Signal-to-noise ratio (imaging)

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Signal-to-noise ratio (SNR) is used in imaging to characterize image quality. 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.

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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. [1]

SNR is sometimes quantified in decibels (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 of the signal : [2] [3]

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).[ further explanation needed ]

See also

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Exposure (photography)

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135 film Photographic film format

135 film, better known as 35 mm film, is a format of photographic film used for still photography. It is a cartridge film with a film gauge of 35 mm (1.4 in), typically used for hand-held photography in 35 mm film cameras. Its engineering standard for the film is controlled by ISO 1007.

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In photography, exposure value (EV) is a number that represents a combination of a camera's shutter speed and f-number, such that all combinations that yield the same exposure have the same EV. Exposure value is also used to indicate an interval on the photographic exposure scale, with a difference of 1 EV corresponding to a standard power-of-2 exposure step, commonly referred to as a stop.

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Guide number

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Image sensor format

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References

  1. ISO 12232: 1997 Photography – Electronic Still Picture Cameras – Determining ISO Speed
  2. Janesick, James R. (2007). Photon Transfer. doi:10.1117/3.725073. ISBN   978-0-8194-7838-2.
  3. Rowlands, Andy (April 2017). Physics of Digital Photography. IOP Publishing. ISBN   978-0-7503-1243-1.

Further reading