Basic guidelines in selecting a machine vision camera interface

Industrial machine vision camera interfaces have continued to develop allowing cameras to transfer megapixel images at extremely high frame rates. These advancements are opening up endless applications, however each machine vision camera interface has its own pro’s and con’s.

Selecting the best digital camera interface can be done by taking in several considerations first and in doing so, can window down your selection.

The following are some considerations in making an interface selection.

Bandwidth (Resolution and frame rate)
Cable Length
Cost
Complexity

Bandwidth: This is one of the biggest factors in selecting an interface as it essentially is the size of the pipe to allow data to flow. Bandwidth can be calculated by resolution x frame rate x bit depth. You essentially find out pixels / second x the frame bit depth resulting in your total Megabits / second (Mb/sec). Large frame sizes at high speeds will require a large data pipe! If not, you’ll be bandwidth limited, so one would need to reduce the frame rate and image size or a combination of both.

Cable Length: The application will dictate the distance between the camera and industrial computer. In factory automation applications, the cameras can be located in most cases within meters from the computer vs a stadium sports analytics application requiring 100’s of meters.

Cost: Budgets dictate in most cases, so this must also be considered. Interfaces such as USB are very low cost versus a CoaxPress interface which will require a $2K frame grabber and more expensive cables.

Complexity: Not all interfaces are plug and play and require more complex configuration. If you are leaning towards interfaces using frame grabbers and have no vision experience, you may want to elect using a certified systems integrator.

The considerations above will start to dictate the interface for the machine vision application. The chart below provides an overview to help in the selection process. For a PDF of this chart, please email jonc@1stvision with subject “Interface chart”

Digital machine vision camera interfaces.

The interfaces each have pro’s and con’s aside from the designated bandwidth, cable lengths and costs, and outlined as follows:

USB2.0 is an older standard for machine vision cameras and now superseded by USB3.0 / 3.1 . Early on, this was popular allowing cameras to easily plug and play with standard USB ports. This is still a great option for lower frame rate applications and comes with low cost. Click here for USB2 cameras.

USB3.0 / 3.1 is the next revision of USB2.0 allowing high data rates, plug and play capabilities and is ratified by the AIA standards, being “USB3 Vision” compliant. This allows plug and play with 3rd party software following the GENICAM standards. Cables lengths are limited to 5 meters, but can be overcome with active and optical cables. Click here for USB3 cameras

GigE Vision was introduced in 2006 and is a widely accepted standard following GENICAM standards. This is a the most popular high bandwidth interface allowing plug and play capabilities and allowing long cable lengths. Power Over Ethernet (PoE) will allow 1 cable to be used for data and power making a simpler installation. GigE is still not was fast as USB3.0, but has benefits of 100 meter cable lengths. Click here for GigE cameras.

5 GiGe (aka N-base T) & 10GigE similar to USB2 moving to USB3, is the next iteration of the GigEVision standard providing more bandwidth. Both follow the same GigE Vision standards, but now at higher bandwidths. Specific NIC cards will be required to handle the interface. Click here for 5 GigE cameras.

CoaxPress (CXP) is a relatively new standard released in 2010, supported by GENICAM, utilizing coax cable to transmit data, trigger signals and power using one cable.. It is a scaleable interface via additional coax cables supporting up to 25Gb/s (3125MB/s) and higher now with CXP12. The interface can support extremely high bandwidth as seen in the above chart with long cable lengths to 100+ meters depending on the configuration. This interface requires a frame grabber which adds cost and some complexity in the overall setup. Click here for CoaxPress cameras

Camera link is a well established standard, dedicated machine vision standard released in 2000 allowing high speed communications between cameras and frame grabbers. It includes provisions for data, communications, camera timing and real time signaling to the camera. A frame grabber is required similar to CXP adding cost and some complexity and is limited in cable lengths to 10 meters. Longer cable lengths can be achieved with active and fiber optic cable solutions which additionally add cost. Click here for CameraLink cameras

CameraLink HS is a dedicated machine vision standard taking key aspects of CameraLink and expanding upon it with more features. This is a scaleable high speed interface with reliable data transfer and long cable lengths up to 300+ meters with low cost fiber connections. Similar to CXP and camera link a frame grabber is required adding cost. Click here for Cameralink HS cameras

Some caveats: In calculating bandwidth, you can calculate the theoretical data rate, but in some interfaces, the real world practical will be different. In Camera link and CoaxPress, the theoretical and practical are the same. In Cameralink HS, limits will be set by the computer interface (i.e PCIe x 8, Gen 3 is 6.8 Gigabyte / sec and an Xtium CHLS frame grabber can capture 7 Gigabyte / sec!)

