Python OpenCV find all triangles in image

Question

I trying to find all triangle in image with that code without success

import numpy as np
import cv2

img = cv2.imread('2.jpg')

for gray in cv2.split(img):
    canny = cv2.Canny(gray,50,200)

    contours,hier = cv2.findContours(canny,1,2)
    for cnt in contours:
        approx = cv2.approxPolyDP(cnt,0.02*cv2.arcLength(cnt,True),True)
        if len(approx)==3:
            cv2.drawContours(img,[cnt],0,(0,255,0),2)
            tri = approx

for vertex in tri:
    cv2.circle(img,(vertex[0][0],vertex[0][1]),5,255,-1)

cv2.imshow('img',img)
cv2.waitKey(0)
cv2.destroyAllWindows()

So from this picture

I want get this ( Look at licence plate, I filled with red lines triangles)

That what I get now

Answer 1

If the triangles are always the same colour you can preprocess the image to only display that colour, then use the code you have already written to find those triangles.

This link should get you started:

http://opencv-python-tutroals.readthedocs.org/en/latest/py_tutorials/py_imgproc/py_colorspaces/py_colorspaces.html

Hope this helps