Sunday, March 15, 2009

USB Cameras for machine vision

Have you ever wondered why there are so many FireWire/1394 cameras for machine vision yet so few cameras that use the tried and tested USB interface? As USB webcams are so inexpensive, the temptation to go this route and save hundreds of dollars on a camera is clear. But, you probably reason to yourself, there must a downside to USB otherwise the FireWire camera people would go out of business.

Yes, there are downsides to USB for machine vision, and they are summarized in this excellent “Knowledge Base” article from Point Grey Research, “
Differences of USB Cameras Compared to FireWire Cameras.”

As I have no wish to be accused of plagiarism, I’m not going to reproduce their article here (use the link and read it yourself,) but I will give you the bottom line: for a single camera, low speed application where the PC is within a few feet of the camera, USB can work quite well. However, if you need accurate timestamps on your images, longer cable lengths, or multiple cameras, FireWire is the way to go.

If you go shopping for industrial USB cameras you’ll probably end up at
Lumenera. They offer a wide range of camera models, and I have to say that my experience with them has been good. However, as pricing is similar to that of FireWire cameras you may wonder if there are any other pros and cons to be aware of.

Just one, to my knowledge: FireWire cameras generally comply with the DCAM specification, while USB cameras do not (with the exception of the
Chameleon from Point Grey.) The benefit of DCAM is that it gives you greater control over camera functions and parameters, like exposure and gain, than you get with USB.

So the bottom line is this: USB is OK for just grabbing pictures, but more complex machine vision applications really need FireWire.

Did someone ask, “What about CameraLink”?

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