RichardScottOZ

Ripping data from pseudocolour images

Because viridis, like all good colourmaps, is perceptually linear, it's easy to get the data from it: just use a greyscale version of the image. But you can rip the data from any pseudocolour image if you know (or can guess) the colourmap.

In the rip-data.py example, here's the approach:

Read the image and transform the values to the range 0-1.
Guess the colourmap, in this case it's viridis. Matplotlib conveniently gives us the RGB triples that make up a colourmap.

	import logging
	import subprocess as sp
	import tempfile
	import threading

	import geopandas as gpd
	import numpy as np
	import rioxarray
	import xarray as xr
	from rasterio.enums import Resampling

	#!/bin/sh

	log() {
	format="$1"; shift
	# shellcheck disable=SC2059
	>&2 printf "$format\n" "$@"
	}

	usage() {
	>&2 cat <<EOF