Editing Decibel (section)

=== Video and digital imaging ===
In connection with video and digital [[image sensor]]s, decibels generally represent ratios of video voltages or digitized light intensities, using 20&nbsp;log of the ratio, even when the represented intensity (optical power) is directly proportional to the voltage generated by the sensor, not to its square, as in a [[CCD imager]] where response voltage is linear in intensity.<ref>
{{cite book
 | title = The Colour Image Processing Handbook
 | author = Stephen J. Sangwine and Robin E. N. Horne
 | publisher = Springer
 | year = 1998
 | isbn = 978-0-412-80620-9
 | pages = 127–130
 | url = {{Google books |plainurl=yes |id=oEsZiCt5VOAC |page=127 }}
}}</ref>
Thus, a camera [[signal-to-noise ratio]] or dynamic range quoted as 40&nbsp;dB represents a ratio of 100:1 between optical signal intensity and optical-equivalent dark-noise intensity, not a 10,000:1 intensity (power) ratio as 40&nbsp;dB might suggest.<ref>
{{cite book
 | title = Introduction to optical engineering
 | author = Francis T. S. Yu and Xiangyang Yang
 | publisher = Cambridge University Press
 | year = 1997
 | isbn = 978-0-521-57493-8
 | pages = 102–103
 | url = {{Google books |plainurl=yes |id=RYm7WwjsyzkC |page=120 }}
}}</ref>
Sometimes the 20&nbsp;log ratio definition is applied to electron counts or photon counts directly, which are proportional to sensor signal amplitude without the need to consider whether the voltage response to intensity is linear.<ref>
{{cite book
 | title = Image sensors and signal processing for digital still cameras
 | chapter = Basics of Image Sensors
 | author = Junichi Nakamura
 | editor = Junichi Nakamura
 | publisher = CRC Press
 | year = 2006
 | isbn = 978-0-8493-3545-7
 | pages = 79–83
 | chapter-url = {{Google books |plainurl=yes |id=UY6QzgzgieYC |page=79 }}
}}</ref>

However, as mentioned above, the 10&nbsp;log intensity convention prevails more generally in physical optics, including fiber optics, so the terminology can become murky between the conventions of digital photographic technology and physics. Most commonly, quantities called ''dynamic range'' or ''signal-to-noise'' (of the camera) would be specified in {{nowrap|20 log dB}}, but in related contexts (e.g. attenuation, gain, intensifier SNR, or rejection ratio) the term should be interpreted cautiously, as confusion of the two units can result in very large misunderstandings of the value.

Photographers typically use an alternative base-2 log unit, the [[F-number#Stops.2C f-stop conventions.2C and exposure|stop]], to describe light intensity ratios or dynamic range.