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Many experts also once forecast the death of analog. And, while certainly no longer dominant, analog still is viable for many applications. Many OEMs, Crawford says, still use it because it works well, is well understood and very cost effective.
Analog frame grabbers accept and process analog video signals, include an input signal conditioner to buffer the analog video input signal and protect downstream circuitry; a circuit to recover the horizontal and vertical synchronization pulses from the input signal; an analog to digital converter; and an NTSC/SECAM/PAL decoder (National Television System Committee/Sequential Color with Memory/Phase Altering Line. Different countries use different decoding systems), which also can be implemented in software.
Digital frame grabbers, which accept and process analog video streams, include a physical interface to the digital source, such as Camera Link and GigE. Circuitry common to both analog and digital frame grabbers includes memory for storing the image; a bus interface through which a processor can control the acquisition and access the data; and a general purpose I/O for triggering image acquisition or controlling external equipment.
When deciding on a digital frame grabber, interface becomes a consideration. Camera Link, GigE, IEEE-394 all are niches that must be reviewed. GigE, of course, is coming on strong. "There doesn't seem to be any specific trend," Inder Kohli, product manager at DALSA (Montreal, Quebec, Canada), told Paul Kellett of the Automated Imaging Association during an AIA panel discussion. "Some have opted to make GigE Vision frame grabbers with added functionality such as I/O capability [and] on-board processing. Some others have started making cameras. If 10 GigE becomes reality, which no doubt will happen, need for a dedicated frame grabber will continue."
He added that the main advantage of GigE and IEEE-1394 is reduced total cost. "It's hard to predict if an NIC (network interface card) will do what a dedicated frame grabber does and still maintain the low cost. It appears more like a pipe dream than business reality."