FEATURE MACHINE VISION SYSTEMS MAKING THE MOST OF GIGE VISION
the operating conditions, such as illumination effects. Maintaining constant image brightness
is particularly important for visualisation when there are significant changes in ambient lighting conditions. Auto exposure and auto gain can also be useful in extracting detail from images which have both very bright and very dark regions within them. The auto levels can be set independently to optimise image detail in whichever region is the most significant for the user. Usually auto exposure is used first until exposure periods reach levels where the frame rate may be compromised, and then auto gain can be added.
igE Vision continues to be one of the most popular machine vision standards used in industrial inspection applications. Users benefit from the fact that cameras from any manufacturer that are GigE Vision compliant can be used interchangeably, in addition to the fact that Gigabit Ethernet cameras allow the transmission of images at high rates over distances up to 100 metres using standard Ethernet cables and components. This interchangeability means that
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camera manufacturers need to look carefully at ways of differentiating their products while conforming to the requirements of the standard. This can be achieved in terms of size, sensor type and construction, but enhancing the functionality of the camera is an important consideration. One way of achieving this is through the use of firmware. This not only ensures that cameras are sold with the latest capabilities, but that cameras in the field can be upgraded to the latest version rather than be limited to their original functionality. A good example of this is the recent firmware upgrade for all IDS GigE Vision cameras, which brings new and useful features such as auto exposure, auto gain, subsampling, black level, LUT and gamma, as well as providing new standard pixel formats and new bandwidth management capabilities.
IMAGE QUALITY With a rich array of monochrome and colour CMOS sensors available, including those from Sony, ON Semiconductor and e2v, users can select a camera based on the resolution, frame rate and overall image quality needed for the specific application. However, functionality such as auto exposure and auto gain and others give users the ability to adjust camera performance in the context of
18 DECEMBER/JANUARY 2018 | AUTOMATION
BANDWIDTH MANAGEMENT Bandwidth management in GigE Vision is particularly important for optimising data transmission, especially in multi-camera systems. GigE Vision cameras transmit image data in small packets over the network, even before a captured sensor image is read out completely. This minimises delays in image transfer. However, if too much data is transferred at the same time, the maximum bandwidth of a GigE network (120MBps) can be exceeded very quickly. In addition, if data packets are incorrectly transferred, the transport layer used within the standard can request the missing data packets to be sent again. To relieve the network load in multi-camera operation or to relieve a processing system, it is necessary to reduce the network bandwidth of the transmitting devices. The GigE Vision standard provides for inter-packet delays to be introduced to create transmission pauses to prevent bandwidth bottlenecks. However, this causes the total transmission time to increase, since the image data is sent slower than before, thus reducing the data
throughput. Increasing the transmission time also results in a reduction of the maximum frame rate achievable. Unfortunately, choosing a suitable delay between the data packets is not very straightforward making it difficult to use. However, the GigE Vision standard also allows maximum bandwidth of data sent from a device to be limited and using this, the delay between the packets can be calculated to make control easier.
INCREASING VERSATILITY IDS has, however, further extended this functionality in its GigE Vision cameras through its camera firmware which not only calculates the required packet delays from the bandwidth limit that has been set but also calculates the maximum possible frame rate that can be reached when using that limit. In addition, the bandwidth of the device theoretically available without the restriction is automatically calculated, eliminating time-consuming calculations for each camera. Since IDS GigE Vision cameras use the bandwidth limit to independently limit the data output and also show the frame rate and the calculated bandwidth for the current camera settings, these settings can be optimised in order to maintain the bandwidth limit, bringing added versatility. It is also possible to optimise the settings of individual cameras in a multi-camera system to operate on the same Gigabit Ethernet port without exceeding the maximum bandwidth as well as prioritising the cameras on the basis of the throughput limits set for the individual cameras. This effectively avoids bottlenecks that would otherwise lead to errors in image transmission.
MOVING FORWARD Firmware provides the perfect platform to establish new functionality in GigE Vision cameras, and IDS has further enhancements planned over the coming months. New features will include extended trigger capabilities for setting up image acquisition, such as factoring in delays which gives customers the benefit of being able better adjust the timing of the image acquisition to suit their application. In addition, the cameras will be capable of generating a pulse that can be transmitted via digital I/O in order to control an illumination source, for example.
IDS Imaging Development Systems T: 01256 698153
www.ids-imaging.com
/AUTOMATION
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