Enhances edges in a two-dimensional NDF using a shadow effect

#### Description:

This routine enhances a two-dimensional NDF  by creating a bas-relief or shadow effect, that causes features in an array to appear as though they have been illuminated from the side by some imaginary light source. The enhancement is useful in locating edges and fine detail in an array.

#### Parameters:

The two-dimensional NDF to be enhanced.
##### OUT = NDF (Write)
The output NDF containing the enhanced image.
##### SHIFT( 2 ) = _INTEGER (Read)
The shift in x and y pixel indices  to be used in the enhancement. If the x shift is positive, positive features in the original array will appear to be lit from the positive x direction, i.e. from the right. Similarly, if the y shift is positive, the light source will appear to be shining from the top of the array. A one- or two-pixel shift is normally adequate. [1,1]
The title  for the output NDF. A null value will cause the title of the NDF supplied for Parameter IN to be used instead. [!]

#### Examples:

This enhances the NDF called aa by making it appear to be illuminated from the bottom left, and stores the result in the NDF called aash, which has the title "Bas relief".