Python pretty image histogram with cdf

hist.py

import numpy
import sys
from PIL import Image
import matplotlib.pyplot as plt


def get_rgb(r: int, g: int, b: int):
    if 0 <= r <= 255 and 0 <= g <= 255 and 0 <= b <= 255:
        return '#%02x%02x%02x' % (r, g, b)


try:
    image_path = sys.argv[1]
except IndexError:
    print('USAGE: python3 hist.py [image path]')
    sys.exit()

image = Image.open(image_path)
image = image.convert('RGB')
r, g, b = image.split()

fig = plt.figure()
hist_ax = fig.add_subplot(111)
cdf_ax = fig.add_subplot(111, frame_on=False)

for i, value in enumerate(r.histogram()):
    color = get_rgb(i, 0, 0)
    hist_ax.bar(i, value, color=color, edgecolor=color, alpha=0.3)

cdf = numpy.array(r.histogram()).cumsum()
cdf_ax.plot([x for x in range(256)], list(cdf), 'r--')

for i, value in enumerate(g.histogram()):
    color = get_rgb(0, i, 0)
    hist_ax.bar(i, value, color=color, edgecolor=color, alpha=0.3)
cdf = numpy.array(g.histogram()).cumsum()
cdf_ax.plot([x for x in range(256)], list(cdf), 'g--')

for i, value in enumerate(b.histogram()):
    color = get_rgb(0, 0, i)
    hist_ax.bar(i, value, color=color, edgecolor=color, alpha=0.3)
cdf = numpy.array(b.histogram()).cumsum()
cdf_ax.plot([x for x in range(256)], list(cdf), 'b--')

cdf_ax.yaxis.tick_right()
cdf_ax.yaxis.set_label_position('right')
cdf_ax.set_ylabel('cdf y', fontsize=15, color='C1')
hist_ax.set_ylabel('hist y', fontsize=15, color='C3')
cdf_ax.set_xticks([])
hist_ax.set_xticks([0, 50, 100, 150, 200, 255])
plt.title('histogram of %s' % image_path, fontsize=24)
plt.savefig('hist.png', bbox_inches='tight')