v4l2_camera

A ROS 2 camera driver using Video4Linux2

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README

v4l2_camera

A ROS 2 camera driver using Video4Linux2 (V4L2).

Features

• Lists and exposes all user-settable controls of your camera as ROS 2 parameters.

• Uses cv_bridge to convert raw frames to ROS 2 messages, so supports a wide range of encoding conversions.

• Supports image_transport to enable compression.

• Supports composing the camera node and using ROS 2 intra-process commmunication with zero-copy messaging.

Supported Cameras

The package should work with any camera that properly supports V4L2, which for instance should include most USB cameras. A good way to check your camera is to install the v4l2-utils package (on Debian based systems), and run the v4l2-compliance tool. If that reports no, or limited amounts of, failures or warnings, you should be good to go.

The following cameras have in any case been proven to work:

Brand	Type	Driver	Notes
Logitech	C920	uvcvideo
Logitech	BRIO 4K Pro	uvcvideo
Microdia	Integrated Webcam HD	uvcvideo	Integrated laptop camera, e.g. Dell XPS series
Raspberry Pi	Camera Module V2 (Noir)	bm2835 mmal	See Raspberry Pi Support notes below

Do let us know about other devices you successfully use this driver for, for instance through a merge request.

Raspberry Pi Support

Raspberry Pi has moved to a new camera stack based on libcamera. As part of this, by default the Broadcom Unicam driver will be loaded for Raspberry Pi camera modules. This is still a V4L2 driver, however it has a very limited scope and only provides raw Bayer images. Any available Image Signal Processors, that can turn those raw images into more useful formats such as RGB or JPEG, are now exposed as separate V4L2 devices. This means that responsibility is pushed to an application such as v4l2_camera to operate the multiple devices, rather than the single all-in-one device that most other V4L2 drivers expose. Supporting this is out of scope of this package.

You can find out whether the Unicam driver is used by installing the v4l-utils package, running:

v4l2-ctl -D

and checking for bcm2835-unicam. You can also install and run the v4l2_camera node, which mentionsunicam as part of the driver name.

Luckily, for at least some devices, it is possible to load the legacy driver instead of the new Unicam driver, by changing settings in the /boot/config.txt file:

• Set camera_autodetect=0 to prevent hardware overlays that use the Unicam driver to be loaded.

• Set start_x=1 to enable the camera using the legacy driver.

Now when you reboot and run v4l2-ctl -D again, or the v4l2_camera node, you should see the driver being referred to as bm2835 mmal instead. The v4l2_camera node should then operate as normal.

Installation

ROS package install

This package is available from the ROS package repositories and can therefore be installed with the following command and your ROS version name:

sudo apt-get install ros-${ROS_DISTRO}-v4l2-camera

Building from source

To build this package from source, simply clone this repository into your workspace, install dependencies, and build it using colcon:

git clone --branch ${ROS_DISTRO} https://gitlab.com/boldhearts/ros2_v4l2_camera.git src/v4l2_camera
rosdep install --from-paths src/v4l2_camera --ignore-src -r -y
colcon build

That should be sufficient in most cases, but this article goes into further detail. It focuses on Raspberry Pi OS with the Raspberry Pi Camera Module V2, but the steps should be generally applicable.

Basic Usage

Run the camera node to publish camera images, using the default parameters:

ros2 run v4l2_camera v4l2_camera_node

You can use rqt-image-view to preview the images (open another terminal):

sudo apt-get install ros-${ROS_DISTRO}-rqt-image-view
ros2 run rqt_image_view rqt_image_view

Nodes

v4l2_camera_node

The v4l2_camera_node interfaces with standard V4L2 devices and publishes images as sensor_msgs/Image messages.

Published Topics

• /image_raw - sensor_msgs/Image

  The image.

Parameters

• video_device - string, default: "/dev/video0"

  The device the camera is on.

• pixel_format - string, default: "YUYV"

  The pixel format to request from the camera. Must be a valid four character ‘FOURCC’ code supported by V4L2 and by your camera. The node outputs the available formats supported by your camera when started. Currently supported: "YUYV", "UYVY", or "GREY"

• output_encoding - string, default: "rgb8"

  The encoding to use for the output image. Can be any supported by cv_bridge given the input pixel format. Currently these are:

  • "YUYV": "yuv422_yuy2" (no conversion), or "mono8", "rgb8", "bgr8", "rgba8" and "bgra8", plus their 16 bit variants

  • "UYVY": "yuv422" (no conversion), or "mono8", "rgb8", "bgr8", "rgba8" and "bgra8", plus their 16 bit variants

  • "GREY": "mono8" (no conversion), "rgb8", "bgr8", "rgba8" and "bgra8", plus their 16 bit variants

• image_size - integer_array, default: [640, 480]

  Width and height of the image.

• Camera Control Parameters

  Camera controls, such as brightness, contrast, white balance, etc, are automatically made available as parameters. The driver node enumerates all controls, and creates a parameter for each, with the corresponding value type. The parameter name is derived from the control name reported by the camera driver, made lower case, commas removed, and spaces replaced by underscores. So Brightness becomes brightness, and White Balance, Automatic becomes white_balance_automatic.

Compressed Transport

This package uses image_transport to publish images and make compression possible. However, by default it only supports raw transfer, additional plugins are required to enable compression. These need to be installed separately, either cloning an building them from source, or installing the ready made package:

sudo apt-get install ros-${ROS_DISTRO}-image-transport-plugins

Once installed, they will be automatically used by the driver and additional topics will be available, including /image_raw/compressed.