How to build elevation scale from an RGB map?

Question

I need to build a correspondence map between colors and altitudes. The elevation file has blue color for sea and green/yellow/brown colors for elevation. The advice says:

Find the pixel of the Mont Blanc (4810 m).

I'm working with Python. I don't know how to solve this. I converted the map into a NumPy array of shape (2860,4490,3) with RGB values and want to transform into (2860,4490) with elevation value in meter.

Answer 1

Convert the RGB image to HSV colorspace to see with 'Hue' landmass can be linearly mapped. Treat water separately.

• Read slide 13 here.
• Last answer here illustrates this.
• You could use scikit image for processing:

from skimage.color import rgb2hsv

rgb_img = np.array(your_image)
hsv_img = rgb2hsv(rgb_img)
hue_img = hsv_img[:, :, 0]

Taken from here.