[gdal-dev] gdal2tiles.py of transparent background vrt/png gives black background tiles

John W. Glendening glendening at drjack.net
Mon Apr 24 16:25:27 PDT 2017

And finally I have kludged myself to a solution by using flags -type
Truecolor -depth 8 in my ImageMagick TIF creation, which produces only 3
bands.  Altering the vrt accordingly, and using -a 0,0,0 in
pdal2tiles.py, I get the expected result.  This has the effect of
removing any pure black in the overlay, but that is not significant for
my case.  

Still, I would hope to find a cleaner solution.  In particular, since in
my pre-kludge case I start from a RGBA TIF and since gdal2tiles.py
produces RGBA PNGs, I would have thought I could get an overlay which
has a partial opacity.  My original case did have one partial opacity
polygon, which I removed after I learned that only a 0/1 opacity
solution was possible.  I can live without that, but it does surprise me
that there appears no way to pass on the TIF opacity to the PNG opacity.

John Glendening

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