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(python2.1-lib.info)jpeg

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Read and write JPEG files
=========================

Read and write image files in compressed JPEG format.

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.

`error'
     Exception raised by `compress()' and `decompress()' in case of
     errors.

`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.

`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()'.

`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.

See also:
     `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.}