This page gives an overview of the Matte Shadow Render Channel and how it may be used in compositing.
Overview
The Matte/Shadow channel shows areas where light doesn't reach. Compare with the Raw Shadow channel, which gives areas of cast shadows. While technically not part of the Beauty render channels, the Matte Shadow channel can be used to lighten cast shadows by adding it to the Raw Lighting channel. It can also be used to assist in adding 3D elements to a background image or footage in the composite.
UI Path
||Node Editor|| > Add > Render Channels > Color Channel > Type > Matte/Shadow
Common uses
The Matte/Shadows channel is useful for changing the appearance of shadowed areas in compositing or image editing software. Below are examples of its use.
Matte Shadows Render Element
Original Beauty Composite
Lightened Matte Shadows Render Element
Tinted Matte Shadows Render Element
Shadows lightened by adding to the Raw Lighting Render Element in composite
Shadows warmed by combining a color-corrected Matte Shadow added to the Raw Lighting Render Element