2001.10.26 20:54 "Re: 16-bit ICC L*a*b* ?", by Martí Maria
There are two photometric tag values for Lab color in TIFF.
value 8 is defined as "1976 CIE L*a*b*"
value 9 is defined as "ICC L*a*b"
That is!. Seems Dwight Kelly discovered the difference. I'm sending to you a small TIFF16 I have. It is labeled as Photometric 8. I'm pretty shure your big image is labeled as Photo=9. So, using ICC encoding. That is, an offset of 128 applied to a, b. Photo 8 is using the signed word way. Or at least that is what seems.
Pfew!, if this is the case, seems I can avoid your 30Mb sample ;-)