Video Gamma Space

Video Gamma Space

Because log space certainly doesn’t look natural, it probably
comes as no surprise that it is a bad color space to work
in. But there is another encoding color space that you have
been intimately familiar with for your entire computerusing
life and no doubt have worked in directly: the video
space of your monitor.
You may have always assumed that 8-bit monitor code value
128, halfway between black and white, makes a gray that is
half as bright as white. If so, you may be shocked to hear
that this is not the case. In fact, 128 is much darker—not
even a quarter of white’s brightness on most monitors.
A system where half the input gives you half the output is
described as linear, but monitors (like many things in the
real world) are nonlinear. When a system is nonlinear, you
can usually describe its behavior using the gamma function,
shown in Figure 11.16 and the equation
Output = inputgamma 0 <= input <= 1
In this function, the darkest and brightest values (0.0 and
1.0) are always fi xed, and the gamma value determines
how the transition between them behaves. Successive
applications of gamma can be concatenated by multiplying
them together. Applying gamma and then 1/gamma has
the net result of doing nothing. Gamma 1.0 is linear.