Correct usage of shadow_matte AOV in compositing package

[donat]

The documentation about the shadow_matte AOV's is somewhat limited, in my opinion. (https://support.solidangle.com/display/A5NodeRef/shadow_matte)

"

aov_shadow

Direct light shadow AOV.

aov_shadow_diff

A difference AOV which can be used to eliminate the shadow from the direct component.

aov_shadow_mask

This AOV can be used in comp to localize and tweak the shadow.

"

Could you elaborate more on those and explain how those three AOV's should be used in a compositing program ?

Thanks in advance

[Anonymous]

I know it's a very late answer .. but in order to separate the shadows from objects, I do this (using Photoshop):

layer with beauty:

RGBA ..and as mask >>> shadow.mask (inverted)

layer with shadows:

SHADOW.RGB ..and as mask >>> shadow.diff (set transparency on "multiply")

It works very well, also with foreground transparent object (like glass) covering the shadows on the ground 🙂 I use it for many renders showing metal machinery on white infinite backgrounds.