Camera interface standards

It's my impression that the machine vision industry has pretty much standardized on one interface. It’s GigE for area or matrix cameras, leaving USB3 to the scientific/medical community and falling back on CameraLink for linescan applications. (Though I notice Dalsa now has a family of GigE linescan cameras.) However, I know other industries like other formats.

So, when I saw a post on the excellent Adimec blog asking, “Which digital video interface is best for global security systems?” I didn’t expect to learn much. But there were a couple of interesting snippets.

First, regarding GigE, “Processing required to pack and unpack video generates additional heat and uncertain latency…” Now that is news to me. Yes I have noticed a couple of my favorite GigE cameras seem to run very hot, but I hadn’t compared them with USB3 equivalents. Now I think I will.

Second, someone seems to have a bit of a downer on USB3:

“Cons

• Large connector and interface driver
• Maximum throughput unpredictable (chipset, PC motherboard and driver dependent)
• Sustainable speed is much lower than theoretical limit
• Unreliable operation with longer cables (>3 m)”

Interesting points. There’s been so much hype over USB3 that the downsides seem to have been forgotten. Good to see Adimex removing the rose-tinted specs.

This is why it’s important to keep reading the machine vision blogs. You never know quite what you’ll learn. (And kudos to Adimec for providing consistently good content.)

Detecting part orientation

When you’re assembling components orientation is usually critical. That becomes an even bigger issue when the assembly is automated, but machine vision can of course help out.

European vision components distributor Framos has an interesting example in the Case Studies section of the website, (though it was Vision Systems Design (VSD) that first brought it to my attention.) This describes an application where it was essential to know if one component was tilted. The solution was to …

Click the links to find out more, but I will say it involved projecting a pattern. A classic case of a priori knowledge; knowing what the pattern should be, it’s possible work out why it appears differently.

One side note for you: GigE cameras from Smartek were used. I’d never heard of them so I followed the links from the VSD article. Turns out they’re a newish camera manufacturer based in Croatia. I couldn’t find out pricing on their range of matrix cameras, but I would guess they can undercut Basler by a few Euros.

When cable length becomes an issue

CameraLink has a limit of 10 meters. That’s plenty long enough for my applications but I believe some machine vision users find that a problem. If you’re one of those, here’s a solution:

Moog Protokraft, based in Tennessee, has recently launched a CameraLink to GigE Vision converter. The Eagle Series GigE Vision Video Converter looks a pretty sturdy device and lets you take advantage of Gigabit Ethernet’s 100 meter cable length.

Nothing about pricing on the website, so I imagine they’ve made it just a little cheaper than replacing your CameraLink cameras with GigE equivalents. Could be very useful in some applications.

USB3 Vision Clarification

If you read the Comments my ramblings sometimes attract you’ll see that “USB3 Vision versus GigE Vision” drew some questions. As the writers took the time to read what I had to say I’d like to pay them the courtesy of a reply.

First off, I should have cited my sources. Most of my information came from the Basler paper referenced in “Understanding USB3 Vision” although I did pick up a few other points from Stemmer and others. Regrettably, I didn’t save the links but if you Google “Advantages of USB3” or some similar phrase you’ll find the pages I used. Lesson learned.

And now, to the questions (or should that be answers?):

• Regarding USB3 cable length – yes I’m sure you can use repeaters but everything I’ve seen says the effective limit is around 3m.
• On cable security – I meant the provision of screw-in connectors, but I also included immunity to noise. It’s my understanding that USB3 cables offer superior construction in this regard.
• On how I calculated the CPU load scores for USB and GigE – confession time – I didn’t calculate anything. It was a subjective assessment again based on what I read in the Basler paper. In my defense, my intention was to highlight relative strengths and weaknesses rather than assign absolute scores, and I think I accomplished that.

If anyone has any different information that runs counter to what I’ve said, I’d be glad to hear from them.

