v1.2

Added

• Added prep_imdata() to Tile and Tile subclasses. This method can
  be used to prepare image data before feature detection and matching,
  for example, by converting a 16-bit image to an 8-bit image.

Changed

• Fixed bug stitching mosaics that have not been aligned and that have
  inconsistent row heights or column widths. The tiles making up each
  row must still have the same height, and those making up each column
  must have the same width.
• The Mosaic.align() method now raises RuntimeError if it fails to
  detect any features or align at least two tiles.