8

1042 Glossary
Gamma Correction
Changing gamma value to match a monitor’s middle gray
Gamma correction compensates for the differences
in color display on different output devices so that
images look the same when viewed on different
monitors.
A gamma value of 1 corresponds to an "ideal"
monitor; that is, one that has a perfectly linear
progression from white through gray to black.
However,theidealdisplaydevicedoesn’texist.
Computer monitors are "nonlinear" devices. The
higher the gamma value is set, the greater t he
degree of nonlinearity. The standard gamma value
forNTSCvideois2.2. Forcomputermonitors,
gamma values in the range of 1.5 t o 2.0 are
common.
When you create an image on your computer , you
base your color values and intensities on what
you see on your monitor. Thus, when you save an
imagethatlooksperfectonyourownmonitor,
you’re compensating for the var iance caused by
the monitor gamma. The same image displayed on
another monitor (or recorded to another media
affected by gamma) will look different, depending
on that media’s gamma values.
Two basic procedures are required to compensate
for changes in gamma:
• Calibrate your output display devices so that
the mid-tones generated by the software are
accurately duplicated on your display device.
Yo u d o t h i s i n t h e
Gamma panel (page 3–873)
of the Preferences dialog (Display Gamma).
• D etermine the gamma value to be applied to
files output by the renderer and files input into
the software, such as texture maps. This control
is also in the Gamma panel of the Preferences
dialog (Files Gam m a).
The most important rule about gamma correction
is to do it only once. If y ou do it twice, the image
qualityisoverlybrightandlosescolorresolution.
W ith regard to output file gamma, video devices
such as video tape recorders have their own
hardware gamma-correction circuitr y. Therefore,
you need to decide whether to let the software do
the output gamma correction or to let the output
device handle it.
Gamma correction is not required for hardcopy
print media.
Filescomingintothesoftwarefromprograms
such as Adobe Photoshop will have been
gamma-corrected already. If you’ve been viewing
thefilesonthesamemonitorandtheylookgood,
you won’t need to set input file gamma.
Geometric Primitives
Simple primitive objects such as, spheres, boxes,
cylinders, and so on.