2005.12.21 20:51 "RE: [Tiff] Oddball Old Style JPEG image", by Jason Frank
Yep, I know all about Old-Style JPEG's. What I don't know is who created these images. The internal content of the TIF cannot be read by any view that I know about (and I know a lot), and the JPEG data is just weird.
If I can find the vendor to give me their specs, I can write a custom decoder. And I'll do the appropriate evangelism at that point. But first, I need to find who created these images. I'm in contact with the company that gave them to me, maybe I can get something done via that route.
From: Joris [mailto:email@example.com] Sent: Wednesday, December 21, 2005 2:31 PM To: Frank, Jason; firstname.lastname@example.org Subject: Re: [Tiff] Oddball Old Style JPEG image
Frank, Jason wrote:
> Does anyone know anything about the hardware/software that is > producing these images? They appear to be all messed up, but I've got
> to deal with them anyway :-(...
> Compression Scheme: Old-style JPEG
> Photometric Interpretation: YCbCr
Yes, they are all messed up, because the original specification is all messed up, and some reputable firms have been recycling old code for over a decade now instead of staying up to date and noticing the specification supplement corrects the fatal mistake.
The responsible thing to do is the contact the vendor, if you can find him, and point him to the following documents:
http://www.remotesensing.org/libtiff/TIFFTechNote2.html This is a document by Tom Lane, that enumerates the many reasons why the original TIFF 6.0 jpeg-in-tiff scheme is totally faulty. This document also presents an alternive, proper jpeg-in-tiff scheme
http://partners.adobe.com/public/developer/tiff/index.html This page by Adobe hosts the complete specification, and thus clearly shows the supplements have authority. The second supplement includes the alternative new jpeg-in-tiff scheme originally designed by Tom Lane.
There have been attempts at decoding old-style jpeg-in-tiff and including a proper decoder inside LibTiff. This is however not easy. The original faulty spec is unclear in several areas, simply impossible in at least one area, and breaks the encapsulating TIFF spec in several others. This lead to multiple mutually exclusive vender specific implementations, and building a decoder that reads them all is quite a challenge.
The previous attempt at old-style jpeg-in-tiff decoder was more or less abandonded, because it had multiple flaws and some vulnerabilities. It's still there, but it's not enabled by default, and I don't really recommend it.
There are plans to build and include a new old-style jpeg-in-tiff decoder in LibTiff. I have a totally newly designed approach to tackle the problem, that works fine on my test images, and I plan to translate it into the LibTiff whole and contribute it. I've tried finding funds for that project, since I simply can't really afford to spend huge amounts of time right now. If this project is important for you, perhaps you can consider contributing some funds. Also, finding testimages from as much as possible different sources is crucial to this project, so if you can, please feel free to mail me some of your files. Please use my private email address.
Joris Van Damme
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