Release Notes

Open Source Used In AsyncOS 8.8 for Cisco Web Security Appliances

particular the widely used JFIF file format. The library can be used by

surrounding code to process interchange or abbreviated JPEG datastreams that

are embedded in more complex file formats. (For example, this library is

used by the free LIBTIFF library to support JPEG compression in TIFF.)

Outline of typical usage

------------------------

The rough outline of a JPEG compression operation is:

Allocate and initialize a JPEG compression object

Specify the destination for the compressed data (eg, a file)

Set parameters for compression, including image size & colorspace

jpeg_start_compress(...);

while (scan lines remain to be written)

jpeg_write_scanlines(...);

jpeg_finish_compress(...);

Release the JPEG compression object

A JPEG compression object holds parameters and working state for the JPEG

library. We make creation/destruction of the object separate from starting

or finishing compression of an image; the same object can be re-used for a

series of image compression operations. This makes it easy to re-use the

same parameter settings for a sequence of images. Re-use of a JPEG object

also has important implications for processing abbreviated JPEG datastreams,

as discussed later.

The image data to be compressed is supplied to jpeg_write_scanlines() from

in-memory buffers. If the application is doing file-to-file compression,

reading image data from the source file is the application's responsibility.

The library emits compressed data by calling a "data destination manager",

which typically will write the data into a file; but the application can

provide its own destination manager to do something else.

Similarly, the rough outline of a JPEG decompression operation is:

Allocate and initialize a JPEG decompression object

Specify the source of the compressed data (eg, a file)

Call jpeg_read_header() to obtain image info

Set parameters for decompression

jpeg_start_decompress(...);

while (scan lines remain to be read)

jpeg_read_scanlines(...);

jpeg_finish_decompress(...);

Release the JPEG decompression object

This is comparable to the compression outline except that reading the