39.12. jpeg — Read and write JPEG files — Python documentation
39.12. jpeg — Read and write JPEG files
Deprecated since version 2.6: The jpeg module has been removed in Python 3.
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 togl.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
and100
(default is75
). 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.
See also
- JPEG Still Image Data Compression Standard
- The canonical reference for the JPEG image format, by Pennebaker and Mitchell.
- Information Technology - Digital Compression and Coding of Continuous-tone Still Images - Requirements and Guidelines
- The ISO standard for JPEG is also published as ITU T.81. This is available online in PDF form.