PDA

View Full Version : "Shadow catching" object? help!



Turner
10-27-2004, 08:36 AM
Hi All -

Ok, I asked this in general, but nobody's answered so far...

Basically, I need shadows rendered that will be superimposed over another background - for example, the shadow from a lamp on a wall - so that I can add the lamp/shadow to the background image of various types of walls in Photoshop.

In Carrara, there's a setting which lets you specify an object as a "shadow catcher" - this makes it so that the object is only visible where it is in shadow... so, if you use an object with a black surface, you get an object with a nice black shadow on a white background (when background is set to white of course). If you use and object with an orange and purple polka-dot surface... you get an orange and purple polka-dot shadow.

Any way to do this in LW? I don't know what it's even called, if it's possible.

thx
Andrew

Darth Mole
10-27-2004, 09:08 AM
LW used to have a Shadow Catcher, and I wanted to do this recently but couldn't find it - or even any reference to it.

In the end, I rendered the shadows separately on a solid white backdrop (objects were set to be invisible to camera, the 'floor' was a luminous white).

With this separate pass I comped it in After Effects using Multiply (or something, I forget). Also, I might have inverted the white/black to make it work on top of the layer below - you'll need to experiment a little.

I had to tweak the levels to make sure the whites were pure white and the shadows were pure black. Then it's a matter of tweaking the transparency and adding some blur, if needed. Not ideal, I grant you, but it works...

I would hope someone has a much slicker solution than this!

ingo
10-27-2004, 09:22 AM
Well you can render a shadow pass with Render buffer view (image filter), or you can render it into the Alpha Channel by setting the Alpha Channel to Shadow Density in the advanced surface settings of the shadow catching surfce.

Turner
10-27-2004, 09:39 AM
Hi Darth -

I knew I'd get a quick reply in here!

My Mac buddies!

Ok, anyway - for the time being, I've put a white (255/255/255) surface behind the model, and boosted the surface's luminosity to about 50%.

Still experimenting..

Andrew

Turner
10-27-2004, 10:20 AM
Hey thanks!

I'm off to try it...

Andrew


Well you can render a shadow pass with Render buffer view (image filter), or you can render it into the Alpha Channel by setting the Alpha Channel to Shadow Density in the advanced surface settings of the shadow catching surfce.

jdavidbakr
10-29-2004, 07:59 AM
In Carrara, there's a setting which lets you specify an object as a "shadow catcher" - this makes it so that the object is only visible where it is in shadow... so, if you use an object with a black surface, you get an object with a nice black shadow on a white background (when background is set to white of course). If you use and object with an orange and purple polka-dot surface... you get an orange and purple polka-dot shadow.
Make the shadow catching object the color of your shadow (black? orange and purple polka-dot?) and set the surface alpha (in the Advanced tab) to Shadow Density. Then you can comp this onto your live footage.

Darth Mole
11-01-2004, 07:59 AM
I knew there was a slicker way of doing it! I'll give it a try too.

Turner
11-04-2004, 07:06 AM
cool, thanks!