opencv_017.py

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


def custom_hist(gray):
    h, w = gray.shape
    hist = np.zeros([256], dtype=np.int32)
    for row in range(h):
        for col in range(w):
            pv = gray[row, col]
            hist[pv] += 1

    y_pos = np.arange(0, 256, 1, dtype=np.int32)
    plt.bar(y_pos, hist, align='center', color='r', alpha=0.5)
    plt.xticks(y_pos, y_pos)
    plt.ylabel('Frequency')
    plt.title('Histogram')

    # plt.plot(hist, color='r')
    # plt.xlim([0, 256])
    plt.show()


def image_hist(image):
    cv.imshow("input", image)
    color = ('blue', 'green', 'red')
    for i, color in enumerate(color):
        hist = cv.calcHist([image], [i], None, [256], [0, 256])
        plt.plot(hist, color=color)
        plt.xlim([0, 256])
    plt.show()


src = cv.imread("./test.png")
cv.namedWindow("input", cv.WINDOW_AUTOSIZE)
gray = cv.cvtColor(src, cv.COLOR_BGR2GRAY)
cv.imshow("input", gray)
# custom_hist(gray)
image_hist(src)
cv.waitKey(0)
cv.destroyAllWindows()