[gdal-dev] Extracting Subsampled Mask Band from VRT Returning 1st Band Rather Than Mask Band

[Patrick Young]

Hi all,

I'm experiencing some strange behavior when extracting a mask band using
gdal_translate from a VRT vs the source GTiff at a reduced resolution.  I
have a 3 band, 8 bit JPEG compressed (YCbCR) RGB geotiff with an internal
no data mask and with internal overviews.  Making a VRT of this and running

gdal_translate -b mask in.vrt mask.tif


Returns the expected no data mask.

However, if I add in "-outsize 10% 0", I instead get the first band back as
the mask tif rather than the mask band.  Any -outsize setting has the same
effect.

Repeating this with the source geotiff rather than the vrt works as
expected.

Interestingly, running

gdalinfo -oo OVERVIEW_LEVEL=1 in.vrt

reports no mask flags set at all (they are reported without the -oo
option), but running on the original geotiff rather than the vrt does
report the mask flags.

Anyone have thoughts on what the VRT driver is doing?

Thanks,
Patrick
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