bmp.py

   1 # bmp - bitmap processing
   2 # ref: https://en.wikipedia.org/wiki/BMP_file_format
   3
   4 from struct import unpack
   5
   6 class FormatError(Exception): pass
   7 class MagicError(FileFormatError): pass
   8 class CompressionError(FormatError): pass
   9 class BppError(FormatError): pass
  10
  11 class Bmp(object):
  12         def __init__(self, fn_or_fo):
  13                 fo = fn_or_fo
  14                 if isinstance(fn_or_fo, basestring):
  15                         fo = open(fn, 'rb')
  16                 self.fo = fo
  17                 self._read()
  18         def _read(self):
  19                 header = self.fo.read(14)
  20                 magic, filesize, start_address = unpack("<2sI2x2xI", header)
  21                 if magic != "BM": raise MagicError("wrong BMP header magic")
  22                 dib = self.fo.read(40)
  23                 magic, pixelwidth, pixelheight, bpp, compression = unpack("<III2xHI4x4x4x4x4x", dib)
  24                 if magic != 40: raise MagicError("wrong DIB header magic")
  25                 if compression != 0: raise CompressionError("compression not supported")