I'm rendering something as a preview for building it.  So, I 
plan to combine it with a photograph of my back yard and 
compose the ray-traced gazebo into it.  I can get the angles 
and perspective and shadow angle to match OK, just by taking 
enough measurements and keying off of a flat template of the 
octogon shape in the real photo.

My question is: wasn't there talk of some feature, a long 
time ago, about rendering a "mask" from a scene?  Basically, 
I could use that to punch out the location in the photo.  I 
get pretty close by using a constant background color and 
selecting that in PhotoShop. But I seem to remember talk 
about generating a mask layer directly.

The interesting part, that I need some help with, is dealing 
with the shadows.  Assuming I put my object into a scene 
that has props for the real objects the shadows will fall 
on, how can I copy those in Photoshop to darken the photo?

--John

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> My question is: wasn't there talk of some feature, a long
> time ago, about rendering a "mask" from a scene?

Well you can use the +ua command line switch to get pov to output an alpha
channel (so that your background will be transparent).

> The interesting part, that I need some help with, is dealing
> with the shadows.  Assuming I put my object into a scene
> that has props for the real objects the shadows will fall
> on, how can I copy those in Photoshop to darken the photo?

What I would suggest is render a second image with all the textures set to pure
white, and all the finishes set to have brilliance 0. This should mean you end
up with a flat white image where only the areas in shadow are darker (it won't
cope well with coloured lights but you can probably get round that with some
tweaking in photoshop).

Then, put that into photoshop and make it multiply the colours in your
photograph (it has to multiply because that's what shadows do).

That should get the effect you're after.

-- 
Tek
www.evilsuperbrain.com

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