Source code:

[python]
import cv2
import numpy as np

def nothing(x):
pass

cap = cv2.VideoCapture(0)
cv2.namedWindow("Trackbars")

cv2.createTrackbar("L – H", "Trackbars", 0, 179, nothing)
cv2.createTrackbar("L – S", "Trackbars", 0, 255, nothing)
cv2.createTrackbar("L – V", "Trackbars", 0, 255, nothing)
cv2.createTrackbar("U – H", "Trackbars", 179, 179, nothing)
cv2.createTrackbar("U – S", "Trackbars", 255, 255, nothing)
cv2.createTrackbar("U – V", "Trackbars", 255, 255, nothing)

while True:
_, frame = cap.read()
hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)

l_h = cv2.getTrackbarPos("L – H", "Trackbars")
l_s = cv2.getTrackbarPos("L – S", "Trackbars")
l_v = cv2.getTrackbarPos("L – V", "Trackbars")
u_h = cv2.getTrackbarPos("U – H", "Trackbars")
u_s = cv2.getTrackbarPos("U – S", "Trackbars")
u_v = cv2.getTrackbarPos("U – V", "Trackbars")

lower_blue = np.array([l_h, l_s, l_v])
upper_blue = np.array([u_h, u_s, u_v])
mask = cv2.inRange(hsv, lower_blue, upper_blue)

result = cv2.bitwise_and(frame, frame, mask=mask)

cv2.imshow("frame", frame)
cv2.imshow("mask", mask)
cv2.imshow("result", result)

key = cv2.waitKey(1)
if key == 27:
break

cap.release()
cv2.destroyAllWindows()
[/python]