[GRASSLIST:4088] Re: Sharpening Lansat images

[Ian MacMillan]

The method that I have used with the most success is i.rgb.his, then  
i.his.rgb.  The colors sometimes get a little screwy, but usually  
playing with the resultant bands using d.histogram and r.rescale can  
give you something useful.  An order of operations that I have used is  
below to produce a fairly decent "true" color image with landsat.

combine bands 2 and 4 for more vivid greens and blues with

g.region rast=band2
r.mapcalc band2and4 = '(band2 + band4)/2'

i.rgb.his red_input=band3 green_input=band2and4 blue_input=band1  
hue_output=hue saturation_output=sat intensity_output=int

g.region res=15
i.his.rgb hue_input=hue saturation_input=sat intensity_input=band8  
red_output=red green_output=green blue_output=blue

r.colors color=grey map=red
r.colors color=grey map=green
r.colors color=grey map=blue

d.rgb r_map=red g_map=green b_map=blue

if things look a little off, use

d.erase blue
d.histogram red
then look at the curve and note where it drops off to zero on both  
ends.  rescale your image with
r.rescale input=red output=red.rescale from=xx,xx to=0,255
repeat for blue and green

Good luck,
Ian

On Aug 3, 2004, at 11:55 AM, tatel at euskalnet.net wrote:

> 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
>
>
>