e; left-right
   flip and top-bottom flip) for arbitrary image depth.
   And we provide implementations of affine, projective and bilinear
   transforms, with both sampling (for speed) and interpolation
   (for antialiasing).

6. Sequential algorithms

   We provide a number of fast sequential algorithms, including
   binary and grayscale seedfill, and the distance function for
   a binary image.  The most efficient binary seedfill is
   pixSeedfill(), which uses Luc Vincent's algorithm to iterate
   raster