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2007.01.17 18:35 "Re: Elevation Data", by Joris Van Damme
Frank, Frank Warmerdam wrote: > Joris wrote: > > In any case, when it comes to a recommendation for writers, would > > you agree that recommending them to stick with the 'intrinsic' > > range of the samples, as I explained it, is best and most likely to > > lead to good interchange (as far as there is interchange of > > floating point image data, at all)? > > floating point *elevation* data! Yes, I am confused on this issue, due to lack of knowledge of your sort of application. I would expect you guys were writing this sort of thing as an extra sample, tagged as Undefined, as as to accompany a colour image of the same area or something. But the original poster seemed to imply the elevation data he was seeking to write was covered under the MinIsBlack photometric, thus leading me to think you write greyscale data to be re-interpreted as elevation data by those apps that know its intention. Which is it? > rescaling in the file to some "natural image range" loses all the > value of the actual elevations. We've Celsius and Fahrenheit, and metres and foot, and as long as we're talking floating point I take that to mean rescaling doesn't lose anything. We're coding the Cb and Cr channels of YCbCr with an offset, so as to loos the inconvenience of the sign, but not really loos at as we know what it means and agree on the encoding. That is no doubt a very naive point of view, stemming from lack of knowledge of your application. But I'm eager to find out more. Best regards, Joris Van Damme info@awaresystems.be http://www.awaresystems.be/ Download your free TIFF tag viewer for windows here: http://www.awaresystems.be/imaging/tiff/astifftagviewer.html