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I'm using Grass 6.4.3 in Linuxmint 16. I don't have a very big problem but I'm trying to understand what is Grass doing, if I'm applying the process correctly and if there is something wrong with my image files.

I'm trying to pansharpen a SPOT image. I have two files, one the panchromatic band and the other is the multiband file.

I import them to grass as, for example, 'spotimage.pan' (panchromatic) and the other file is automatic named by grass as 'spotimage.1', 'spotimage.2', 'spotimage.3' and 'spotimage.4'.

I think that in the original file, the bands order is inverted, I mean that the first band is NIR, the second one is Red and the third one is Green. This is because original image composite was done in order to obtain a false color image when is displayed as R,G,B = B1, B2, B3

So, if I do

d.rgb -o red=spotimage.1 green=spotimage.2 blue=spotimage.3

I obtain a false color view of the image.

Then, to pansharpen the image I use

i.fusion.brovey -s ms1=spotimage.3 ms2=spotimage.2 ms3=spotimage.1 pan=spotimage.pan outputprefix=spotimage.pansh

I inverted the order, where I should use the SPOT Band 1, I'm using the band 3 of my image and where I should use the SPOT Band 3, I'm using the band 2 of my image.

This because, in the dialog box of i.fusion.brovey, where it says "Name of input raster map (green: tm2 | qbird_green | spot1)" I suppose I have to use the name of the SPOT Band 1 and, where it says Name of input raster map (MIR; tm5 | qbird_red | spot3)" I suppose I have to use the name of the SPOT Band 3.

Is it correct?

The output are three raster files: pansh.red, pansh.green and pansh.blue.

But I cannot manage to obtain again a false color view with any combination of these pansharpened bands.

What am I doing wrong?

Are pansh.red the "pansharpened version" of spotimage.2, pansh.green the pansharpened version of spotimage.3 and pansh.blue the pansharpened version of spotimage.1? Remember thar the bands order is inverted.

Should I use i.landsat.rgb? Can I use it with a SPOT image?

  • I think you've done everything right so far. All you need now is r.composite to get a three band colored image. And the result ("false color" or "true color") Depends on which of the original bands you choose. – Micha Jun 28 '14 at 11:10
  • Thanks Micha, I'm trying r.composite and i.group to obtain a multiband pansharpened image. – Lucas Jun 30 '14 at 15:27
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First of all, you should note that the brovey algorithm implemented in GRASS only works with 3 bands, and you have 4 bands. So, if you want to have four bands you need to to run it twice (once with b1,B2, B3, then once with B2,B3,B4). You then combine the B1,B2,B3 of the first run with the B4 of the second run using r.composite.

Concerning the order of the band, it is not important for the final result to assign a particular order. I would therefore recommend that you keep the same order as in the original image, so that anyone can find the good band order by knowing that is is SPOT.

Finally, you have no blue band in SPOT, so you can't create a true color composite. The output blue , green and red correspond to the input b1,b2 and b3.

As a remark, brovey assumes that the panchromatic band is the sum of the other band, but in fact with SPOT it only covers the first two bands, so Brovey is not the best method.

  • Thanks radouxju, I'll follow your advice to pansharpen the four bands. – Lucas Jun 30 '14 at 15:28

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