NAME:
  dispmask
 PURPOSE:   (one line only)
  Combine an image and a mask so that you can see both using color
 DESCRIPTION:
 CATEGORY:
  Image display
 CALLING SEQUENCE:
  bim = dispmask(im,mask,zf)
 INPUTS:
  im   - byte image pre-scaled for display, 2-D
  mask - byte mask image, same size as im
  zf   - zoom factor for output color cube
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
  return is a cube for tv,true=3
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  Written by Marc W. Buie,  Southwest Research Institute, 2020/06/30