| 1 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> |
| 2 | <html> |
| 3 | <head> |
| 4 | <link rel="STYLESHEET" href="lib.css" type='text/css' /> |
| 5 | <link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" /> |
| 6 | <link rel='start' href='../index.html' title='Python Documentation Index' /> |
| 7 | <link rel="first" href="lib.html" title='Python Library Reference' /> |
| 8 | <link rel='contents' href='contents.html' title="Contents" /> |
| 9 | <link rel='index' href='genindex.html' title='Index' /> |
| 10 | <link rel='last' href='about.html' title='About this document...' /> |
| 11 | <link rel='help' href='about.html' title='About this document...' /> |
| 12 | <link rel="prev" href="module-imgfile.html" /> |
| 13 | <link rel="parent" href="sgi.html" /> |
| 14 | <link rel="next" href="sunos.html" /> |
| 15 | <meta name='aesop' content='information' /> |
| 16 | <title>20.12 jpeg -- Read and write JPEG files</title> |
| 17 | </head> |
| 18 | <body> |
| 19 | <DIV CLASS="navigation"> |
| 20 | <div id='top-navigation-panel' xml:id='top-navigation-panel'> |
| 21 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> |
| 22 | <tr> |
| 23 | <td class='online-navigation'><a rel="prev" title="20.11 imgfile " |
| 24 | href="module-imgfile.html"><img src='../icons/previous.png' |
| 25 | border='0' height='32' alt='Previous Page' width='32' /></A></td> |
| 26 | <td class='online-navigation'><a rel="parent" title="20. SGI IRIX Specific" |
| 27 | href="sgi.html"><img src='../icons/up.png' |
| 28 | border='0' height='32' alt='Up One Level' width='32' /></A></td> |
| 29 | <td class='online-navigation'><a rel="next" title="21. SunOS Specific Services" |
| 30 | href="sunos.html"><img src='../icons/next.png' |
| 31 | border='0' height='32' alt='Next Page' width='32' /></A></td> |
| 32 | <td align="center" width="100%">Python Library Reference</td> |
| 33 | <td class='online-navigation'><a rel="contents" title="Table of Contents" |
| 34 | href="contents.html"><img src='../icons/contents.png' |
| 35 | border='0' height='32' alt='Contents' width='32' /></A></td> |
| 36 | <td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png' |
| 37 | border='0' height='32' alt='Module Index' width='32' /></a></td> |
| 38 | <td class='online-navigation'><a rel="index" title="Index" |
| 39 | href="genindex.html"><img src='../icons/index.png' |
| 40 | border='0' height='32' alt='Index' width='32' /></A></td> |
| 41 | </tr></table> |
| 42 | <div class='online-navigation'> |
| 43 | <b class="navlabel">Previous:</b> |
| 44 | <a class="sectref" rel="prev" href="module-imgfile.html">20.11 imgfile </A> |
| 45 | <b class="navlabel">Up:</b> |
| 46 | <a class="sectref" rel="parent" href="sgi.html">20. SGI IRIX Specific</A> |
| 47 | <b class="navlabel">Next:</b> |
| 48 | <a class="sectref" rel="next" href="sunos.html">21. SunOS Specific Services</A> |
| 49 | </div> |
| 50 | <hr /></div> |
| 51 | </DIV> |
| 52 | <!--End of Navigation Panel--> |
| 53 | |
| 54 | <H1><A NAME="SECTION00221200000000000000000"> |
| 55 | 20.12 <tt class="module">jpeg</tt> -- |
| 56 | Read and write JPEG files</A> |
| 57 | </H1> |
| 58 | |
| 59 | <P> |
| 60 | <A NAME="module-jpeg"></A> |
| 61 | <p class="availability">Availability: <span |
| 62 | class="platform">IRIX</span>.</p> |
| 63 | |
| 64 | <P> |
| 65 | The module <tt class="module">jpeg</tt> provides access to the jpeg compressor and |
| 66 | decompressor written by the Independent JPEG Group |
| 67 | <a id='l2h-5218' xml:id='l2h-5218'></a>(IJG). JPEG is a standard for |
| 68 | compressing pictures; it is defined in ISO 10918. For details on JPEG |
| 69 | or the Independent JPEG Group software refer to the JPEG standard or |
