OpenCV/Python 中摄像机参数的设置

我正在使用 OpenCV (2.4)和 Python (2.7.3)以及来自 Thorlab (DC1545M)的 USB 摄像头。

我正在做一些视频流的图像分析，我希望能够改变我的视频流的一些摄像机参数。令人困惑的是，我能够改变一些相机属性，但不是全部，我不确定我做错了什么。

下面是在 Python 中使用 cv2绑定的代码，我可以确认它运行:

import cv2




#capture from camera at location 0
cap = cv2.VideoCapture(0)
#set the width and height, and UNSUCCESSFULLY set the exposure time
cap.set(cv2.cv.CV_CAP_PROP_FRAME_WIDTH, 1280)
cap.set(cv2.cv.CV_CAP_PROP_FRAME_HEIGHT, 1024)
cap.set(cv2.cv.CV_CAP_PROP_EXPOSURE, 0.1)


while True:
ret, img = cap.read()
cv2.imshow("input", img)
#cv2.imshow("thresholded", imgray*thresh2)


key = cv2.waitKey(10)
if key == 27:
break




cv2.destroyAllWindows()
cv2.VideoCapture(0).release()

作为参考，Cap.set ()命令中的第一个参数指的是相机属性的枚举，如下所示:

0. CV_CAP_PROP_POS_MSEC Current position of the video file in milliseconds.
1. CV_CAP_PROP_POS_FRAMES 0-based index of the frame to be decoded/captured next.
2. CV_CAP_PROP_POS_AVI_RATIO Relative position of the video file
3. CV_CAP_PROP_FRAME_WIDTH Width of the frames in the video stream.
4. CV_CAP_PROP_FRAME_HEIGHT Height of the frames in the video stream.
5. CV_CAP_PROP_FPS Frame rate.
6. CV_CAP_PROP_FOURCC 4-character code of codec.
7. CV_CAP_PROP_FRAME_COUNT Number of frames in the video file.
8. CV_CAP_PROP_FORMAT Format of the Mat objects returned by retrieve() .
9. CV_CAP_PROP_MODE Backend-specific value indicating the current capture mode.
10. CV_CAP_PROP_BRIGHTNESS Brightness of the image (only for cameras).
11. CV_CAP_PROP_CONTRAST Contrast of the image (only for cameras).
12. CV_CAP_PROP_SATURATION Saturation of the image (only for cameras).
13. CV_CAP_PROP_HUE Hue of the image (only for cameras).
14. CV_CAP_PROP_GAIN Gain of the image (only for cameras).
15. CV_CAP_PROP_EXPOSURE Exposure (only for cameras).
16. CV_CAP_PROP_CONVERT_RGB Boolean flags indicating whether images should be converted to RGB.
17. CV_CAP_PROP_WHITE_BALANCE Currently unsupported
18. CV_CAP_PROP_RECTIFICATION Rectification flag for stereo cameras (note: only supported by DC1394 v 2.x backend currently)

(请注意，正如评论家 Markus Weber 在下面指出的那样，在 OpenCV 4中，你必须从属性名称中删除“ CV”前缀，例如 cv2.CV_CAP_PROP_FRAME_HEIGHT -> cv2.CAP_PROP_FRAME_HEIGHT)

我的问题是:

是否可以通过 python/opencv 设置相机曝光时间(或其他相机参数) ？

如果没有，我将如何设置这些参数？

注意: 相机制造商提供了 C + + 代码来演示如何实现这一点，但是我并不是 C + + 方面的专家(从长远来看) ，并且希望得到任何基于 Python 的解决方案。

先谢谢你！

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最佳答案

Not all parameters are supported by all cameras - actually, they are one of the most troublesome part of the OpenCV library. Each camera type - from android cameras to USB cameras to professional ones offer a different interface to modify its parameters. There are many branches in OpenCV code to support as many of them, but of course not all possibilities are covered.

What you can do is to investigate your camera driver, write a patch for OpenCV and send it to code.opencv.org. This way others will enjoy your work, the same way you enjoy others'.

There is also a possibility that your camera does not support your request - most USB cams are cheap and simple. Maybe that parameter is just not available for modifications.

If you are sure the camera supports a given param (you say the camera manufacturer provides some code) and do not want to mess with OpenCV, you can wrap that sample code in C++ with boost::python, to make it available in Python. Then, enjoy using it.

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I had the same problem with openCV on Raspberry Pi... don't know if this can solve your problem, but what worked for me was

import time
import cv2




cap = cv2.VideoCapture(0)


cap.set(cv2.CAP_PROP_FRAME_WIDTH, 1280)


cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 1024)


time.sleep(2)


cap.set(cv2.CAP_PROP_EXPOSURE, -8.0)

the time you have to use can be different

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To avoid using integer values to identify the VideoCapture properties, one can use, e.g., cv2.cv.CV_CAP_PROP_FPS in OpenCV 2.4 and cv2.CAP_PROP_FPS in OpenCV 3.0. (See also Stefan's comment below.)

Here a utility function that works for both OpenCV 2.4 and 3.0:

# returns OpenCV VideoCapture property id given, e.g., "FPS"
def capPropId(prop):
return getattr(cv2 if OPCV3 else cv2.cv,
("" if OPCV3 else "CV_") + "CAP_PROP_" + prop)

OPCV3 is set earlier in my utilities code like this:

from pkg_resources import parse_version
OPCV3 = parse_version(cv2.__version__) >= parse_version('3')
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I wasn't able to fix the problem OpenCV either, but a video4linux (V4L2) workaround does work with OpenCV when using Linux. At least, it does on my Raspberry Pi with Rasbian and my cheap webcam. This is not as solid, light and portable as you'd like it to be, but for some situations it might be very useful nevertheless.

Make sure you have the v4l2-ctl application installed, e.g. from the Debian v4l-utils package. Than run (before running the python application, or from within) the command:

v4l2-ctl -d /dev/video1 -c exposure_auto=1 -c exposure_auto_priority=0 -c exposure_absolute=10

It overwrites your camera shutter time to manual settings and changes the shutter time (in ms?) with the last parameter to (in this example) 10. The lower this value, the darker the image.

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If anyone is still wondering what the value in CV_CAP_PROP_EXPOSURE might be:

Depends. For my cheap webcam I have to enter the desired value directly, e.g. 0.1 for 1/10s. For my expensive industrial camera I have to enter -5 to get an exposure time of 2^-5s = 1/32s.


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