I have a tif image of soil thorium content (ppm) measured by gamma aerial spectroscopy. The original file is a 8 bit RGB image set in a rainbow-similiar pallet (blue>green>yellow>red>magenta). I have a jpg file about the legend, which was attached with the original file. The thorium content ranges from 2 (blue) to 36 ppm (Fig. 1).

enter image description here

For modelling purposes, I want to convert this RGB file to a single raster of thorium content. I have already tested the a processing module of QGIS:

Raster > Conversion > RGB to PCT

The module transformed to a single band, but it produced a palleted band containing a unsorted color ramp (Fig. 2)

Fig. 2

Could I sort the color ramp and reclassify the raster values to match with the original values from the jpg legend? If it is possible, how could I sort the colors?

Is there another way to transform the RGB image to a gray-scale single band?

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.