USB3 Vision versus GigE Vision

If you couldn’t wade through the presentation I offered in my last post, “Understanding USB3 Vision” here’s a graphical comparison of the two interface formats.

I think the message here is that USB3 is a good choice when you have large images from single camera systems and you don’t need a long cable length. However, most single camera machine vision applications are, in my humble opinion, best met with smart cameras. If you go towards a PC solution you’re probably using either linescan or multiple cameras, in which case I think you’ll want CameraLink or GigE.

In other words, I’m still on the fence about the benefits of USB3 in machine vision.

Good results from Basler

It’s good to see German camera-maker Basler doing well. There was a period when their results were kind of flat, but that’s certainly not been the case in 2013. In fact, with sales up 28% to €32.2m at the half and earnings up 77% you could say business is booming. The only fly in the ointment would seem to be the cash flow, down 30%. But as that probably stems from the sales growth I doubt it’s really a problem (in my unqualified opinion anyway.)

As for why business is so good, well Basler management points to three factors: strong demand for GigE cameras, growth in Asia, and a pruning of end-of-life models. I’d suggest there’s a fourth factor at work too. Now they’ve got out of the “Solutions” business they’re able to focus just on making cameras.

There were a couple of other points in the reports that I’d like to share. R&D spend was up 7%, but actually fell as a percentage of sales. I can understand a reluctance to twist the R&D tap based on just six months of sales, but assuming the volume of business remains stable, or even continues to grow, I would hope to see more R&D investment in 2014.

And second, a comment I found interesting was, “… we see our expectations confirmed predicting that GigE Vision and USB3 Vision will be the dominant interface technologies for industrial cameras in the years to come.”

I would agree that GigE has clearly become the default choice and has left FireWire for dead, but USB3? Personally, I think the jury is still out. I’m not even sure if there’s room for two “mainstream” interfaces. Isn’t that just going to create additional complexity and cost?

But leaving that debate for another time, it’s good to see Basler looking healthy. It bodes well for our industry.

CMOS and GigE

I’ve been reading about Basler’s racer linescan cameras. They’re pretty interesting. I hadn’t appreciated that they are both CMOS-based and GigeE. That’s a combination that yields some interesting benefits: less heat generated and no high-end framegrabber or expensive CameraLink cable required.

And where did I learn this? From “The Benefits of Modern CMOS Sensors in Industrial Line Scan Cameras”, available as a pdf download from Basler’s Document Downloads page. (Name and email required, but it is worth it.)

Now obviously, Basler’s White Paper isn’t exactly impartial, but it is well-written and filled with technical “meat”, so I suggest you take a look.

Camera trends

The love-fest that is Vision 2012 is less than a month away and already vendors are giving us sneak-peeks at their latest and greatest. Some of the most intriguing come from camera-maker AVT who, besides some ho-hum range extensions, have an entirely new product, the Mako.

As I write this, the Mako page on the AVT website doesn’t have any content, so instead I will direct you their press release. Now this camera looks much like the reliable old Guppy, but whereas that was a FireWire camera, this will be offered with both GigE and USB3 interfaces.

I see that as highly significant. In fact I’d go so far as to say it means FireWire is on its death-bed, at least in the machine vision world. Some years back AVT saw how the wind was blowing when they snapped up Prosilica, thereby gaining a GigE product line up, and now they’re backing the new USB standard. I’d say that means the future is GigE and USB3, for everything except really large sensor formats and very high data rates.

Just out of curiosity, does anyone think we’ll see a linescan USB3 camera before the year end?

Let’s hear it for FireWire

Last week I said that FireWire is “just falling by the wayside,” (“Mastering the GigE interface” September 6^th, 2012,) and then I read “Firewire Cameras: The Future of FireWire” on the Vision & Sensors website, which opens by asking, “Is FireWire dying?” Probably a coincidence, but who knows?

The article was written by Point Grey, takes a fairly pro-FireWire stance, and makes some good points. FireWire is a single cable system (power goes through the camera cable,) and it has some neat features like daisy-chaining. But I do disagree with the speed claims.

