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BeagleBoard V4L2 Video Capture, Overo V4L2 Video Capture, PandaBoard V4L2 Video Capture, Raspberry Pi V4L2 Video Capture

Capture video from USB camera using V4L2

Library

Simulink Support Package for BeagleBoard Hardware

Simulink Support Package for Gumstix Overo Hardware

Simulink Support Package for PandaBoard Hardware

Simulink Support Package for Raspberry Pi Hardware

Description

Capture live video from a USB video camera, using the V4L2 (Video for Linux Two API) driver framework. The output is in row major format. During simulation, the model outputs a moving colorbar image.

The Ubuntu Linux image used on the target hardware supports video capture from USB cameras listed as Universal Video Class (UVC). In addition to being a UVC class camera, the camera itself must support data acquisition in YUYV mode.

The following cameras have been tested:

  • Logitech QuickCam Pro 9000

  • Logitech QuickCam Pro 3000

  • Logitech Webcam C600

  • Logitech HD Webcam C310

For a list of Logitech webcams that support UVC, see http://logitech-en-amr.custhelp.com/app/answers/detail/a_id/6471. For a list of UVC cameras supported by Ubuntu, see http://www.ideasonboard.org/uvc/.

For BeagleBoard hardware only: If you connect any USB camera to a USB Host port on the board, the video output contains artifacts that look like small dark scratches. This is a known hardware issue, and is independent of the Linux distribution. To work around this issue, connect the camera to the BeagleBoard's USB OTG port using a "Micro USB OTG to USB 2.0 Adapter". The USB OTG port is labelled "OTG" and is located next to the BeagleBoard's "5V" or "5VDC" connector. This issue is discussed at:

Dialog

Device Configuration

Device name

Enter the path and name of the video device. This parameter value defaults to '/dev/video0'.

The Linux kernel creates a video device file when you connect a supported USB video camera to the board. By default, the Linux kernel supports all USB video class (UVC) devices.

To see the list of video device files, open a command line session with the board and enter: ls -al /dev/video*.

Image size ([width, height])

Specify the width in pixels and height in lines of the image to capture.

This parameter value defaults to [640, 480].

Pixel format

Select the video format of the video device, RGB or YCbCr 4:2:2.

RGB represents the red, green, and blue components of a pixel using an 8-bit value. RGB color space is device-dependent.

YCbCr 4:2:2 uses three channels to represent color image data for each pixel:

  • Y is the luma component (essentially a grayscale signal).

  • Cb is the blue-difference chroma component.

  • Cr is the red-difference chroma component.

The Cb and Cr components are sampled at half the sample rate of Y. See http://en.wikipedia.org/wiki/Chroma_subsampling.

This parameter value defaults to YCbCr 4:2:2.

Sample time

Select the sample time of the video device. This parameter value defaults to 1/10

Smaller values require the processor to complete the same number of instructions in less time, which can cause task overruns.

See Also

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External Web Sites

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