20histogram_with_mask.py

from matplotlib import pyplot as plt
import numpy as np
import argparse
import cv2

def plot_histogram(image, title, mask = None):
	chans = cv2.split(image)
	colors = ("b", "g", "r")
	plt.figure()
	plt.title(title)
	plt.xlabel("Bins")
	plt.ylabel("# of Pixesl")

	for (chan, color) in zip(chans, colors):
		hist = cv2.calcHist([chan], [0], mask, [256], [0,256])
		plt.plot(hist, color = color)
		plt.xlim([0, 256])

	# plt.show()

ap = argparse.ArgumentParser()
ap.add_argument("-i", "--image", required = True, help = "Path to the image")
args = vars(ap.parse_args())

image = cv2.imread(args["image"])
cv2.imshow("Origina", image)
plot_histogram(image, "Histogram for Original Image")

mask = np.zeros(image.shape[:2], dtype = "uint8")
cv2.rectangle(mask, (15, 15), (130, 100), 255, -1)
cv2.imshow("Mask", mask)

masked = cv2.bitwise_and(image, image, mask = mask)
cv2.imshow("Applying the Mask", masked)
# cv2.waitKey(0)

plot_histogram(image, "Histogram for Masked Image", mask = mask)
plt.show()
cv2.waitKey(0)