View source for Signal-to-noise ratio (imaging)

{{short description|Measure of image quality}}
{{See also|Film speed#Measurements and calculations}}
{{other uses|Signal-to-noise (disambiguation)}}
{{Use dmy dates|date=August 2019}}

'''Signal-to-noise ratio''' ('''SNR''') is used in [[imaging]] to characterize [[image quality]].  The [[sensitometry|sensitivity]] of a [[photography|(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 [[Film speed|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.<ref>{{citation |url=https://www.iso.org/standard/21020.html |title=ISO 12232: 1998 Photography – Electronic Still Picture Cameras – Determining ISO Speed}}</ref>

SNR is sometimes quantified in [[decibels]] (dB) of signal [[power (physics)|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&nbsp;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 <math>\mu_\mathrm{sig}</math> to the [[standard deviation]]  of the signal <math>\sigma_\mathrm{sig}</math>:<ref>{{cite book |url=https://www.spiedigitallibrary.org/ebooks/PM/Photon-Transfer/eISBN 9780819478382/10.1117/3.725073 |doi=10.1117/3.725073 |title=Photon Transfer |year=2007 |last1=Janesick |first1=James R. |isbn=978-0-8194-7838-2}}</ref><ref>{{cite book |last=Rowlands |first=Andy |date=April 2017 |publisher=[[IOP Publishing]] |title=Physics of Digital Photography |isbn=978-0-7503-1243-1}}</ref>
:<math> \mathrm{SNR} = \frac{\mu_\mathrm{sig}}{\sigma_\mathrm{sig}}</math>

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).{{explain|date=March 2021}}

==See also==
* [[Coefficient of variation]]
* [[Contrast-to-noise ratio]]
* [[Minimum resolvable contrast]]
* [[Minimum resolvable temperature difference]]
* [[Optical transfer function]]
* [[Signal-to-noise ratio]]
* [[Signal transfer function]]

==References==
{{Reflist}}

==Further reading==
* [https://www.iso.org/standard/28835.html 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.
* [https://www.iso.org/standard/37777.html ISO 12232:2006, Photography – Digital still cameras – Determination of exposure index, ISO speed ratings, standard output sensitivity, and recommended exposure index]: 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.

{{Noise}}
{{Photography}}

{{DEFAULTSORT:Signal To Noise Ratio (Imaging)}}
[[Category:Image processing]]
[[Category:Physical quantities]]
[[Category:Science of photography]]


{{Engineering-stub}}