Frame Grabber – interface card
Capture, convert, process
These days we live in a world of digital data. Almost all of our electronic devices use some kind of memory to store our data, but first, the data has to be captured and transferred to the storage. When it comes to Machine Vision industry the amounts of data transferred can be enormous and cannot be transferred directly to the storage. To deal with that issue the industry developed a frame grabber – the intermediary card that connects the camera to a PC and ‘grabs’ frames captured by the camera and provides smooth data transfer to the storage device. This electronic device allows you to capture and convert data to still digital frames that can be further processed and stored.
Interfaces
Although our smart devices use wireless connectivity, the industrial realm mostly uses wired connections to ensure the best data rates and overall security. There are few modern interfaces when it comes to interfaces in Machine Vision and each of those has its advantages and limitations, so the final decision has to be made by the customer.
Camera Link
Camera Link is one of the standard industrial interfaces. Designed with robustness and high performance in mind CL can be a great solution for cameras in all price ranges and for a wide range of specs – from small, low-resolution cameras to top-notch cameras with high frame-rate and several megapixels resolutions. Camera Link interface is recommended for data rates from 100 MB/s to about 800 MB/s. To be classified as Camera Link compliant – components must meet a series of standards.
Advantages
great middle ground between price and performance
high data rates
standardized cables
high variety of compatible components
CoaXPress 2.0
High-speed interface, perfect choice for multi-camera application with high data throughput. CXP-12 interface cards can handle 12.5 Gbps per channel with up to 4 channels available. CoaXPress 2.0 can take full advantage of the best cameras with no issues or data restrictions. The highest possible data transfers over long distances make CXP-12 a unique interface in MV realm.
Advantages
suitable for highest demand applications
robust connectors for industrial solutions
wide range of compatible cameras and other accessories
GigE
Gigabit Ethernet or ‘GigE’ is the most used camera interface in Machine Vision. This interface is defined by the GigE vision standard from 2006. Current iteration of GigE is capable of handling data throughput rates (up to 120 MB/s) over distances up to 100 meters. GigE applications are easy to set up especially with cameras with PoE (Power over Ethernet) allowing transfer of data and power the camera with a single cable. Gigabit Ethernet with its standard RJ-45 plug is often the preferred choice for integrators. Expansion cards for GigE allow you to add 2 or 4 cameras to your setup and are equipped with features like PoE (Power-over-Ethernet).
USB 3 (USB 3.1 Gen 1)
Over the last few years, USB has developed as one of the most commonly used standards in Machine Vision. Easy setup, familiar plug format and overall great performance make it a universal choice for various MV applications. Since its introduction, USB has undergone some improvements, of which the major one was with introduction of USB 3.0 – higher performance and increased robustness made a USB 3.0 even more desirable choice in Machine Vision applications. Second important event in USB 3.0 was the official release of USB3 Vision Standard. This standard introduced in January 2013 ensures that compliant components meet strict requirements and offer the highest performance. Although USB cameras do not require framegrabber explicitly, sometimes an expansion card might be required to set up multi-camera systems. Variants of cards with 2, 3, or 4 independent ports are available.
Advantages
bandwidth up to 350 MB/s
high compatibility with other components
stability and great error handling
PCI
As frame grabber links camera and PC together, it is important to make sure that data can be efficiently transferred to your PC. Current standard PCIe x4 (Peripheral Component Interconnect Express) allows very high performance and reliability but your host has to be compatible with PCIe x4 to establish robust and efficient data flow.
Pre-processing
To relieve partly from computational stress at CPU side, frame grabbers can pre-process incoming image data. Modern pre-processing features in interface cards safely transfer acquired data without losses in quality. Features like compression or automatic selection of image areas (Region of Interest, ROI) can reduce the strain on the host and make the whole processing smoother.
FPGA
Field-programmable gate array as the name suggests enables the integrator to program the card according to the needs of the current system. The extremely efficient and high-performing circuitry of the FPGA is especially crucial in the most demanding applications.
Some of the available preprocessing possibilities
• High quality debayering
• Look-up tables (LUT)
• Mirroring, flipping, obracanie obrazu
• Dead pixel compensation
• White balancing
• Dead pixel compensation
• Shading correction
• Remove blurred areas
• Reduce noise in the image, by averaging or using different filters, e.g. smoothing filters
• High dynamic range (HDR) to compensate for areas of the image that are too bright or too dark
• Geometric rectification to normalize the shapes of structures, e.g. by affine transformations
• Increase contrast, e.g. by using Look-Up-Tables (LUT) already during image acquisition as well as histogram flattening or stretching
• Color space conversion
• Filtering
VisualApplets
VisualApplets is an IDE – integrated development environment for real-time applications designed for FPGA processors by Mannheim branch (formerly Silicon Software). VA software helps to program FPGA in a easy graphical interface without hardware programming with the possibility to add your own libraries to adjust your system to the demands. Setting a robust system requires to take into consideration all the components that the system is going to consist of. High performance camera with perfectly suited lens and other accessories will not perform at its best if the data cannot be transferred to the storage and analyzed. Framegrabber acts like an intermediary – connects the camera with the host PC and ensures that the performance stays on the same top-level at all times.