Cisco Cisco IPICS Dispatch Console Licensing Information

 

 

FILE FORMAT WARS

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Some JPEG programs produce files that are not compatible with our library.

The root of the problem is that the ISO JPEG committee failed to specify a

concrete file format.  Some vendors "filled in the blanks" on their own,

creating proprietary formats that no one else could read.  (For example, none

of the early commercial JPEG implementations for the Macintosh were able to

exchange compressed files.)

 

The file format we have adopted is called JFIF (see REFERENCES).  This format

has been agreed to by a number of major commercial JPEG vendors, and it has

become the de facto standard.  JFIF is a minimal or "low end" representation.

We recommend the use of TIFF/JPEG (TIFF revision 6.0 as modified by TIFF

Technical Note #2) for "high end" applications that need to record a lot of

additional data about an image.  TIFF/JPEG is fairly new and not yet widely

supported, unfortunately.

 

The upcoming JPEG Part 3 standard defines a file format called SPIFF.

SPIFF is interoperable with JFIF, in the sense that most JFIF decoders should

be able to read the most common variant of SPIFF.  SPIFF has some technical

advantages over JFIF, but its major claim to fame is simply that it is an

official standard rather than an informal one.  At this point it is unclear

whether SPIFF will supersede JFIF or whether JFIF will remain the de-facto

standard.  IJG intends to support SPIFF once the standard is frozen, but we

have not decided whether it should become our default output format or not.

(In any case, our decoder will remain capable of reading JFIF indefinitely.)

 

Various proprietary file formats incorporating JPEG compression also exist.

We have little or no sympathy for the existence of these formats.  Indeed,

one of the original reasons for developing this free software was to help

force convergence on common, open format standards for JPEG files.  Don't

use a proprietary file format!

 

 

TO DO

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The major thrust for v7 will probably be improvement of visual quality.

The current method for scaling the quantization tables is known not to be

very good at low Q values.  We also intend to investigate block boundary

smoothing, "poor man's variable quantization", and other means of improving

quality-vs-file-size performance without sacrificing compatibility.

 

In future versions, we are considering supporting some of the upcoming JPEG

Part 3 extensions --- principally, variable quantization and the SPIFF file