Overview Camera¶
LectureSight requires an overview camera which captures the entire presentation area.
Camera Types¶
USB webcams, other v4l devices such as analog SD video cameras connected to a fast frame grabber, or any image source which can be provided through a GStreamer pipeline can be used.
For real time operation, devices that provide raw video streams are recommended, as encoding and decoding of frames can lead to several hundred milliseconds of delay.
Though the resolution for the overview camera should not be too high in order not to jeopardize real-time performance (usually VGA), the image quality of the model chosen as overview camera directly impacts tracking accuracy and reliability. Cheap USB webcams, for example, sometimes show a habit of aggressively adjusting color channels. Such behavior can compromise correct function of the tracker. With higher quality (720p) webcams, color- and contrast-stable images can be achieved which is optimal for the video analysis.
Also most stationary analog video cameras produce a stable image that meets the needs of the tracking algorithms. In order to use an analog video camera as the overview camera, a frame grabber has to convert the analog signal to digital frames. It is suggested to use internal PCI(e) frame grabber hardware with direct memory access (DMA). Such frame grabbers write raw frame directly into the host system’s memory from where they can directly be copied to GPU memory, thus avoding unnecessary memory copy or encoding/decoding operations that can produce delays.
USB WebCams¶
In general any USB WebCam that is compatible with Video4Linux can serve as overview camera for LectureSight. Experiments with different models have shown that the more stable the image delivered by camera is the more stable is the tracking. Especially automatic color adjustment can cause the object tracker to reset frequently. The following USB cameras have been tested with the system:
Logitech
- HD Pro Webcam C910
- HD Pro Webcam C920
- HD Pro Webcam C930
- FaceVision (no longer in business)
- TouchCam N1
The following USB extension products have been tested with LectureSight, for cases where the capture agent is not located near to the overview camera:
- Unitek Y-262 20m USB 2.0 active extension cable
- ATEN USB 2.0 extender over CAT5/6 cabling (up to 60m)
IP Cameras¶
IP Cameras can be used through the GStreamer Framesource bundle, which supports any GStreamer pipeline, including RTSP sources. See LS-60 for details.
Overview cameras which have been tested include:
- Axis P1428-E network camera (with a stream configured for 1280x720 or 640x360).