Point Grey Flea3 GigE Technical Reference
B FlyCapture SDK Examples
This functionality is achieved by specifying a number of events, which are tied to various locations in the image. The
events are then signalled as the corresponding portion of the image arrives on the PC. This allows the user to start
processing the data immediately without having to wait for image transmission to complete. If you specify one event, it
occurs at the end of the image. If you specify two events, the first occurs near the beginning of the image, and the
second occurs at the end. If you specify more than two events, they are spread evenly among the remainder of the
image.
Partial image event notification is particularly useful in applications requiring extremely low latency, such as moving the
camera and stopping only to take pictures. In this case, setting two events, with the first occurring near the beginning of
the image, is a good method for indicating the end of integration and that it is safe to move the camera without
disrupting image capture.
Partial image event notification is also available in custom image mode; however, there are some additional
considerations when using this mode. Event notifications must be set on packet boundaries, so you must compute the
total image size, including padding, when deciding where to set event sizes. There will be at most one padded packet
transmitted, so the ceiling of the computed image size divided by the packet size returns the number of packets
transmitted per image:
numOfPackets = ceiling(( rows * cols * bytesPerPixel)/bytesPerPacket)
If the camera has already been started with the chosen bytes per packet, this value can be queried from the format 7
registers. See the entry for PACKET_PER_FRAME_INQ (0x048) in the Point Grey Digital Camera Register Reference.
Partial image event notification operates differently between the Windows and Linux operating
systems in the following ways:
n
On Windows, if more than one image event is specified, the first event occurs after the PC
receives the first packet. The remainder of the events are equally distributed along the length
of the image. On Linux, all events are equally distributed along the image. However, if an
image is transmitted in more than one packet, there are no notifications after the first
packet is transmitted.
n
On Linux, synchronizing image transmission on the sy-bit is disabled when using partial
image event notification. As a result, in certain cases when the CPU is heavily loaded and the
image rendering software is not cycling for a long period, the image stream may fall out of
synch and become corrupted. To re-synchronize transmission, stop and re-start isochronous
image grabbing and transmission.
Depending on your operating system, for this example to work on your PC, you may need to install a
hotfix from Microsoft.
Title
Article
Recommended or required Windows Service Packs and
Hotfixes
Knowledge
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Revised 10/29/2013
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