a test script for OpenCV trackbar

cv2trackbar_test.py

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


def printing(position):
    #print(position)
    return


def make_hist(src: np.ndarray):
    gray = cv2.cvtColor(src, cv2.COLOR_BGR2GRAY)
    fig, ax = plt.subplots()
    ax.hist(gray.flatten(), bins=32, ec='k')
    fig.canvas.draw()
    data = fig.canvas.tostring_rgb()
    w, h = fig.canvas.get_width_height()
    c = len(data) // (w * h)
    dst = np.frombuffer(data, dtype=np.uint8).reshape(h, w, c)
    dst = cv2.cvtColor(dst, cv2.COLOR_RGB2BGR)
    plt.close()
    return dst


img = cv2.imread(sys.argv[1])

cv2.namedWindow("window")
cv2.namedWindow("control")

hist = make_hist(img)
cv2.imshow('control', hist)

threshold = 150

offsetx = 100
offsety = 60
r = 1.75

cv2.createTrackbar("track", "control", threshold, 255, printing)
while True:
    ret, th = cv2.threshold(img, threshold, 255, cv2.THRESH_BINARY)
    threshold = cv2.getTrackbarPos("track", "control")
    cv2.imshow('window', th)
    histol = hist.copy()
    cv2.line(histol, (int(r*threshold+offsetx), offsety), (int(r*threshold+offsetx), offsety+370), (0,0,255), thickness=1, lineType=cv2.LINE_AA)
    cv2.imshow('control', histol)
    if cv2.waitKey(10) == 27:
        break

cv2.destroyAllWindows()