Motion tracker using Raspberry pi 3, OpenCV and Python

Question

error tells me "too many values to unpack".

This code is written for OpenCV 2.0, however I am using OpenCV3.1.

Am I encountering a reverse compatibility issue here or is it something more trivial?

Answer 1

The line contours, hierarchy = cv2.findContours(thresholdimage,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE) is giving the error as cv2.findContours returns 3 values but you are assigning them to two variables. So, correct code is -,contours, hierarchy = cv2.findContours(thresholdimage,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE) assuming you don't want the first returned value.

cv2.findContours doc: http://docs.opencv.org/3.1.0/d4/d73/tutorial_py_contours_begin.html

Answer 2

I have updated this code to run under opencv2 and 3 per code snippet below. Rather than test for opencv3, I just do a try except and use alternate syntax if there is an error. This works OK but may slow code a little due to continually having to perform check. This is the price of adapting to code differences. I also thought of putting in a boolean variable to indicate if code is running under opencv2 or 3 but the code would still need to check the boolean for the proper syntax. The code below adapts without user intervention.

    differenceimage = cv2.absdiff(grayimage1, grayimage2)
    differenceimage = cv2.blur(differenceimage,(BLUR_SIZE,BLUR_SIZE))
    # Get threshold of difference image based on THRESHOLD_SENSITIVITY variable
    retval, thresholdimage = cv2.threshold( differenceimage, THRESHOLD_SENSITIVITY, 255, cv2.THRESH_BINARY )         
    try:
        thresholdimage, contours, hierarchy = cv2.findContours( thresholdimage, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE )        
    except:       
        contours, hierarchy = cv2.findContours( thresholdimage, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE )