Roto is basically to isolate required objects from the background plate so that the compositor can place it into another scene or another background.
DO'S
Analyze the Shot
The first step in any roto job is to analyze all of the frames in the shot. Study how the object is moving, and how it's shape is changing during the entire shot. Look at all the parts of the object, and study the different shapes that make up the object. One needs to find out how many shapes are needed to define the overall shapes.
Keying the Roto
* Find the approximate keyframes. Keyframes are frames in an animation that contain the most important positions of a shape's over all movement.
Start determining keyframes with the frame that is the most complex or has the most detail. This is where one has to create the most points. Then there will be no need to add or delete futher points.
* Make the roto shape on the frame where you will have to add maximum number of points.
* Move all the shapes of the body together while rotoing the shot.
* Need to fine tune the rotos for a particular frame range and then move on to the rotos for the next frame range.
Next Method is Tracking the rotos
* Many times you might have solid shapes to roto and also some characters which wont be having much of movement but the camera has a pan or some sort of a movement, at this occasion you can use the tracking.
* This increases the accuracy, reduces jitters and also saves a lot of time.
Reduce jitter / chatter
To help to minimize jitters and chatter one can do the following:
* When creating a shape one should ensure that the points correspond to the same relative location on the object, through out.
* Keeping the edge line that one creates in the same position relative to the edge of the object. Sometimes it's better to draw the edge line a little bit inside,or outside of the actual edge of the object, or else exactly on the edge of it.
* No matter which option you choose, it's more important to maintain that same relative position and remain consistent with it throughout the frame range.
DONT's
* More control points will lead to more time being spent putting them into position, thus adding to work time.
* The more control points there are, the more difficult it becomes to keep relative positioning of the control points accurate from frame to frame.
* Each additional control point adds to the file size.
* Also while doing the roto if some objects come in between one should not disturb the primary roto to adjust it. It is always easy and fast to do a separate one for that object.
* Do not modify the main shape to accommodate a new shape but create a new shape always.
