cap = cv2.VideoCapture(0)
cap.set(3, 640)
cap.set(4, 480)
cap.set(5, 60)
f = open("output.csv","w")
f.write("t,x,y\n")
start = time.time()

while(True):
    ret, frame = cap.read()

    hsv = cv2.cvtColor(frame,cv2.COLOR_BGR2HSV)

    low_color = np.array([160, 100, 150])#75
    upper_color = np.array([180, 160, 255])

    ex_img = cv2.inRange(hsv,low_color,upper_color)

    x = np.argmax(np.sum(ex_img,axis=0))
    y = np.argmax(np.sum(ex_img,axis=1))

    t = time.time() - start
    f.write(str(t)+","+str(x)+","+str(y)+"\n")
    print(str(t)+","+str(x)+","+str(y)+"\n")

    cv2.circle(frame,(x,y),10,(0,255,0))

    cv2.imshow('frame',frame)

    if t > 20:
        break

    key = cv2.waitKey(1) & 0xFF

cap.release()
cv2.destroyAllWindows()
f.close()

これを実行すると

error processing request: /tmp/binarydeb/ros-kinetic-opencv3-3.2.0/modules/imgproc/src/color.cpp:9815: error: (-215) (scn == 3 || scn == 4) && (depth == CV_8U || depth == CV_32F) in function cvtColor

となります
どうしたらいいですか？