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In Apply: USB Cameras on Jetson

The brand new “In Apply” collection takes an in depth look on the way to work with the Jetson with developer instruments and exterior {hardware}. On this article we’re working with USB Cameras. Looky right here:

In a earlier article, “In Depth: Cameras” we mentioned how digital cameras work. Right here, we are going to go over the way to combine a USB digital camera with a Jetson Developer Package.

Introduction

The NVIDIA Jetson Developer Kits help direct join digital camera integration utilizing two foremost strategies. The primary is to make use of a MIPI Camera Serial Interface (CSI). The MIPI Alliance is the identify of the trade group that develops technical specs for the cell ecosystem. On Jetsons just like the Nano, this is likely to be a sensor module just like the acquainted Raspberry Pi V2 digital camera primarily based on the Sony IMX219 Picture Sensor.

The second kind of digital camera is a digital camera that connects through a USB port, for instance a webcam. On this article, we are going to talk about USB cameras. 

Jetson Digital camera Structure

At its core, the Jetsons use the Linux kernel module Video 4 Linux (model 2) (V4L2).  V4L2 is a part of Linux, and never distinctive to the Jetsons. V4L2 does all kinds of duties, right here we consider video seize from cameras.

Right here is the Jetson Digital camera Structure Stack (from the NVIDIA Jetson documentation):

Digital camera Structure Stack

CSI Enter

As talked about beforehand, there are two foremost methods to amass video from cameras straight related to the Jetson. The primary, by means of the CSI ports, makes use of libargus which is a Jetson particular library that connects the digital camera sensor to the Tegra SoC Image Signal Processor (ISP). The ISP {hardware} does all kinds of picture processing duties, similar to debayering a picture, manages white stability, distinction and so forth. That is non-trivial, and requires particular instruments and experience with the intention to produce top quality video. For more information: NVIDIA Jetson ISP Management Description from RidgeRun.

USB Enter

The video from a USB digital camera takes a special route.  The USB Video Class driver (uvcvideo) is a Linux kernel module. The uvcvideo module helps exstress unit controls (XU controls) to V4l2 by means of mapping and a driver-specific ioctl interface. Input/Output Controls (ioctls) are the interface to the V4L2 API. For more information: The Linux USB Video Class (UVC) driver

What this implies is {that a} driver in a USB digital camera machine can specify completely different machine dependent controls, with out uvcvideo or V4l2 having to particularly perceive them. The USB digital camera driver fingers a code for a function, together with a variety of potential values, to uvcvideo. When the consumer specifies a function worth for the digital camera, uvcvideo checks the bounds of the argument and passes it to the digital camera together with the function code. The digital camera then adjusts itself accordingly.

As a result of a USB digital camera doesn’t interface straight with the ISP, there’s a extra direct path to consumer area. Right here’s a diagram:

The time period consumer area refers to the place customers have entry to the cameras of their functions.

Exterior the USB Field

That is one path to get USB digital camera video into the Jetson. Not all digital camera producers present such a implementation. Most “plug and play” webcams do, in addition to many mature “specialty” cameras. Let’s outline right here that specialty are cameras with particular or a number of sensors. Many thermal cameras present this functionality, in addition to depth cameras just like the Stereolabs ZED digital camera and Intel RealSense cameras. 

Nonetheless, some specialty cameras could have restricted entry to their function set by means of V4L2, or could have a stand alone SDK. In spite of everything, it’s easier to have a stand alone SDK that merely reads from a given USB serial port and never need to take care of going by means of the kernel interface. Individuals then interface with the digital camera by means of the SDK. We’re not discussing these kinds of cameras right here.

Digital camera Capabilities

Digital camera capabilities describe many features of how a digital camera operates. This consists of many options together with pixel codecs, obtainable body sizes, and body charges (frames per second). You can too look at completely different parameters that management the digital camera operation, similar to brightness, saturation, distinction and so forth.

