During the process georeferencing a Grayscale image, the image must be converted to a RGB image (-expand rgb -ot Byte) before calling gdal_translate setting the GCP's.
After gdalwarp, the image is of course then RGB (3 Bands) - and is rendered looking as a Grayscale image in QGIS My question is: how to convert this back to the original Grayscale? I assume, during the '-expand', the gray values have been separated into the 3 bands according to some default logic so that it renders as a Grayscale image when viewed. I have seen samples of converting a (truly) coloured image to Grayscale: gdal_calc.py -A input.tif --A_band=1 -B input.tif --B_band=2 -C input.tif --C_band=3 --outfile=result.tif --calc="A*0.2989+B*0.5870+C*0.1140" Would it be something in this form? Mark Johnson, Berlin, Germany
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