Editing RGB color model (section)

====Nonlinearity====
{{Main|Gamma correction}}

In classic CRT devices, the brightness of a given point over the [[fluorescence|fluorescent]] screen due to the impact of accelerated [[electron]]s is not proportional to the voltages applied to the [[electron gun]] control grids, but to an expansive function of that voltage. The amount of this deviation is known as its [[gamma correction|gamma]] value (<math>\gamma</math>), the argument for a [[power law]] function, which closely describes this behavior. A linear response is given by a gamma value of 1.0, but actual CRT nonlinearities have a gamma value around 2.0 to 2.5.

Similarly, the intensity of the output on TV and computer display devices is not directly proportional to the R, G, and B applied electric signals (or file data values which drive them through digital-to-analog converters). On a typical standard 2.2-gamma CRT display, an input intensity RGB value of (0.5,&nbsp;0.5,&nbsp;0.5) only outputs about 22% of full brightness (1.0,&nbsp;1.0,&nbsp;1.0), instead of 50%.<ref>{{cite book | title = Digital Compositing for Film and Video | author = Steve Wright | publisher = Focal Press | isbn = 0-240-80760-X | year = 2006 | url = https://books.google.com/books?id=IpSRykrRamgC&q=display+gamma+2.2+0.5&pg=PA265 }}</ref> To obtain the correct response, a [[gamma correction]] is used in encoding the image data, and possibly further corrections as part of the [[color calibration]] process of the device. Gamma affects [[black-and-white]] TV as well as color. In standard color TV, broadcast signals are gamma corrected.