Doc/lib/libimghdr.tex

   1 \section{\module{imghdr} ---
   2          Determine the type of an image.}
   3 \declaremodule{standard}{imghdr}
   4
   5 \modulesynopsis{Determine the type of image contained in a file or byte stream.}
   6
   7
   8 The \module{imghdr} module determines the type of image contained in a
   9 file or byte stream.
  10
  11 The \module{imghdr} module defines the following function:
  12
  13
  14 \begin{funcdesc}{what}{filename\optional{, h}}
  15 Tests the image data contained in the file named by \var{filename},
  16 and returns a string describing the image type.  If optional \var{h}
  17 is provided, the \var{filename} is ignored and \var{h} is assumed to
  18 contain the byte stream to test.
  19 \end{funcdesc}
  20
  21 The following image types are recognized, as listed below with the
  22 return value from \function{what()}:
  23
  24 \begin{tableii}{l|l}{code}{Value}{Image format}
  25   \lineii{'rgb'}{SGI ImgLib Files}
  26   \lineii{'gif'}{GIF 87a and 89a Files}
  27   \lineii{'pbm'}{Portable Bitmap Files}
  28   \lineii{'pgm'}{Portable Graymap Files}
  29   \lineii{'ppm'}{Portable Pixmap Files}
  30   \lineii{'tiff'}{TIFF Files}
  31   \lineii{'rast'}{Sun Raster Files}
  32   \lineii{'xbm'}{X Bitmap Files}
  33   \lineii{'jpeg'}{JPEG data in JFIF format}
  34   \lineii{'bmp'}{BMP files}
  35   \lineii{'png'}{Portable Network Graphics}
  36 \end{tableii}
  37
  38 You can extend the list of file types \module{imghdr} can recognize by
  39 appending to this variable:
  40
  41 \begin{datadesc}{tests}
  42 A list of functions performing the individual tests.  Each function
  43 takes two arguments: the byte-stream and an open file-like object.
  44 When \function{what()} is called with a byte-stream, the file-like
  45 object will be \code{None}.
  46
  47 The test function should return a string describing the image type if
  48 the test succeeded, or \code{None} if it failed.
  49 \end{datadesc}
  50
  51 Example:
  52
  53 \begin{verbatim}
  54 >>> import imghdr
  55 >>> imghdr.what('/tmp/bass.gif')
  56 'gif'
  57 \end{verbatim}