The theoretical and practical limits for USB and Ethernet can be quite different and there will always be some difference. For example, large frames and low frame rate generates less interrupts, providing less overhead to the CPU. A small frame with high frame rate generates more interrupts causing more load to the CPU.

As a note: This blog post covers the basics of each of the interfaces. There is much more information 1stVision can share with you to be sure you are taking all aspects of the vision application into consideration. We have several additional resources we can share to help, so don’t hesitate to contact us for free consultation!

1st Vision’s sales engineers have over 100 years of combined experience to assist in your camera selection. With a large portfolio of lenses, cables, NIC card and industrial computers, we can provide a full vision solution!

Ph: 978-474-0044 / info@1stvision.com / www.1stvision.com

Related Blogs

Learn about the new 5GigE camera interface

Learn about CoaXpress and frame rates achievable with Allied Vision’s “Bonito Pro” cameras with CXP-6

What Is Offered in an Industrial PC Machine Vision Computer?

December 10, 2018December 17, 2018

Learn about the new 5GigE camera interface

Machine vision interfaces have continued to evolve over the years increasing data throughput and cable lengths. Commonly used interfaces are GigE and USB3. However, 5GigE is an interface now gaining attention in the industrial imaging / machine vision market with some nice advantages.

We will outline the benefits of 5GigE, but first, lets give a brief overview of the commonly used camera interfaces, with their pluses and minuses:

GigE / GigE Vision

110 MB/s of sustainable throughput. In real world terms, a HD, 2MP camera can get 50-55 fps in 8 bit mono or 8 bit color mode. Note, this isn’t real HD, since you need 60 FPS.
Data cable lengths up to 100m using regular CAT 5e/6 cable.
Easy to put multiple cameras on a system.

USB 3 / USB3 Vision

420 MB/s of data throughput. A HD 2MP camera can run 60 fps in 8 bit mono or color and can also run RGB at 60 FPS no problem. With the higher throughput, a 5MP camera can achieve 85 fps in 8 bit mode.
Data cables up to 5 meters and up to 20 meters with active cables. However, active cables can be quite costly, adding up to $200 in cost.
Not as easy as GigE to put multiple cameras on a system, and gets harder with each additional camera, especially if you have limited USB3 controllers.

As a note, there is no cost difference when using cameras with the same sensor from the same manufacturer with USB or GigE! They will cost about the same with no premium for one interface over the other.

What are the limitations of GigE and USB3 now solved by 5GigE?

USB3 is limited in cable length, so going faster than GigE is great, but you can not have long cable lengths.
GigE has cable lengths up to 100 meters, but is limited to ~ 110MB/s of data, so you do not have the high frame rates as in a USB3 camera.
USB3 in 4+ camera systems is not as stable as GigE AND you’re still limited on cable lengths.

Wait! – What about 10GigE?

Up until now, 10G was the next interface. However, the jump to 10G has quite a few limitations as outlined below.

Heat generation is significant, so cameras are large and not in the smaller 29 x 29mm cube form factor.
Not a lot of demand for very high speed 10G, so not a lot of sensors being offered
Minimal number of manufacturers for 10G, higher cost.
Special cabling, either optical or high quality cat 7.

What we have found is that there are several types of applications for 10G cameras and are as follows

Applications where you need 10G of speed of course (high resolution + fast frame rates)
Require greater than 110MB/s of data and need long cable lengths.
Where there is the required combination of 110MB/s for high frame rates, multiple cameras and long cable lengths, 10G is a perfect solution.

We have seen that the need for higher bandwidth + long cable lengths is more prominent vs. the real need for 10GigE!

Introducing 5GigE that provides increased bandwidth, long cable lengths at reasonable prices! or N Base T.

5GigE (also known as N Base T) has become a new standard for industrial, machine vision cameras.

