Convert a colormap to BW based on the lightness component of LAB

cmap_to_bw.py

from skimage import color
def cmap_to_bw(cmap, minlight = 60):
    """
    Converts a hex colormap to a colormap of contrasting black and white colors.
    
    Args:
      cmap: a colormap as iterable of hex values, eg bokeh.palettes.plasma(10)
      minlight: a threshold for the lightness
    """
    cols = [tuple(int(h[i+1:i+3], 16)/256 for i in (0, 2, 4)) for h in cmap]
    lightness = color.rgb2lab(cols)
    return ["#000000"
            if col[0] > minlight
            else "#ffffff" 
            for col  in lightness]