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 removed in Python 3. 12 13 14 15 .. index:: single: Independent JPEG Group 16 17 The module :mod:`jpeg` provides access to the jpeg compressor and decompressor 18 written by the Independent JPEG Group (IJG). JPEG is a standard for compressing 19 pictures; it is defined in ISO 10918. For details on JPEG or the Independent 20 JPEG Group software refer to the JPEG standard or the documentation provided 21 with the software. 22 23 .. index:: 24 single: Python Imaging Library 25 single: PIL (the Python Imaging Library) 26 single: Lundh, Fredrik 27 28 A portable interface to JPEG image files is available with the Python Imaging 29 Library (PIL) by Fredrik Lundh. Information on PIL is available at 30 http://www.pythonware.com/products/pil/. 31 32 The :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 96
