Справочник Пользователя для National Instruments Image Acquisition Software

Chapter 3

Programming with NI-IMAQ

©

 National Instruments Corporation

3-11

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.

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.

UM.book  Page 11  Monday, July 13, 1998  9:49 AM