| \section{Built-in Module \sectcode{jpeg}} |
| \label{module-jpeg} |
| \bimodindex{jpeg} |
| |
| The module \module{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 \module{jpeg} module defines an exception and some functions. |
| |
| \begin{excdesc}{error} |
| Exception raised by \function{compress()} and \function{decompress()} |
| in case of errors. |
| \end{excdesc} |
| |
| \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{gl.lrectread} |
| return data can immediately be passed to \function{compress()}. |
| Currently only 1 byte and 4 byte pixels are allowed, the former being |
| treated as greyscale and the latter as RGB color. |
| \function{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{gl.lrectwrite}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{setoption}{name, value} |
| Set various options. Subsequent \function{compress()} and |
| \function{decompress()} calls will use these options. The following |
| options are available: |
| |
| \begin{tableii}{|l|l|}{code}{Option}{Effect} |
| \lineii{'forcegray'}{% |
| Force output to be grayscale, even if input is RGB.} |
| \lineii{'quality'}{% |
| Set the quality of the compressed image to a value between |
| \code{0} and \code{100} (default is \code{75}). \\ |
| &This only affects compression.} |
| \lineii{'optimize'}{% |
| Perform Huffman table optimization. Takes longer, but results in |
| smaller compressed \\ |
| &image. This only affects compression.} |
| \lineii{'smooth'}{% |
| Perform inter-block smoothing on uncompressed image. Only useful |
| for low-quality \\ |
| &images. This only affects decompression.} |
| \end{tableii} |
| \end{funcdesc} |