[gdal-dev] pansharpen subset of multispectral bands

[Joe McGlinchy]

There is a band_nums parameter (and weights) you can provide to gdal_pansharpen, which led to me thinking about this question in the first place.


band_nums: Optional[Sequence[int]] = None

weights: Optional[Sequence[float]] = None

So, providing either band_nums=[1,2,3,4] along with weights and extracting bands 1 and 4 after-the-fact, or band_nums=[1,4] and providing the corresponding weights for those bands, in my mind should produce something similar? I haven't tried it just yet.
________________________________
From: Barry DeZonia <bdezonia at gmail.com>
Sent: Thursday, January 9, 2025 14:04
To: Even Rouault <even.rouault at spatialys.com>
Cc: Joe McGlinchy <joe at aidash.com>; gdal-dev at lists.osgeo.org <gdal-dev at lists.osgeo.org>
Subject: Re: [gdal-dev] pansharpen subset of multispectral bands

EXTERNAL SENDER. DO NOT click links, or open attachments, if the sender is unknown, or the message seems suspicious in any way. DO NOT provide your user ID or Password.





Does that snippet of code need to be that way? It seems it could
pretty easily be changed to work a band at a time and a weight of zero
would contribute nothing. Now I do not know the domain at all and
maybe that violates some assumptions. Curious as to what you think.

On Thu, Jan 9, 2025 at 2:36 PM Even Rouault via gdal-dev
<gdal-dev at lists.osgeo.org> wrote:
>
>
> Le 09/01/2025 à 20:27, Joe McGlinchy via gdal-dev a écrit :
>
> Hello,
>
> I'm wanting to pansharpen only a subset of multispectral bands I have available. Say for instance I have blue-green-red-nir, and a panchromatic band, I can calculate the relative weights to specify when using `gdal_pansharpen` on the full multispectral dataset. If I want to only pansharpen, for example, the red and NIR bands, is it best to perform the pansharpening on the full dataset and only retain the bands I need? Or can i provide only the weights specific to the bands I want to pansharpen? If I can do the latter (which I can, given the parameter set to `gdal_pansharpen`), do I need to recalculate those weights, or only provide the subset of weights for those specific bands?
>
> Given the formula at https://gdal.org/en/stable/drivers/raster/vrt.html#gdal-vrttut-pansharpen
>
> pseudo_panchro[pixel] = sum(weight[i] * spectral[pixel][i] for i=0 to nb_spectral_bands-1)
> ratio = panchro[pixel] / pseudo_panchro[pixel]
> for i=0 to nb_spectral_bands-1:
>     output_value[pixel][i] = input_value[pixel][i] * ratio
>
>
> if you only provide a subset of the input spectral bands, you won't be able to reconstruct a plausible pseudo_panchro values, hence the scaling ratio will not be accurate.
>
>
> If your spectral dataset has bands in the R,G,B,NIR order, you can achieve what you want with:
>
>
> $ gdal_pansharpen panchro.tif rgbnir.tif,band=1 rgbnir.tif,band=2 rgbnir.tif,band=3 rgbnir.tif,band=4 out.tif -b 1 -b 4
>
> Even
>
> --
> http://www.spatialys.com
> My software is free, but my time generally not.
> Butcher of all kinds of standards, open or closed formats. At the end, this is just about bytes.
>
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/gdal-dev
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/gdal-dev/attachments/20250109/257ac975/attachment.htm>