There’s a command line software which you should use to look at digital camera capabilities named v4l2-ctl. As proven within the video, to put in v4l2-ctl set up the v4l-utils debian package deal:

$ sudo apt set up v4l-utils

Listed here are some helpful instructions:

# Checklist hooked up units
$ v4l2-ctl --list-devices
# Checklist all information a couple of given machine
$ v4l2-ctl --all -d /dev/videoX
# The place X is the machine quantity. For instance:
$ v4l2-ctl --all -d /dev/video0
# Checklist the cameras pixel codecs, photographs sizes, body charges
$ v4l2-ctl --list-formats-ext -d /dev/videoX

There are lots of extra instructions, use the assistance command to get extra data.

The video demonstrates a GUI wrapper round v4l2-ctl. The code is obtainable within the JetsonHacks Github repository camera-caps. Please learn the set up instructions within the README file.

Interfacing along with your Utility

Within the Jetson Digital camera Structure, a V4L2 digital camera stream is obtainable to an utility in two alternative ways. The primary method is to make use of the V4L2 interface straight utilizing ioctl controls, or by means of a library that has a V4L2 backend. The second method is to make use of GStreamer which is a media processing framework.

ioctl

The most well-liked library on the Jetson for interfacing with V4L2 cameras through ioctl on the Jetson is the Github repository dusty-nv/jetson-utils. Dustin Franklin from NVIDIA has C/C++ wrapper Linux utilities for digital camera, codecs, GStreamer, CUDA and OpenCV within the repository. Try the ‘digital camera‘ folders for samples on interfacing with V4L2 cameras through ioclt.

GStreamer

GStreamer is a serious a part of the Jetson Digital camera Structure. The GStreamer structure is extensible. NVIDIA implements DeepStream parts which when added to the GStreamer pipeline present deep studying evaluation of a video stream. NVIDIA calls this Clever Video Analytics.

GStreamer has instruments which permits it to run as a stand alone utility. There are additionally libraries which permit GStreamer to be a part of an utility. GStreamer will be built-in into an utility in a number of methods, for instance utilizing OpenCV. For instance, the favored Python library on Github NVIDIA-AI-IOT/jetcam makes use of OpenCV to assist handle the digital camera and show.

OpenCV

OpenCV is a well-liked framework for constructing pc imaginative and prescient functions. Many individuals use OpenCV to deal with digital camera enter and show the video in a window. This may be achieved in just some strains of code. OpenCV can be versatile. Within the default Jetson distribution, OpenCV can use both a V4L2 (ioctl) interface or a GStreamer interface. Additionally, OpenCV can implement GTK+ or QT shows for graphics.

The straightforward digital camera functions proven within the video make the most of OpenCV. The examples are on the JetsonHacks Github repository: USB-Digital camera. usb-camera-simple.py makes use of V4L2 digital camera enter. usb-camera-gst.py makes use of GStreamer for its enter interface.

One observe right here, in case you are utilizing a special model of OpenCV than the default Jetson distribution, then you will have to ensure that have the suitable libraries linked in, similar to V4L2 and GStreamer.

Trying round Github, you need to have the ability to discover different Jetson digital camera helpers. It’s at all times enjoyable to have a look round and see what others are doing!

USB Notes

As talked about within the video, the USB bandwidth for the Jetson could not match your expectations. For instance on the Jetson Nano and Xavier NX, there are 4 USB 3 ports. Nonetheless, the USB ports are related to 1 hub internally on the Jetson. Which means that you’re restricted to the pace of the hub, which is lower than 4 tremendous pace USB ports.

Additionally, with the intention to preserve energy the Jetson implements what is known as ‘USB autosuspend‘. This powers down a USB port when not in use. Most USB cameras deal with this accurately and don’t let the USB port autosuspend. Nonetheless, sometimes it’s possible you’ll encounter a digital camera that doesn’t do that.

You’ll normally encounter this conduct when the whole lot seems to be working accurately for a short time, after which simply stops. It’s a bit of baffling in case you don’t know what’s occurring.

Fortuitously, you’ll be able to flip off USB autosuspend. It is a little bit completely different on completely different OS releases and Jetson sorts. You need to have the ability to search the Jetson boards for the way to management this on your explicit configuration.

Conclusion

Hopefully that is sufficient data to get you began. This space is without doubt one of the most necessary areas of Jetson improvement. This must be sufficient data to get you asking the suitable questions for superior improvement.



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