Apple Shake 4 - Manual (Page 828)

828 Chapter 27 Warping and Morphing Images
It’s important to understand that boundary shapes don’t eliminate distortion from the
surrounding image; they minimize it.
It may take more than one boundary shape to completely lock down an image.
Fortunately, you can create as many boundary shapes as necessary to eliminate
unwanted distortion in an image.
Important: Target shapes should never cross boundary shapes. Doing so may create
unwanted distortion, possibly tearing in the resulting image.
There are many ways you can use boundary shapes to isolate parts of an image from
deformation. One technique is to use a closed shape to surround a pair of source/
target shapes, thus minimizing their effect on the surrounding area of the image.
Warp with boundary shape