digital Negative (DNG) Specification. San Jose: Adobe, 2005. Vers. 1.1.0.0. p. 9. Accessed on October 10, 2007.
- ^ Anderson, Richard. The Universal Photographic Digital Imaging Guidelines. Ed. Michael Stewart. 2006. Vers. 2.0. UPDIG: Universal Photographic Digital Imaging Guidelines. p. 8. Accessed on October 12, 2007
