[ros-users] [Discourse.ros.org] [Next Generation ROS] ROS2 usb_cam, imgui, image manipulation nodes

[Lucas Walter]

I've spent some time over the past few weeks learning ros2 and converting a few ros1 nodes to ros2 bouncy- so far at only a superficial level:

**USB cameras**

https://github.com/lucasw/usb_cam/tree/bouncy usb_cam (which would more accurately be called v4l2_cam and have less confusion with uvc_cam). Camera parameter setting was offloaded to v4l2ucp below.

It would be nice to push this as a branch into ros-drivers/ros2-drivers.

I wonder if the sort of user & application integrating a webcam is not interested ros2 at this point? I haven't touched uvc_camera in a while but I could try converting that next if there are advantages (image format conversion is easier?).

https://github.com/lucasw/v4l2ucp/tree/bouncy v4l2ucp is based on the non-ros v4l2ucp utility but here is a non-gui ros interface to v4l devices that can alter settings like exposure or contrast on the same device being used by usb_cam (or any other software using a /dev/video).

**ImGui**

![imgui_ros|689x419](upload://q1gvPTopYKtA8wLa6MRyqlEG3ZD.png) 

https://www.youtube.com/watch?v=UH5tKfWn-KM

https://github.com/lucasw/imgui_ros/tree/bouncy - ROS UI using imgui https://github.com/ocornut/imgui 'Bloat-free Immediate Mode Graphical User interface for C++ with minimal dependencies'. Currently it can display std_msgs topic values and simple plots, and images, and publish to same std_msgs with slider controls- all of which are created via service calls. The resting cpu usage is higher than a native gui but it ought to scale better for lots of graphics (especially 3D graphics later) and changing values. I'm currently using the SDL2 + OpenGL3 backend but could separate that out so any backend could be integrated.

I'd really like to eventually develop node graph viewing or even editing like in https://github.com/ocornut/imgui/issues/306#issuecomment-439653417 .

For use with v4l2ucp there is a script that reads parameters set for the type, min, & max of each parameter the v4l device supports (probably should make them delivered in response to a service call instead) and then calls the imgui_ros service call to create a slider or dropdown menu to change the parameter via a topic (though ros parameters instead of topics probably are better for this).

**Image Manipulation**

https://github.com/lucasw/image_manip/tree/bouncy

iir_image - subscribe to a number of image topics and combine them with parameter coefficients (e.g. 0.5 * image_0 + 0.5 * image_1). Or instead of multiple topics keep a buffer of received image on one topic and use the coefficients to combine the current image with images from the past.

roto_zoom - rotate and scale an image.

save_image - save a sequence of images with a parameter defined prefix and add a node start time timestamp and a sequence number to the file name. Capture all images received or only 1 when a trigger message is received.

resize - resize image and add vertical or horizontal black bars (letterbox) if the output size aspect ratio is different than input.

**Other**

The launch files use argparse to get command line parameters into yaml files in /tmp/ for loading by ros2 nodes:

https://github.com/lucasw/usb_cam/blob/bouncy/launch/demo_launch.py

Some notes on using and converting ros1 to ros2 bouncy are here https://gist.github.com/lucasw/76a903f98bce3179da6282baf9021f30 - there is too much to follow up on immediately as I encounter it, anything without a good workaround I'll probably get back to later especially if it hasn't been addressed in crystal.





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