Use cv2.threshold to Apply Image Thresholding

You can use the cv2.threshold function to apply image thresholding to an image.

Thresholding allows you to turn all pixels above a certain greyscale value either white or black. It is useful as a pre-processing step for image contouring.

Before you apply thresholding, your image should be greyscale or converted to greyscale.

To apply thresholding, run:

import cv2 as cv
import numpy as np
from matplotlib import pyplot as plt
 
image = cv.imread('example.png', cv.IMREAD_GRAYSCALE)
_, thresholded = cv.threshold(image, 127, 255, cv.THRESH_BINARY)

Above, replace 127 with the threshold value.

The code above will automatically turn any pixel whose greyscale value is over 127 with black and any pixel whose value is under 127 with white. If you need the opposite, use cv.THRESH_BINARY_INV.