[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 mlennert):

 Replying to [comment:5 nikosa]:
 >  However, I'd like to kindly ask again if it is possible to alter the
 documentation?  It is not a nice surprise trying to work with i.pansharpen
 and getting strange colors or empty images as a result.  See also
 [http://gis.stackexchange.com/q/39174/5256].  At least mention the current
 limitation or... other ideas?  Then again, it is in G7, the development
 version :-)

 I just (r57332) added a sentence to the NOTES section about the module
 currently working only for 8-bit images.

 Several remarks to justify that:

 - The histogram matching algorithm in the module is limited to 8-bit as it
 reclasses only sources values between 0 and 255 to target value between 0
 and 255 (it also calls r.stats with the -i flag, and so rounds everything
 to integer, IIUC). In other words, any values above 255 silently ignored !
 To check, just comment out line where the temporary histogram matched
 (reclassed) images are g.removed. As the histogram matching is used in all
 three algorithms, they are all limited to 8-bit.

 - the i.rgb.his/i.his.rgb modules are also limited to 8-bit, AFAIK. There
 is an old ticket with a patch proposed by Hamish on that: #774. See also
 [1]

 So, in conclusion, to be able to use i.pansharpen with >8-bit images, the
 histogram matching algorithm needs to be rewritten. You could try to just
 skip the histogram matching part (just comment out the relevant call to
 the function and replace the panmatch images by the pan image and see what
 happens (I'll have to read up on the theory again to understand why
 histogram matching is necessary here).

 You can also apply the brovey or pca method yourself using r.mapcalc and
 i.pca.

 [1]  http://lists.osgeo.org/pipermail/grass-
 user/2009-September/052573.html

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Ticket URL: <https://trac.osgeo.org/grass/ticket/2048#comment:13>
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