| 70 | the documentation provided with the software. |
| 71 | |
| 72 | <P> |
| 73 | A portable interface to JPEG image files is available with the Python |
| 74 | Imaging Library (PIL) by Fredrik Lundh. Information on PIL is |
| 75 | available at <a class="url" href="http://www.pythonware.com/products/pil/">http://www.pythonware.com/products/pil/</a>. |
| 76 | <a id='l2h-5219' xml:id='l2h-5219'></a> |
| 77 | |
| 78 | <P> |
| 79 | The <tt class="module">jpeg</tt> module defines an exception and some functions. |
| 80 | |
| 81 | <P> |
| 82 | <dl><dt><b><span class="typelabel">exception</span> <tt id='l2h-5214' xml:id='l2h-5214' class="exception">error</tt></b></dt> |
| 83 | <dd> |
| 84 | Exception raised by <tt class="function">compress()</tt> and <tt class="function">decompress()</tt> |
| 85 | in case of errors. |
| 86 | </dd></dl> |
| 87 | |
| 88 | <P> |
| 89 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 90 | <td><nobr><b><tt id='l2h-5215' xml:id='l2h-5215' class="function">compress</tt></b>(</nobr></td> |
| 91 | <td><var>data, w, h, b</var>)</td></tr></table></dt> |
| 92 | <dd> |
| 93 | Treat data as a pixmap of width <var>w</var> and height <var>h</var>, with |
| 94 | <var>b</var> bytes per pixel. The data is in SGI GL order, so the first |
| 95 | pixel is in the lower-left corner. This means that <tt class="function">gl.lrectread()</tt> |
| 96 | return data can immediately be passed to <tt class="function">compress()</tt>. |
| 97 | Currently only 1 byte and 4 byte pixels are allowed, the former being |
| 98 | treated as greyscale and the latter as RGB color. |
| 99 | <tt class="function">compress()</tt> returns a string that contains the compressed |
| 100 | picture, in JFIF<a id='l2h-5220' xml:id='l2h-5220'></a> format. |
| 101 | </dl> |
| 102 | |
| 103 | <P> |
| 104 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 105 | <td><nobr><b><tt id='l2h-5216' xml:id='l2h-5216' class="function">decompress</tt></b>(</nobr></td> |
| 106 | <td><var>data</var>)</td></tr></table></dt> |
| 107 | <dd> |
| 108 | Data is a string containing a picture in JFIF<a id='l2h-5221' xml:id='l2h-5221'></a> format. It |
| 109 | returns a tuple <code>(<var>data</var>, <var>width</var>, <var>height</var>, |
| 110 | <var>bytesperpixel</var>)</code>. Again, the data is suitable to pass to |
| 111 | <tt class="function">gl.lrectwrite()</tt>. |
| 112 | </dl> |
| 113 | |
| 114 | <P> |
| 115 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 116 | <td><nobr><b><tt id='l2h-5217' xml:id='l2h-5217' class="function">setoption</tt></b>(</nobr></td> |
| 117 | <td><var>name, value</var>)</td></tr></table></dt> |
| 118 | <dd> |
| 119 | Set various options. Subsequent <tt class="function">compress()</tt> and |
| 120 | <tt class="function">decompress()</tt> calls will use these options. The following |
| 121 | options are available: |
| 122 | |
| 123 | <P> |
| 124 | <div class="center"><table class="realtable"> |
| 125 | <thead> |
| 126 | <tr> |
| 127 | <th class="left" >Option</th> |
| 128 | <th class="left" >Effect</th> |
| 129 | </tr> |
| 130 | </thead> |
| 131 | <tbody> |
| 132 | <tr><td class="left" valign="baseline"><code>'forcegray'</code></td> |
| 133 | <td class="left" >Force output to be grayscale, even if input is RGB.</td></tr> |
| 134 | <tr><td class="left" valign="baseline"><code>'quality'</code></td> |
| 135 | <td class="left" >Set the quality of the compressed image to a value between |
| 136 | <code>0</code> and <code>100</code> (default is <code>75</code>). This only affects |
| 137 | compression.</td></tr> |
| 138 | <tr><td class="left" valign="baseline"><code>'optimize'</code></td> |
