Thursday, June 16, 2011

GigE versus FireWire

I’ve found the GigE camera interface pretty easy to use, providing I use a card with the Intel Pro 1000 chipset, so I’ve not spent much time comparing it with FireWire. But a recent Technical application Note from Point Grey has me reconsidering.

A Guide to Transitioning from the Flea3 FireWire to the Flea3 GigE Camera” (revised May 18th, 2011,) provides an interesting comparison of the two standards. I recommend downloading the note in its entirety, but for lazy readers I shall cut ‘n’ paste what I consider the most salient points here.

GigE has higher data throughput but places a higher load on the CPU. “GigE Vision applications may consume more resources because the CPU must process both data packet handling and image processing tasks. The CPU in FireWire systems handles only image processing tasks because data packets are delivered directly to main memory using direct memory access (DMA).”

FireWire may be superior for multi-camera applications. “The FireWire bus provides dedicated bandwidth and guaranteed timing for data packets, which guarantees packet delivery, particularly on systems with multiple cameras on the bus. In contrast, the User Datagram Protocol (UDP) used by the GigE Vision standard provides no guaranteed transmission or fixed timing mechanism.”

FireWire is a single cable solution (power is included.) In contrast, GigE (unless PoE,) needs a separate power supply.

Now I tend to be skeptical each time a camera vendor tells me that they’ve chosen the best solution. As Mandy Rice-Davies almost said, “Well they would say that, wouldn’t they? But I don’t think Point Grey has an axe to grind on this matter, so it might be worth your while to spend some time in the support area of their website.


LH said...

I'm not sure if Point Grey is a truly neutral observer. They seem to have placed their development bets on IEEE 1394 and USB3 as I don't recall any GigE cameras at their booth at Vision 2010 (at least none with POE). I am not questioning the validity of their app note, but in light of their product offerings, Ms. Davies's quote may still apply.

Mark Willamson said...

I think the reality is both interfaces are good with advantages and disadvantages.

Firewire cable length 10m GEVision 100m ( unless you use a firewire fiber adaptor).

Industrial fire wire uses a fixed register map defined by DCAM but this is limited and to get the special features on most cameras you need to use the manufacturers SDK where GEVision is a true expandable standard and you can choose the software you want.

Firewire uses DMA but they are very small transfers the interface has limited memory. Yes the loading on GE vision is slightly more (dependent on the GE implementation of the driver) but you can use a full GE frame grabber if this is really an issue ( 1 or 2 % CPU on most systems). An example is the Silicon Software Micro Enable IV. This is one DMA transmission per image.

GEVision has error detection built in Firewire as does not have this as a standard although some manufacturers such as AVT have detection built in to their SDK and cameras but its not defined in the standard.

GEVision with LAG can go 2.5x the speed of Firewire and as its Genicam compliant you can choose a Genicam SDK such as Stemmer Imagings CVB Camerasuite and you can migrate to new camera and new Genicam interfaces without redeveloping your application. You cant do that with firewire.

Firewire is a good interface and has served the industry well but there is no clear future roadmap and while the comments in the point grey article are correct they have only painted part of the picture.

For 95% of applications both will do the job well and firewire is still probably used in more systems and there is no real need to change if you have a good working system BUT if you are starting out AND want to have future proffing AND supplier independence choose an independednt SDK that is Genicam compliant and go with GE Vision.

If you go with GEVision and a manufacturers SDK there is not a lot of difference between them

B Grey said...

@ LH ... I see Point Grey as being firmly in the FireWire camp, BUT ... they do have a CameraLink offering - the Gazelle - and they do offer some USB cams.

@ Mark Williamson ... you make some great points. Thanks for reading and posting!