9

912 Glossary
ratio of width to height, regardless of t he image’s
resolution (page 3–1003).
Aspectratioisusuallyexpressedeitherasaratio
ofwidthoverheight(forexample,4:3)orasa
real va lue relative to 1 (for example, 1.333). For
example, pre-1950s movies and 35 mm slides have
an aspect 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).
•Whensettingupaviewport background (page
1–38),youcanspecifywhethertousethe
view por t, bitmap or rendering output aspect
ratio to display the bitmap.
•Whenyoumakeaspotlightaprojector(page
2–1341), you can use the Bitmap Fit option
to match the spotlight’s aspect ratio to the
bitmap’s, and th us prevent the bitmap from
distorting.
Attachments (IK )
Inbipedanimation,thebipedhandsandfeetcan
be linked to the world, another object in the scene,
or to the biped’s ow n body. This lin k ing is also
cal led IK attachment. Attachment can be blended:
this lets you s tart with one attachment and end
with another. For example, if the biped is catching
a ball, you can start with the hand in bo dy 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. O bjects far from the light source
appear darker than objects near the source. This
effect is known as 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, especial ly 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 u nits.
Attenua tion a nd S ta ndar d Li ghts
By default, st andard lights don’t attenuate.
Consequent ly, an object’s distance from the light
doesn’t matter, and only the angle of light to the
surface has any effect on illumination unless you
turn on attenuation. You can manually control the
rate of attenuation for standard lights. You can also
use attenuation with the Ray trace m ap. If your
scene uses standard lig hts, you should consider
adding attenuation whenever possible, for two
reasons:
• Attenuation provides greater subtlety and
realism in your lighting.