Documentation

V4L2 Video Capture

Capture video from USB camera using V4L2

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

To capture video from the Raspberry Pi Camera Board, search Help for "Add Support for Raspberry Pi Camera Board".

Parameters

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.

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