INTERFACE FunGradFeatures2D;
(*
  A feature mapper that merely returns the function and its gradient, 
  computed from the pixel and its 4 nearest neighbors. 
  Each image layer generates 3 consecutive features. *)

IMPORT FeatureMapper2D AS Mapper;
FROM Mapper IMPORT NAT;

TYPE
  T <: Public;
  Public = Mapper.T OBJECT METHODS
      init(NL: NAT): T; (* Initializes the mapper for "NL" layers. *)
    END;

END FunGradFeatures2D.