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send usenet/news.answers/jpeg-faq/part1 

 

send usenet/news.answers/jpeg-faq/part2 

 
 
RELATED SOFTWARE 
================ 
 
Numerous viewing and image manipulation programs now support JPEG.  (Quite a 
few of them use this library to do so.)  The JPEG FAQ described above lists 
some of the more popular free and shareware viewers, and tells where to 
obtain them on Internet. 
 
If you are on a Unix machine, we highly recommend Jef Poskanzer's free 
PBMPLUS software, which provides many useful operations on PPM-format image 
files.  In particular, it can convert PPM images to and from a wide range of 
other formats, thus making cjpeg/djpeg considerably more useful.  The latest 
version is distributed by the NetPBM group, and is available from numerous 
sites, notably ftp://wuarchive.wustl.edu/graphics/graphics/packages/NetPBM/. 
Unfortunately PBMPLUS/NETPBM is not nearly as portable as the IJG software 
is; 
you are likely to have difficulty making it work on any non-Unix machine. 
 
A different free JPEG implementation, written by the PVRG group at Stanford, 
is available from ftp://havefun.stanford.edu/pub/jpeg/.  This program 
is designed for research and experimentation rather than production use; 
it is slower, harder to use, and less portable than the IJG code, but it 
is easier to read and modify.  Also, the PVRG code supports lossless JPEG, 
which we do not.  (On the other hand, it doesn't do progressive JPEG.) 
 
 
FILE FORMAT WARS 
================ 
 
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.)