[GRASSLIST:4086] Sharpening Lansat images

[tatel at euskalnet.net]

Hi all,

I've tried to sharpen some landsat images with HSV method to get a
Hi-Res true color composite. Not really very successful. After
sharpening, resultant colors are distorted (vegetation becomes blue)

In http://esibert.is-a-geek.net/sig/cartes/landsat/multi/compose/ I have
seen a sharpened true color composite with "good colors".

This website references to
http://www.cis.rit.edu/people/faculty/salvaggio/references/pdf/PERS1991v57n3p295-303.pdf)

This pdf document speaks about an HPF (high pass filter) method which
"distorted the spectral characteristics of the data the least" so I guess...

a)This HPF method was used to make the good color composite

b)This method seems to be the same as FF (filter fusion) method in
http://wwwcs.uni-paderborn.de/cs/ag-kao/de/persons/kao/pdfPapers/osee.pdf
where I've found this equation:

HiResImg=i.ifft{LPF{i.fft(LowResImage)+HPF{i.fft(PanImg)}}

However i.fft gives me a "ERROR: G_malloc: out of memory" message when
usin region settings from low-res raster, and gives me a segmentation
fault when using region settings from pan raster.

Not using i.fft and i.ifft works but gives me very ugly results

Questions are:

1) Is there really a sharpening method without color distortion?
2) Is this HPF method woeful?
3) What could I do?

Thanks in advance

Roman