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author Guido van Rossum <guido@python.org>
date Thu, 17 Jul 1997 16:29:42 +0000
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1 \section{Built-in Module \sectcode{jpeg}}
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2 \bimodindex{jpeg}
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3
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4 The module \code{jpeg} provides access to the jpeg compressor and
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5 decompressor written by the Independent JPEG Group. JPEG is a (draft?)\
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6 standard for compressing pictures. For details on jpeg or the
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7 Independent JPEG Group software refer to the JPEG standard or the
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8 documentation provided with the software.
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9
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10 The \code{jpeg} module defines these functions:
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12 \renewcommand{\indexsubitem}{(in module jpeg)}
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13 \begin{funcdesc}{compress}{data\, w\, h\, b}
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14 Treat data as a pixmap of width \var{w} and height \var{h}, with \var{b} bytes per
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15 pixel. The data is in SGI GL order, so the first pixel is in the
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16 lower-left corner. This means that \code{lrectread} return data can
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17 immediately be passed to compress. Currently only 1 byte and 4 byte
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18 pixels are allowed, the former being treated as greyscale and the
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19 latter as RGB color. Compress returns a string that contains the
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20 compressed picture, in JFIF format.
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21 \end{funcdesc}
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22
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23 \begin{funcdesc}{decompress}{data}
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24 Data is a string containing a picture in JFIF format. It returns a
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25 tuple
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26 \code{(\var{data}, \var{width}, \var{height}, \var{bytesperpixel})}.
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27 Again, the data is suitable to pass to \code{lrectwrite}.
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28 \end{funcdesc}
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29
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30 \begin{funcdesc}{setoption}{name\, value}
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31 Set various options. Subsequent compress and decompress calls
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32 will use these options. The following options are available:
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33 \begin{description}
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34 \item[\code{'forcegray' }]
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35 Force output to be grayscale, even if input is RGB.
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36
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37 \item[\code{'quality' }]
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38 Set the quality of the compressed image to a
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39 value between \code{0} and \code{100} (default is \code{75}). Compress only.
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40
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41 \item[\code{'optimize' }]
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42 Perform Huffman table optimization. Takes longer, but results in
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43 smaller compressed image. Compress only.
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45 \item[\code{'smooth' }]
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46 Perform inter-block smoothing on uncompressed image. Only useful for
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47 low-quality images. Decompress only.
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48 \end{description}
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49 \end{funcdesc}
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50
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51 Compress and uncompress raise the error \code{jpeg.error} in case of errors.