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<font face="Times New Roman, Times, serif">Hi,<br>
<br>
I have a set of unreferenced RGB images with black borders I want
to cut off. I do this by adding a fourth alpha band to the image
when warping it, and filling this with 255 within the data
rectangle, and 0 outside, using gdal_rasterize ( I have the exact
georeferenced boundaries of the image as vector data). Nothing
happens. When I do the same thing for the first three bands,
results are as expected, but whatever I do with the fourth band
has no effect at all.<br>
<br>
Theoretically, this should work, but is there a problem with
gdal's implementation of alpha transparency? The following post
seems to suggest it:<br>
<br>
<a moz-do-not-send="true" class="moz-txt-link-freetext"
href="http://osgeo-org.1803224.n2.nabble.com/gdal-dev-Need-help-generating-output-with-alpha-channels-using-Python-API-td6169886.html">http://osgeo-org.1803224.n2.nabble.com/gdal-dev-Need-help-generating-output-with-alpha-channels-using-Python-API-td6169886.html</a><br>
<br>
I didn't try out the suggested solution yet, as I would prefer the
simpler method above. Is there really a problem with gdal's
handling of alpha transparency, or is there another workaround?<br>
<br>
Jan<br>
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