User Manual

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Working with Aux Deep Channels
Certain image formats can contain channels other than RGBA color, called aux deep channels.
Stereo Disparity and OpticalFlow deal directly with auxiliary deep channels.
Aux channels supported in Fusion include:
RGBA: These are the standard colors.
Z: The eyespace Z coordinate is almost always negative because in eyespace, Fusion’s
camera sits at (0, 0, 0) looking down the Z-axis. Z values start at Z = 0 at the camera
focal point and progressively become more negative for objects deeper in the scene.
Coverage: The percentage of the pixel covered by the frontmost pixel, used for
antialiased Z-compositing.
Object ID: These are user-assigned integers to meshes.
Material ID: These are user-assigned integers to materials.
Texture Coords: Normalized texture coordinates stored as (u, v) pairs.
Normal Vector: Normal vector (nx, ny, nz) where the components are
typically in the range [–1, +1].
Background Color: The color of the pixel if the frontmost layer were removed,
used for antialiased Z-compositing.
Vector: The forward motion vector is an offset (vx, vy) that compares every pixel’s
position in one frame to the same pixel’s position in the next frame.
Back Vector: The backward motion vector is an offset (vx, vy) that compares every
pixel’s position in one frame to the same pixel’s position in the previous frame.
World Position: The position (wx, wy, wz) of the pixel in world coordinates.
Disparity: An offset (dx, dy) that maps a pixel in the Left > Right or Right > Left frames.
Some extra channels are used by specific Fusion nodes. For example:
Merge can use the Z channel to perform a depth merge. If the Coverage
and BackgroundColor channels are present, it can do a better job on
antialiased edges during the Z merge.
Most image-processing nodes (e.g., BrightnessContrast) have options on
their common controls tab to limit their processing by MaterialID and ObjectID.
The Fog and DepthBlur nodes make use of the Z channel.
The Texture node makes use of the TexCoord channel.
The Shader node makes use of the Normal channel.
There are a couple of ways to retrieve or generate those
extra channels within Fusion. For example:
The Renderer3D node is capable of generating most of these channels.
The OpticalFlow node generates the Vector and BackVector channels, and then
TimeStretcher and TimeSpeed can make use of these channels.
The Disparity node generates the Disparity channels, and then DisparityToZ, NewEye,
and StereoAlign nodes can make use of the Disparity channels.
The OpenEXR format can be used to import or export aux channels into Fusion by
specifying a mapping from EXR attributes to Fusion Aux channels using CopyAux.
Chapter – 79 Optical Flow and Stereoscopic Nodes 1619