opencv error : error while displaying rectangle
Question: i m not able to rectify the error. i m following the official opencv python
tutorial. I m passing a video here and doing meanshift.

source: <https://opencv-python-
tutroals.readthedocs.org/en/latest/py_tutorials/py_video/py_meanshift/py_meanshift.html#meanshift>

Below is my code:

    
    
    import numpy as np
    import cv2
    
    cap = cv2.VideoCapture("slow.mp4")
    
    # take first frame of the video
    ret,frame = cap.read()
    
    # setup initial location of window
    r,h,c,w = 250,90,400,125  # simply hardcoded the values
    track_window = (c,r,w,h)
    
    # set up the ROI for tracking
    roi = frame[r:r+h, c:c+w]
    hsv_roi =  cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)
    mask = cv2.inRange(hsv_roi, np.array((0., 60.,32.)),   np.array((180.,255.,255.)))
    roi_hist = cv2.calcHist([hsv_roi],[0],mask,[180],[0,180])
    cv2.normalize(roi_hist,roi_hist,0,255,cv2.NORM_MINMAX)
    
    # Setup the termination criteria, either 10 iteration or move by atleast 1 pt
    term_crit = ( cv2.TERM_CRITERIA_EPS | cv2.TERM_CRITERIA_COUNT, 10, 1 )
    
    while(1):
        ret ,frame = cap.read()
    
        if ret == True:
            hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)
            dst = cv2.calcBackProject([hsv],[0],roi_hist,[0,180],1)
    
            # apply meanshift to get the new location
            ret, track_window = cv2.meanShift(dst, track_window, term_crit)
    
            # Draw it on image
            x,y,w,h = track_window
            img2 = cv2.rectangle(frame, (x, y), (x+w, y+h), (255, 0, 0), 2)
            cv2.imshow('img2',img2)
    
            k = cv2.waitKey(60) & 0xff
            if k == 27:
                break
            else:
                cv2.imwrite(chr(k)+".jpg",img2)
    
         else:
             break
    
    cv2.destroyAllWindows()
    cap.release()
    
    
    
    
    
    
    
     cv2.imshow('img2',img2)
    

this line is showing the error. execution stops at this line. I have done
debugging too.

error is following :

    
    
    OpenCV Error: Assertion failed (size.width>0 && size.height>0) in imshow, file /build/buildd/opencv-2.4.8+dfsg1/modules/highgui/src/window.cpp, line 269
    Traceback (most recent call last):
      File "programs/test14.py", line 36, in <module>
       cv2.imshow('img2',img2)
    cv2.error: /build/buildd/opencv-2.4.8+dfsg1/modules/highgui/src/window.cpp:269: error: (-215) size.width>0 && size.height>0 in function imshow
    


Answer: In OpenCV2.4.x
[`rectangle`](http://docs.opencv.org/modules/core/doc/drawing_functions.html#cv2.rectangle)
function return `None` \- it's modify image in-place. You could use OpenCV3 or
slightly modify your code:

    
    
    cv2.rectangle(frame, (x, y), (x+w, y+h), (255, 0, 0), 2)
    cv2.imshow('img2',frame)
    

instead of

    
    
    img2 = cv2.rectangle(frame, (x, y), (x+w, y+h), (255, 0, 0), 2)
    cv2.imshow('img2',img2)
    

