Alpha Shadows

[danf]

I know there's been a lot of alpha channel talk lately, but I don't think this has been touched on-

 

I'm using a .TGA sequence to rotoscope a 3D element into my real footage.

 

 

One problem is the shadows. While I've read tutorials that suggested making objects that match those in the scene, and then project the same decal from your main camera onto those, I think having a live actor in the shot makes this more complicated.

 

What would be ideal to me as compositor, would be a way to export the ball and some darkness under itself softened by another alpha layer. In my mind the way to do that would be to make the surfaces that receive shadows, and then tell it to render with alpha, but to exclude the surfaces, while including their shading.

 

 

That sounds partly impossible while I say it, so it might not be the right way, but if anyone knows how to solve this problem in any way, I'd be interested to hear how.

[robcat2075]

Are you trying to get the shadow of the ball or the underside of it that is darker than the topside?

[danf]

Shadow of the ball. If it looks like it's there in that first shot that's a deception. When making contact the lack of shadow is the most conspicuous.

[Rodney]

If you mean to have a shadow on the foot you'll have to have the geometry there for the shadow to be cast upon.

You could use a simple model (like Thom's leg).

For the floor and cabinets a few simple planes should do.

 

The lighting in your shot may be a little hard to match as you've got shadows on the floor and on the cabinet. I suppose you could match one light at a time and composite the shadows from each separately.

[robcat2075]

Shadow of the ball. If it looks like it's there in that first shot that's a deception. When making contact the lack of shadow is the most conspicuous.

 

If you want the shadow as a separate file you can use "shadow buffers".

 

As noted you will need some geometry in the scene to catch it. in the shadow options for that geom set it to "shadows only" and enable "alpha" and "shadow buffer" in the render options.

 

you will get a file that looks black, but the alpha channel will have the image of the shadow. For compositing.

 

 

You will need to render twice. Once for the ball. Once for the shadow.

[danf]

in the shadow options for that geom set it to "shadows only" and enable "alpha" and "shadow buffer" in the render options.

 

you will get a file that looks black, but the alpha channel will have the image of the shadow. For compositing.

 

I was able to do all of this except the shadow buffer... I found a "light buffer" option in the render options, but no shadow buffer. Is there anywhere else I should be looking? Could this be a Mac version difference?

[Caroline]

I found a "light buffer" option in the render options, but no shadow buffer

Are you sure you are still rendering to .tga? jpg, png and other options do not have the shadow buffer.