How to do it...

To complete this recipe, the steps are as follows:

1. First create an OpenCV window named window:

import cv2, numpy as np

cv2.namedWindow('window')

2. Create a variable that will contain the fill color value for the image. The variable is a NumPy array with three values that will be interpreted as blue, green, and red color components (in that order) from the [0, 255] range:

fill_val = np.array([255, 255, 255], np.uint8)

3. Add an auxiliary function to call from each trackbar_callback function. The function takes the color component index and new value as settings:

def trackbar_callback(idx, value):
    fill_val[idx] = value

4. Add three trackbars into window and bind each trackbar callback to a specific color component using the Python lambda function:

cv2.createTrackbar('R', 'window', 255, 255, lambda v: trackbar_callback(2, v))
cv2.createTrackbar('G', 'window', 255, 255, lambda v: trackbar_callback(1, v))
cv2.createTrackbar('B', 'window', 255, 255, lambda v: trackbar_callback(0, v))

5. In a loop, show the image in a window with three trackbars and process keyboard input as well:

while True:
    image = np.full((500, 500, 3), fill_val)
    cv2.imshow('window', image)
    key = cv2.waitKey(3)
    if key == 27: 
        break
cv2.destroyAllWindows()