Modifying an image

This snippet of Fortran shows an existing image being accessed so that it can be modified in place (that is, without creating a new copy):

*  Access an existing image.
      CALL IMG_MOD( 'IN', NX, NY, IP, ISTAT )

*  Fill the image with a value.
      CALL DOFILL( %VAL( IP ), NX, NY, ISTAT )

*  Free the image.
      CALL IMG_FREE( 'IN', ISTAT )