Introduction to video capture and
Motion Detection

Written by Joe Janson,
Project lead at Omega Unfold Inc



I have a motion detection project, what do I need to know?


A motion detector systems can give your PC eyes, letting it respond to external events by capturing images, or triggering actions. However, there’s a bewildering array of possible set ups, not all of them useful to you. You need to carefully identify webcam for motion detectionyour needs, and then get tools that are good enough without being too much... overkill can kill your budget!

You'll require both hardware and software. You’ll also need advice, because motion detection and video capture are still emerging technologies and might not be as "plug & play" as you would like. Hopefully, the following will help you get started….

"I need my computer to be able to see...
really see, not just act like a glorified VCR."


What does motion detection software do?

Motion detection software captures video from an input device and processes this video in real-time to find significant changes between frames. How it responds to these changes depends on what you’ve programmed it to do. Historically, most serve complex security systems and require special equipment. However, general purpose motion detection software like Zone Trigger is now available. 

General purpose motion detection is intended for the ordinary users and moves motion detection away from its original security context, bringing it to new places where it can be used to interact with people, automate processes, and replace costly custom hardware with simple non-intrusive monitoring.

For example, the following applications show how general motion capture can reduce costs, increase quality or enable something that wasn't possible before:
  • Monitor the state of boxes on a shelf using a single standard camera rather than many specialized sensors.
  • Enhance interaction with clients viewing a conference stand by using a multi-zone motion detection.
  • Achieve a new level of audience immersion by adding motion detection to an artistic installation.
  • Optimize flow through your bricks and mortar store by monitoring motion through various zones.

Good general purpose motion detection software should let you determine exactly what kind of motion to look for and then permit a range of responses, e.g. taking pictures, recording videos and sending e-mail notifications. The best software should also be able to analyse the movement itself. Typical operations include:
  • Motion Detection: This is the simplest and most versatile technique. The software looks for anything that is different from one video frame to another. It compares pixel color and brightness (chrominescence and luminescence) without trying to identify anything. It can be trigged by moving objects, lights on/off, shadows, and even vibrations.
  • Flow Control: Using motion detection techniques, the software goes one step further and finds the general flow of motion within the video.
  • Pattern Matching: The software tries to match the input image to a reference image.
Scientists and animators also use software that supports motion tracking in a controlled environment. Future advances in hardware and software may make this viable “in the wild”, along with routine gesture recognition- something with a myriad of possible applications.


What kinds of cameras work for motion detection?

USB cameras (“webcams”)
USB connections for webcamsUSB cameras, usually called “webcams”, are the quick and dirty solution to hooking a camera to your PC.  All you need is the supplied driver software, so you can be up and running in minutes. Better yet, USB cameras are Direct-X compatible and work with almost any video capture software.

However, there are snags. Though you can connect lots of webcams to a single computer, they’re more or less limited to arm’s reach because a USB cable is not designed for distance.

More importantly, USB cameras vary in quality. Cheap ones don’t always provide clear or accurate images. Artefacts (visible defects) include motion blur and oddness caused by compressing the image before sending it to your PC. Some also do badly in poor light conditions, providing grainy images and low frame rate.

The good news is that some good quality USB cameras have a high resolution and fast frame rate video. Some even come with zoom lenses (note that an automatic variable focus lens is not desirable as it may introduce movement when auto-focusing). Video resultion varies greatly depending on the model, from standard 320x240 to "doesn't fit the screen". Don't let this amount of pixels be your only guide for judging the quality of a camera; The price of the camera is your first clue about the quality of its images.

DV cameras (“camcorders”)
Firewire connections for camcordersDV cameras – the DV stands for “Digital Video” - are the high-end solution. Often called “camcorders”, these provide awesome image quality and a fast frame-rate. They are almost always equipped with a zoom,  and may have nice features such as night-vision. Compatible with Direct-X, they should work with most any recent video capture software. 

Like USB cameras, DV cameras are tied to your PC by cable length, this time Fire-Wire (IEEE 1394).  However, the main downside is that they’re expensive.

