python - OpenCV灰度转换错误

Question

我正在尝试在 OpenCV 中打开要处理的视频源文件。我正在关注这里给出的教程:http://docs.opencv.org/trunk/doc/py_tutorials/py_video/py_lucas_kanade/py_lucas_kanade.html#lucas-kanade

每次我尝试打开要处理的 .avi 视频文件时，都会收到以下错误:

    Traceback (most recent call last):
  File "C:\Users\Adam\Desktop\LastProjectAI\sources\samples\python2\lines.py", line 22, in <module>
    old_gray = cv2.cvtColor(old_frame, cv2.COLOR_BGR2GRAY)
error: ..\..\..\src\opencv\modules\imgproc\src\color.cpp:3402: error: (-215) scn == 3 || scn == 4

我从其他帖子中读到，当源视频文件既不是 3 channel 也不是 4 channel 时会引发这样的错误。但是，我使用的是 OpenCV 教程提供的视频，所以我不明白为什么它们不起作用。

这是我正在使用的完整代码:

import numpy as np
import cv2

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

# params for ShiTomasi corner detection
feature_params = dict( maxCorners = 100,
                       qualityLevel = 0.3,
                       minDistance = 7,
                       blockSize = 7 )

# Parameters for lucas kanade optical flow
lk_params = dict( winSize  = (15,15),
                  maxLevel = 2,
                  criteria = (cv2.TERM_CRITERIA_EPS | cv2.TERM_CRITERIA_COUNT, 10, 0.03))

# Create some random colors
color = np.random.randint(0,255,(100,3))

# Take first frame and find corners in it
ret, old_frame = cap.read()
old_gray = cv2.cvtColor(old_frame, cv2.COLOR_BGR2GRAY)
p0 = cv2.goodFeaturesToTrack(old_gray, mask = None, **feature_params)

# Create a mask image for drawing purposes
mask = np.zeros_like(old_frame)

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

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

    # Select good points
    good_new = p1[st==1]
    good_old = p0[st==1]

    # draw the tracks
    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
    if k == 27:
        break

    # Now update the previous frame and previous points
    old_gray = frame_gray.copy()
    p0 = good_new.reshape(-1,1,2)

cv2.destroyAllWindows()
cap.release()

应注意以下几点:

我在 Windows 8 中使用 Python 编辑器 IDLE。

我尝试加载的视频文件与 Python 文件直接相同。

我尝试了多个视频文件，但没有成功。有没有人有任何建议来解决这个错误？

编辑:

从视频捕获对象中读取帧后，我可以直接显示帧。但是，如果我尝试在绘制轨道的 for 循环之后加载帧，则会收到此错误:

OpenCV Error: Bad flag (parameter or structure field) (Unrecognized or unsupported array type) in cvGetMat, file /build/buildd/opencv-2.4.5+dfsg/modules/core/src/array.cpp, line 2482
Traceback (most recent call last):
  File "prac.py", line 55, in <module>
    cv2.imshow('frame2', frame)
cv2.error: /build/buildd/opencv-2.4.5+dfsg/modules/core/src/array.cpp:2482: error: (-206) Unrecognized or unsupported array type in function cvGetMat

Answer 1

我认为该程序无法找到您的视频文件。每当您尝试加载视频或图像文件时，请不要忘记制作 if condition检查视频/图像是否已加载。
if frame data is nothing -->> print "frame is empty"
否则要确保视频中的帧已成功加载，您可以尝试在加载后立即显示该帧，但不要忘记放置 waitKey(0)在 imshow statement 之后

首先检查是否加载了视频帧并让我们知道。