opencv/samples/python/houghlines.py
Aleksandar Atanasov 14deab252b Fix houghlines.py when no lines found
In the C++ equivalent of this example a check is made whether the vector (here in Python we have a list) actually has any lines in it that is whether the Hough lines function has managed to find any in the given image. This check is missing for the Python example and if no lines are found the application breaks.
2016-06-02 11:00:23 +02:00

54 lines
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Python
Executable File

#!/usr/bin/python
'''
This example illustrates how to use Hough Transform to find lines
Usage:
houghlines.py [<image_name>]
image argument defaults to ../data/pic1.png
'''
# Python 2/3 compatibility
from __future__ import print_function
import cv2
import numpy as np
import sys
import math
if __name__ == '__main__':
print(__doc__)
try:
fn = sys.argv[1]
except IndexError:
fn = "../data/pic1.png"
src = cv2.imread(fn)
dst = cv2.Canny(src, 50, 200)
cdst = cv2.cvtColor(dst, cv2.COLOR_GRAY2BGR)
if True: # HoughLinesP
lines = cv2.HoughLinesP(dst, 1, math.pi/180.0, 40, np.array([]), 50, 10)
a,b,c = lines.shape
for i in range(a):
cv2.line(cdst, (lines[i][0][0], lines[i][0][1]), (lines[i][0][2], lines[i][0][3]), (0, 0, 255), 3, cv2.LINE_AA)
else: # HoughLines
lines = cv2.HoughLines(dst, 1, math.pi/180.0, 50, np.array([]), 0, 0)
if lines != None:
a,b,c = lines.shape
for i in range(a):
rho = lines[i][0][0]
theta = lines[i][0][1]
a = math.cos(theta)
b = math.sin(theta)
x0, y0 = a*rho, b*rho
pt1 = ( int(x0+1000*(-b)), int(y0+1000*(a)) )
pt2 = ( int(x0-1000*(-b)), int(y0-1000*(a)) )
cv2.line(cdst, pt1, pt2, (0, 0, 255), 3, cv2.LINE_AA)
cv2.imshow("source", src)
cv2.imshow("detected lines", cdst)
cv2.waitKey(0)