In the general compute world, a much much larger market than vision, there has also been a need to go faster than GigE. However, the issue of replacing the existing cabling is the major issue preventing this. If you think of a big box store, say a Home Depot for instance, the amount of cabling is huge. Ripping that out and rewiring far exceeds the cost of the equipment to use it!

5G was made to go faster, but use existing cabling. Regular cat6e cable can be used, and 5G is a subset of 10G, so all switches etc. can be kept in service.

5G gives users in the vision market USB3 speeds, but with ALL of the regular GigE features, at a very small premium!

July 18, 2018September 5, 2018

Dalsa Nano M2450 polarized camera: Resolving defects that are undetectable with traditional imaging!

The first Genie Nano camera model with a quad-polarizer filter using the Sony Pregius IMX250-MZR 5.1MP monochrome image sensor is now available. The Teledyne Dalsa Nano M2450 camera incorporates the nanowire polarizer filter allowing detection of both the angle and amount of polarized light.

What problems can the Nano M2450 polarized camera solve?

Polarized filtering can reduce the effects of reflections and glare from multiple directions and reveal otherwise undetectable features in the target scene. Polarization enables detection of stress, birefringence, through-reflection and glare from surfaces like glass, plastic, and metal. Sony’s newest image sensor, with its pixel-level polarizer structure, enables the detection of both the amount and angle of polarized light across a scene.

Four different angled polarizers (90°, 45°, 135° and 0°) are positioned on each pixel, and every block of four pixels comprises a calculation unit.

How does polarization work? Theory of operation

Polarization direction is defined as the electrical direction. Light, with its electrical field oscillating perpendicular to the nano wire grid, passes through the filter while that in the parallel direction is rejected.

For Polarized light, only the portion of the light vector perpendicular to the angle of the nanowire filter grid passes.

For example, with a wire-grid polarizer filter at 90 deg. to the maximum transmission is for polarized light at an angle of 0 deg.

The polarizer filter is placed directly on the sensor’s pixel array, beneath the micro-lens array. This design, compared to polarize filters on top of the micro lens array reduced the possibility of light at a polarized angle being misdirected into adjacent pixels (cross talk) and incorrectly detected at the wrong angle.

The Genie Nano’s polarizer filter on the camera sensor is a 2 x 2 pattern, with each pixel having a nanowire polarizer filter with different angles (90, 45, 135 and 0 degree’s)

The image output pattern of the monochrome camera is arranged in 2 x 2 pixel block as follows:

That is, the first line output is an alternating sequence of pixels 0 & 35 degrees, with the following line of 45 and 90 degrees.

Given the proportion of light available through these four filters, any angle of polarized light can be calculated. Any given state of polarization can be composed by two linearly polarized waves in perpendicular directions. The state of polarization is determined by the relative amplitude and difference in phase between the two component waves.

Calculations on the 2×2 filter blocks result in a single pixel for each polarizer filter angle, therefore the resulting image is one fourth the original image resolution. For example, with an original image of 2464×2056, the resulting image is 1232×1028 (original buffer width/2 and original buffer height/2) for a single polarizing angle.

Teledyne Dalsa offers a Polarization demo user interface making it easy to test the polarization techniques for various applications. This includes the ability to see the results of various processing algorithms with the summed images.

Dalsa Polarization demo — As part of the demo program, images can be displayed with pseudo-color mapping

In summary, the new Dalsa Nano M2450 polarized camera can help resolve defects not detected by traditional imaging! Contact 1st Vision to arrange a camera demo in which we will provide the demo polarization software as well or discuss your application. Or click HERE to request a quote

Need line scan? – With the addition of the Genie Nano polarized model, Teledyne DALSA is the first company to offer polarization for both area and line scan (Piranha™4 polarization) cameras

Related Posts

Dalsa line scan polarization camera makes invisible visible!

Teledyne Dalsa TurboDrive 2.0 breaks past GigE limits now with 6 levels of compression

April 25, 2018April 26, 2018

3-CMOS machine vision cameras bring color fidelity to the market at half the price as previous models

Single sensor machine vision cameras use a mosaic filter placed on the sensor to create color images. This is also called a ‘Bayer’ filter, named after the person who invented it. However, color images from this filter lose resolution and color fidelity compared to ‘true’ color images. Spatial resolution is lost due to interpolation, while the Bayer filter pattern reduces true color representation, sensitivity and dynamic range. To overcome these issues, multi-sensor (3-CCD / 3-CMOS) machine vision cameras can be used.

