Cisco Cisco MediaSense Release 9.1(1) Licensing Information

If you want to understand how the JPEG code works, we suggest reading one or

more of the REFERENCES, then looking at the documentation files (in roughly

the order listed) before diving into the code.

 

 

OVERVIEW

========

 

This package contains C software to implement JPEG image encoding, decoding,

and transcoding.  JPEG (pronounced "jay-peg") is a standardized compression

method for full-color and gray-scale images.  JPEG's strong suit is compressing

photographic images or other types of images that have smooth color and

brightness transitions between neighboring pixels.  Images with sharp lines or

other abrupt features may not compress well with JPEG, and a higher JPEG

quality may have to be used to avoid visible compression artifacts with such

images.

 

JPEG is lossy, meaning that the output pixels are not necessarily identical to

the input pixels.  However, on photographic content and other "smooth" images,

very good compression ratios can be obtained with no visible compression

artifacts, and extremely high compression ratios are possible if you are

willing to sacrifice image quality (by reducing the "quality" setting in the

compressor.)

 

This software implements JPEG baseline, extended-sequential, and progressive

compression processes.  Provision is made for supporting all variants of these

processes, although some uncommon parameter settings aren't implemented yet.

We have made no provision for supporting the hierarchical or lossless

processes defined in the standard.

 

We provide a set of library routines for reading and writing JPEG image files,

plus two sample applications "cjpeg" and "djpeg", which use the library to

perform conversion between JPEG and some other popular image file formats.

The library is intended to be reused in other applications.

 

In order to support file conversion and viewing software, we have included

considerable functionality beyond the bare JPEG coding/decoding capability;

for example, the color quantization modules are not strictly part of JPEG

decoding, but they are essential for output to colormapped file formats or

colormapped displays.  These extra functions can be compiled out of the

library if not required for a particular application.

 

We have also included "jpegtran", a utility for lossless transcoding between

different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple

applications for inserting and extracting textual comments in JFIF files.

 

The emphasis in designing this software has been on achieving portability and

flexibility, while also making it fast enough to be useful.  In particular,