Am 29.06.2010 18:23, schrieb Chaitanya kumar CH:
Stefan,
I haven't tested the script but doesn't the current code copy the
alpha band? If it does, it might be more preferable to copy all the
pixels and the alpha band.
Yes the current code copies the alpha band, but it uses the same nodata
settings as the other bands.
This gets interesting if I want to merge overlapping images which define
their valid area by an alpha channel. In the current code, I would have
to specify nodata=0 to get the alpha channel to merge correctly. This is
counterintuitive, as I expect images with alpha to merge correctly
without specifying a value for nodata.
If nodata isn't specified the merged alpha of overlapping images is
incorrect (as opaque areas get overwritten with the transparent parts
(nodata) )
Please create a ticket at http://trac.osgeo.org/gdal/newticket and
attach your patch.
Done... http://trac.osgeo.org/gdal/ticket/3669
Regards
Stefan
On Tue, Jun 29, 2010 at 8:19 PM, Stefan Klug <[email protected]
<mailto:[email protected]>> wrote:
Hi,
gdal_merge.py doesn't handle tiff files with alpha masks so I've
added this functionality.
My patch changes the behaviour of gdal_merge as follows:
- If a band is recognized as Alpha Band it is automatically
treated as having a NODATA value of 0.
I'm not sure if this is the way to go. But it makes some sense, as
the resulting alpha channel is a correct alpha merge, independent
of the nodata value used for the other bands.
- If a band has mask flag GMF_ALPHA set, the mask band controls
the parts that get written to the destination
Would be great if someone could review and possibly checkin the patch.
Regards
Stefan
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Best regards,
Chaitanya kumar CH.
/tʃaɪθənjə/ /kʊmɑr/
+91-9494447584
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