Using a webcam with a HoloLens SpectatorView rig

Following on from my previous post regarding HoloLens SpectatorView, I had been wondering if it was possible to use a webcam instead of a DSLR. It changes the mounting concepts but, just for testing, it wasn’t hard to place a Logitech C920 webcam on top of the HoloLens and get it aligned enough physically so that the calibration data numbers looked reasonable.

An immediate problem was that the code was not setting the webcam’s frame size. A quick look at OpenCVFrameProvider.cpp showed the problem. The code was trying to set the frame width and height before opening the capture object which doesn’t work. This is the original:

The fix is put line 44 before line 41. Then it works fine. The preview window in the calibration code has red and blue swapped but the processed images are correct. Once it was calibrated, I could go on and run the Unity app and look at the composite output – now pretty decent 1080p video.

Using a webcam like the C920 is far from perfect however. The field of view was measured at 75 degrees by the calibration software which really isn’t enough to be useful. Another problem is the autofocus which causes frequent focus breathing. And then there’s the challenge of proper mounting but at least the C920 does have a 1/4 inch thread so there are possibilities.

A decent DSLR (this would be my choice as it can output clean 4k 4:2:2 video over HDMI apparently at a decent price and I have all the lenses 🙂 ) is going to give better results for sure. On the other hand, there may be many applications where a webcam is just fine and you can’t argue with the price.

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