Hello,
I'm having some difficulties understanding how to get GDAL to generate images
with usable alpha channels. I have 3-channel RGB input JPEG image, delivered to
GDAL as a VRT with a projection and ground control points, which I'm warping to
an output that's no longer rectangular, leaving background areas exposed. Here
is an example output:
http://things.teczno.com/gnomotile.png
The black parts are intended to be transparent, but I haven't been able to
understand how to make that work. Here's the relevant part of my Python code:
http://dpaste.com/hold/500308/
I've tried to switch to a four channel output which gets me what I think are
CMYK channels. I've tried to use SetNoDataValue on the destination bands to
make the background purple so it can be easily knocked out. I've tried to
create the GTiff output dataset using the ALPHA=YES creation option, but it
seemingly doesn't make a difference. None of these ideas has worked - does
anyone have any ideas on how the Python API can be used to create transparent
output?
-mike.
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michal migurski- [email protected]
415.558.1610
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