e rectangle
  [-1,1]^2). 'orientation' is the clockwise rotation (as the Y
  axis points downards). 'anisotropy' (&gt;= 1) is the ratio of the
  the largest over the smallest axis of the blob (the smallest
  axis length is set by 'sigma'). Set 'cut' to TRUE to cut half
  half of the blob.
</pre><dl><dt>
A stock image
</dt><dd><p>
Any of 'box', 'roofs1', 'roofs2', 'river1', 'river2', 'spotted'.
</p></dd></dl><p>
All pattern accept a SIZE parameter [WIDTH,HEIGHT]. For all but
the stock images, the default siz