/Doc/library/jpeg.rst
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- :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.