UVC Camera Control for Mac OS X
For a recent computer vision project I needed to pull images out of a Logitech QuickCam 9000 and track some markers with the help of the ARToolKitPlus library. I connected the camera to my Mac and was quite surprised to see that it just works. There was no need to install any drivers. As I learned later, that's because the QuickCam 9000 is a UVC webcam for which Mac OS X 10.4.9 already provides a driver. I was able to get to the raw camera images through the QTKit Framework in no time.
However, the QuickCam 9000 has its auto exposure enabled by default, which is absolutely deadly for stable tracking results. I thought I could just turn the auto exposure off and set it to a fixed value through some QTKit API – but no, there's no way to change the exposure of a UVC camera with QTKit. In fact, there's no way to change any parameters of your camera. No exposure values, no white balance, no gain, nothing. Apple just implemented the bare minimum in its UVC driver and the QTkit Framework.
Well, maybe I could get to these parameters through the older Sequence Grabber Framework then? After all, there's a VDIIDCSetFeatures function and a vdIIDCFeatureExposure key! But nope, as the name implies, this stuff only works for IIDC cameras. What's an IIDC camera? Wil Shipley asked the same questions almost 3 years ago - even back then, IIDC cameras were pretty much deprecated. Still, these cameras are the only devices that Apple provides an API for, if you want to change some esoteric parameters no one would ever need to change, like oh, the exposure time or white balance temperature for instance.
Apple is aware of the problem but hasn't done anything to solve it. And Logitech apparently doesn't see the need to provide a Mac driver for their cameras, since Mac OS X already ships with one. Great.
But wait, UVC is a standard, right? USB.org provides a documentation for all device classes, and the Video Class is no exception. So, I poked around in the documentation for a while, read some Linux UVC driver sourcecode and used Apple's USB Prober to see what's going on. After some more hours of playing around with the Kernel Framework's USB API, I was finally able to control some of the QuickCam's settings!