2007.01.17 02:25 "[Tiff] Elevation Data", by Craig Bruce

I would like to write signed 16-bit elevation data to a TIFF image file, but according to the TIFF 6.0 specification, there doesn't appear to be a correct way to do this. The specification allows the use of the SampleFormat to specify that the samples are signed 16-bit integers, but this range of values is incompatible with the PhotometricInterpretation tag, which must be present. The obvious PhotometricInterpretation to use is BlackIsZero, but its range is defined as 0 to 2**nbits-1 (i.e., unsigned integers).

So, how does one make a correct image using a SampleFormat other than unsigned integer? What is the most compatible incorrect approach?

Also, is there a semantic difference between SMinSampleValue and MinSampleValue? The spec explicitly states that MinSampleValue is just statistical and isn't part of a valid-sample-range definition, but it's much more coy about SMinSampleValue. If it isn't part of a hard range definition, then how can one make an interoperable image with floating-point samples?

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Dr. Craig S. Bruce        | Ph 819-771-8303 x205 |             CubeWerx Inc.
Senior Software Developer |   Fax 819-771-8388   |  Gatineau, Québec, Canada
csbruce@cubewerx.com      |  http://csbruce.com/ |  http://www.cubewerx.com/
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             "Sixteen exabytes ought to be enough for anybody."