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January 2007
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2007.01.17 02:25 "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? --------------------------+----------------------+-------------------------- 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/ --------------------------+----------------------+-------------------------- "Sixteen exabytes ought to be enough for anybody."