How to track white color on black background

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I have a code that doesn't works to white and black color.

On the code I select the ROI, and after that this code is supposed to keep tracking the ball, but it doesn't happen

I have this video : http://tinypic.com/r/2q1rk1g/8

and this code :

import numpy as np
import cv2

cap = cv2.VideoCapture('video.avi')


ret,frame = cap.read()


r,h,c,w = 490,50,895,50  # It is where the ball is.  
track_window = (c,r,w,h)
frame = cv2.cvtColor(frame, cv2.COLOR_GRAY2BGR)

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)

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)

        ret, track_window = cv2.meanShift(dst, track_window, term_crit)

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

I have no clue about what should I do, I tried to convert from gray to bgr, but it didn't works.