Bit by bit of OpenCV calling USB camera

1 Preface

Most of the cameras used in general projects are industrial cameras , Its manufacturers are equipped with perfect secondary development SDK, Rich interfaces .

But I recently came across a camera , The biggest advantage is that it is cheap （ It is a fraction of the price of the same industrial camera ）, Unfortunately, there is no SDK Provide （ only one amcap.exe）, This is embarrassing for users .

OpenCV Medium vediocapture Class contains access and control USB Camera functions ( The premise is that the camera itself supports , Not all USB Cameras are supported by vediocapture Direct access ).

2 VideoCapture It takes too long to turn on the camera

If the cv::VideoCapture capture(device_index); Turn on the camera device , The program runs abnormally slowly , Output a large number of loads in the output window pdb Information of symbols , It's probably going to take 30s To successfully open the device , This is obviously maddening .

2.1 The analysis reason

CV_WRAP explicit VideoCapture(int index, int apiPreference = CAP_ANY);

cv::VideoCapture Which background driver is suitable for polling one by one , This traversal is obviously time-consuming .

We didn't specify apiPreference When parameters are , It defaults to traversing one by one , It may be time-consuming .

2.2 terms of settlement

Direct designation apiPreference Parameters , Specify the background used to start the camera API. Can be specified as CAP_DSHOW Or other ( Adjust measures to local conditions ).

cv::VideoCapture capture(device_index, cv::CAP_DSHOW);

The time to turn on the device instantly starts from 30s Reduced to less than 200ms.

3 Exposure time setting

capture.set(cv::CAP_PROP_EXPOSURE, -5);

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