User manual - V-N500取扱説明書(2014年05月07日)

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RELATED SOFTWARE
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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
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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.