The 3D Channel Extract effect makes auxiliary channels visible as either grayscale or multichannel color images. You can then use the resulting layer as a control layer for other effects. For example, extract the depth information in a 3D channel image file and then use it as an influence map in the Particle Playground effect, or extract values from the unclamped RGB channel to produce a matte that generates glowing highlights.
To display 3D channel values for a pixel in the Info panel, apply the 3D Channel Extract effect, choose the channel from the 3D Channel menu in the Effect Controls panel, and then click the pixel in the Composition panel or Layer panel using the Selection tool.
This effect works with 8-bpc color.
Much of the following information is based on information provided by Lutz Albrecht, who also provides a two-part document on the Adobe website about integrating 3D applications with After Effects:
- White Point, Black Point
- The value that is mapped to white or black.
- 3D Channel
- The channel to extract from the 3D image
- Represents the distance of a given shaded pixel from the camera. White represents the greatest distance; black pixels are closest to the camera. Effects such as the Lens Blur effect can use this information to generate depth-of-field effects. When you apply the channel directly as a luma matte, you get fog. This channel is anti-aliased.
- For best results, match the White Point and Black Point settings of the effect with the near and far settings of your camera in the 3D application that generated the 3D image.
- Object ID
- Each object can be assigned a separate ID value in the 3D application. You can use a map generated using this channel to selectively apply effects to certain objects in a 3D scene—for example, to apply selective color adjustments. This channel is not anti-aliased.
- Texture UV
- This channel contains the mapping coordinates of the textures of your object, mapped to the red and green channels. This channel is not anti-aliased.
- This channel can be used to check your UV maps or as input for the Displacement Map effect. The RE:Vision Effects RE:Map plug-in suite can be used to map alternative textures onto objects. For information, see the RE:Vision Effects website.
- Surface Normals
- This channel maps the direction vector of each point on the surface of an object to the RGB channels. The vectors are relative to the camera. Third-party plug-ins can use this channel as the basis for dynamic relighting and relief rendering. This channel is anti-aliased.
- The behavior for this channel varies for various 3D applications. It is used to mark areas near the edges and contours of objects to provide information about their anti-aliasing and overlap behavior.:::This channel contains the colors from the 3D application as they were presented to the 3D application’s renderer before it applied exposure and gamma adjustments. This channel is anti-aliased.
- Background RGB
- This channel contains all RGB pixel values of the background without any foreground objects. It is mostly used to store dynamic environmental effects unique to 3D programs such as skies or backgrounds generated from procedural textures. This channel is anti-aliased.
- Unclamped RGB
- This channel contains the colors from the 3D application as they were presented to the 3D application’s renderer before it applied exposure and gamma adjustments. This channel is anti-aliased.
- Material ID
- Each material can be assigned a separate ID value in the 3D application. You can use a map generated using this channel to selectively apply effects to certain materials in a 3D scene. This channel is not anti-aliased.