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


def histogram(color):
    array = np.array(color).flatten()
    unique, counts = np.unique(array, return_counts=True)
    array_h = np.zeros(np.max(unique)+1)
    array_h[unique] = counts
    return array_h


def grey_scale(red_c, green_c, blue_c):
    red_a = np.array(red_c)
    green_a = np.array(green_c)
    blue_a = np.array(blue_c)
    gray_scale_a = 0.299 * red_a + 0.587 * green_a + 0.114 * blue_a
    gray_scale_a = gray_scale_a.astype(int)
    return Image.fromarray(gray_scale_a)


image = Image.open("img.jpg")
red, green, blue = image.split()
grey = grey_scale(red, green, blue)

red_h = histogram(red)
green_h = histogram(green)
blue_h = histogram(blue)
grey_h = histogram(grey)


fig, ax = plt.subplots(4)
ax[0].set_title("Red Histogram")
ax[0].plot(red_h, '-r')
ax[1].set_title("Green Histogram")
ax[1].plot(green_h, '-g')
ax[2].set_title("Blue Histogram")
ax[2].plot(blue_h, '-b')
ax[3].set_title("Grey Scale Histogram")
ax[3].plot(grey_h, '-g')
plt.show()