Tutorials

Launching image_proc Components

While each of the components is available as a ROS 2 node, the recommended way to build pipelines is using the components as this will save overhead by not having to serialize messages between components.

The example below creates two composable nodes:

rectify_node subscribes to image_raw, rectifies the image and publishes it at image_rect.
crop_decimage_node subscribes to the rectified image_rect, decimates it to half the size and publishes the image_downsized.

from launch import LaunchDescription
from launch_ros.actions import ComposableNodeContainer
from launch_ros.descriptions import ComposableNode

def generate_launch_description():

    composable_nodes = [
        ComposableNode(
            package='image_proc',
            plugin='image_proc::RectifyNode',
            name='rectify_node',
            remappings=[
                ('image', 'image_raw'),
                ('image_rect', 'image_rect')
            ],
        ),
        ComposableNode(
            package='image_proc',
            plugin='image_proc::CropDecimateNode',
            name='crop_decimate_node',
            remappings=[
                ('in/image_raw', 'image_rect'),
                ('out/image_raw', 'image_downsized')
            ],
            parameters={
                'decimation_x': 2,
                'decimation_y': 2,
            }
        )
    ]

    container = ComposableNodeContainer(
        name='image_proc_container',
        package='rclcpp_components',
        executable='component_container',
        composable_node_descriptions=composable_nodes,
    )

    return LaunchDescription([container])

Using Compressed Image Transport

All of the components and nodes in image_proc support image_transport. This allows a subscriber to specify the transport to be used. By default, this is raw, which means an uncompressed sensor_msgs/Image. When transmitting images over limited bandwidth networks, such as WiFi, it can be helpful to use compressed format.

$ ros2 run image_proc rectify_node --ros-args -p image_transport:=compressed

Remapping camera_info Topics

See tutorial in image_pipline.

Using QoS Overrides

See tutorial in image_pipline.

Using image_proc Launch File

Make sure your camera driver is running. To see the available raw image topics from compatible drivers you can check:

$ ros2 topic list | grep image_raw

Normally the raw image from the camera driver is not what you want for visual processing, but rather an undistorted and (if necessary) debayered image. This is the job of image_proc. If you are running on a robot, it’s probably best to run image_proc there. For example, if the driver is publishing topics /my_camera/image_raw and /my_camera/camera_info you would do:

$ ros2 launch image_proc image_proc.launch.py namespace:=my_camera

Notice that we push our image_proc launch file down into the /my_camera namespace, in which it subscribes to the image_raw and camera_info topics. All output topics are likewise published within the /my_camera namespace.

In a separate terminal (on your home machine, if you are running on a robot):

$ ros2 run image_view image_view --ros-args -r image:=my_camera/image_rect_color

This will display an undistorted color image from my_camera.

Using the TrackMarkerNode

When generating markers, be sure to pay attention to the selection of the dictionary. The default dictionary is DICT_6X6_250 which means you want your marker to be of the 6X6 size, with an ID of 0-249.

There are two ways to generate markers:

The OpenCV Tutorial shows programmatic ways to generate markers.

There are a variety of online Aruco marker generation webpages, this one <https://chev.me/arucogen/> is very easy to generate individual markers.

Once the marker is printed, be sure to set the marker_id and marker_size parameters for the node. It is recommended to measure the marker size as printing the marker could incur scaling.