39.12. jpeg — Read and write JPEG files

The module jpeg provides access to the jpeg compressor and decompressor written by the Independent JPEG Group (IJG). JPEG is a standard for compressing pictures; it is defined in ISO 10918. For details on JPEG or the Independent JPEG Group software refer to the JPEG standard or the documentation provided with the software.

A portable interface to JPEG image files is available with the Python Imaging Library (PIL) by Fredrik Lundh. Information on PIL is available at http://www.pythonware.com/products/pil/ .

The jpeg module defines an exception and some functions.

exception jpeg. error

Exception raised by compress() and decompress() in case of errors.

jpeg. compress ( data, w, h, b )

Treat data as a pixmap of width w and height h, with b bytes per pixel. The data is in SGI GL order, so the first pixel is in the lower-left corner. This means that gl.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.

jpeg. decompress ( data )

Data is a string containing a picture in JFIF format. It returns a tuple (data, width, height, bytesperpixel). Again, the data is suitable to pass to gl.lrectwrite().

jpeg. setoption ( name, value )

Set various options. Subsequent compress() and decompress() calls will use these options. The following options are available:

Option	Effect
'forcegray'	Force output to be grayscale, even if input is RGB.
'quality'	Set the quality of the compressed image to a value between 0 and 100 (default is 75). This only affects compression.
'optimize'	Perform Huffman table optimization. Takes longer, but results in smaller compressed image. This only affects compression.
'smooth'	Perform inter-block smoothing on uncompressed image. Only useful for low- quality images. This only affects decompression.