2002.03.20 16:37 "Changing Orientation Tag", by Erika Nesse

2002.03.23 05:38 "Re: Changing Orientation Tag", by Tom Lane

I would lay the blame for this inconsistency in viewer behaviour on the Tiff 6.0 spec itself, which states:

"[The Orientation tag] is recommended for private (non-interchange) use only. Most images are scanned and stored in the Orientation = 1 format, and most TIFF readers can only handle this case."

It makes me wonder why this tag was even included in the spec.

TIFF has always been designed on the principle that the writer can write anything he damn pleases, and perhaps the reader will be able to make sense of it. Look through the spec: surely 75% of it describes features that a run-of-the-mill reader would be unable to cope with. (Show me a reader that will do something sensible with YCbCr, associated-alpha, 32-bit-float-sample images... to take just one example. If you say your code can handle that nicely, I'll start asking about tiles, padding, downsampling, and planar configuration.)

I think the spec is being quite honest here to tell you what part of the described feature set is actually likely to be portable.

If this approach to compatibility doesn't thrill you, perhaps you should consider another file format. For instance, PNG, which was designed in large part on the principle that TIFF blew this issue badly. The PNG spec expects that every reader should be able to do something sensible with every PNG file, which is certainly not the design assumption of TIFF. On the other hand, you can't stick a YCbCr, associated-alpha, 32-bit-float-sample image into a PNG. You pays your money and you takes your choice...

regards, tom lane
organizer, Independent JPEG Group
member, PNG development group
onetime member, TIFF advisory committee