Luminance (Y)
Luminance (Y) – Video originates with linear-light (tristimulus) RGB primary components, conventionally contained in the range 0 (black) to +1 (white). From the RGB triple, three gamma-corrected primary signals are computed, each is essentially the 0.45-power of the corresponding tristimulus value, similar to a square-root function. In a practical system such as a television camera, however, in order to minimize noise in the dark regions of the picture it is necessary to limit the slope (gain) of the curve near black. It is now standard to limit gain to 4.5 below a tristimulus value of +0.018, and to stretch the remainder of the curve to place the Y-intercept at -0.099 in order to maintain function and tangent continuity at the breakpoint: Rgamma = (1.099 * pow(R,0.45)) – 0.099 Ggamma = (1.099 * pow(G,o.45) – 0.099 Bgamma = (1.099 * pow (B,0.45) – 0.099 Luma is then computed as a weighted sum of the gamma-corrected primaries. Y = 0.299 * Rgamma + 0.587 * Ggamma + 0.114 * Bgamma The three coefficients in this equation correspond to the sensitivity of human vision to each of the RGB primaries standardized for video. For example, the low value of the blue coefficient is a consequence of saturated blue colors being perceived as having low brightness. The luma coefficients are also a function of the white point (or chromaticity of reference white). Computer users commonly have a white point with a color temperature in the range of 9300 K, which contains twice as much blue as the daylight reference CIE D65 used in television. This is reflected in pictures and monitors that look too blue. Although television primaries have changed over the years since the adoption of the NTSC standard in 1953, the coefficients of the luma equation for 525 and 625 line video have remained unchanged. For HDTV, the primaries are different and the luma coefficients have been standardized with somewhat different values. The signal which represents brightness, or the amount of light in the picture. This is the only signal required for black and white pictures, and for color systems it is obtained as the weighted sum (Y = 0.3R + 0.59G + 0.11B) of the R, G and B signals.
Source: http://download.tek.com/secure/25W_15215_1.pdf?nvb=20151220132843&nva=20151220133343&token=0538ce9690041d6978723
Web site to visit: http://www.tek.com/
Author of the text: http://www.tek.com/
If you are the author of the text above and you not agree to share your knowledge for teaching, research, scholarship (for fair use as indicated in the United States copyrigh low) please send us an e-mail and we will remove your text quickly. Fair use is a limitation and exception to the exclusive right granted by copyright law to the author of a creative work. In United States copyright law, fair use is a doctrine that permits limited use of copyrighted material without acquiring permission from the rights holders. Examples of fair use include commentary, search engines, criticism, news reporting, research, teaching, library archiving and scholarship. It provides for the legal, unlicensed citation or incorporation of copyrighted material in another author's work under a four-factor balancing test. (source: http://en.wikipedia.org/wiki/Fair_use)
The information of medicine and health contained in the site are of a general nature and purpose which is purely informative and for this reason may not replace in any case, the council of a doctor or a qualified entity legally to the profession.
The following texts are the property of their respective authors and we thank them for giving us the opportunity to share for free to students, teachers and users of the Web their texts will used only for illustrative educational and scientific purposes only.
All the information in our site are given for nonprofit educational purposes
The information of medicine and health contained in the site are of a general nature and purpose which is purely informative and for this reason may not replace in any case, the council of a doctor or a qualified entity legally to the profession.
www.riassuntini.com