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| 2 | :mod:`jpeg` --- Read and write JPEG files
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| 3 | =========================================
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| 4 |
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| 5 | .. module:: jpeg
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| 6 | :platform: IRIX
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| 7 | :synopsis: Read and write image files in compressed JPEG format.
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| 8 | :deprecated:
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| 9 |
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| 10 | .. deprecated:: 2.6
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| [391] | 11 | The :mod:`jpeg` module has been removed in Python 3.
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| [2] | 12 |
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| 13 |
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| 14 |
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| 15 | .. index:: single: Independent JPEG Group
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| 16 |
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| 17 | The module :mod:`jpeg` provides access to the jpeg compressor and decompressor
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| 18 | written by the Independent JPEG Group (IJG). JPEG is a standard for compressing
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| 19 | pictures; it is defined in ISO 10918. For details on JPEG or the Independent
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| 20 | JPEG Group software refer to the JPEG standard or the documentation provided
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| 21 | with the software.
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| 22 |
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| 23 | .. index::
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| 24 | single: Python Imaging Library
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| 25 | single: PIL (the Python Imaging Library)
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| 26 | single: Lundh, Fredrik
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| 27 |
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| 28 | A portable interface to JPEG image files is available with the Python Imaging
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| 29 | Library (PIL) by Fredrik Lundh. Information on PIL is available at
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| 30 | http://www.pythonware.com/products/pil/.
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| 31 |
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| 32 | The :mod:`jpeg` module defines an exception and some functions.
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| 33 |
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| 34 |
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| 35 | .. exception:: error
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| 36 |
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| 37 | Exception raised by :func:`compress` and :func:`decompress` in case of errors.
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| 38 |
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| 39 |
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| 40 | .. function:: compress(data, w, h, b)
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| 41 |
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| 42 | .. index:: single: JFIF
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| 43 |
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| 44 | Treat data as a pixmap of width *w* and height *h*, with *b* bytes per pixel.
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| 45 | The data is in SGI GL order, so the first pixel is in the lower-left corner.
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| 46 | This means that :func:`gl.lrectread` return data can immediately be passed to
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| 47 | :func:`compress`. Currently only 1 byte and 4 byte pixels are allowed, the
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| 48 | former being treated as greyscale and the latter as RGB color. :func:`compress`
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| 49 | returns a string that contains the compressed picture, in JFIF format.
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| 50 |
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| 51 |
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| 52 | .. function:: decompress(data)
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| 53 |
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| 54 | .. index:: single: JFIF
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| 55 |
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| 56 | Data is a string containing a picture in JFIF format. It returns a tuple
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| 57 | ``(data, width, height, bytesperpixel)``. Again, the data is suitable to pass
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| 58 | to :func:`gl.lrectwrite`.
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| 59 |
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| 60 |
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| 61 | .. function:: setoption(name, value)
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| 62 |
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| 63 | Set various options. Subsequent :func:`compress` and :func:`decompress` calls
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| 64 | will use these options. The following options are available:
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| 65 |
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| 66 | +-----------------+---------------------------------------------+
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| 67 | | Option | Effect |
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| 68 | +=================+=============================================+
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| 69 | | ``'forcegray'`` | Force output to be grayscale, even if input |
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| 70 | | | is RGB. |
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| 71 | +-----------------+---------------------------------------------+
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| 72 | | ``'quality'`` | Set the quality of the compressed image to |
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| 73 | | | a value between ``0`` and ``100`` (default |
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| 74 | | | is ``75``). This only affects compression. |
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| 75 | +-----------------+---------------------------------------------+
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| 76 | | ``'optimize'`` | Perform Huffman table optimization. Takes |
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| 77 | | | longer, but results in smaller compressed |
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| 78 | | | image. This only affects compression. |
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| 79 | +-----------------+---------------------------------------------+
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| 80 | | ``'smooth'`` | Perform inter-block smoothing on |
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| 81 | | | uncompressed image. Only useful for low- |
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| 82 | | | quality images. This only affects |
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| 83 | | | decompression. |
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| 84 | +-----------------+---------------------------------------------+
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| 85 |
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| 86 |
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| 87 | .. seealso::
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| 88 |
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| 89 | JPEG Still Image Data Compression Standard
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| 90 | The canonical reference for the JPEG image format, by Pennebaker and Mitchell.
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| 91 |
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| 92 | `Information Technology - Digital Compression and Coding of Continuous-tone Still Images - Requirements and Guidelines <http://www.w3.org/Graphics/JPEG/itu-t81.pdf>`_
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| 93 | The ISO standard for JPEG is also published as ITU T.81. This is available
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| 94 | online in PDF form.
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| 95 |
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