BG_VALUE

[Nikhil Singh]

We currently have a BACKGROUND_STRATEGY_ZERO but no ability to extrapolate with a given value other than zero. We should be able to extrapolate with any scalar or vector value. For example if we extrapolate a Jacobian determinant image, the background value should be 1.0.

[Sam Preston]

BACKGROUND_STRAGETY_VAL added to image interpolation by 9bef507, but this has not yet been exposed to function interfaces -- right now this will be equivalent to BACKGROUND_STRATEGY_PARTIAL_ZERO since the default VAL of zero cannot be overridden