Raster images have a finite set of digital
values, called picture elements
. The digital image contains a fixed number of rows and columns of pixels. Pixels are the smallest individual element in an image, holding antiquated 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
Raster images can be created
by a variety of input devices and techniques, such as digital cameras
, 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
Some digital cameras
give access to almost all the data captured by the camera, using a raw image format
. The Universal Photographic Imaging Guidelines (UPDIG)
suggests these formats be used when possible since raw files produce the best quality images. These file formats allow the photographer and the processing agent the greatest level of control and accuracy for output. Their use is inhibited by the prevalence of proprietary information (trade secrets
) for some camera makers, but there have been initiatives such as OpenRAW
to influence manufacturers to release these records publicly. An alternative may be Digital Negative (DNG)
, a proprietary Adobe product described as "the public, archival format for digital camera raw data".
Although this format is not yet universally accepted, support for the product is growing, and increasingly professional archivists and conservationists, working for respectable organizations, variously suggest or recommend DNG for archival purposes.
resulted from mathematical geometry (vector
). In mathematical terms, a vector consists of both a magnitude, or length, and a direction.
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).
Example of vector file types are EPS
, and AI
Image viewer software displays images. Web browsers
can display standard internet image formats including JPEG
. 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.
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.
Some viewers offer a slideshow
utility to display a sequence of images.
The first scan done by the SEAC
The SEAC scanner
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
, Bell Labs
and the University of Maryland
, among others, used digital images to advance satellite imagery
, wirephoto standards conversion, medical imaging
technology, character recognition
, and photo enhancement.
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
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
Digital image sensors
The first semiconductor image sensor was the CCD, developed by Willard S. Boyle
and George E. Smith
at Bell Labs in 1969.
While researching MOS technology, they realized that an electric charge was the analogy of the magnetic bubble and that it could be stored on a tiny MOS capacitor
. As it was fairly straightforward to fabricate
a series of MOS capacitors in a row, they connected a suitable voltage to them so that the charge could be stepped along from one to the next.
The CCD is a semiconductor circuit that was later used in the first digital video cameras
for television broadcasting
Digital image compression
In digital imaging, a mosaic
is a combination of non-overlapping images, arranged in some tessellation
. Gigapixel images
are an example of such digital image mosaics. Satellite imagery
are often mosaicked to cover Earth regions.
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Last edited on 16 March 2021, at 23:40
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