## ABSTRACT

W hen the light source is infinitely far away (d = oo), incident light rays a t all object points are parallel to one another such th a t the laws of or­ thographic projection apply. T he illum inating cone then collapses in to a line ( 7 = 0 °) while the phase angles ||g|{ range between 0 ° and 180° since gmax = 180°. In th is case, the com putation of the illum ination angles a t the highlight and a t the brightest visible point simplifies to

T he am ount o f body reflection a t these points is then determ ined by

/ /n\ f cos(0) = 1 if g < 90° . m iH - coa(g/2)m bI,oealMax - j CQ^ g _ 9 Qo) _ sin(9) if g > 90o (C.2)

Accordingly, the quotient q o f the two body reflection com ponents is given by

o cos(» /2) i f f f < 9 0 ° °° \ c o s (s /2 ) / 8in (9 ) = l /(2 s in (y /2 ) ) if g > 90°. ^ '