Troubleshooting webcams
Written by Joe Janson,
Project Lead at Omega Unfold Inc


This document gives a few tips and common reasons why a webcam would behave erratically, provide bad video or disconnect. Here are the questions you should ask when troubleshooting a webcam.




Are there USB hubs or cable extensions?

There is a limit on the length of USB cable you can use. Usually, 10 feet is the most you can get without suffering from signal loss. It is possible to daisy-chain amplified USB hubs to get more distance, but this adds latency and its a clumsy way to go.

If you need a USB webcam to be away from the computer, you best bet is to use amplified USB extension cable. You can rarely find this in stores, but you can easily order it online by searching for "active usb cable".

Important note: make sure the USB cable does not pass near magnetic sources, such as lights or home appliances.



Can the USB controller handle this many devices?

You can connect many webcams on a computer, this usually does not cause a conflict, as long as the computer can handle the extra incoming data.

A USB controller has a limit on the amount of data that can be transferred at the time (bandwidth). For example, a webcam streaming images may use 30% of the controller's capacity. This number will vary depending on many factors:
  • Resolution of the images
  • Frame rate of the video
  • Compression of the images by the camera when sending to the computer
  • Availability of sound
If a webcam is using too much bandwidth, it may hinder other devices/webcams connected to the same controller, and ultimately prevent them from working at all.

To troubleshoot this you need to know a few things...

  • Computers typically have between 2 and 8 USB controllers.
  • A USB controller can be:
    •   -reserved for a device inside the computer
    •   -linked to a single USB plug on the computer
    •   -linked to many USB plugs on the computer
  • There are no labels on USB plugs to indicate to which controller it is linked.

So...


If you want to connect many cameras on a computer, you may need to spread the cameras over the available usb controllers. You. Can do this by experimenting; connect the webcams on different USB plugs until it works.

Another way to do it is by manually map your USB ports. Here is how to do it:
  1. Start your webcam software, make a webcam active.
  2. Go to the Windows Control Panel, the to the Device manager.
  3. At the bottom of the device list, you'll find the USB controllers. There should be a few.
  4. Right-click on a USB controller to see its Properties.
  5. In the Properties window, go to the Advanced tab.
  6. Check out the Bandwidth Used section, this will give you a clue if the webcam is connected on a USB port bound to this controller.
Using this technique, you can see which devices are using which USB controller's bandwidth, so this way you can map the USB plugs and have a better idea of how to spread the webcams across all USB controller.



Is the computer's CPU working too hard?

Most software may start working erratically when the CPU usage is too high; the user interface will lag, there may be frame skipping, weird error message and even crashing.

You can check the CPU usage by going to the Windows Task Manager (shortcut Ctrl-Esc), the usage is indicated at the bottom of this window. As a general rule, the system is too busy if it reaches 75%.

To reduce CPU usage, try these:
-Bring down to capture resolution. Some cameras default to 640x480, which is 4 times more pixels than at 320x240.
-If you are recording video files, try another codec or compression method, some are faster.
-If you are capturing from many video sources at once, you may have to compromise;  most netbook cannot  only just handle 2 cameras in low resolution.



Is there enough light for the camera?

If you are working in a low-light environment, as is often the case indoors, the webcam may have to expose a little longer for each frame. The resulting compromise will be twofold: often a slower framerate, and most likely the moving objects will be blurred.

For some webcams, there may be a fix; disabling auto-adjustment or the sensor's sensitivity (also called "gain") in the camera's advanced settings will allow you to set the light sensitivity, providing maximum framerate and minimal motion blur. The cost will likely be darker images. This may be unacceptable for taking pictures, but it is a pretty good deal when in the context of motion detection if you are using hot spots on brighter parts of the image.

Note: not all camera provide advanced settings. When using Webcam Zone Trigger, right-click on the video...?



Is the lens adjusted for correct focus?

Most webcams have a fixed-focus lens, meaning that you can only adjust it manually by turning the lens. Check the camera for a rotating piece around the lens, play with it until you get a clear image on the live video.



Are moving objects blurred on live or saved images/video?

Check the tip above.
Note that some cheap webcams simply will not provide sharp images.




Are you using a multi-channel DVR device for video capture?


Most multi-channel video capture devices are designed to function only with the software that is bundled with it. Most of the time, the video device will not register at all in the list if video capture devices you can connect to. Some such devices will be displayed in the list, but will behave as if it had only one capture channel.

The reason for this is that there is not existing standard for multi-channel video capture devices, each manufacturer does it in his own way. Because if this, DirectX does not support these devices, and most 3rd party software will not be able to use multi-channel DVR devices.

In this case, there isn't much you can do about it...




Are the drivers correctly installed?

You can always re-install the drivers.

First thing you should do before re-installing drivers is to go to http://www.update.microsoft.com , run the auto-scan and check if there is an update available for your webcam. This checks for files versions, and will notify you if some more recent driver files are available for your webcam.

If the driver appears up to date, but you still suspect that something is wrong with your current files, just run the webcam installation program again.

If you are still having issues with the drivers after that, that is you are receiving disgruntled error messages when you connect the camera, or are getting odd behavior that does not seem to be covered by the rest of this article, a good practice is to go to the manufacturer's website and request support; debugging drivers issues can be a real maze.




References

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

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






More articles...
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3 things to check for better motion detection

Interactive Digital Signage How-To

Troubleshooting Webcams


Using Zone Trigger software with the microsoft Kinect


USB bandwidth and connection issues


High-framerate webcams (60-120fps+)




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