8

1006 Glossary
ratio of width to heig ht, regardless of the image’s
resolution (page 3–1097) .
Aspectratioisusuallyexpressedeitherasaratio
ofwidthoverheight(forexample,4:3)orasa
real value relative to 1 (for example, 1.333). For
example, pre-1950s movies and 35 mm slides have
an aspec t ratio of 4:3.
Aspectratiosareusedanywhereabitmapis
createdorused.Forexample:
• When preparing to render, you can specify an
aspect ratio for your rendered images with the
Image Aspect parameter on the
Render Scene
dialog (page 3–2)
.
•Whensettingupa
view por t background (page
1–38)
,youcanspecifywhethertousethe
view por t, bitmap or rendering output aspect
ratio to display the bitmap.
•Whenyou
makeaspotlightaprojector(page
2–1185)
, you can use the Bitmap Fit option
to mat ch the spotlight’s aspect ratio to the
bitmap’s, and thus prevent the bitmap from
distort ing.
Attachments (IK )
Inbipedanimation,thebipedhandsandfeetcan
be linked to the world, another object in the scene,
or to the biped’s ow n body. This linking is also
cal led IK attachment. Attachment can be blended:
this lets you start with one attachment and end
with another. For example, if the biped is c atching
a ball, you can star t with the hand in body space
and end with the hand in the coordinate space of
the ball.
Attenuation
Image on right rendered with attenuation
In the real world, the intensity of light diminishes
over distance. Objects far from the light s ource
appear darker than objects near t he s ource. This
effect is known a s attenuation.
In nature, light attenuates at an inverse square rate;
that is, its intensity diminishes in proportion to
thesquareofthedistancefromthelightsource.
It is common for attenuation to be even greater
whenlightisoccludedbysmallparticlesinthe
atmosphere, especially when there are clouds or
fog present.
Attenuation a nd Photometric Lights
Photometric lights always attenuate at the inverse
squarerate. Thisisoneofthereasonsitis
important for scenes with a radiosity solution to
use real-world dimensions and units.
Attenua tion and Sta nda rd Lights
By default, standard lights don’t attenuate.
Consequent ly, an object’s distance from the light
doesn’t matter, and only the angle of lig ht to the
surface has any effect on illumination un less you
turn on attenuation. You can manually control the
rate of attenuation for standard lights. You can also
use attenuation with the Ray trace map. If your
scene uses standard lights, you should consider
adding attenuation whenever possible, for two
reasons:
• Attenuation provides greater subtlety and
realism in your lig hting.