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Luma is the weighted sum of gamma-compressed R′G′B′ components of a color video—the prime symbols ′ denote gamma compression. The word was proposed to prevent confusion between luma as implemented in video engineering and relative luminance as used in color science (i.e. as defined by CIE).
Luminance only, Chrominance only, and full color image. Chrominance ( chroma or C for short) is the signal used in video systems to convey the color information of the picture (see YUV color model), separately from the accompanying luma signal (or Y' for short).
"Luminance" can mean several things even within the context of video and imaging: luminance is the photometric brightness of an object (in units of cd/m 2), taking into account the wavelength-dependent sensitivity of the human eye (the photopic curve); relative luminance is the luminance relative to a white level, used in a color-space encoding ...
A short video explaining the concept of video codecs. A video codec is software or hardware that compresses and decompresses digital video.In the context of video compression, codec is a portmanteau of encoder and decoder, while a device that only compresses is typically called an encoder, and one that only decompresses is a decoder.
The sun has a luminance of about 1.6 × 10 9 cd/m 2 at noon. [3] Luminance is invariant in geometric optics. [4] This means that for an ideal optical system, the luminance at the output is the same as the input luminance. For real, passive optical systems, the output luminance is at most equal to the input.
PQ is the basis of HDR video formats (such as Dolby Vision, [2] [9] HDR10 [10] and HDR10+ [11]) and is also used for HDR still picture formats. [12] [13] PQ is not backward compatible with the BT.1886 EOTF (i.e. the gamma curve of SDR), while HLG is compatible. Chart showing the PQ electro-optical transfer function.
10 −2: 5 mcd/m 2: Approximate scotopic/mesopic threshold [8] 10 −1: 10 0: cd/m 2: 2 cd/m 2: Floodlit buildings, monuments, and fountains [9] 10 1: 5 cd/m 2: Approximate mesopic/photopic threshold [8] 25 cd/m 2: Typical photographic scene at sunrise or sunset [7] 30 cd/m 2: Green electroluminescent source [5] 10 2: 55 cd/m 2: Standard SMPTE ...
SDR video with a conventional gamma curve and a bit depth of 8-bits per sample has a dynamic range of about 6 stops, assuming a luminance quantisation threshold of 5% is used. [10] A threshold of 5% is used in the paper (instead of the standard 2% threshold) to allow for the typical display being dimmer than ideal.