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v2.5.0 features a renewed Shadows AOV. This is one of the various fixes or improvements made in the rich compositing system introduced in v2.4.x.

The new Shadows AOV has some very interesting properties:

  • It catches shadows coming from every feature in the engine (emitters, sky/sun, env).
  • It catches shadows coming from the GI as well (not just direct shadows).
  • It catches the HDR color and power of the incoming light/GI in the unshadowed areas.
  • As expected, it is decoupled from the reflectance of the BSDF of the shadows catcher.

To allow for this all, the Shadows AOV is now HDR RGB (compared to LDR grayscale as it was before).

Here’s a visual example, where the following channels have been rendered for a test scene:

  • Main.
  • Shadows (backdrop set as shadows catcher).
  • MtlID mask (backdrop set to mask).

 

Main AOV.
Main AOV.

 

Shadows AOV.
Shadows AOV.

 

MtlID Mask AOV.
MtlID Mask AOV.

 

And here’s a quickie where the rendered objects have been incrustated in a photographed backplate:

 

Photographed backplate.
Photographed backplate.

 

Incrustated render.
Incrustated render.

 

Note that one of the key properties of this renewed Shadows AOV is that it is an HDR RGB channel, where (all) the incoming light arriving to the shadows catcher is captured, keeping its real power and spectral color. This provides a much more complete solution to render/photo incrustation than a simple direct-lighting only, or grayscale-only Shadows AOV.

Note also how the new Shadows AOV (as expected) is decoupled from the reflectance of the BSDF of the shadows catcher (although the GI cast by the shadows catcher correctly affects the GI received by itself). This allows the user to set a shadows catcher that resembles the final backplate, if desired. However, using a default lambertian for the shadows catcher is often more than enough.

Here’s the same example, where the backdrop is textured. The Shadows AOV has a slight red shift now, but the checkerboard is absent as expected.

 

GI affecting the Shadows AOV.
GI affecting the Shadows AOV.

 

GI affecting the Shadows AOV.
GI affecting the Shadows AOV.