Paul Shapley wrote:
I want to use the following Landsat 8 workflow to obtain some
pansharpened
images but have a problem when i convert the DN values to 8bit for
pansharpening. Here is my preferred workflow in Grass 7.0.0RC2.
· r.in.gdal (success)
· i.landsat.toar (success)
· r.rescale bands 432 & 8 (convert reflectance
'DN'
values to 0-255, 8bit)
· i.pansharpen bands 432 with 8
· r.rescale (convert 0-255 values back to
reflectance
'DN)
· i.colors.enhance (pansharp bands)
· d.rgb
My question...is this a valid workflow? because i'm getting the same
two
errors below and the images when displayed look solid grey when
viewed with
d.rgb:
Paul,
just some thoughts:
- why mix the term "Digital Number (DN)" with Reflectance? DN's are
(supposed to be) the result of the quantisation (and calibration) of the
energy that hits the sensor. And Reflectance (unitless) is the result
of radiometrically processing the DN values.
- Not sure if the values of the end-product, as in the work-flow you
outline above, can be called Reflectance.
- Landsat8 is 16-bit. Once you downscale down to 8-bit, how would you
come back to the 16-bit details? I think the radiometric detail is
lost.
Instead, import > DN to ToAR > Pan-Sharpen with i.fusion.hpf (to not
loose the fine digits which are important if you seek for more than just
sharp visuals for viewing purposes).
Best, Nikos
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