ANS (1)
(A) The BRDF is constant for a Lambertian surface. The BRDF is defined as the ratio of radiance in the
outgoing direction to the incident radiance
BRDF =
Radiance in Outgoing direction/ Incident Irradiance.
It is given that the BRDF
is constant . This is when the outgoing radiance is independent of angle.
This is
the case of ideal diffuse surfaces or Lambertian surfaces .
The albedo and the BRDF is related as follows:
Р
d
=
pi *
Р
BRDF
So
Р
BRDF =
Р
d
/ pi
The maximum value of the albedo can be 1 as the maximum value of sin and cos can be 1 . Hence the
maximum value of BRDF is 1/pi
AnS
(B)
The surface absorbs 20 % incident and reflects 80 % .
So out of the 100 percent incident radiation , only 80 percent is outgoing radiation. Hence
Albedo (Р
d
) =
80/100 = 0.8
BRDF = 0.8 / pi
AnS
Ans (2)
Given
a)
Shape of the Umbra : Square
: square source and square occluder. Both are parallel to a plane and hence parallel to each other.
They are vertically one another with their centers aligned.
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 Fall '09
 Ab
 Computer Graphics, Elementary algebra, M0 motorway, Motorways in Hungary, Radiometry

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