[GRASS-dev] [GRASS GIS] #2048: i.pansharpen limited to 8-bit imagery

[GRASS GIS]

#2048: i.pansharpen limited to 8-bit imagery
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 Reporter:  nikosa                                                     |       Owner:  grass-dev@…              
     Type:  defect                                                     |      Status:  new                      
 Priority:  normal                                                     |   Milestone:  7.0.0                    
Component:  Imagery                                                    |     Version:  svn-trunk                
 Keywords:  i.pansharpen, sharpening, fusion, brovey, ihs, pca, 8-bit  |    Platform:  Unspecified              
      Cpu:  All                                                        |  
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 Getting 11-bit IKONOS bands pan-sharpened by using i.pansharpen works only
 if the bands are rescaled to 8-bit, i.e. to range inside [0, 255]. In this
 case, color re-balancing (i.e. of Blue, Green and Red fusion-ed with Pan
 -IKONOS spectral bands) after the sharpening appears acceptable.


 Any other attempts using out of [0, 255] range values, for example using
 Top-of-Atmosphere Reflectances (floating point values < 1.0)  or  the raw
 IKONOS bands that range between [0, 2047], are not successful.


 Rescaling, however, might lead to some loss of spectral information (?).
 Hence, it may not be desired as pan-sharpening should not be limited in
 creating nice looking (pseudo-)color composites for viewing tasks (i.e.
 image interpretation) or printing. Sharpened/Fusioned images might as well
 be used as an input for segmentation/classification etc.


 Looking at the i.pansharpen source code ([http://lists.osgeo.org/pipermail
 /grass-user/2013-July/068700.html as suggested by Moritz Lennert in the
 grass-user mailing list]) ''I see that in all algorithms a function for
 histogram matching is called and IIUC, in that function, values seem to be
 limited to [0,255]''.

 Related code(lines):
 [http://trac.osgeo.org/grass/browser/grass/trunk/scripts/i.pansharpen/i.pansharpen.py#L348
 def matchhist] and
 [http://trac.osgeo.org/grass/browser/grass/trunk/scripts/i.pansharpen/i.pansharpen.py#L379
 arrays[i] = np.zeros((256,),dtype=('i4,f4'))]


 Not sure if this is a defect or an enhancement request.  Many of the High
 Resolution images are frequently delivered in >8-bit formats.

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Ticket URL: <http://trac.osgeo.org/grass/ticket/2048>
GRASS GIS <http://grass.osgeo.org>