39.12. "jpeg" — Read and write JPEG files
*****************************************

2.6 版後已棄用: The "jpeg" module has been removed in Python 3.

The module "jpeg" provides access to the jpeg compressor and
decompressor written by the Independent JPEG Group (IJG). JPEG is a
standard for compressing pictures; it is defined in ISO 10918.  For
details on JPEG or the Independent JPEG Group software refer to the
JPEG standard or the documentation provided with the software.

A portable interface to JPEG image files is available with the Python
Imaging Library (PIL) by Fredrik Lundh.  Information on PIL is
available at http://www.pythonware.com/products/pil/.

The "jpeg" module defines an exception and some functions.

exception jpeg.error

   Exception raised by "compress()" and "decompress()" in case of
   errors.

jpeg.compress(data, w, h, b)

   Treat data as a pixmap of width *w* and height *h*, with *b* bytes
   per pixel. The data is in SGI GL order, so the first pixel is in
   the lower-left corner. This means that "gl.lrectread()" return data
   can immediately be passed to "compress()". Currently only 1 byte
   and 4 byte pixels are allowed, the former being treated as
   greyscale and the latter as RGB color. "compress()" returns a
   string that contains the compressed picture, in JFIF format.

jpeg.decompress(data)

   Data is a string containing a picture in JFIF format. It returns a
   tuple "(data, width, height, bytesperpixel)".  Again, the data is
   suitable to pass to "gl.lrectwrite()".

jpeg.setoption(name, value)

   Set various options.  Subsequent "compress()" and "decompress()"
   calls will use these options.  The following options are available:

   +-------------------+-----------------------------------------------+
   | Option            | Effect                                        |
   +===================+===============================================+
   | "'forcegray'"     | Force output to be grayscale, even if input   |
   |                   | is RGB.                                       |
   +-------------------+-----------------------------------------------+
   | "'quality'"       | Set the quality of the compressed image to a  |
   |                   | value between "0" and "100" (default is       |
   |                   | "75").  This only affects compression.        |
   +-------------------+-----------------------------------------------+
   | "'optimize'"      | Perform Huffman table optimization.  Takes    |
   |                   | longer, but results in smaller compressed     |
   |                   | image.  This only affects compression.        |
   +-------------------+-----------------------------------------------+
   | "'smooth'"        | Perform inter-block smoothing on uncompressed |
   |                   | image.  Only useful for low- quality images.  |
   |                   | This only affects decompression.              |
   +-------------------+-----------------------------------------------+

也參考:

  JPEG Still Image Data Compression Standard
     The canonical reference for the JPEG image format, by Pennebaker
     and Mitchell.

  Information Technology - Digital Compression and Coding of
  Continuous-tone Still Images - Requirements and Guidelines
     The ISO standard for JPEG is also published as ITU T.81.  This is
     available online in PDF form.
