ATIS Telecom Glossary
Wednesday, October 22, 2014

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aliasing
In any technology or process involving (a) sampling a signal, e.g., an electrical signal or (a series of images of) a moving subject; (b) processing, storing, or transmitting representations of the samples; and (c) replicating the original signal from the representations: the production of artifacts as a result of sampling at intervals too great to permit faithful replication of the original signal. Note 1: A common example of aliasing in video or motion picture technology is the apparent slowing, freezing, or even reversing of direction of, the motion of spokes in the wheels on a moving vehicle. Note 2: In the sampling and replication of electrical signals, if the sampling interval is too great, high-frequency components may, for example, be replicated as low-frequency components, distorting the replicated signal. Note 3: Faithful reproduction of a sampled electrical signal requires a theoretical sampling interval not greater than one-half the inverse of the highest Fourier frequency component in the sampled signal (Nyquist interval). In practice, to achieve a given level of fidelity in the replicated signal, the sampling interval must usually be somewhat shorter than the theoretical (Nyquist) interval, because the samples are usually processed, stored, or transmitted in digital form, and quantization errors in the digitizing process will also result in distortion of the (waveform of the) replicated signal. Note 4: The effects of aliasing in the replicated signal may be avoided by filtering the original signal to remove frequency components that are higher than those desired in the replicated signal. Note 5 (from SMPTE): Video images are sampled in two or three dimensions, and computer graphics are sampled in three. In a composite (complex) spectral channel, any crosstalk of the information cannot be eliminated by filtering, and will produce aliasing, for example as cross-color and/or cross-luminance. In a rectilinearly sampled system, lines not parallel to a sampling axis will appear stepped unless anti-aliasing processing algorithms have been applied.

 

 

 

 

 

 

 

 

 

 



 
These definitions were prepared by ATIS Committee PRQC
 
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