问题描述

我正在制作一个非常简单的程序，它使用 python 中的 opencv 从 Raspberry pi 相机捕获视频.我正在使用 Raspbian 作为操作系统.我已经用 opencv 2.4.5 版本制作了一些程序，现在我已经安装了 opencv 2.4.9.我过去在以前版本的 opencv 上运行的所有程序现在都无法运行，我想我找到了程序给我错误的地方.只是尝试启动以下代码:

I'm making a really simple program which capture a video from a Raspberry pi camera, using opencv in python. I'm using Raspbian as OS. I've already made a few programs with the version 2.4.5 of opencv and now i've installed opencv 2.4.9. All the programs that i used to run on the previous version of opencv are not working now, and i think i found the point in which the programs gives me errors. Just trying to launch the following code:

import cv2
import numpy as np

cap = cv2.VideoCapture(0)
resAcquisitionWidth = 160
resAcquisitionHeight = 120
cap.set(3, resAcquisitionWidth);
cap.set(4, resAcquisitionHeight);
cv2.namedWindow('frame')  
i = 0
while(True):
    print(i)
    i = i + 1
    ret, frame = cap.read()
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    cv2.imshow('frame',frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cap.release()
cv2.destroyAllWindows()

我得到了错误

分段错误

我发现如果我运行相同的代码，但不尝试调整分辨率(因此在第 7-8 行没有 cap.set() 命令)，一切正常.所以它应该与此相关.我已经看过其他关于类似错误的帖子，所有这些似乎都是出于其他原因.有人知道原因可能是什么吗?

I found out that if i run the same code, but without trying to adjust the resolution (so without the cap.set() commands on the lines 7-8) everything works fine. So it should be something related with that. I've already seen other posts about similar errors, and all of those seem to come for other reasons. Anybody know what the resasone could be ?

推荐答案

问题可能是 y0u 4re n0t c0d1ng s4f3ly:

cap = cv2.VideoCapture(0)
if not cap:
    print "!!! Failed VideoCapture: unable to open device 0"
    sys.exit(1)

当调用 cap.set() 时，您对正在发生的事情的描述可以被视为 cap 为 null 的证据，因此碰撞.当 VideoCapture() 无法打开该设备时会发生这种情况.

You description of what's going on can be seen as evidence that cap is null when cap.set() is called, hence the crash. This happens when VideoCapture() is unable to open that device.

这是什么意思?

• 相机不是设备0(试试其他号码)；
• 相机可能未安装(驱动程序问题)或未正确连接到您的设备；
• OpenCV 不支持摄像头.

然而，在与 OP(提出问题的人)交换了几条消息后，很明显崩溃的可能原因是相机不支持指定的分辨率.这就是为什么检查 API 并注意函数的返回如此重要的原因.这似乎只是 n0t c0d1ng s4f3ly 的另一种情况.

However, after exchanging a few messages with the OP (person that asked the question), it became clear that the probable cause of the crash is the camera not supporting the specified resolution. That's why is so important to check the API and be aware of the return of the functions. This really seems to be just another case of n0t c0d1ng s4f3ly.

根据文档，set() 根据操作的成功/失败返回真/假:

According to the docs, set() returns true/false depending on the success/failure of the operation:

Python:cv.SetCaptureProperty(capture, property_id, value) → retval

Python: cv.SetCaptureProperty(capture, property_id, value) → retval

确保测试这些调用的返回，如果 set() 失败，不要让程序继续执行.

Make sure to test the return of these calls, and do not let the execution of the program continue if set() fails.

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