2005.09.08 23:08 "Re: [Tiff] creating JPEG file", by Joris Van Damme

More specifically, the file format that most people call "JPEG" is actually the JFIF format ("JPEG File Interchange Format").

Yes. Of course you're absolutely correct, Bob, but it's hard to mention this too and not become too confusing...

Not every JPEG is necessarilly a JFIF, and a JPEG compressed strip/tile is a JPEG but should not be a JFIF... Fun, isn't it? I think I need to clarify, or at least try to.

In short, JFIF adds a little to the older JPEG specification, in order to have good ways to communicate such properties as color space and densitity and such in a JPEG file. But JFIF does not change nor specificy the actual compression scheme, JPEG does.

The little that JFIF adds, is

• not important when talking about JPEG compression inside TIFF, since it shouldn't be there in the tile/strip data, since it should only be there on the TIFF IFD level.
• important when talking about good interchangable JPEG files, since pre-JFIF JPEG may be hard to make sense of.
• essentially more or less what you need to add to a JPEG compressed tile/strip data as coded inside a TIFF, to end up with a valid independent JPEG file, if the tile/strip does include its own tables.

Joris Van Damme
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