Hi Rob,
I can't think an easy way of doing what you want.
Well, you can definitely do that using a VRT Python pixel function, that
would essentially do your --calc expression
Cf
https://gdal.org/drivers/raster/vrt.html#using-derived-bands-with-pixel-functions-in-python
The example of
https://gdal.org/drivers/raster/vrt.html#vrt-that-adds-2-or-more-rasters
is probably the closest starting point. (you can add <SourceBand> to the
<SimpleSource>'s to specify bands 1 and 4)
A nice exercice for (Pythonist) contributors would be to add a -f VRT
capability to gdal_calc.py that would essentially automate the writing
of such VRT using Python pixel functions. Just saying...
Even
Le 19/01/2024 à 17:40, Robert Coup via gdal-dev a écrit :
Maybe it's just Friday, but I could use a pointer here :-)
My input raster is a RGBA byte image, where the alpha channel value is
0 or 255 (ie: effectively a mask). The output is ideally a VRT file,
RGB with Int16 data type, using nodata=-1.
So I want to convert the alpha channel to a nodata value.
The alpha/nodata/mask/band options to translate/warp haven't got me
very far, neither has hand-crafting various UseMaskBand/MaskBand
elements in a VRT.
I can do it to concrete tif files with something like this,
repeating for R,G,B and merge the output bands together, but it's a
lot of processing.
gdal_calc.py -A src.tif -B src.tif \
--outfile out_b1.tif --co TILED=YES --type=Int16 --NoDataValue=-1 \
--A_band=1 --B_band=4 --calc="where(B >= 128, A, -1)"
I feel like I'm probably missing a simpler path? (Which I will
definitely add to an Examples section somewhere)
Thanks,
Rob :)
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