2005.04.26 18:27 "Re: [Tiff] TIFF Technote 3, draft 2", by Chris Cox
I can provide a recommendation about range for viewing - but that's about all it is.
1.0 should be diffuse white in the scene, specular highlights can go over -- this matches typical camera behavior and provides a useful image to preview using a trivial (1.0 -> 255, 0.0 -> 0) mapping.
Converting is another story, and optimal conversions are VERY >image dependent when dealing with HDR data.
To make floating point a more meaningful format within the tiff spec, it would be nice to shift away from the simple 0.0 -> 1.0 mapping approach to a real world scene reference.
Again, it is not a requirement, just a suggestion to make previews more efficient (so the preview application/OS does not have to know about toning algorithms to get a reasonable representation of the image).
Most floating point data have some kind of reference to what 1.0 means, or simply expect the data representing some physical unit (cd/sqr meter or the like). The stonits tag make sense with unconverted XYZ data, while XYZ data are not covered directly by the current tiff spec.
You can store XYZ as an RGB image, with an XYZ ICC profile attached (takes less than 100 bytes).