Line Follow using CV green sign dection

Follower_cv_2.py

from picamera.array import PiRGBArray
from picamera import PiCamera
import time
import cv2
import numpy as np
import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BOARD)
GPIO.setup(40, GPIO.OUT)
GPIO.output(40, GPIO.HIGH)

camera = PiCamera()
camera.resolution = (640, 360)
camera.rotation = 180
rawCapture = PiRGBArray(camera, size=(640, 360))
time.sleep(0.1)

for frame in camera.capture_continuous(rawCapture, format="bgr", use_video_port=True):
	Greendected = False
	image = frame.array
	roi = image[200:250, 0:639]
	Blackline = cv2.inRange(roi, (0,0,0), (50,50,50))
	Greensign = cv2.inRange(roi, (0,65,0), (100,200,100))
	kernel = np.ones((3,3), np.uint8)
	Blackline = cv2.erode(Blackline, kernel, iterations=5)
	Blackline = cv2.dilate(Blackline, kernel, iterations=9)
	Greensign = cv2.erode(Greensign, kernel, iterations=5)
	Greensign = cv2.dilate(Greensign, kernel, iterations=9)	
	img_blk,contours_blk, hierarchy_blk = cv2.findContours(Blackline.copy(),cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)
	img_grn,contours_grn, hierarchy_grn = cv2.findContours(Greensign.copy(),cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)
	if len(contours_grn) > 0 :
	   Greendected = True	
	   x_grn, y_grn , w_grn, h_grn = cv2.boundingRect(contours_grn[0])
	   centerx_grn = x_grn + (w_grn/2)	   
	   cv2.line(image, (centerx_grn, 200), (centerx_grn, 250),(0,0,255),3)	
	if len(contours_blk) > 0 :
	   x_blk, y_blk , w_blk, h_blk = cv2.boundingRect(contours_blk[0])
	   centerx_blk = x_blk + (w_blk/2)	   	   
	   cv2.line(image, (centerx_blk, 200), (centerx_blk, 250),(255,0,0),3)
	if Greendected : 
	   if centerx_grn > centerx_blk :
	      cv2.putText(image, "Turn Right", (350,180), cv2.FONT_HERSHEY_SIMPLEX, 1.5, (0,255,0),3)
	   else :
	      cv2.putText(image, "Turn Left", (50,180), cv2.FONT_HERSHEY_SIMPLEX, 1.5, (0,255,0),3)
	else :       
	   setpoint = 320
	   error = centerx_blk - setpoint
	   centertext = "Error = " + str(error)
	   cv2.putText(image, centertext, (200,340), cv2.FONT_HERSHEY_SIMPLEX, 1.5, (255,0,0),3)	
	cv2.imshow("orginal with line", image)		
	rawCapture.truncate(0)	
	key = cv2.waitKey(1) & 0xFF	
	if key == ord("q"):
		break

GPIO.output(40, GPIO.LOW)