My issue is not that the info is inaccurate – it isn’t – but that the 800Mbit/sec rate assumes the use of FireWire b. Now I’ve always had a problem with this, because Windows doesn’t support this speed. Yes, I realize Point Grey provides ways around this, but it detracts from the essential easiness of FireWire.

Don’t misunderstand me, I like FireWire, but as the numbers in the article show, GigE is gaining ground. After all, some people still use analogue cameras but that doesn’t mean it’s where the future is. So bottom line – I stand by my contention that FireWire is “falling by the wayside.”

Mastering the GigE interface

GigE is probably the de facto standard interface for machine vision. USB is fine for lab work but not really seen as industrial. CameraLink is the natural upgrade path when more speed is needed, and FireWire is just falling by the wayside. But if you’ve set up a GigE camera you’ve probably found it wasn’t exactly plug-and-play. That’s been my experience anyway.

The problem seems to be all the Ethernet-related terminology – ports, jumbo frames, IP addresses and so on - so I asked my best friend, (Google,) to help. Of course, Google throws up a gazillion links to ethernet primers, some of which are better than others. So in my self-appointed role as provider of useful machine vision information, here are my suggestions for learning more.

A good place to start is “How Ethernet Works” by Nick Pidgeon and posted on the howstuffworks website. It’s not detailed but in 10 minutes or less you can get a decent overview.

From there I’d go to “Ethernet Basics”, published by Nortel Networks. This is a 26 page pdf that goes in to CSAM/CD and MAC addressing. (Until I read this I never really grasped why smart cameras have a MAC address.)

Having taken that on-board, you should be ready to delve in to the OSI seven layer model, which is handled by the JDS Uniphase white paper, “Fundamentals of Ethernet”. (It’s another substantial pdf download.)

By now you should be ready for data packets and Ethernet devices, and here I have two suggestions. “Back to Basics: Data packets” on the Control Engineering website is a pretty easy read, and then there’s yet another pdf, “Fundamentals of Ethernet Technology” on the Krone website.

If you want to get a deeper understanding of the nitty-gritty – things like TCP, ports, IP addressing, subnet masks and so on – “Ethernet 101 – Basics of Ethernet Communication” is for you. Now this does get a little yawn-inducing because the narrator insists on reading his 48 slides, but at times he ad-libs to expand on important points, so stick with it; it’s good stuff.

Now I realize that this is a lot of reading and some of you might prefer to watch a movie. Inevitably, there’s a ton of Ethernet material on YouTube, although much of it I found rather poor. Some of the better stuff came from ProfessorNVCC and his series titled “Ethernet Basics Part 1”, followed of course by Part 2, Part 3 and so on.

And when you’ve digested all that, you’ll be an expert. Well not quite, but you will be ready to face the GigE Vision standard, downloadable from the AIA’s website.

Have fun!

Another twist to camera interfaces

With various groups making plays for their preferred new standard – USB 3.0, CameraLink HS and CoaXPress – camera interfaces are in the news of late. Everyone talks about data rates and cable lengths - I’ve done my part, with “King of the (camera interface speed) hill” and “Everything you ever wanted to know about USB3.0” – but writing in the Adimec blog, Gretchen Alper offers another factor to consider: the cost of the cables. (“How to save cabling costs with new machine vision interfaces” August 29^th, 2012.)

Now I knew that CameraLink cables were expensive, but I hadn’t appreciated just how expensive in comparison to GigE, FireWire, USB 3.0 and CoaXPress. (Read Gretchen’s blog post to see the actual numbers.) CoaxPress is of course just plain old co-ax cable, which is why it’s so cheap. As backers of this new standard, Adimec aren’t exactly neutral, so I would expect them to have done their best to ‘spin’ the cable cost issue, but even so, the numbers are pretty startling.

I wonder if this might change your choice of interface next time you spec out a system?

Can GigE be trusted?

