13.4 Built-in Module jpeg

   

The 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 jpeg module defines these functions:

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 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.

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 lrectwrite.

setoption (name, value)

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

'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). Compress only.

'optimize'

Perform Huffman table optimization. Takes longer, but results in smaller compressed image. Compress only.

'smooth'

Perform inter-block smoothing on uncompressed image. Only useful for low-quality images. Decompress only.

Compress and uncompress raise the error jpeg.error in case of errors.