A digital image is a numeric representation (normally binary) of a two-dimensional image. Depending on whether the image resolution is fixed, it may be of vector or raster type. By itself, the term "digital image" usually refers to raster images or bitmapped images.
- Raster file formats 1.1
- Vector 2
- Image viewing 3
- History 4
- See also 5
- References 6
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.
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.
Raster file formats
Most users come into contact with raster images through digital cameras, which use any of several image file formats.
- Digital Negative (DNG) Specification. San Jose: Adobe, 2005. Vers. 184.108.40.206. p. 9. Accessed on October 10, 2007.
- universal photographic digital imaging guidelines (UPDIG): File formats - the raw file issue
- Archaeology Data Service / Digital Antiquity: Guides to Good Practice - Section 3 Archiving Raster Images - File Formats
- University of Connecticut: "Raw as Archival Still Image Format: A Consideration" by Michael J. Bennett and F. Barry Wheeler
- Inter-University Consortium for Political and Social Research: Obsolescence - File Formats and Software
- JISC Digital Media - Still Images: Choosing a File Format for Digital Still Images - File formats for master archive
- International Digital Enterprise Alliance, Digital Image Submission Criteria (DISC) Guidelines & Specifications 2007 (PDF)
- The J. Paul Getty Museum - Department of Photographs: Rapid Capture Backlog Project - Presentation
- American Institute for Conservation - Electronic Media Group: Digital Image File Formats
- Archives Association of British Columbia: Born Digital Photographs: Acquisition and Preservation Strategies (Rosaleen Hill)
- Fiftieth Anniversary of First Digital Image.
- Azriel Rosenfeld, Picture Processing by Computer, New York: Academic Press, 1969
- Gonzalez, Rafael, C; Woods, Richard E (2008). Digital Image Processing, 3rd Edition. Pearson Prentice Hall. p. 577.
- Jähne, Bernd (1993). Spatio-temporal image processing, Theory and Scientific Applications. Springer Verlag. p. 208.
- Computer printer
- Digital image editing
- Digital geometry
- Digital photography
- Geocoded photo
- Optical character recognition
- Signal processing
- Digital image correlation
Advances in microprocessor technology paved the way for the development and marketing of charge-coupled devices (CCDs) for use in a wide range of image capture devices and gradually displaced the use of analog film and tape in photography and videography towards the end of the 20th century. The computing power necessary to process digital image capture also allowed computer-generated digital images to achieve a level of refinement close to photorealism.
Rapid advances in digital imaging began with the introduction of microprocessors in the early 1970s, alongside progress in related storage and display technologies. The invention of computerized axial tomography (CAT scanning), using x-rays to produce a digital image of a "slice" through a three-dimensional object, was of great importance to medical diagnostics. As well as origination of digital images, digitization of analog images allowed the enhancement and restoration of archaeological artifacts and began to be used in fields as diverse as nuclear medicine, astronomy, law enforcement, defence and industry.
Early Digital fax machines such as the Bartlane cable picture transmission system preceded digital cameras and computers by decades. The first picture to be scanned, stored, and recreated in digital pixels was displayed on the Standards Eastern Automatic Computer (SEAC) at NIST. The advancement of digital imagery continued in the early 1960s, alongside development of the space program and in medical research. Projects at the Jet Propulsion Laboratory, MIT, Bell Labs and the University of Maryland, among others, used digital images to advance satellite imagery, wirephoto standards conversion, medical imaging, videophone technology, character recognition, and photo enhancement.
Some viewers offer a slideshow utility to display a sequence of images.
Some scientific images can be very large (for instance, the 46 gigapixel size image of the Milky Way, about 194 Gb in size).  Such images are difficult to download and are usually browsed online through more complex web interfaces.
Image viewer software displays images. Web browsers can display standard internet image formats including GIF, JPEG, and PNG. Some can show SVG format which is a standard W3C format. In the past, when Internet was still slow, it was common to provide "preview" image that would load and appear on the web site before being replaced by the main image (to give at preliminary impression). Now Internet is fast enough and this preview image is seldom used.
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).