I spoke with a gentleman a few days back who advised me not to use GigE because it “drops frames.” His recommendation was to do everything with CameraLink. Now while I agree that CameraLink is robust and reliable I’d not heard of GigE “dropping frames,” so I did some research.

In my library of useful machine vision stuff I found two relevant papers. One is “GigE Vision cameras and network performance,” published by Leutron Vision back in 2009, (unfortunately I can’t find a link on their website.) The other, more recent paper is “4 Critical Factors: Deploying GigE Vision in Real-Time Industrial Imaging” available in the Knowledge Center area of Teledyne Dalsa’s website. (I believe you’ll have to register for access.)

These papers both talk about overhead, packet size, flow control, selecting the right network card and use of Ethernet switches, but there’s little about the possibility of dropping frames. The nearest I came was a comment in the Leutron paper about the risk of dropping packets if the CPU load is too high. Dropping packets would be bad, although it strikes me the risk is low unless you’ve loaded a lot of other processing onto an older PC. But dropping frames?

GigE is rapidly becoming the standard camera interface for machine vision, so presumably the community is happy with how it performs. But are there pitfalls lurking for the unwary?

If you have any knowledge, experience, or perhaps most important, verifiable facts about the reliability of GigE, please use the Comment function to share.

Camera interface trends

I won’t be buying the AIA’s new Machine Vision Camera Study: at $950 for nonmembers it’s a little rich for me, but I was interested to hear about one of the major trends recognized.

In “Vision Standards Prepare the Industry for a Wide Spectrum of Applications” (May 22^nd, 2012,) Winn Hardin rambles on about work on CameraLink HS and CameraLink 2.0 before mentioning the dominant standard. Apparently the AIA study reveals that GigE is now the interface leader.

Now I imagine that’s in terms of units sold, not the dollar value of sales. GigE tends to be found in the more run-of-the-mill cameras, high-speed, high-res still using CameraLink, but clearly end users have learnt that GigE works and is inexpensive. I tend to use it for everything these days: my FireWire cameras are little more than dust collectors.

Clearly, FireWire camera maker AVT saw this coming a few years back when they took the plunge into GigE by buying Prosilica. Smart move, but will USB3 see off GigE the same way?

Yet another camera communication standard

FireWire, GigE, USB 3.0 … do we need another standard? Well some machine vision users do, yes.

The problem is that every standard has its strengths and weaknesses. I touched on this last month under the heading of “Pros and Cons” (take a look for details,) so some users want something that does better – “better” usually meaning higher speeds over long cable lengths.

That’s where CameraLink High Speed (CLHS) comes in. Promoted by Teledyne Dalsa, this aims to be “future proof” so as you upgrade to ever higher resolution cameras the infrastructure can remain unchanged. Personally I think this is more of an issue in traffic and surveillance applications, but it’s something we industrial/manufacturing types should be aware of.

So how do you learn more? Well as always, you click the link I shall provide. In this case it takes you to “Vision & Sensors: Machine Vision Standards”, published on the Vision & Sensors site, March 8^th 2012.

Be aware though that CLHS may not be the last word in camera interfaces: there’s CoaXPress too.

“A revision of GigE Vision”

GigE is fast becoming the primary camera communication format in the machine vision world, and on the principle that if you know what happens under the hood you can be a better driver, I thought I’d share a couple of links to a whole bunch of technical stuff.

“Standard Gives Machine Vision Systems a New Image” is a two part series published on the Vision Systems Design website (January 1^st, 2012,) that details how GigE actually works. It was written by Vincent Rowley of Pleora Technologies, so it’s about as close to the source as it’s possible to get.

Part 1, linked to above, provides background on the standard. Part 2, gets into details about the benefits. Obviously, bumping the speed up to 10Gbits/s (10 GigE) is the big deal, but there are other enhancements too.

