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
--- /home/stefan/src/gdal-1.7/swig/python/scripts/gdal_merge.py 2010-06-29 12:50:04.000000000 +0200
+++ gdal_merge_with_alpha.py 2010-06-29 16:46:51.000000000 +0200
@@ -27,9 +27,11 @@
try:
from osgeo import gdal
+ from osgeo import gdalconst
gdal.TermProgress = gdal.TermProgress_nocb
except ImportError:
import gdal
+ import gdalconst
import sys
import glob
@@ -44,6 +46,15 @@
t_fh, t_xoff, t_yoff, t_xsize, t_ysize, t_band_n,
nodata=None ):
+ s_band = s_fh.GetRasterBand( s_band_n )
+ if s_band.GetMaskFlags() & gdalconst.GMF_ALPHA:
+ return raster_copy_with_mask(
+ s_fh, s_xoff, s_yoff, s_xsize, s_ysize, s_band_n,
+ t_fh, t_xoff, t_yoff, t_xsize, t_ysize, t_band_n )
+
+ elif s_band.GetColorInterpretation() == gdalconst.GCI_AlphaBand:
+ nodata = 0
+
if nodata is not None:
return raster_copy_with_nodata(
s_fh, s_xoff, s_yoff, s_xsize, s_ysize, s_band_n,
@@ -55,7 +66,7 @@
% (s_xoff, s_yoff, s_xsize, s_ysize,
t_xoff, t_yoff, t_xsize, t_ysize ))
- s_band = s_fh.GetRasterBand( s_band_n )
+
t_band = t_fh.GetRasterBand( t_band_n )
data = s_band.ReadRaster( s_xoff, s_yoff, s_xsize, s_ysize,
@@ -93,6 +104,36 @@
t_band.WriteArray( to_write, t_xoff, t_yoff )
return 0
+
+# =============================================================================
+def raster_copy_with_mask( s_fh, s_xoff, s_yoff, s_xsize, s_ysize, s_band_n,
+ t_fh, t_xoff, t_yoff, t_xsize, t_ysize, t_band_n ):
+ try:
+ import numpy as Numeric
+ except ImportError:
+ import Numeric
+
+ if verbose != 0:
+ print('Copy %d,%d,%d,%d to %d,%d,%d,%d.' \
+ % (s_xoff, s_yoff, s_xsize, s_ysize,
+ t_xoff, t_yoff, t_xsize, t_ysize ))
+
+ s_band = s_fh.GetRasterBand( s_band_n )
+ m_band = s_band.GetMaskBand()
+ t_band = t_fh.GetRasterBand( t_band_n )
+
+ data_src = s_band.ReadAsArray( s_xoff, s_yoff, s_xsize, s_ysize,
+ t_xsize, t_ysize )
+ data_mask = m_band.ReadAsArray( s_xoff, s_yoff, s_xsize, s_ysize,
+ t_xsize, t_ysize )
+ data_dst = t_band.ReadAsArray( t_xoff, t_yoff, t_xsize, t_ysize )
+
+ mask_test = Numeric.equal(data_mask, 0)
+ to_write = Numeric.choose( mask_test, (data_src, data_dst) )
+
+ t_band.WriteArray( to_write, t_xoff, t_yoff )
+
+ return 0
# =============================================================================
def names_to_fileinfos( names ):
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