Converting .hgt files to 16bit PNG does not work

[trnrez]

If I use "gdal_translate -ot Int16 -of PNG infile.hgt outfile.png" I get an 8 bit grayscale image. If I use "gdal_translate -ot UInt16 -of PNG infile.hgt outfile.png " I get a 16 bit grayscale image but appears to be pure black.

Please review the FWTOOLS thread for perhaps a better explanation.

 http://lists.maptools.org/pipermail/fwtools/2009-January/001474.html

If you need my help in any other way please let me know.

Thanks, Jonathan Jones

[rouault]

For the first point, "-ot Int16", the result you observe is expected. The PNG driver only handles Byte and UInt16 data types, and in the other cases (silently) defaults to Byte. If you add '-strict' to the command line, you'll get an explicit error message and no conversion. But I agree that in the not strict case, a warning would be appropriate and that's what I've added in trunk in r16192.

For the second point, "-ot UInt16", I've displayed the resulting PNG with OpenEV and it looks fine. I would suspect that you use a viewer that doesn't support 16bit PNG. But 16bit PNG are an uncommon formulation of PNGs, and more generally most general-purpose image viewers don't support 16bit images. Perhaps if your aim is just to colorize the DEM as grayscale, you could use the '-scale -ot Byte' options of gdal_translate so that to remap properly the dynamics of your input data to 8bit.

So I'm closing this ticket. Please reopen if necessary.