FLIR GRASSHOPPER 3 Series Technical Reference page 109

This example illustrates how users can implement partial image event notification. Partial image event
notification is a mechanism that provides the user with access to image data as it arrives in the PC's memory,
before the entire image is available.
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 FLIR Machine Vision Camera Register
Reference.
2/10/2017
©2013-2017
FLIR Integrated Imaging
Solutions Inc. All rights reserved.
Note:
Partial image event notification operates differently between the
Windows and Linux operating systems in the following ways:
On Windows, if more than one image event is specified, the first
n
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.
On Linux, synchronizing image transmission on the sy-bit is
n
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.
Grasshopper
®
3 PGE Technical Reference
B FlyCapture SDK Examples
98