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

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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 format.
As always, speeding things up is of great interest.
Please send bug reports, offers of help, etc. to [e-mail].
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