Typically, machine vision 3-CCD cameras were high cost, until now with CMOS sensors becoming the leading image sensor technology. Now, machine vision 3-CMOS machine cameras provide major benefits over Bayer cameras and at more attractive entrance cost.

CMOS sensor technology has lowered the price of 3 image sensor cameras by 50% providing a better alternative to Bayer color cameras for many applications. JAI’s Apex Series 3-CMOS cameras are the game changer for demanding color applications.

Watch this video to learn more about 3-CCD/3-CMOS cameras

Machine Vision 3-CMOS cameras Vs Bayer cameras provide major benefits for color applications

Better color precision – Accurate RGB values are obtained for each pixel so there is no interpolation/estimation of colors as found in Bayer cameras. This can be critical for paint/ink matching, printing inspection systems, digital pathology, or other applications where color values must be extremely accurate.

Better spatial resolution – The Bayer interpolation process also tends to blend edges and small details. While this can be pleasing to the eye, it can make spatial measurements or bar code reading imprecise or error prone, causing the use of more expensive high resolution Bayer cameras or requiring a second monochrome camera for imaging these details

Higher sensitivity – The prism glass in the AP-3200T-USB and associated cameras, has better light transmission properties than the polymer filters in a standard Bayer sensor. This enables more light to reach the pixels for better overall sensitivity and lower lighting requirements.

Lower noise, higher dynamic range – White balancing on a JAI prism camera can be done on individual channels with shutter adjustments instead of adding gain to the image. This results in lower noise and higher usable dynamic range.

What about “improved” Bayer capabilities like 5×5 interpolation?

Several camera manufacturers claim vastly improved capabilities for color imaging, including 5×5 de-Bayering, color-anti-aliasing, denoising
and improved sharpness. But consider the following: 5×5 interpolation
means you are using an even larger area within the image to estimate each pixel’s color value. So while this can do a better job of “smoothing” color transitions to the eye, it can actually result in less-precise color values for image processing, especially where color variation is high.

This is illustrated in the following images, under identical conditions, by a camera with 5 x 5 debayering and a JAI Apex 3-CMOS camera. The CIE L*a*b* reference chart provides a set of exact color values when expected under specified lighting conditions. The result: 5×5 debayering results in 40% out of match to the expected colors vs 13% for the JAI Apex 3-CMOS camera!

More advanced color imaging features

JAI’s Apex 3-CMOS machine vision cameras provide additional advanced features aside from excellent color fidelity and highlighted as follows:

Color Space conversion: Color data from the camera can be provided using built in conversions to several color spaces including sRGB, Adobe RGB, CIE XYZ and HSI. Custom RGB conversions can also be done using the cameras color matrix circuit.
Color Enhancer Function: Allows the 3-CMOS cameras to “boost” the intensity of 6 colors to help features stand out, such as the red color of blood vs surrounding tissue in a medical application. Additionally, degree’s of edge enhancement can be to increase the contrast of color boundaries.
Color Binning: While most Bayer cameras do not offer this, due to the prism architecture of the 3-CMOS cameras, you can easily bin pixels by 1×2, 2×1 and 2×2 to increase sensitivity, reduce shot noise and / or increase the frame rate.
Color temperature presets from 3200K, 5000K, 6500K and 7000K

All of these features, along with reduced costs for 3-CMOS color cameras, now make this a very attractive solution for demanding color applications! Applications in eye diagnostics, pathology, surgical imaging, meat/food inspection, print inspection and automotive color matching are a few that would highly benefit from the JAI Apex 3-CMOS camera series.

Need to proof 3-CMOS / 3-CCD prism based cameras will enhance your application? Let’s discuss sending you a demo camera!

Currently there are 6 new CMOS models outlined below and full specifications can be found HERE.

1st Vision is the leading provider of industrial imaging components with over 100 years of combined imaging experience. Do not hesitate to contact us regarding the new prices of the 3-CMOS cameras!

Be sure to visit our related blogs on 3-CCD and Prism based cameras

How does a 3CCD camera improve color accuracy and spatial resolution versus standard Bayer color cameras?

White Paper – Learn about High Dynamic Range (HDR) Imaging techniques for Machine Vision

White Paper -How does prism technology help to achieve superior color image quality?