GigE Vision ®GigE Vision® is a recent camera interface standard developed using the Gigabit Ethernet communication protocol. GigE Vision® is the first standard to allow for fast image transfer using standard low cost cables across long lengths. With GigE Vision®, hardware and software from different vendors can interoperate seamlessly over GigE connections. Historically, the machine vision industry designed high-performance applications around short, point-to-point image transfer protocols like Camera Link and LVDS (low-voltage differential signal). Gig-E is an inexpensive transport medium capable of traversing long distances - 100m to 150m. It supports a wide variety of networking and processing options and supports bandwith high enough to stream video data from a camera (or cameras) to a digital video recorder in real time. GigE Vision® offers many benefits including:
The GigE interface resides inside the camera enclosure. It acquires image data, converts it to IP packets, queue it for transfer, and transmits it over Ethernet. it also sends control signals from the GigE link and other inputs to the camera head, and handles network functions such as boot-up and packet resend. There are two primary classes of GigE interfaces: purpose-built hardware and software applications on an embedded processor. In general, purpose-built hardware is capable of higher-performance, processing and transmitting image data at a full, 1Gbps rate. They are also power efficient, drawing as little as 2W, regardless of how much data they transmit. The software-implemented GigE interface requires a real time operating system (RTOS) and a processor with higher clock speeds. Power required for a typical application can draw 20 + watts, which can be problematic in certain applications. One way to reduce the power consumption of the embedded processor is to add a co-processor for some of the protocol processing tasks. This results in a two-chip GigE solution, which drives up cost, increases the design footprint, and requires more power, thus rendering it much less desirable than purpose-built hardware. Why GigE Vision?Rather than using a frame grabber, which can be pricey) a GigE Vision camera typically uses a Network Interface Card (NIC). It is important to use dedicated drivers to avoid unexpected behavior associated with standard NIC drivers, like delays in data transfer. These dedicated drivers use DMA transfers, allowing the CPU to be dedicated to image processing. Typically there are two drivers available from the camera manufacturer: A Filter Driver that separates incoming IP packets and transfers the image data packets directly to the application. Check with the camera manufacturer for the average CPU load as it can vary depending on how this driver has been written. And, a High Performance Driver which separates incoming packets and transfers these directly to the application (DMA). These drivers will be written for specific NIC chipsets as they operate at the‘hardware level. The most commonly supported is a range of Intel’s chipsets. CPU load is less than when using the Filter Driver. Keep in mind adding more cameras in the same network then maximum frame rate at which they operate will decrease. If you have only one physical connection to the NIC, a switch to interface multiple cameras would be used and the bandwidth would then be shared between all cameras. If there are multiple physical connections to a NIC (i.e., a multi port NIC card), each camera could be connected directly to the NIC (up to the maximum number of ports) and operate up to 100MB/sec. What to look for when buying a GigE Vision camera Is the camera Gigabit Ethernet or GigE Vision? If it is GigE Vision compliant the camera will have an official ‘stamp’ which can only be obtained if the camera conforms to the official standard. What is the CPU load of the Filter Driver and High Performance Driver which are supplied with camera? You normally want this to be as low as possible so that the CPU has maximum power to process the incoming images. What I/O support does the camera offer? |