[GRASS-user] unexpected i.pansharpen results

[Moritz Lennert]

On Mon, July 29, 2013 01:45, Nikos Alexandris wrote:
> Eric Goddard wrote:
>
>> > I gave up on that pansharpening attempt. I can test some of my imagery
>> > tomorrow and let you know if I still have issues with it.
>
> Nikos Alexandris wrote:
>
>> [rest deleted]
>>
>> I can't get any decent looking colors, with any of the methods.  I
>> wonder if
>> my images are not properly "aligned" or the like. PCA seems to approach
>> it
>> right -- the value ranges seem to fit the reflectance scheme (below 1.0)
>> but the colors are so fancy... ?
>>
>> Will work on it later in the evening.
>
> To-day/-night I got it to work with 11-bit images!  I rescaled them to [0,
> 255] and that seems to work just fine.  Even color rebalancing (i.e. of
> Blue,
> Green and Red fusioned with Pan -IKONOS spectral bands) after the
> sharpening
> appears acceptable.
>
> A bit skeptical though since the rescaling action throws away some of the
> data's details... :-?
>
> All of my other attempts using out of [0, 255] range values, for example
> using
> Top-of-Atmosphere Reflectances (floating point values < 1.0)  or  the raw
> IKONOS bands that range between [0, 2047], were not successful.
>
> So, does i.pansharpen expect only 8-bit images?  Can someone confirm or
> reject?


Looking at the i.pansharpen source code, I see that in all algorithms a
function for histogram matching is called and IIUC, in that function,
values seem to be limited to [0,255].

Maybe you should open a ticket on that.

Moritz