To find the largest blob.

find_largest_contour.py

from cv2 import *
import numpy as np
import serial

# Use camera
camera = cv.CaptureFromCAM(1)
photo = cv.QueryFrame(camera)

matrix = cv.GetMat(photo)
#convert image
image = np.asarray(matrix)
imwrite("/tmp/test.jpg", image)

# convert to grayscale
#image = cvtColor(image,cv2.COLOR_BGR2GRAY)
image = imread('/tmp/test.jpg', CV_LOAD_IMAGE_GRAYSCALE)

thr = 180

(thresh, dest) = threshold(image, thr, 255, THRESH_BINARY )
(contour, hierarcy) = findContours(dest, cv.CV_RETR_LIST, cv.CV_CHAIN_APPROX_NONE)

# find the largets contour
largest = 0
largestArea = 0.0
i = 0

while i < len(contour):
    area = contourArea(contour[i])
    if area > largestArea:
        largest = i
        largestArea = area
    i = i + 1

print "largest contour is:",
print i
print "Area",
print largestArea

# Polyhedron approximation
approxPoly = approxPolyDP(contour[largest], 0.1*arcLength(contour[largest],True), True)

# Bounding Rectagle
x,y,width, height = boundingRect(approxPoly)

print "Starting points",
print x,y
print "Dimentions",
print width, height



# send serial data
port = '/dev/ttyUSB0'
baudrate=9600

arduino = serial.Serial(port, baudrate)

try:
    arduino.write('A')
    #sleep(1)
    arduino.write(width)
    arduino.write('B')
    arduino.write(1)

except:
    print "Error!"
    exit()