I have a raster layer in QGIS that is stored as a three color image. I want to do some analyses on it and would like to have it just as values 1,2,3 (and then I can leave the presentation to later)
The raster is red, yellow, green and the band values are
255,0,0 0,245,0 240,240,0
So I should be able to use either the red band or the yellow band to extract my information.
This could easily be coded as
value=redband.value if value==255: return(3) if value==240: return(2) if value==0: return(1)
To return red yellow and green as 3,2 and 1 respectively.
But in the field calculator, I can only see how to do mathematical expressions. Is it possible to run a script in the field calculator or do I have to rewrite this as a python script to run in the python console?
(I know it possible to turn a raster with only three distinct values into a polygon layer, but due to the structur of the raster, the polygon gets quite unwieldy and the analysis I am going to do on this later requires a raster)