2D Tracking - Nuke 101: Professional Compositing and Visual Effects - page 222

• You don't have to track on all channels. Sometimes the best reference is only on,
say,thegreenchannel.Therearemanyreasonsforchoosingdifferentchannelsand
you will learn this as you gain experience. For example, the blue channel usually
has a lot of noise in it, which can create a jerky track. Turning the blue channel off
might help smooth the track a little.
• The Epsilon parameter stands for how accurate a track needs to be (I'm sure if
they'd put their thinking caps on they could have found a slightly friendlier term).
By default, Epsilon is set to 99%—or 1% wrong. This means that if the tracker
found the pattern in the next frame with 99% accuracy, it won't bother looking
to see if there's a better match elsewhere. If you know your pattern changes dra-
matically from frame to frame, this might need to be reduced. If you want a more
precise track, you might want to increase the Epsilon property.
• Max_error means in what level of accuracy the track will fail. By default, an error
rate of 20% and above will stop the tracker.
• Changing the Grab New Pattern every n frame to something beyond 0 causes the
pattern area to update according to the value set in the field. A value of 2 means
that a new pattern is grabbed for matching every two frames. This is good for
patterns that change dramatically from frame to frame, due to light fluctuations,
distortion, or even simple scaling. Notice that the second property in that section