The function as.matrix.owin converts a window to a
  logical matrux.  It first converts the window x into a binary pixel mask
  using as.mask. It then extracts the pixel entries
  as a logical matrix.
  The resulting matrix has entries that are
  TRUE if the corresponding pixel is inside the window,
  and FALSE if it is outside.
  
  The function as.matrix is generic. The function
  as.matrix.owin
  is the method for windows (objects of class "owin").
  Use as.im to convert a window to a pixel image.