How to programmatically disable the auto-focus of a webcam?

Question

I am trying to do computer vision using a webcam (the model is Hercules Dualpix). I know it is not the ideal camera to use, but I have no choice here.

The problem is the auto-focus makes it hard/impossible to calibrate the camera. Anyone knows a way to disable the auto-focus feature. Or, if someone has an idea to deal with it and calibrate the camera with the auto-focus.

Shelbyshelden

Answer 1

The Hercules cameras are UVC compliant, so they should work with the DirectShow Interface IAMCameraControl. You can set the focus to a specific value, and use the flags to set that you do not want it to be automatic. You can use IAMCameraControl::Get to poll the current state, because not all cameras do support turning off the focus.

IAMCameraControl *pCameraControl; 
HRESULT hr; 
hr = pFilter->QueryInterface(IID_IAMCameraControl, (void **)&pCameraControl); 
if (hr == S_OK) {
  long defaultFocusValue;
  hr = pCameraControl->GetRange(CameraControl_Focus,
                                NULL, // min
                                NULL, // max
                                NULL, // minstep
                                &defaultFocusValue, // default
                                NULL); // capflags
  hr = pCameraControl->Set(CameraControl_Focus, // property
                           defaultFocusValue, // value
                           CameraControl_Flags_Manual); 
} 

Focus has a range which is defined by each camera separately, so you should query it as shown to find the default value and the min, max if you want. In this example the pFilter is a pointer to the input filter that you have from DirectShow. You can get it by enumerating the devices and finding the one you want.

Welldefined

Thanks. Exactly what I wanted! First it did not work, but I upgraded the camera driver and firmware, and everything is working. – Shelbyshelden

How to do this for several webcams? – Beefsteak

its all windows, were is the option for Linux? – Barnie

Answer 2

Try using uvcdynctrl where -l flag shall list you the features and -s can be used to set any feature http://manpages.ubuntu.com/manpages/natty/man1/uvcdynctrl.1.html

Notion

My goal was to do it programatically. – Shelbyshelden

You can use something like system("uvcdynctrl -s Backlight\ Compensation 0"); – Notion

Answer 3

With the a little help of OpenCV and Python you can do this very easy:

cap = cv2.VideoCapture(1) # my webcam cap.set(3, 1280) # set the resolution cap.set(4, 720) cap.set(cv2.CAP_PROP_AUTOFOCUS, 0) # turn the autofocus off

I use OpenCV 3.1.0-dev, Python 2.7.5 and the Logitech HD Pro Webcam C920

Scalf

But this does not work to capture images with multiple exposure. – Nutrition