I wonder wether pansharpening of each channel is necessary to classify a
QuickBird-Scene using i.maxlik and i.smap or wether I can just add the
pan channel to the group.
_If_ pansharpening is necessary: What is the best way to do it?
i.fusion.brovey and (i.rgb.his -> exchange intensity -> i.his.rgb) only
work with three channels, so I'd have to do this twice with different
combinations of channels!?
What about principal components? Is it possible to transform them back,
so I could exchange the first component?
Thanks!
Georg
I can't answer for i.fusion.brovey specifically, but generally pan-sharpening in not recommended before classification as the process of image fusion generally does not preserve the Spectral integrity of the original data. There are fusion algorithms out there that claim to preserve the spectral integrity of the input data (Smoothing Filter-based Image Modulation being one that I've considered trying to implement in Grass) but when I played with SFIM, I found that it was far from perfect (visual artifacts around strong edges and the Blue channel wasn't well correlated with the input blue channel... Atmospheric effects?). Seems there is no free lunch. FWIW, SFIM and a Local correlation fusion are implemented in OSSIM.
I'm unfamiliar with Quickbirds channels, but the panchromatic channel usually overlaps with the lower resolution multispectral channels. i.e., on landsat 7, the panchromatic band encompasses the Spectral range from 500nm to 910nm (green, red & NIR). This results in the panchromatic band being highly correlated with the green, red and NIR bands. In fact, you can do a linear combination of the three which will closely match the Panchromatic band. The end result is that the panchromatic band really doesn't add anything new to the classification and are not normally added to the classification.
Something else to consider... you could try generating texture images and incorporating them into you group.
Cheers,
Mike
On 29-Jul-09, at 2:56 AM, Georg Kaspar wrote:
I wonder wether pansharpening of each channel is necessary to classify a
QuickBird-Scene using i.maxlik and i.smap or wether I can just add the
pan channel to the group.
_If_ pansharpening is necessary: What is the best way to do it?
i.fusion.brovey and (i.rgb.his -> exchange intensity -> i.his.rgb) only
work with three channels, so I'd have to do this twice with different
combinations of channels!?
What about principal components? Is it possible to transform them back,
so I could exchange the first component?
Thanks!
Georg_______________________________________________
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