planet_terrain.py

a,b = shape[0]/2, shape[1]/2
n = 1024
r = 125
y,x = np.ogrid[-a:n-a, -b:n-b]
# creates a mask with True False values
# at indices
mask = x**2+y**2 <= r**2

black = [0, 0, 0]
island_world = np.zeros_like(color_world)

for i in range(shape[0]):
    for j in range(shape[1]):
        if mask[i][j]:
            island_world[i][j] = color_world[i][j]
        else:
            island_world[i][j] = black
            
toimage(island_world).show()