I have an scene as follows,

#include "functions.inc"
#declare fn_Image=function{
   pigment{
     image_map{
       tga "C:\Data\3D\POV\isotest01.tga"
       map_type 1
       once
     }
   }
}
isosurface{
   function{f_sphere(x, y, z, 1)-fn_Image(x, y, z).gray}
   contained_by{sphere{0,2.01}}
   accuracy 0.001
   max_gradient 100
   pigment{color rgb 1}
}

This behaves in the follwing manner:  a sphere with radius 1 has
extrusions based on the grey value of a pixel, with 255 extending
1 unit from the surface of the sphere.  If I change the equation to

   function{f_sphere(x, y, z, 1)+fn_Image(x, y, z).gray}

(to make the grey values indentations) or reduce the radius of the
sphere, i.e.

   function{f_sphere(x, y, z, 0.5)-fn_Image(x, y, z).gray}

(to decrease the size of the surface failing making indentations) all
that results is a sphere with radius 1 and no surface distortions.

How might I make working versions of formulas 2 and 3, or am I
restricted to extruding from a base sphere of radius 1 or larger?

-- 
Tim Cook
http://home.bellsouth.net/p/PWP-empyrean

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