Contrast-to-noise ratio (CNR) is a measure used to determine image quality. CNR is similar to the metric
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 ...
(SNR), but subtracts a term before taking the ratio. This is important when there is a significant bias in an image, such as from haze. As can be seen in the picture at right, the intensity is rather high even though the features of the image are washed out by the haze. Thus this image may have a high SNR metric, but will have a low CNR metric.
One way to define contrast-to-noise ratio is:
:
where ''S''
''A'' and ''S''
''B'' are signal intensities for signal producing structures ''A'' and ''B'' in the region of interest and ''σ''
o is 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 pure
image noise
Image noise is random variation of brightness or color information in images. It can originate in film grain and in the unavoidable shot noise of an ideal photon detector. In digital photography is usually an aspect of electronic noise, produ ...
.
See also
*
Contrast resolution
References
{{Noise
Image processing