计算光流时，为什么frame没有值？

Question

所以我正在尝试为光流实现这个代码 但是当我尝试调用 cv2.imshow('frame',img) 时出现错误，因为 img、frame 和 mask 都是“None”。

任何人都可以帮助我了解问题出在哪里吗？

这是我的代码：

import cv2
import numpy as np


feature_params = dict( maxCorners = 100,
                   qualityLevel = 0.3,
                   minDistance = 7,
                   blockSize = 7 )


lk_params = dict( winSize  = (15,15),
              maxLevel = 2,
              criteria = (cv2.TERM_CRITERIA_EPS | cv2.TERM_CRITERIA_COUNT, 10, 0.03))


color = np.random.randint(0,255,(100,3))

cap = cv2.VideoCapture(0)
while( cap.isOpened() ) :
    ret,old_frame = cap.read()
    old_gray = cv2.cvtColor(old_frame, cv2.COLOR_BGR2GRAY)
    p0 = cv2.goodFeaturesToTrack(old_gray, mask = None, **feature_params)

    k = cv2.waitKey(30) & 0xff
    if k == 27:
        break


    mask = np.zeros_like(old_frame)
    while (1):
        ret,frame = cap.read()
        frame_gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

        p1, st, err = cv2.calcOpticalFlowPyrLK(old_gray, frame_gray, p0, None, **lk_params)


        good_new = p1[st==1]
        good_old = p0[st==1]


        for i,(new,old) in enumerate(zip(good_new,good_old)):
            a,b = new.ravel()
            c,d = old.ravel()
            mask = cv2.line(mask, (a,b),(c,d), color[i].tolist(), 2)
            frame = cv2.circle(frame,(a,b),5,color[i].tolist(),-1)
        img = cv2.add(frame,mask)

        cv2.imshow('frame',img)


        k = cv2.waitKey(30) & 0xff


        old_gray = frame_gray.copy()
        p0 = good_new.reshape(-1,1,2)

    cv2.destroyAllWindows()
    cap.release()

Answer 1

你有

mask = cv2.line(...)
frame = cv2.circle(...)

但是 cv2.line 和 cv2.circle 返回 None.

Answer 2

使用 cv2.inRange 函数或 cv2.calcBackProject 函数创建一个掩码，然后试试这个。