[gdal-dev] gdalwarp alpha band resampling bug
even.rouault at spatialys.com
Fri Sep 17 16:18:40 PDT 2021
I can't reproduce the issue you describe. There's not a single white
pixel in the output image (the max of the green and blue bands is <
255). But I suspect this could be related to a pre-existing
composite-bl.tif file you might have. gdalwarp doesn't overwrite by
default the output image. It blends into it. If you add -overwrite, you
should get a reasonable output.
Le 18/09/2021 à 01:06, Patrick Young a écrit :
> I've found behavior in gdalwarp related to compositing an image with a
> variable alpha band. Under bilinear resampling, the alpha compositing
> in areas where the alpha band is between 0 and 255 results in
> completely white pixels.
> To reproduce, I've first grabbed a rgba image from the test suite, e.g.:
> gdal_create -ot Byte -bands 3 -burn 71 147 240 -outsize 162 150 -a_srs
> EPSG:3857 -a_ullr 0 162 150 0 background.tif
> gdal_translate -a_srs EPSG:3857 -a_ullr 0 162 150 0
> stefan_full_rgba.tif foreground.tif
> gdalwarp -r bilinear background.tif foreground.tif composite-bl.tif
> In this case, composite-bl.tif is white wherever the alpha is in [1,
> 254]. Trying
> gdalwarp background.tif foreground.tif composite-nn.tif
> produces a reasonable image, although it is blocker than when I
> overlay background.tif and foreground.tif in qgis.
> Thanks for any tips about what I'm seeing, happy to file a bug if it
> is one! I've tested this on gdal 3.2.2 on macos (from brew).
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
My software is free, but my time generally not.
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