Reverse colour-ramped DEM to its original elevation value?

Question

A have a GeoTIFF LIDAR image which display DEM in its color-ramp version (color relief) from blue (minimum value) to red (maximum value) and green (in between).

I don't have the original elevation data.

Is there any application or algorithm to turn this 'color coded' maps into its original DEM? (elevation data).

Suppose from another measurement, I know the elevation at multiple point in the DEM to reference the color-map. (or in case I'm sure that some region is the sea, I'll assign zero to it).

Answer 1

I believe it is possible, but probably not very accurate. Multiple elevations do not have same RGB value if the ramp is continuous and not like having red at both extremes.

I would probably start by reducing the number of colors and saving the result into a paletted image by using rgb2pct-py. Then, I would vectorize the paletted version with gdal_polygonize. Last step would be to attach height values into the polygons and that would require some manual work with for example QGIS. The polygons will have at this stage the source color as an attribute which saves works because all polygons with the same palette entry can be joined to corresponding height range by the same.

The result depends on how well the color ramp that is used in your maps suits for polygonization.