[gdal-dev] pansharpen subset of multispectral bands

[Joe McGlinchy]

Thank you, Even!

In the event that we are provided only 4 bands, but from an 8-band system, will this still hold? It is what we have to work with, unfortunately or not.

-Joe
________________________________
From: Even Rouault <even.rouault at spatialys.com>
Sent: Thursday, January 9, 2025 13:24
To: 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


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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

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