9

948 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 the
degree of nonlinearity. The standard gamma value
forNTSCvideois2.2. Forcomputermonitors,
gamma values in the range of 1.5 to 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 variance caused by
the monitor gamma. T he same image displayed on
another monitor (or recorded to another media
affected by gamma) w i ll 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.
You do this in the Gamma panel (page 3–824)
of the Preferences dialog (Displa y 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 a ls o in the Gamma panel of the Preferences
dialog (Files Gamma).
The most important rule about gamma correction
is to do it only once. If you 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 circuitry. Therefore,
you need to decide w hether 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 v iewing
thefilesonthesamemonitorandtheylookgood,
you won’t need to set input file gamma.
Geometric Primitives
Simple primitive objects such as, spheres, boxes,
cylinders, and so on.