libuvc_server

Connects to a UVC compatible USB camera and publishes live frames over ZeroMQ socket.

Problem

Let's say you want to use some specific webcam with Python to perform some image processing tasks.

You'll probably use OpenCV to perform most of these image processing tasks.

While using OpenCV, you can also grab images from, almost, any webcam via VideoCapture class but the problem is low level exposure / gain / brightness / FPS / etc. controls doesn't work for every webcam out there with VideoCapture methods.

Also, you still want to use Python.

Solution

libuvc is a cross-platform C library for USB video devices, built on top of libusb. It enables fine-grained control over USB video devices exporting the standard USB Video Class (UVC) interface.

You can access all sort of low level (exposure, gain, brightness, gain, focus, specific frame rates etc.) details of your camera using libuvc directly.

So, I created this small libuvc_server executable as a glue program that:

• Connects to a specific camera defined by USB vendor id, product id and serial number pair
• Sets specific parameters of the camera at start
• Publishes each grabbed frame from the camera over ZeroMQ socket for other programs to receive

After you run libuvc_server as a process, you can receive the frames from your webcam with ZeroMQ using Python.

Usage

After compilation, run the server from the command line:

Usage: libuvc_server [--help] [--version] --width VAR --height VAR --fps VAR --exposure VAR --gain VAR --vid VAR --pid VAR [--serial VAR]

Optional arguments:
  -h, --help    shows help message and exits
  -v, --version prints version information and exits
  --width       Frame Wdith [required]
  --height      Frame Height [required]
  --fps         Frames Per Second [required]
  --exposure    Exposure Time (miliseconds) [required]
  --gain        Sensor Gain [1, 65335] [required]
  --vid         USB Vendor ID [required]
  --pid         USB Product ID [required]
  --serial      USB Device Serial Number [default: ""]

Example run with Logitech C270 camera is as follows:

sudo ./libuvc_server --vid 1133 --pid 2085 --width 1280 --height 960 --fps 5 --exposure 1.0 --gain 1

Then, you can subscribe to a ZeroMQ socket running at TCP port 8002 from your client application.

Check out ./client/imgrab.py for an example client.

What about 'pyuvc'?

pyuvc is a great library for using libuvc under Python.

But, I don't want to run python as root completely.

With my solution I only need to run this libuvc_server executable as root and I can run my python program as a standard user.

Possible improvements

• Hotplug handling inside the server.
• Ability to control camera parameters while the server is running without restarting the process using another ZeroMQ socket.