Yes, that’s certainly possible, though as I think you observed, you won’t get correct shadows from such a post-process. For example, you could create a “deep pixel” image with rtrace like so:

```
vwrays -ff -x 1024 -y 1024 [view] | rtrace -fff -ovpn [options] octree > deepimg.flt
```

Then process it with rcalc:

```
rcalc -if9 -of -e 'ri=$1;gi=$2;bi=$3;px=$4;py=$5;pz=$6;nx=$7;ny=$8;nz=$9' -f clight.cal -e '$1=ri+rl;$2=gi+gl;$3=bi+bl' deepimg.flt | pvalue -h -r -df -Y 1024 +X 1024 > lightadded.hdr
```

Your “clight.cal” file would define how the variables “rl”, “gl” and “bl” are computed from the intersection location (px,py,pz) and surface normal (nx,ny,nz). Normally, this would simply be the direction vector between the source and intersection point, and a dot product with the surface normal, times the light source radiance in red, green, and blue, respectively, times the source area divided by the square of the distance. For example:

```
{ Source position }
spx1 : 5; spy1 : 7; spz1 : 4;
{ Source area }
area1 : 0.58;
{ Source radiance }
L1r : 1000; L1g : 900; L1b : 800;
{ Calculate contribution from light 1 }
vx1 = spx1 - px;
vy1 = spy1 - py;
vz1 = spz1 - pz;
d1sq = vx1*vx1 + vy1*vy1 + vz1*vz1;
dotp = (vx1*nx + vy1*ny + vz1*nz)/sqrt(d1sq);
m1 = if(dotp, dotp*area1/d1sq, 0);
rl = L1r*m1;
gl = L1g*m1;
bl = L1b*m1;
```

Keep in mind that light area is in squared world units, and should correspond to the parallel projection of a source that is assumed to be round(ish). So, a spherical source of radius 5 would have a projected area of 25pi, for example.

The rtrace command is meant to be illustrative only – you would actually use the surface color in place of the computed pixel color in your case, or modify the calculation to take the diffuse reflectivity into account some other way.

-Greg