2006.09.27 20:39 "Re: [Tiff] Status of ISO JBIG and CIELAB JPEG support", by Joris Van Damme

Wandering,

I've put a copy of a reference ITULAB JPEG in HTTP space.

http://users.skynet.be/joris.at.lebbeke/itulab.jpg

Thank you, Joris. WHen you (or Yves) mentioned that Photoshop could decode this correctly, which version were you (or was he) referring to?

I don't think anyone said that. In fact, I recall Chris Cox stepping in and saying Photoshop doesn't support ITULAB, or at least it doesn't support ITULAB in TIFF. Chris can be trusted to know such stuff. I've checked the ITULAB support for JPEG in Photoshop 7.0, and there's none.

What you may be thinking of is that Yves double-checked the ITULAB-TIFF-in-discuise with Photometric CIE Lab, by taking it into Photoshop and next correcting Photoshop's wrong take on this caused by the wrong Photometric, with various dials and bells, such that the image would start making sense if it was ITULAB despite of its Photometric. And it did start making sense.

Every decoder I use decodes this with incorrect colours (white is cyanish, etc).

Yes, they're interpreting the ITULAB JPEG as YCbCr. IIRC, what they should be doing instead is taking a closer look at the APP1 marker. Seeing there are no indications of this being a JFIF or Adobe JPEG, and seeing the APP1 marker data starts with 'G3FAX' or something similar if I remember correctly, they should know it's ITULAB.

This is not uncommon. I've some very old RGB JPEGs laying about that predate the JFIF standard, and mainstream viewers incorrectly interpret these as YCbCr too.

LibJpeg offers callback hooks for seeing APP markers when scanning through the first bits. You can use these to detect this sort of situation.

I appreciate the file. I'm surprised more reference test images aren't available online, or at least discoverable. Were these standards aborted or deployed only within such a surgically narrow market that for all intents and purposes, they don't really exist?

It is hard to answer that question. There's no means of objective measurement. And however small the market is that is concerned with ITULAB, you can bet your anything it'll be vitally important to at least some people, like maybe some fax people perhaps. This is a big planet, a surgically narrow market from some people's point of view, means the world and livelyhood to some others.

Best regards,

Joris Van Damme
info@awaresystems.be

http://www.awaresystems.be/
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