Best value for threshold in Canny

Question

I have an image which I want to detect edges on that. I found Canny has been used a lot ( I don\'t know whether I have a better option than that). I have set the values as f

Answer 1

As Samer said it could be case by case. Here is some code that uses trackbars in opencv, and displays the canny image next to the original, in order to quickly experiment with different threshold values.

import cv2
import numpy as np 
import matplotlib.pyplot as plt 

def callback(x):
    print(x)

img = cv2.imread('your_image.png', 0) #read image as grayscale


canny = cv2.Canny(img, 85, 255) 

cv2.namedWindow('image') # make a window with name 'image'
cv2.createTrackbar('L', 'image', 0, 255, callback) #lower threshold trackbar for window 'image
cv2.createTrackbar('U', 'image', 0, 255, callback) #upper threshold trackbar for window 'image

while(1):
    numpy_horizontal_concat = np.concatenate((img, canny), axis=1) # to display image side by side
    cv2.imshow('image', numpy_horizontal_concat)
    k = cv2.waitKey(1) & 0xFF
    if k == 27: #escape key
        break
    l = cv2.getTrackbarPos('L', 'image')
    u = cv2.getTrackbarPos('U', 'image')

    canny = cv2.Canny(img, l, u)

cv2.destroyAllWindows()