[Radiance-general] Alpha channel/object matte

[Greg Ward]

Hi Kirk,

Here's my own example of image-based lighting and the commands I used.  
I have two processors to work with, which is why I run two renderings 
at the same time:

#!/bin/csh -fex
#
# Render our image-based lighting example
#
#       Oct 2004        Greg Ward

# Set parameters
set res=(-x 2272 -y 1704)
set vw=(-vf plate.vf -pa 0)
set amb=(-ab 1 -aa 0 -ad 256 -as 0)

# Render synthetic objects
oconv environ.rad railing.rad chess3d.rad \
         | rpict -ps 1 -pj 0 $vw $res $amb \
         > chess3d.hdr &

# Determine foreground objects
oconv chess3d.rad > stencil.oct
vwrays -ff $vw $res \
         | rtrace -fff -oL $res stencil.oct \
         | pvalue -r -df -b \
         | pcomb -e 'lo=if(gi(1)-1e5,0,1)' - \
         > stencil.pic
rm stencil.oct

# Render base for shadows
oconv environ.rad railing.rad \
         | rpict -ps 1 -pj 0 $vw $res $amb \
         > unshadowed.hdr

# Wait for first render
wait

# Composite final image with shadow map and blurred foreground
pcomb -e 'ro=f(ri);go=f(gi);bo=f(bi)' \
         -e 'f(inp)=inp(1)*(gi(3) + (1-gi(3))*inp(2)/inp(4))' \
         '\!pfilt -1 -r 1.35 chess3d.hdr' \
         -o SunrisePlate.hdr \
         '\!pfilt -1 -r 1.35 stencil.pic' \
         '\!pfilt -1 -r 1.35 unshadowed.hdr' \
         > composite.hdr

---------------------
Resulting image (tone-mapped JPEG and gzip'ped input and picture files):

	http://www.anyhere.com/gward/pickup/chess3d_balcony.jpg
	http://www.anyhere.com/gward/pickup/chess2.tar.gz

Pillo's method works as well, but has problems sometimes for 
transparent surfaces.  The -oL output of rtrace is the only truly 
reliable method I've found.  You also need the -ps 1 -pj 0 rendering 
options shown to avoid disagreement between boundary pixels in the 
final composite.  My example includes blurring of the IBL objects to 
simulate depth of field, which you probably don't want in general.  
(The pfilt -1 -r 1.35 commands in the final pcomb can be replaced by 
the straight files.)

-Greg