COMPUTER VISION NETWORKS

The specialized networks dedicated to vision computing offer structures providing high performances and data exchange interfaces well adapted to machine vision. As images acquisition ( digital cameras, frame grabbers ) and images computing are greedy for bandwidth and need to exchange huge amount of data ( the images ) while vouching for very short response time, depending of the application requirements.

When image treatment is embedded in the vision sensor, the main constraint is the big amount of data to be exchanged in a determined space of time. This constraint depends on the amount of images the user wishes to receive inside a defined period, it depends on the frequency needed for archiving and it depends on the amount of cameras in the network.

More, when image computing is external to image acquisition it is necessary to transfer all the frames from the sensor down to the computing system in a reasonable slice of time from an application point of view, with the objective to warrant a sufficient operating duration and to allow a quite good vision system reactivity.

There are many different kinds of image acquisition devices, and these dedicated networks provide standard interface to make operations easier while allowing to be relatively hardware independent.

• With the intention to complete this subject, you can read this interesting article with considerations about the choice of the right camera bus.

  National Instruments - www.ni.com

« Camera link » is a hardware only specification designed by camera manufacturers to access cameras implemented in a network, in order to quickly read the frames and to control these cameras. It is based on the « National Semiconductors » ( nowadays « Texas Instruments » ) Channel Link interface. The current « Camera link » specifications are provided by the AIA ( www.automate.org ) which maintains them. Typically, its performances allow the data transfer rate to be about 2 Gbit/s for the basic configuration and around 5.5 Gbit/s for the medium and for the full configuration.

• Detailed description of the Cameralink connection.

  You will get here the connection diagram for the plugs for each mode. In addition, you can get the cable specifications ( These informations are included in the Cameralink specifications pdf file, see below ).

  www.siliconimaging.com

Even these specifications could not be up to date, you will find all the informations you want about the Camera Link technology : the signals, the port assignments, the bit assignments according each available configuration and the description of the connections.

www.imagelabs.com

The « IEEE 1394 » standard protocol is also known as « DCAM » ( Digital CAMera protocol ), « IIDC » ( Instrumentation and Industrial Digital Camera ), « Firewire », « iLink » or « I-Link ». It has been originally developed by the Apple company and it is quite the concurrent of the USB technology.

Right at the start, this high speed serial bus has been designed for digital audio and video consumer usages. It operates both isochronous and asynchronous data transfers, what leads to real time capabilities. However, its features are compliant with industrial usages in order to operate machine vision installations at low cost, according to its performances.

Damien DOUXCHAMPS is an engineer particularly involved in the world of the digital cameras and in the world of the « IEEE 1394 » standard. He provides a lot of informations and published some useful utilities of its own related to the digital video devices.

• You can download the complete IEEE 1394 specifications from the V 1.04 version up to the current version.

  You can look at this comprehensive standard summary ( ) in order to well understand how the numerous specifications are organized.

  ---

• Damien DOUXCHAMPS maintains and provides the probably most complete « Firewire » digital camera list, including their main characteristics and their price.

  This list is related to scientific cameras, to industrial cameras and to any other machine vision cameras since 1999 ( the list is really impressive ! ).

  ---

• Libdc1394 is a high level IEEE 1394 programming interface used to control cameras based on « Firewire ». It has been developed by Damien DOUXCHAMPS himself and a team of colleagues.

  ---

• Coriander is a Linux based IEEE 1394 graphic user interface which control directly a camera over the « DCAM » bus.

Damien DOUXCHAMPS - https://damien.douxchamps.net

These slides show how compliant can be this network for industrial applications such as imaging, industrial field bus, motion control and remote sensors access. They compare some features of the standard with those of the Gige Vision standards ( the topology, the performances, the usability, the hardware requirements ) and they show why the IEEE 1394 is reliable for automation networking, especially concerning the « IEEE 1394b » version of the standard.

1394 standard association.

• IEEE 1394 overview.

  www.skipstone.com

  ---

• Introduction to the IEEE 1394 high speed serial network. ( )

  These slides are a good overview about the technology, by quickly presenting its main features.

  Jerry Fife - [ Archives ]

• Firewire technical reference tutorial.

