[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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Comment(by cmbarton):

 Actually, looking at the code again, I'm pretty sure that it works as well
 with floating point values and ranges beyond 256 as it does with 8bit
 images--for the Brovey and PCA sharpening. The histogram matching routine
 accepts floating points numbers. It runs them through r.stats to create a
 0-255 histogram. So it converts them to 8bit before outputting them.

 But I don't think this is what is causing your color problems. Some images
 I ran through this in testing came out great and other did not, using the
 same resolution of image (all 8 bit in my tests). I think that the issue
 is preprocessing. IIRC, the best results come if you can estimate radiance
 (i.e., dealing with atmospheric corrections and shadows due to topography)
 at the surface and the worst come from uncorrected images.

 You can do some color correction post facto using Markus' landsat color
 correction script. But mostly you need to do a significant amount of
 preprocessing to get the best results. It would be good if someone with
 more image processing experience could weigh in and offer some insight.

 The ideal script--or perhaps better the ideal workflow--would combine a
 set of preprocessing steps with the pan sharpening. The latter is a set of
 processing algorithms that is completely ignorant of color.

 Michael

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Ticket URL: <http://trac.osgeo.org/grass/ticket/2048#comment:6>
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