#!F-adobe-helvetica-medium-r-normal--18*
#!N 
#!N  #!Ropacom Opacities Component #!N #!N #!N The 
"opacities" component plays a role similar to that of colors components, 
except that it specifies a floating-point opacity for rendering. Its interpretation 
differs depending on whether the connections represent a surface (triangles or 
quads), or a volume (tetrahedra, cubes, and so on). In the 
surface case, the opacity is a number from 0 to 1 
specifying the opacity of the surface. In the volume case, the 
opacity represents the instantaneous attenuation of light per unit distance traveled. 
Like the colors components, it can be position- or connection-dependent. #!N 
#!N The interpretation of "colors" and "opacities" differs between surfaces and 
volumes. For surfaces, a surface of color  #!F-adobe-times-medium-i-normal--18*   c[f] #!EF and 
opacity  #!F-adobe-times-medium-i-normal--18*   o #!EF is combined with the color  #!F-adobe-times-medium-i-normal--18*   c[b] 
#!EF of the objects behind it resulting in a combined color 
 #!F-adobe-times-medium-i-normal--18*   c[f]o + c[b](1 - o) #!EF . #!N #!N For 
volumes, the "dense emitter" model is used, in which the opacity 
represents the instantaneous rate of absorption of light passing through the 
volume per unit thickness, and the color represents the instantaneous rate 
of light emission per unit thickness. If  #!F-adobe-times-medium-i-normal--18*   c(z) #!EF represents 
the color of the object at  #!F-adobe-times-medium-i-normal--18*   z #!EF and  #!F-adobe-times-medium-i-normal--18*   
o(z) #!EF represents its opacity at  #!F-adobe-times-medium-i-normal--18*   z #!EF , then 
the total color of a ray passing through the volume is 
given by: #!N c = integral to infinity from - infinity 
c ( z ) 'exp' (- integral to z from - 
infinity o ( zeta ) d zeta) dz #!N #!N #!N 
#!N  #!F-adobe-times-medium-i-normal--18*   Next Topic #!EF #!N #!N  #!Ltall210,dxall210 h Color Map and Opacity Map Components  #!EL  #!N  #!F-adobe-times-medium-i-normal--18*   #!N 

