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CameraPlugin, 17th May 2010 11:00:00
- Rewrote for more general use (Squeak, Etoys, XO, etc)
- Supports multiple simultaneously open cameras
- Dependency on libv4l2 dropped but...
- Code now attempts to open libv4l2 and uses it available
- Additional pixel format conversions (if no libv4l2)
- Redesigned so future version can do frame skipping without
incurring conversion delays on skipped frames. To support
this the Scratch API would need to change...
CameraGetFrame(int camNum, unsigned char* buf, int pixelCount)
to...
CameraGetFrame(int camNum, unsigned char* buf, int pixelCount, int skipFrameCount)
- Why is frame skipping required? To support "snapshot" type
use-cases such as the following and particularly when the
camera would be shut down between uses to preserve power:
- taking a picture at any ad hoc moment,
- taking a picture at a specific/precise time,
- taking a picture at periodically, eg, time-lapse photgraphy
Webcams are generally designed for streaming and drivers
typically use various degrees of buffering to improve
performance. Buffering can mean that, eg, a five second
time-lapse captured image could actually be five, ten or
more seconds old. In one such test I needed to skip 20
frames to get the latest one! Some cameras/ drivers are
designed for this type of operation but "CameraPlugin"
is being specifically designed for maximum general use
across various hw platforms and many different types of
camera.
- More info: http://info.scratch.mit.edu/Linux_installer/Linux_Camera_Plug-in
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