
Luminance and lightness 20
In
Color science for video,
on
page 233, I will describe how
spectral power distributions
(SPDs) in the range 400 nm to
700 nm are related to colors.
The term
luminance
is often care-
lessly and incorrectly used to refer
to
luma. See Relative luminance,
on page 206, and Appendix A,
YUV and luminance considered
harmful,
on page 595.
Nonlinear coding of luminance is essential to maximize
the perceptual performance of an image coding system.
This chapter introduces luminance and lightness, or
what is loosely called
brightness.
Luminance,
denoted Y, is what I call a
linear-light
quan-
tity; ...