Negative light to individually generate the AO of any object.

[wevon]

Making some projects with Motion Tracking, and illuminating the scene with an HDRI, I found that it was impossible to capture a projected shadow of one object into another object, since there is no direct light source.
For this reason I have thought that through an object with negative light, was possible to project a shadow around the desired object. This shadow could be used for creating a mask of other shades.

In the scene I show, there are four monkeys, two with white diffuse material, and two duplicates emitting negative light from the last layer. By adding 1 to the “AO SHADOW CACHER” render layer get the desired shadow.

I leave here, the scene I have used and capture.

Dropbox - Error

En esta escena la sombra està muy exagerada. La solución esta pensada para escenas con la luz menos contrastada i más indirecta, pero creo que de este modo se ve más claro.

[RhinoFlip]

This seems interesting. I haven’t download the blend file, it’s too late at night and i’m not planning to open blender. I’m just curious if the result is satisfying enough. In other words, isn’t ambient occlusion easier way to archieve the result? This seems to be totally independent on light conditions of scene. When using HDRi, you just can simply set main light from the spot where is the biggest intensity of light and render shadows. But still… negative light. Good idea man