This attribute indicates the method to be used when finding the
output value of a LutMapLutMap for an input value part way between two
table entries. If it is set to 0 (the default) then linear
interpolation is used. Otherwise, nearest neighbour interpolation
is used.
Using nearest neighbour interpolation causes AST__BAD to be returned
for any point which falls outside the bounds of the table. Linear
interpolation results in an extrapolated value being returned based
on the two end entries in the table.