Basler SCOUT LIGHT User Manual download pdf (Page 81)

Image Acquisition Control

Basler scout light 73

6.11.1 Effect of the Packet Size Setting on the Maximum

Allowed Frame Rate

After a camera acquires a frame, the image data is read out from the sensor into a buffer. Once the

frame has been read out to the buffer, the data is packetized and transmitted across the IEEE 1394b

bus to your host PC.

A parameter called Packet Size determines the number of bytes of data that will be included in each

packet transferred across the bus. The minimum value for the Packet Size parameter is 1 and the

maximum value is 8192. Normally, the value of the Packet Size parameter is set to the maximum

and at maximum, the Packet Size parameter has no noticeable effect on the operation of the

camera.

If you lower the value of the Packet Size parameter, the amount of image data included in each

packet transmitted across the bus will be lower. This means that it will take more packets to transmit

each frame and since the cycle time of the IEEE 1394b bus is fixed, it also means that it will take

more time to transmit each frame. If you lower the Packet Size parameter enough, the slower data

transfer rate can begin to affect the maximum allowed frame capture rate of your camera. If you

look at the formulas the previous section, you will notice that one of the factors that can limit the

maximum allowed frame rate is the number of packets needed to transmit a frame. The number of

packets per frame is directly related to the Packet Size parameter setting.

You can see the effect of changing the Packet Size parameter by looking at the read only parameter

called Resulting Frame Rate Abs. The Resulting Frame Rate Abs parameter indicates the

maximum frame rate with the current camera settings. If you gradually decrease the setting for the

Packet Size parameter, you will eventually find that the value of the Resulting Frame Rate Abs

parameter will also decrease.

If you are operating a single camera on your IEEE 1394b bus, you would ordinarily leave the Packet

Size parameter set at the maximum. However, if you are operating multiple cameras on a single

IEEE 1394b bus, you will probably need to change the Packet Size parameter so that the cameras

can effectively share the available bus bandwidth.

You can set the value of the Packet Size parameter and read the current value of the resulting

Frame Rate parameter from within your application software by using the pylon API. The following

code snippet illustrates using the API to work withthe parameter values:

// Set packet size

Camera.PacketSize.SetValue( 4096 );

// Get resulting framerate

double resultingFps = Camera.ResultingFrameRateAbs.GetValue();

For detailed information about using the pylon API, refer to the Basler pylon Programmer’s Guide

and API Reference.

You can also use the Basler pylon Viewer application to easily set the parameters.

For more information about using multiple cameras on a single bus, see Section 10 on page 133.

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Basler SCOUT LIGHT User Manual Page 81