Editing Colors of noise (section)

===Blue noise===
[[Image:Blue noise spectrum.svg|thumb|right|Blue spectrum (+3.01&nbsp;dB per octave)]]

Blue noise is also called azure noise. Blue noise's power density increases <math>10\log_{10}2 = </math> 3.01&nbsp;dB per octave with increasing frequency (density proportional to ''f''&nbsp;) over a finite frequency range.<ref>{{cite web|url=https://www.its.bldrdoc.gov/fs-1037/dir-005/_0685.htm|url-status=dead|archive-url=https://web.archive.org/web/20210608074403/https://www.its.bldrdoc.gov/fs-1037/dir-005/_0685.htm|archive-date=8 June 2021|title=Definition: blue noise|website=its.bldrdoc.gov}}</ref> In computer graphics, the term "blue noise" is sometimes used more loosely as any noise with minimal low frequency components and no concentrated spikes in energy. This can be good noise for [[dither]]ing.<ref>{{cite book | last1=Mitchell | first1=Don P. | title=Proceedings of the 14th annual conference on Computer graphics and interactive techniques | chapter=Generating antialiased images at low sampling densities | year=1987 | volume=21 | issue=4 | pages=65–72 | doi=10.1145/37401.37410| isbn=0897912276 | s2cid=207582968 }}</ref> [[Retina]]l cells are arranged in a blue-noise-like pattern which yields good visual resolution.<ref>{{cite journal | last1 = Yellott | first1 = John I. Jr | year = 1983 | title = Spectral Consequences of Photoreceptor Sampling in the Rhesus Retina | journal = Science | volume = 221 | issue = 4608| pages = 382–85 | doi = 10.1126/science.6867716 | pmid = 6867716 | bibcode = 1983Sci...221..382Y | url = https://escholarship.org/uc/item/0qq9b8zx }}</ref>

[[Cherenkov radiation]] is a naturally occurring example of almost perfect blue noise, with the power density growing linearly with frequency over spectrum regions where the permeability of index of refraction of the medium are approximately constant. The exact density spectrum is given by the [[Frank–Tamm formula]]. In this case, the finiteness of the frequency range comes from the finiteness of the range over which a material can have a [[refractive index]] greater than unity. Cherenkov radiation also appears as a bright blue color, for these reasons.



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