2005.04.11 00:03 "[Tiff] TIFF Technote 3, draft 1", by Chris Cox

2005.04.26 17:26 "Re: [Tiff] TIFF Technote 3, draft 2", by Kai-Uwe Behrmann

Is it possible to provide recommendations for this without stepping on someone's toes?

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.

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. Alternatively the range description, suggestion by Bob, can be extended to add a physical value to the lower and upper 'normal' bounds.

The physical units often have no relationship to ideal default "viewing" parameters for a computer display. For RGB data it is useful to know a recommended "black point" and "white point" for the image. It is also useful to know the normal range of the data. The image data is scaled for display so that values under the black point are "black" and values over the white point are "white". This is of course only a crude approximation but it is better than nothing.

The word 'Alternatively' used by mine was somewhat missleading.

I want suggest an additional information, providing a physical unit for all those image values. Maybe gradiation information is needed then as well if the image is not linear.

Applications, which dont know how to handle physical units in this context, can simply ignore and use instead "black point" and "white point", which referes to 'image values used as black' and 'image value representing diffuse white'.

Thanks for pointing out.

Kai-Uwe Behrmann
                                + development for color management
                                + imaging / panoramas
                                + email: ku.b@gmx.de
                                + http://www.behrmann.name