OpenCV BGR color palette with trackbars-Python

Creating a color palette helps in exploring and visualizing colors interactively. Using OpenCV in Python, we can add trackbars for Blue, Green and Red (BGR) channels. Adjusting these trackbars changes the values (0–255) in real time, making it easy to identify and use the corresponding RGB colors.

Prerequisites:

• OpenCV (cv2)
• Numpy

Install them using pip if not already installed:

pip install opencv-python numpy

Approach

1. Create a black window of size 512 x 512 with three color channels.
2. Use cv2.createTrackbar() to add three trackbars named Blue, Green, and Red.
3. Each trackbar value ranges from 0 to 255.
4. Continuously fetch the current positions of the trackbars using cv2.getTrackbarPos().
5. Update the window background color based on the trackbar positions.
6. Exit when the ESC key is pressed.

Python implementation

import cv2
import numpy as np

def emptyFunction():
    pass

def main():
    image = np.zeros((512, 512, 3), np.uint8) 
    windowName = "OpenCV Color Palette"
    cv2.namedWindow(windowName) 
    cv2.createTrackbar('Blue', windowName, 0, 255, emptyFunction)
    cv2.createTrackbar('Green', windowName, 0, 255, emptyFunction)
    cv2.createTrackbar('Red', windowName, 0, 255, emptyFunction)
    
    while True:
        cv2.imshow(windowName, image)
        if cv2.waitKey(1) == 27:
            break
        blue = cv2.getTrackbarPos('Blue', windowName)
        green = cv2.getTrackbarPos('Green', windowName)
        red = cv2.getTrackbarPos('Red', windowName)
        image[:] = [blue, green, red]
        print("BGR:", blue, green, red)
         
    cv2.destroyAllWindows()

if __name__ == "__main__":
    main()

Output:

Note: Above programs will not run on online IDE.

Explanation:

• np.zeros((512, 512, 3), np.uint8) creates a black image (512×512, 3 color channels).
• cv2.namedWindow(windowName) opens a window to display the palette.
• cv2.createTrackbar() adds Blue, Green, and Red trackbars (0–255).
• cv2.getTrackbarPos() reads current values of the trackbars.
• image[:] = [blue, green, red] updates image with the selected BGR color and displays via cv2.imshow().
• cv2.waitKey(1) == 27 exits on ESC key and cv2.destroyAllWindows() closes the window.