• RJ45 connectors and Cat6A cables are not the only means of physically linking camera to PC; there are also “small-form-factor pluggable-plus” (SPF+) connectors. Vincent notes that these are “The least power-hungry option available to system integrators building 10 GigE systems…”.
• Reduced transmission overhead, making 10 GigE of greater interest for linescan applications.
• Support for interlaced video
• Improved support for multitap sensors (something that’s going to grow in importance as sensor manufacturers strive to increase both resolutions and frame rates.

In short, there’s a lot of detail in these two articles. It might be a bit much for folks who just want to deploy smart camera applications (my machine vision “users”,) but if you have any interest in learning about advances in camera interfaces I recommend taking a look.

I’m so pedestrian

Most of my machine vision applications involve pretty low data rates. It’s rare that I need to move more than a 2Mp image at anything faster than 15fps, so the flurry – no, make that a torrent – of new camera standards has kind of washed over me.

The latest to leave me bemused is GigE Vision 2.0. I’m still just finding my feet with GigE (and I do like it,) but I didn’t realize version 2.0 was even in development. The big deal is higher data rates, along with better support for Link Aggregation, (as used on the Prosilica GX range from AVT,) but there are some other enhancements that will be of interest to the geekier among you. If you’re looking for more info, I suggest you start with “Gige Cameras: GigE Vision 2.0 Has Arrived” on the Vision & Sensors website, January 10^th, 2012.

This won’t tell you all you need to know, but I think it’s a good start point.

The Basler approach to product naming

Britain’s Jeremy Clarkson recently described the MacLaren MP4-12C supercar as sharing its name with a photocopier, and his audience got the joke immediately. Sexy products like supercars should have sexy names: which would you prefer: Aventador or MP4-12C?

I think this also applies to more mundane products like machine vision cameras. “MQ022MG-CM” is an engineering designation that may do a great job of describing the product, but it’s unlikely to lodge in anyone’s cerebellum.

Basler seems to get this, which is why they name their cameras, using words such as Ace, Pilot, and now “racer”. AVT get it too, basing their naming strategy on fish – Pike, Marlin, Guppy and so on. These are all product names that will stick in the mind: when I’m asked to suggest a camera I may not recall the MQ0-12C or whatever it is but I will remember “Stingray” or “Racer”.

The “racer” is an interesting new product. Described as “cost-effective” (which I imagine means “cheaper”,) this is the start on a new linescan family. It’s built around a CMOS sensor and is available with either Power-over-CameraLink or GigE interfaces. The latter of course saves a few hundred bucks on a framegrabber, though whether that’s negated by a price premium over the PoCL version I couldn’t say.

What I will say though is that I’m likely to remember the Racer next time I’m asked to suggest a camera while I doubt the DLC-2048-48-CL (yes, I made that up,) will spring as readily to mind.

USB3 fit for machine vision?

USB cameras have never really been adopted for machine vision. Yes there are some products on the market – Lumenera seems to be leading the pack – but they’ve failed to break through. As I understand it, this is mainly due to the way USB tends to hog more CPU time than does FireWire or GigE, and because it’s difficult to have more than a single camera per PC.

Things seem different with USB3. This interface seems to be building a head of steam with vendors such as Point Grey, Ximea, and Basler all launching USB3 cameras.

What does that mean for we end-users? I think it means life just got a little more complicated. There I was, getting to grips with GigE, learning how to address the cameras (not as easy as the vendors would have you believe,) and now they expect me to try something else. And what does USB3 give that GigE doesn’t?

I’m not sure I know. Speeds are broadly comparable and cable lengths are plenty long enough for my industrial needs. One difference might be that USB3 supplies power, so I can save on a separate power supply. Yes, I could go PoE but that doesn’t really seem to have broken through, so camera choices are limited.

I don’t know about you, but I think I’ll hang back and watch how this all pans out.

New cameras

Over the last few days there’s been a torrent of new product announcements from German camera manufacturer AVT. Might this be connected with the Vision show held last week? How naive do you think I am?