  This 78 pages long document presents all you need to know in order to well understand the DCAM standard and it how such a system works. The content carries on the topology, the architecture, the communication process, the synchronization process, the data structures and so on. This technical tutorial is intended to engineers who are unfamiliar with this technology, in order to make the first contact easier.

  By the 1394 trade association

  ---

• Firewire / 1394 design guide.

  This document presents many detailed considerations related to the system design, the cable power, the link selection, the firmware layers, the mechanical point of view and more.

  By the 1394 trade association.

  ---

• IIDC instrumentation and industrial digital camera specifications version 1.1.0.

  This document is very technical since it is intended to designer teams working for imaging device makers, with the intention to help them to implement a digital interface in their products.

  The globale structure, the registers, their fields as well as the data formats are all well defined and well explained. The data blocks used for controlling image format, transport layer, acquisition, luminance, chroma, LUT, trigger, user set, digital IO, counter and timer are more particularly described precisely.

  By the 1394 association and the JIIA.

This short document has to be grasped in the context of the automotive industry and of the modern vehicles supplied with multimedia systems, in which it compares two solutions - IEEE 1394 automotive with Ethernet AVB audio-video bridging - to operate the multimedia network data transfers.

Quickly, the result of this comparison is that the data rates are similar for both solutions. But when we take in account the topology of a whole multimedia network embedded in a vehicle, the weight of all the associated equipments and of all the associated cabling plus the global costs, the 1394 solution might be rather the best performing one.

By the 1394 trade association

« GIGE VISION » ( Gigabit Ethernet Vision ) is a high performing specialized network system dedicated to machine vision and more generally to image transfer, intended to interface cameras from different manufacturers with any other devices and with any user applications. The Gige Vision standard is based on the Gigabit Ethernet specifications and its designers have chosen using the user datagram protocol UDP rather than using the transport control protocol TCP, probably with the objective to increase the performances. It will very likely evaluate by adopting the 10 Gigabit Ethernet specifications. This normalized interface allows the manufacturers to provide Gige Vision compliant devices without the need of any custom modifications, leading in a quite universal network system easily accessible by any third party.

The full gigabit Ethernet vision technical specifications are divided in four parts : the device discovery, the « Gige Vision control protocol » ( GVCP ), the « Gige Vision stream protocol » ( GVSP ) and the bootstrap registers.

• The device discovery.

  This part describes the process which allows a device to get a connection through a network interface before it describes how to get a valid IP address by using standard protocols. It also details the method which allows an application to list all the devices operating on a network.

  ---

• GVCP - The control protocol.

  This protocol specifies how to operate the configuration of the connected devices, and it warrants the reliability of the image transfers. It is an application layer protocol operating in relation with the UDP transport layer. It provides the necessary support to control a device from a only one application ( the primary application ).

  ---

• GVSP - Streaming Protocol.

  This protocol specifies how to operate the data exchanges. It is itself an application layer protocol too. It allows a receiver to get image data, to get image informations or to get any other information from a transmitter.

  ---

• Bootstrap registers.

  This part specifies the data structure used to describe the features supported by the the connected devices.

  • A standard list is defined to start each device. These registers are common to all the Gige Vision devices and they are set at fixed memory addresses.
  • A manufacturer can add custom registers at a specific address range but these registers can only be read once the device has finished starting.
  • This protocol is based on the Genicam standard, a generic programmable interface XML based.

Advanced imaging association ( AIA )

www.visiononline.org

This well structured and illustrated document presents a technical summary about the most important aspects of the use of Gige Vision cameras, from the perspective of the network performances. After a short presentation of the image acquisition and the transfer process, from a camera to a host machine, the document is talking about the following subjects :

• The most used system configurations.

  ( mono-cameras or multi-cameras over dedicated networks or over general purpose networks )

• The Gige Vision protocol according to the OSI model.
• The restricted size of the TCP/IP packets, and operating judiciously with the jumbo frames.
• The data rate, the latency, the TCP packet delay and the frame delay in various situations.
• The host machines configuration, the network cards and switches selection and configuration, and how important is to operate a very good cabling.
• The Gige Vision drivers used as interfaces between the network card and the host system.

  They take care of filtering, coding and decoding the Gige Vision data in order to decrease the host machine CPU load.

Leutron [ Archives ]