IP cameras (“network cameras”)
RJ45 connections for IP camsIP cameras, often known as “network cameras”, are more complex remote-controlled devices that connect to a network instead of directly to your PC. Since they are digital, some can supply very high-resolution images, often with superior image quality.

IP cameras are not physically tied to your PC since they can broadcast video over a local network (CCTV) or the Internet. Most have embedded web-servers, and some have internal motion-detection systems. You can also find wireless IP cams that will connect directly to your Wifi network.

Network cameras can be expensive, costing about the same as camcorders. Usually lacking Direct-X drivers, they rarely work with motion detection software unless it specifically supports them. I usually recommend Axis IP cameras and Foscam as they use a standard http protocol, and some models even have optionnal Direct-X windows drivers for optimal compatibility. Zone Trigger has been tested with Axis and Foscam network cameras.

Analogue cameras
RCA connections for analog camerasAnalogue cameras belong to a whole different world. They are fast, provide images with no compression, no artefacts, no motion blur, and use any cable length you need. They may be equipped with a zoom or infra-red vision. Some are even “wireless” (but watch the reception quality, since local interference might compromise motion detection). 

The downside of analogue cameras is that they are complicated and resource-intensive. Connecting one to a PC requires video capture hardware. In operation, this can hog the system resources, so your PC probably might not be able to do  anything else! Many analogue cameras produce interlaced images, requiring special – often 3rd party – software filters, which may introduce artefacts or reduce picture quality. Overall, using an analogue camera requires a more powerful computer than a standard USB camera would.

Progressive and Interlaced video image examples


The compatibility of the motion detection software is dependent on the video capture device. Here are a few capture device types:

  • TV capture cards: These turn your PC into a TV -tuner and DVR, and usually have inputs for external devices such as cameras. Most are compatible with Direct-X, but not all software has options to control channels and inputs. Webcam Zone Trigger can use them.
TV capture card, used for connecting a camera to a computer
  • USB video capture dongles: These are easy-to-use connectors enabling you to plug your analogue camera into a USB port. This is great because they are portable, can be used on laptops, and you can have several connected to the same PC. As for TV capture cards, not all software will be able to use them properly. Make sure to select the correct signal from the settings (PAL / NTSC)  Webcam Zone Trigger can use them.
USB video capture dongle, this is the EasyCap device.
  • Multi-channel cards: These support between 4 and 16 cameras at the time, and vary in quality and price. Unfortunately, at present there is no standard for software compatibility. They are usually not Direct-X compatible, meaning that you are probably stuck with the bundled software.
Multi-channel video capture card


What are good conditions for motion detection?

In the best conditions you must have the following:

  • A well fixed camera - stability is key if you want to isolate motion!
  • Stable light, no flickering.
  • Contrasting background - white objects against white background might not produce great results.
  • High camera frame rate and resolution. It goes without saying that if you want to detect a race car, you'll need a fast camera. The motion detection process can only be as good as the input images. If your motion detection needs are simple, than a low-end webcam might be sufficient.

What is Zone Trigger, and what can it bring to my project?

Webcam Zone Trigger motion detection softwareThe Zone Trigger software series is all about enabling anyone to incorporate motion or sound detection in their custom projects. The Zone Trigger softwares can be downloaded and installed in a few seconds. It’s so simple to use that you can set up a custom system within a matter of minutes. 

On detecting motion, Zone Trigger can do almost anything: play sounds, run programs or commands, take control of other software, send email and files over the internet. Plus it has many extra features such as an HTTP server and archive services.

Zone Trigger saves you time, money and effort:
  • No technical skills required, no development time needed.
  • No costly or complicated custom hardware to install.
  • Technical support and advice to get your projects done.
  • One-stop solution for most interaction and automation scenarios.
Hopefully this information has shed some light for you on the various technical aspects of motion detection and video capture.

Good luck with your project!


References

http://www.zonetrigger.com - Motion Detection software download site, download a trial copy of the Zone Trigger software.

http://www.webcam-project.com - Tips and examples for motion detection projects

http://www.axis.com/ - Network cameras
http://www.foscam.com/ - Network cameras

If you have questions about the Zone Trigger products or if you require consultation and advice on your computer vision projects, please contact Omega Unfold's technical support: support@zonetrigger.com








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