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Glossary: N

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Most common measurement of distance for the wavelengths of light. A nanometer is equal to one billionth (10 to the ninth) of a meter. …
National Information Standards Organization
Neutral color
See Achromatic
Neutral test card
See Gray card
Newtons rings
An interference pattern that appears as a series of concentric, alternating light and dark rings of colored light (when imaged in a color mode). This type of interference is caused when smooth transparent surfaces come into contact with small gaps of air between the surfaces. The light waves reflected from the top and…
Founded in 1939, the National Information Standards Organization (NISO) is a non-profit association accredited by ANSI with the mission to identify, develop, maintain, and publish technical standards to manage and provide access to trusted information. Its nearly eighty voting members represent a variety of groups involved in the organization and distribution of information, including…
Data that obscures or corrupts signal, as that term is used in the expression signal-to-noise ratio. Although noise is generally unwanted and signal is wanted, there are exceptions. In some circumstances, for example, dithering (Dither), which produces noise, is deliberately employed to counteract the aliasing that results when certain frequencies in a sound…
See Also Aliasing; Artifact (defect); Dither; Distortion; Signal to noise ratio
Noise Power Spectrum
Abbreviated as NPS, this is an engineering and scientific metric for describing the spatial frequency content of noise. Just as the SFR is a metric for describing the spatial frequency content of signal sources, NPS does so for noise sources. For instance, the common term "white noise" has equal noise power at all spatial frequencies…
Noise, digital audio
Noise has a number of meanings in terms of sound. This definition pertains to the measurement of noise in digitizing equipment, as when the International Association of Sound and Audiovisual Archives (IASA) specifies pass-fail values for the measurement of THD plus noise (THD+N). Different methods are used by different organizations to measure the…
See Also Aliasing; Artifact (defect); Dither; Distortion; Noise; Signal to noise ratio
Noise, root-mean-square (RMS)
Summary measure of radiometric distortion calculated as the standard deviation of the pixel values within a large region of interest.(ROI)…
Noise, white
Any stochastic realization whose spatial frequency power is effectively equivalent for all frequencies. (Stochastic processes are non-deterministic: a given state does not fully determine the next state.)…
See Noise Power Spectrum
Nyquist frequency
The highest possible frequency that can be coded at a given sampling rate in order to be able to fully reconstruct the signal.…
Nyquist principle
Nyquist principle states that the sampling rate must be at least twice the maximum bandwidth of the analog signal in order to allow the signal to be completely represented.…