Cynicism aside, these are some interesting products. Let’s start with the 6 Mp Prosilica GX2750. This uses a Dual GigE Vision® interface to deliver full-frame images from its CCD sensor at 19fps. Impressive numbers, to be sure. I have to say though, since I believe the pixels are just 4.5 microns and the cooling fins imply considerable heat generation, I am a little concerned about noise in the images.

Perhaps then I should look at their cooled camera, the AVT Bigeye with Active Cooling. Presumably resulting from the acquisition of VDS, this features a Peltier cooler to reduce noise. I have a feeling this is something we shall see more of as pixels shrink and resolutions grow.

Last off, (and I lack a good segue into this,) is the AVT Bonito. This is an impressively fast camera – 4Mp at 386fps – but what really intrigues me is the interface: CameraLink.

Okay, there’s nothing particularly earth shattering about CameraLink, but it’s new for AVT. They started out with FireWire, moving into GigE with the acquisition of Prosilica. And now CameraLink?

If other camera companies weren’t already paying close attention to AVT before, they should be now.

Trends in machine vision cameras

CameraLink provides the highest robustness and data rates, FireWire has been superseded by GigE, and USB is irrelevant for machine vision. Oh, and by the way, resolutions are going up.

Well that’s what I told an engineer who emailed me a few days ago asking if he should stick with FireWire cameras, but let’s take a moment to dive deeper.

Few in machine vision would argue that CameraLink, for now at least, provides the best overall performance. It can handle the highest data rates, (up to 6Gbps with 2 cables,) works over cable lengths as long as 10 meters, (enough for most industrial applications,) and never misses a frame, but it does have downsides. Chief among these is cost. CameraLink needs a framegrabber, which can easily cost $500 or more. It also needs special or custom cables – yet more cost. And since Power-Over-CameraLink (PoCL) doesn’t seem to have really caught on, perhaps because it’s limited to 4W, figure on running two or three cables out to the camera.

So what about the alternatives? Well let’s start with USB. Every computer has a USB port, so there’s no need for a framegrabber, making it seem attractive. But when you dig down into the details the problems start to emerge. The basic issue is that USB is something of a processor-hog, thanks to its employing a master-slave architecture. There are also bandwidth issues, meaning that a significant proportion of its 480Mbps is not available to transfer image data. For these reasons few manufacturers of industrial cameras have ventured into this standard. (Scientific and astronomical cameras are a different matter of course because they don’t need high data rates.) The maximum cable length of 5m can also be bothersome in many applications.

And then there’s FireWire, IEEE1394, to use its proper name. 1394 cameras, which need no framegrabber and take their power – up to 45W – from the single cable, come in two flavors, a) and b), the difference being speed. Roughly speaking, a) handles 400Mbps while b) hits 800Mbps. That’s more than enough for a 2Mp camera running at 5 fps, so what’s the problem?

Well first, cable length is limited to 4.5m, which can get to be a problem in even the simplest of industrial settings. Second, and I’m speaking from personal experience here, it’s just not totally reliable. I’m not up in all the details of error detection methodologies, but it’s my understanding that 1394 doesn’t have any. That means a frame can be dropped and you’ll never know. Now in many applications that might not be a problem, but if you need to be 100% confident in your system, think carefully before going this way.

That brings us to GigE, strictly speaking, GigE Vision. This uses plain old network cabling, though you should upgrade to the better shielded CAT 6, to transmit up to 1Gbps of image data as far as 100m. You will need to buy a special purpose card for your PC – the regular network card can probably not handle Jumbo Frames and in any case, you need it for internet and intranet access – but these are far less expensive than a CameraLink grabber. And if power cabling is a concern, Power-over-Ethernet (PoE) will deliver up to 13W – enough for most cameras.

Downsides? Well really, just the fact that you’re limited to 1Gbps, which is more than FireWire b) can offer, so it’s enough for run-of-the-mill applications.

As for resolutions going up, well you knew that already, didn’t you?