[PATCH] gdal_merge.py alpha mask

[stefanklug]

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

[Jukka Rahkonen]

This patch has never been reviewed.

[fxthomas]

The patch worked for me on GDAL 1.10.1, so +1. The raster files I work on generally have alpha masks, which makes gdal_merge.py unusable for most of my use cases.

[Even Rouault]

trunk r29213 "gdal_edit.py: take into account alpha band to avoid writing zones of source images that are fully transparent (#3669, derived from patch by stefanklug)"

[Even Rouault]

Above changeset caused regression. See #6067

[Even Rouault]

Milestone renamed