使用带有 OpenCV 和 Python 的范围滑块（轨迹条）创建蒙版图像

Question

I have written the following program as I am going through a tutorial on OpenCV and Python.

What am i doing wrong or missing that my mask window does not display the HSV image changing based on the slider (trackbar) values?

import cv2
import numpy as np

def empty(i):
    pass

path = "resources/Lena.tiff"
cv2.namedWindow("TrackedBars")
cv2.resizeWindow("TrackedBars", 640, 240)

cv2.createTrackbar("Hue Min", "TrackedBars", 0, 179, empty)
cv2.createTrackbar("Hue Max", "TrackedBars", 179, 179, empty)
cv2.createTrackbar("Sat Min", "TrackedBars", 0, 255, empty)
cv2.createTrackbar("Sat Max", "TrackedBars", 255, 255, empty)
cv2.createTrackbar("Val Min", "TrackedBars", 0, 255, empty)
cv2.createTrackbar("Val Max", "TrackedBars", 255, 255, empty)

img = cv2.imread(path)
imgHSV = cv2.cvtColor(img, cv2.COLOR_BGR2HSV)

hue_min = cv2.getTrackbarPos("Hue Min", "TrackedBars")
hue_max = cv2.getTrackbarPos("Hue Max", "TrackedBars")
sat_min = cv2.getTrackbarPos("Sat Min", "TrackedBars")
sat_max = cv2.getTrackbarPos("Sat Max", "TrackedBars")
val_min = cv2.getTrackbarPos("Val Min", "TrackedBars")
val_max = cv2.getTrackbarPos("Val Max", "TrackedBars")

lower = np.array([hue_min, sat_min, val_min])
upper = np.array([hue_max, sat_max, val_max])
imgMASK = cv2.inRange(imgHSV, lower, upper)

cv2.imshow("Output1", img)
cv2.imshow("Output2", imgHSV)
cv2.imshow("Mask", imgMASK)

cv2.waitKey(0)

Answer 1

You did not define a callback function so results never update with sliders. Also because of initial values the output mask image is white. Here is an easy trackbar tutorial,

https://docs.opencv.org/4.5.0/da/d6a/tutorial_trackbar.html

Code:

import cv2
import numpy as np

def empty(i):
    pass

path = "resources/27.jpg"
cv2.namedWindow("TrackedBars")
cv2.resizeWindow("TrackedBars", 640, 240)


def on_trackbar(val):
    hue_min = cv2.getTrackbarPos("Hue Min", "TrackedBars")
    hue_max = cv2.getTrackbarPos("Hue Max", "TrackedBars")
    sat_min = cv2.getTrackbarPos("Sat Min", "TrackedBars")
    sat_max = cv2.getTrackbarPos("Sat Max", "TrackedBars")
    val_min = cv2.getTrackbarPos("Val Min", "TrackedBars")
    val_max = cv2.getTrackbarPos("Val Max", "TrackedBars")

    lower = np.array([hue_min, sat_min, val_min])
    upper = np.array([hue_max, sat_max, val_max])

    imgMASK = cv2.inRange(imgHSV, lower, upper)

    cv2.imshow("Output1", img)
    cv2.imshow("Output2", imgHSV)
    cv2.imshow("Mask", imgMASK)


cv2.createTrackbar("Hue Min", "TrackedBars", 0, 179, on_trackbar)
cv2.createTrackbar("Hue Max", "TrackedBars", 179, 179, on_trackbar)
cv2.createTrackbar("Sat Min", "TrackedBars", 0, 255, on_trackbar)
cv2.createTrackbar("Sat Max", "TrackedBars", 255, 255, on_trackbar)
cv2.createTrackbar("Val Min", "TrackedBars", 0, 255, on_trackbar)
cv2.createTrackbar("Val Max", "TrackedBars", 255, 255, on_trackbar)

img = cv2.imread(path)
imgHSV = cv2.cvtColor(img, cv2.COLOR_BGR2HSV)

# Show some stuff
on_trackbar(0)
# Wait until user press some key
cv2.waitKey()