2007.01.17 03:35 "Re: [Tiff] Elevation Data", by Frank Warmerdam

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).

Craig,

I just set photometric interpretation to min-is-black and leave it up to the application to find a reasonable way of displaying the elevation values. Simple "photo" programs will likely not show the result well, but general purpose scientific raster displaying problems will know how to handle unusual data ranges.

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?

I have no wisdom here.

Best regards,
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