| 139 | <td class="left" >Perform Huffman table optimization. Takes longer, but results in |
| 140 | smaller compressed image. This only affects compression.</td></tr> |
| 141 | <tr><td class="left" valign="baseline"><code>'smooth'</code></td> |
| 142 | <td class="left" >Perform inter-block smoothing on uncompressed image. Only useful |
| 143 | for low-quality images. This only affects decompression.</td></tr></tbody> |
| 144 | </table></div> |
| 145 | </dl> |
| 146 | |
| 147 | <P> |
| 148 | <div class="seealso"> |
| 149 | <p class="heading">See Also:</p> |
| 150 | |
| 151 | <dl compact="compact" class="seetitle"> |
| 152 | <dt><em class="citetitle" |
| 153 | >JPEG Still Image Data Compression Standard</em></dt> |
| 154 | <dd>The |
| 155 | canonical reference for the JPEG image format, by |
| 156 | Pennebaker and Mitchell.</dd> |
| 157 | </dl> |
| 158 | |
| 159 | <P> |
| 160 | <dl compact="compact" class="seetitle"> |
| 161 | <dt><em class="citetitle"><a href="http://www.w3.org/Graphics/JPEG/itu-t81.pdf" |
| 162 | >Information |
| 163 | Technology - Digital Compression and Coding of |
| 164 | Continuous-tone Still Images - Requirements and |
| 165 | Guidelines</a></em></dt> |
| 166 | <dd>The ISO standard for JPEG is also published as |
| 167 | ITU T.81. This is available online in PDF form.</dd> |
| 168 | </dl> |
| 169 | </div> |
| 170 | |
| 171 | <P> |
| 172 | |
| 173 | <DIV CLASS="navigation"> |
| 174 | <div class='online-navigation'> |
| 175 | <p></p><hr /> |
| 176 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> |
| 177 | <tr> |
| 178 | <td class='online-navigation'><a rel="prev" title="20.11 imgfile " |
| 179 | href="module-imgfile.html"><img src='../icons/previous.png' |
| 180 | border='0' height='32' alt='Previous Page' width='32' /></A></td> |
| 181 | <td class='online-navigation'><a rel="parent" title="20. SGI IRIX Specific" |
| 182 | href="sgi.html"><img src='../icons/up.png' |
| 183 | border='0' height='32' alt='Up One Level' width='32' /></A></td> |
| 184 | <td class='online-navigation'><a rel="next" title="21. SunOS Specific Services" |
| 185 | href="sunos.html"><img src='../icons/next.png' |
| 186 | border='0' height='32' alt='Next Page' width='32' /></A></td> |
| 187 | <td align="center" width="100%">Python Library Reference</td> |
| 188 | <td class='online-navigation'><a rel="contents" title="Table of Contents" |
| 189 | href="contents.html"><img src='../icons/contents.png' |
| 190 | border='0' height='32' alt='Contents' width='32' /></A></td> |
| 191 | <td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png' |
| 192 | border='0' height='32' alt='Module Index' width='32' /></a></td> |
| 193 | <td class='online-navigation'><a rel="index" title="Index" |
| 194 | href="genindex.html"><img src='../icons/index.png' |
| 195 | border='0' height='32' alt='Index' width='32' /></A></td> |
| 196 | </tr></table> |
| 197 | <div class='online-navigation'> |
| 198 | <b class="navlabel">Previous:</b> |
| 199 | <a class="sectref" rel="prev" href="module-imgfile.html">20.11 imgfile </A> |
| 200 | <b class="navlabel">Up:</b> |
| 201 | <a class="sectref" rel="parent" href="sgi.html">20. SGI IRIX Specific</A> |
| 202 | <b class="navlabel">Next:</b> |
| 203 | <a class="sectref" rel="next" href="sunos.html">21. SunOS Specific Services</A> |
| 204 | </div> |
| 205 | </div> |
| 206 | <hr /> |
| 207 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> |
| 208 | </DIV> |
| 209 | <!--End of Navigation Panel--> |
| 210 | <ADDRESS> |
| 211 | See <i><a href="about.html">About this document...</a></i> for information on suggesting changes. |
| 212 | </ADDRESS> |
| 213 | </BODY> |
| 214 | </HTML> |