# cpython-withatomic / Doc / libjpeg.tex

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 \section{Built-in Module \sectcode{jpeg}} \label{module-jpeg} \bimodindex{jpeg} The module \code{jpeg} provides access to the jpeg compressor and decompressor written by the Independent JPEG Group. JPEG is a (draft?)\ standard for compressing pictures. For details on jpeg or the Independent JPEG Group software refer to the JPEG standard or the documentation provided with the software. The \code{jpeg} module defines these functions: \renewcommand{\indexsubitem}{(in module jpeg)} \begin{funcdesc}{compress}{data\, w\, h\, b} Treat data as a pixmap of width \var{w} and height \var{h}, with \var{b} bytes per pixel. The data is in SGI GL order, so the first pixel is in the lower-left corner. This means that \code{lrectread} return data can immediately be passed to compress. Currently only 1 byte and 4 byte pixels are allowed, the former being treated as greyscale and the latter as RGB color. Compress returns a string that contains the compressed picture, in JFIF format. \end{funcdesc} \begin{funcdesc}{decompress}{data} Data is a string containing a picture in JFIF format. It returns a tuple \code{(\var{data}, \var{width}, \var{height}, \var{bytesperpixel})}. Again, the data is suitable to pass to \code{lrectwrite}. \end{funcdesc} \begin{funcdesc}{setoption}{name\, value} Set various options. Subsequent compress and decompress calls will use these options. The following options are available: \begin{description} \item[\code{'forcegray' }] Force output to be grayscale, even if input is RGB. \item[\code{'quality' }] Set the quality of the compressed image to a value between \code{0} and \code{100} (default is \code{75}). Compress only. \item[\code{'optimize' }] Perform Huffman table optimization. Takes longer, but results in smaller compressed image. Compress only. \item[\code{'smooth' }] Perform inter-block smoothing on uncompressed image. Only useful for low-quality images. Decompress only. \end{description} \end{funcdesc} Compress and uncompress raise the error \code{jpeg.error} in case of errors.