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Setting Up Stereo in the Node Editor
The disparity generation is the first operation. This can be configured in the Node Editor in two
different ways.
Two stereoscopic workflows.
In the above example, the workflow on the right takes the left and right eye, generates the
disparity, and then NewEye is used to generate a new eye for the image right away.
The example on the left renders the frames with disparity to intermediate EXR images. These
images are then loaded back into Stereo nodes and used to create the NewEye images.
By using Render nodes to compute the disparity first, the later processing of the creative
operations can be a much faster and interactive experience.
Although not shown in the above diagram, it is usually a good idea to color correct the right eye
to be similar to the left eye before disparity generation, as this helps with the disparity-tracking
algorithm. The color matching does not need to be perfect—for example, it can be
accomplished using the “Match” option in a Color Corrector’s histogram options.
About the Disparity Channel
The Disparity channel stores the displacement vectors that match pixels in one eye to the other
eye. The left image’s Disparity channel will contain vectors that map left>right and the right
image’s Disparity channel will contain vectors that map right>left. For example:
(xleft, yleft) + (Dleft. x, Dleft. y) -> (xright, yright) (xright, yright) +
(Dright. x, Dright. y) -> (xleft, yleft)
You would expect for non-occluded pixels that Dleft = -Dright, although, due to the disparity
generation algorithm, this is only an approximate equality.
NOTE: Disparity stores both X and Y values because rarely are left/right images
perfectly registered in Y, even when taken through a carefully set up camera rig.
Both Disparity and Optical Flow values are stored as un-normalized pixel shifts. In particular,
note that this breaks from Fusion’s resolution-independent convention. After much
consideration, this convention was chosen so the user wouldn’t have to worry about rescaling
the Disparity/Flow values when cropping an image or working out scale factors when importing/
exporting these channels to other applications. Because the Flow and Disparity channels store
Chapter – 79 Optical Flow and Stereoscopic Nodes 1624