National Instruments Image Acquisition Software - Manual (Page 29)

Chapter 3 Programming with NI-IMAQ
© National Instruments Corporation 3-9 NI-IMAQ User Manual
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