:mod:`jpeg` --- Read and write JPEG files

=========================================

.. module:: jpeg

   :platform: IRIX

   :synopsis: Read and write image files in compressed JPEG format.

   :deprecated:

.. deprecated:: 2.6

   The :mod:`jpeg` module has been deprecated for removal in Python 3.0.

.. index:: single: Independent JPEG Group

The module :mod:`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.

.. index::

   single: Python Imaging Library

   single: PIL (the Python Imaging Library)

   single: Lundh, Fredrik

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 :mod:`jpeg` module defines an exception and some functions.

.. exception:: error

   Exception raised by :func:`compress` and :func:`decompress` in case of errors.

.. function:: compress(data, w, h, b)

   .. index:: single: JFIF

   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 :func:`gl.lrectread` return data can immediately be passed to

   :func:`compress`. Currently only 1 byte and 4 byte pixels are allowed, the

   former being treated as greyscale and the latter as RGB color. :func:`compress`

   returns a string that contains the compressed picture, in JFIF format.

.. function:: decompress(data)

   .. index:: single: JFIF

   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 :func:`gl.lrectwrite`.

.. function:: setoption(name, value)

   Set various options.  Subsequent :func:`compress` and :func:`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.                              |

   +-----------------+---------------------------------------------+

.. seealso::

   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 <http://www.w3.org/Graphics/JPEG/itu-t81.pdf>`_

      The ISO standard for JPEG is also published as ITU T.81.  This is available

      online in PDF form.