/Doc/library/jpeg.rst

 1
 2:mod:`jpeg` --- Read and write JPEG files
 3=========================================
 4
 5.. module:: jpeg
 6   :platform: IRIX
 7   :synopsis: Read and write image files in compressed JPEG format.
 8   :deprecated:
 9
10.. deprecated:: 2.6
11   The :mod:`jpeg` module has been deprecated for removal in Python 3.0.
12
13
14
15.. index:: single: Independent JPEG Group
16
17The module :mod:`jpeg` provides access to the jpeg compressor and decompressor
18written by the Independent JPEG Group (IJG). JPEG is a standard for compressing
19pictures; it is defined in ISO 10918.  For details on JPEG or the Independent
20JPEG Group software refer to the JPEG standard or the documentation provided
21with the software.
22
23.. index::
24   single: Python Imaging Library
25   single: PIL (the Python Imaging Library)
26   single: Lundh, Fredrik
27
28A portable interface to JPEG image files is available with the Python Imaging
29Library (PIL) by Fredrik Lundh.  Information on PIL is available at
30http://www.pythonware.com/products/pil/.
31
32The :mod:`jpeg` module defines an exception and some functions.
33
34
35.. exception:: error
36
37   Exception raised by :func:`compress` and :func:`decompress` in case of errors.
38
39
40.. function:: compress(data, w, h, b)
41
42   .. index:: single: JFIF
43
44   Treat data as a pixmap of width *w* and height *h*, with *b* bytes per pixel.
45   The data is in SGI GL order, so the first pixel is in the lower-left corner.
46   This means that :func:`gl.lrectread` return data can immediately be passed to
47   :func:`compress`. Currently only 1 byte and 4 byte pixels are allowed, the
48   former being treated as greyscale and the latter as RGB color. :func:`compress`
49   returns a string that contains the compressed picture, in JFIF format.
50
51
52.. function:: decompress(data)
53
54   .. index:: single: JFIF
55
56   Data is a string containing a picture in JFIF format. It returns a tuple
57   ``(data, width, height, bytesperpixel)``.  Again, the data is suitable to pass
58   to :func:`gl.lrectwrite`.
59
60
61.. function:: setoption(name, value)
62
63   Set various options.  Subsequent :func:`compress` and :func:`decompress` calls
64   will use these options.  The following options are available:
65
66   +-----------------+---------------------------------------------+
67   | Option          | Effect                                      |
68   +=================+=============================================+
69   | ``'forcegray'`` | Force output to be grayscale, even if input |
70   |                 | is RGB.                                     |
71   +-----------------+---------------------------------------------+
72   | ``'quality'``   | Set the quality of the compressed image to  |
73   |                 | a value between ``0`` and ``100`` (default  |
74   |                 | is ``75``).  This only affects compression. |
75   +-----------------+---------------------------------------------+
76   | ``'optimize'``  | Perform Huffman table optimization.  Takes  |
77   |                 | longer, but results in smaller compressed   |
78   |                 | image.  This only affects compression.      |
79   +-----------------+---------------------------------------------+
80   | ``'smooth'``    | Perform inter-block smoothing on            |
81   |                 | uncompressed image.  Only useful for low-   |
82   |                 | quality images.  This only affects          |
83   |                 | decompression.                              |
84   +-----------------+---------------------------------------------+
85
86
87.. seealso::
88
89   JPEG Still Image Data Compression Standard
90      The canonical reference for the JPEG image format, by Pennebaker and Mitchell.
91
92   `Information Technology - Digital Compression and Coding of Continuous-tone Still Images - Requirements and Guidelines <http://www.w3.org/Graphics/JPEG/itu-t81.pdf>`_
93      The ISO standard for JPEG is also published as ITU T.81.  This is available
94      online in PDF form.
95