Signal-to-noise ratio (SNR) is used in
imaging
Imaging is the representation or reproduction of an object's form; especially a visual representation (i.e., the formation of an image).
Imaging technology is the application of materials and methods to create, preserve, or duplicate images.
...
to characterize
image quality
Image quality can refer to the level of accuracy with which different imaging systems capture, process, store, compress, transmit and display the signals that form an image. Another definition refers to image quality as "the weighted combination of ...
. The
sensitivity of a
(digital or film) imaging system is typically described in the terms of the signal level that yields a threshold level of SNR.
Industry standards define sensitivity in terms of the
ISO film speed equivalent, using SNR thresholds (at average scene luminance) of 40:1 for "excellent" image quality and 10:1 for "acceptable" image quality.
SNR is sometimes quantified in
decibels
The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a ...
(dB) of signal
power relative to noise power, though in the imaging field the concept of "power" is sometimes taken to be the power of a voltage signal proportional to optical power; so a 20 dB SNR may mean either 10:1 or 100:1 optical power, depending on which definition is in use.
Definition of SNR
Traditionally, SNR is defined to be the ratio of the average signal value
to the
standard deviation
In statistics, the standard deviation is a measure of the amount of variation of the values of a variable about its Expected value, mean. A low standard Deviation (statistics), deviation indicates that the values tend to be close to the mean ( ...
of the signal
:
:
when the signal is an optical intensity, or as the square of this value if the signal and noise are viewed as amplitudes (field quantities).
See also
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Coefficient of variation
*
Contrast-to-noise ratio
*
Minimum resolvable contrast
*
Minimum resolvable temperature difference
*
Optical transfer function
*
Signal-to-noise ratio
Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in deci ...
*
Signal transfer function
References
Further reading
ISO 15739:2003, Photography – Electronic still-picture imaging – Noise measurements specifies methods for measuring and reporting the noise versus signal level and dynamic range of electronic still-picture cameras. It applies to both monochrome and colour electronic still-picture cameras.
specifies the method for assigning and reporting ISO speed ratings, ISO speed latitude ratings, standard output sensitivity values, and recommended exposure index values for digital still cameras. ISO 12232:2006 is applicable to both monochrome and colour digital still cameras. It revises ISO 12232:1998.
Image processing
Physical quantities
Science of photography
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