Other Semiconductor Devices for Vision
Embedded vision applications involve more than just programmable devices and image sensors; they also require other components for creating a complete system. Most applications require data communications of pixels and/or metadata, and many designs interface directly to the user. Some computer vision systems also connect to mechanical devices, such as robots or industrial control systems.
The list of devices in this “other” category includes a wide range of standard products. In addition, some system designers may incorporate programmable logic devices or ASICs. In many vision systems, power, space and cost constraints require high levels of integration with the programmable device—often into a system-on-a-chip (SoC) device.
Processors can integrate megabytes’ worth of SRAM and DRAM, so many designs will not require off-chip memory. However, computer vision algorithms for embedded vision often require multiple frames of sensor data to track objects. Off-chip memory devices can store gigabytes of memory, although accessing external memory can add hundreds of cycles of latency. For systems with a 3D graphics subsystem, the system will usually already include substantial amounts of external memory to store the frame buffer, textures, Z-buffer, etc. Sometimes this graphics memory is stored in a dedicated, fast memory bank that uses specialized DRAMs.
Some vision implementations store video data locally, in order to reduce the amount of information that needs to be sent to a centralized system. For a solid-state, non-volatile memory storage system, the storage density is driven by the size of flash memory chips. Latest-generation NAND chip fabrication technologies allow extremely large, fast and low-power storage in a vision system.
Networking and bus interfaces
Mainstream computer networking and bus technology has finally started to catch up to the needs of computer vision to support simultaneous digital video streams. With economies of scale, more vision systems will use standard buses like PCI and PCI Express. For networking, Gigabit Ethernet (GbE) and 10GbE interfaces offer sufficient bandwidth even for multiple high-definition video streams. However, the trade association for Machine Vision (AIA) continues to promote Camera Link, and many camera and frame-grabber manufacturers use this interface.