1. What USB devices are now supported by NI image acquisition drivers?
In addition to GigE Vision and IEEE 1394 (FireWire) cameras, the NI-IMAQdx driver now natively supports any USB device with a DirectShow interface. Supported devices include cameras, webcams, microscopes, scopes, scanners, and many other consumer-grade imaging products that expose functionality through a DirectShow interface. These devices will now populate in NI software just as IEEE 1394 and GigE Vision cameras do, and this native driver feature supports acquisition from multiple USB devices using both one-shot (snap) or continuous (grab) acquisition modes.
DirectShow is currently most popular method of supporting image transfer via the USB bus, and a number of USB device manufacturers use the DirectShow framework such as Lumenera, IDS, Point Grey, Logitech, and Creative.
Figure 1: NI-IMAQdx now supports DirectShow compliant USB devices in addition to FireWire and GigE Vision cameras.
2. What is DirectShow?
DirectShow is a framework and API produced by Microsoft that is commonly accepted as a standard for USB image acquisition devices. LabVIEW interfaces with NI-IMAQdx, which communicates with the DirectShow API. Then DirectShow interfaces with the device manufacturer’s driver, which sends data back to the DirectShow API.
Figure 2: Figure 2 shows the interaction between LabVIEW, NI-IMAQdx, the DirectShow API, and a USB device's driver.
The USB device support can also be accessed through other development environments, including Vision Builder for Automated Inspection (AI), and compatible text-based environments such as LabWindows/CVI and Microsoft .NET environments.
3. How do I get started?
You will need to install NI-IMAQdx 3.4 or later (included with the NI Vision Acquisition Software 2009 package or later) in order to take advantage of the native USB device support. In addition, you will need to install the device driver provided by the manufacturer to be able to use your DirectShow compliant device on a machine running a Windows operating system. NI-IMAQdx can be downloaded for a free 7-day trial period or activated for continued use.
- Machine running Windows XP/Vista/7
- NI-IMAQdx 3.4 (NI Vision Acquisition Software 2009) or later
- DirectShow-compliant USB device
- Device manufacturer's DirectShow driver
- Application software (ex. LabVIEW, Vision Builder for Automated Inspection)
4. What are the limitations of the DirectShow interface?
The DirectShow API is designed for consumer-grade devices and is great for many applications. However, if you are looking to use USB cameras for industrial applications, be aware that many camera manufacturers do not expose all of the camera functionality via their DirectShow drivers.
For advanced camera features that are not accessible via DirectShow (may include triggering) and deterministic operation, consider a Camera Link, GigE Vision, or IEEE 1394 interface with NI Vision Acquisition Software.