Справочник Пользователя для National Instruments Image Acquisition Software

Chapter 3

Programming with NI-IMAQ

©

 National Instruments Corporation

3-9

Figure 3-3.  Grab Programming Flowchart

The 

hlgrab.c 

example demonstrates how to perform a grab using 

imgGrabArea

. The example performs multiple grabs until an appropriate 

condition is met. The program configures the session to perform a grab 
operation by calling the 

imgGrabSetup

 function. The program then 

calculates the area to grab using the current ROI, rowPixels, and 
BYTESPERPIXEL, and the acquisition is started by calling 

imgSessionStartAcquisition

. In this example, we allocate our 

own user buffer for grabbing and pass this buffer to 

imgGrabArea

. When 

the acquisition is complete, it stops. The program then frees the user buffer 
and all of the resources associated with this interface by calling 

imgClose

.

imgInterfaceOpen

imgInterfaceOpen

 opens

and configures the interface
according to the file setup by the 
IMAQ Configuration Utility.

imgGrab

 copies the contents of the driver buffer

to a user buffer. This function can be synchronized
to a vertical blank or initiated asynchronously. The
buffer can be passed into 

imgGrab

 or automatically

allocated by NI-IMAQ. 

imgGrab

 can be called

multiple times for high-speed acquisition.

imgSessionOpen

 opens a session that

will be used for all acquisition and configuration.

User-specific image processing

imgClose

 closes the interface and session.

imgGrabSetup

 configures the interface for a

continuous acquisition.

imgSessionOpen

imgGrabSetup

imgGrab

User-Specific Functions

imgSessionStopAcquisition

 stops

the grab function.

imgSessionStopAcquisition

imgClose

(Loop)

imgSessionStartAcquisition

 starts

the acquisition into a driver buffer.

imgSessionStartAcquisition

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