Examples of such color spaces include sRGB, the TV Rec. 601, Rec. 709, and Rec. 2020 the concept is also generalized to optical transfer functions in Rec. 2020. As a result, it is ubiquitously used in the source tristimulus signal, the R'G'B' input. A gamma-corrected signal has the advantage of emulating the logarithmic sensitivity of human vision, with more levels dedicated to the darker levels than the lighter ones. Luma (Y') is differentiated from luminance (Y) by the presence of gamma correction in its calculation, hence the prime symbol added here. A variety of filtering methods can be used to arrive at the resolution-reduced chroma values. The signal is divided into a luma (Y') component and two color difference components ( chroma). In video systems, this is achieved through the use of color difference components. This reduction results in almost no visual difference as perceived by the viewer.Īt normal viewing distances, there is no perceptible loss incurred by sampling the color detail at a lower rate, i.e. In compressed images, for example, the 4:2:2 Y'CbCr scheme requires two-thirds the bandwidth of non-subsampled "4:4:4" R'G'B'. Since the human visual system is much more sensitive to variations in brightness than color, a video system can be optimized by devoting more bandwidth to the luma component (usually denoted Y'), than to the color difference components Cb and Cr. The lower row shows the resolution of the color information.ĭigital signals are often compressed to reduce file size and save transmission time. Note how similar the color images appear. In full size, this image shows the difference between four subsampling schemes.
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