National Instruments Image Acquisition Software - Manual (Page 31)

Chapter 3 Programming with NI-IMAQ
© National Instruments Corporation 3-11 NI-IMAQ User Manual
The HLSeq.c example demonstrates how to perform a sequence
acquisition using imgSequenceSetup . The example sets up a sequence
that uses 10 user-allocated buffers. Unlike the ring example, each buffer in
the sequence has its own skip count associated with it. The skip count is the
number of frames to skip prior to acquiring the next image. The acquisition
is started at setup time and the setup call is synchronous.
High-Level Ring Functions
Ring and sequence functions include imgRingSetup ,
imgSessionStartAcquisition and imgStopAcquisition . Use
these functions to perform a continuous acquisition that loops or stops after
a certain number of images have been captured.
A ring initiates a continuous high-speed acquisition to multiple buffers.
Calling
imgRingSetup initiates a ring. imgRingSetup specifies both the
buffer list that will be used for transfers and the number of buffers. After
imgRingSetup is called, you can monitor the status of the transfer and
perform processing on any of the buffers in the ring. A ring is appropriate
for high-speed applications where you need to perform processing on every
image. You must use multiple buffers because processing times may vary
depending on other applications and processing results. You can configure
a ring to acquire every frame or to skip a fixed number of frames between
each acquisition.
For certain applications, you can temporarily extract a buffer from the ring
to prevent it from being overwritten during the ring’s next pass. Use the
imgSessionExamineBuffer and imgSessionReleaseBuffer
functions to do this. Figure 3-5 illustrates a typical ring programming order.
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