DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Luma A video signal representative of the monochrome – or roughly,
lightness – component of a scene. For SDTV, Rec. 601 standardizes
these coefficients:
601
Y'= 0.299 R'+ 0. 587 G'+ 0. 114 B'
For HDTV, Rec. 709 standardizes these coefficients:
709
Y'= 0. 2126 R'+ 0. 7152 G'+ 0. 0722 B'
Luma coefficients The coefficients of nonlinear (gamma-corrected) R’G’B’ in the
weighted sum that forms luma.
Luminance 1. Luminous flux density in a particular direction: The spectral
radiance of a scene, weighted by the luminous efficiency function
Y(λ) of the CIE Standard Observer. Denoted L v or Y (CIE Y tristimulus
value); properly expressed in units of cd·m -2 , or colloquially,
nit. Luminance is the photometric analog of radiance.
Luminance is related to the brightness sensation of human vision.
2. Luminance (1), normalized to an excursion of 1 or 100 with
respect to a reference white luminance. Properly called relative
luminance (see below).
3. The term luminance is often carelessly used in video engineering
to refer to luma. (See Luma, on page 636).
Much confusion surrounds the term luminance. In color science
and physics, luminance is proportional to intensity (linear-light),
and has the symbol Y; it can be computed as a properly weighted
sum of RGB tristimulus values. In video, luma is computed as
a weighted sum of nonlinear (gamma-corrected) R’G’B’ components,
and is properly denoted Y’; often, the luminance coefficients
are used. The term luma, and the prime, denote the
nonlinear quantity in a manner that avoids ambiguity. However,
the term luminance is often sloppily used for this quantity, and the
prime on the symbol is often omitted. Sloppy use of the word
luminance and omission of the prime renders both the term luminance
and the symbol Y ambiguous: Whether the associated
quantity is CIE luminance (linear) or video luma (nonlinear) must
then be determined from context.
Luminance, relative Luminance (1), as above, normalized to an excursion of 1 or 100
with respect to a reference white luminance. In video, absolute
reproduction of luminance is unnecessary; video normally involves
relative luminance.
Luminance coefficients The coefficients of linear-light (tristimulus) RGB in the weighted
sum that forms luminance.
M-frame In 2-3 pulldown to 29.97Hz interlaced video, the video frame,
unique in the 5-frame video sequence, comprising a first field
from one film frame (conventionally film frame B) and a second
field from another film frame (conventionally film frame C). A film
edit could be present between these fields. See 2-3 pulldown, on
page 610, and A-frame, on page 612.
636 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES