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Chapter 2 Basic Acquisition with NI-IMAQdx
NI-IMAQdx User Manual 2-10 ni.com
Note If you do not have a valid session, a temporary session is created using cam0.
Then, the snap acquires the next incoming image into a user buffer. After
the image is acquired, the program calls image processing and analysis
functions. When the processing and analysis functions are finished, the
program calls the Close Camera function using the camera handle. This
function instructs NI-IMAQdx to free all of the resources associated with
this camera, which releases the session.
Grab
A grab initiates a continuous high-speed acquisition of images to one or
more internal buffers. Figure 2-3 illustrates the typical programming order
of a high-level grab acquisition.
Figure 2-3. High-Level Grab Flowchart
Use a grab for high-speed applications during which you need to process
only one image at a time. You can copy the last acquired buffer to a separate
user buffer for processing or analysis. To use these functions, you must
have a valid session. If you do not have a valid session, the NI-IMAQdx
Configure Grab function creates a session using
cam0.
Opens and configures camera
Copies contents of internal buffer
to user buffer; can call grab function
multiple times for high-speed acquisition
Executes user-specific image processing
Closes the camera session
Configures camera for
continuous acquisition
(Loop)
Open
Configure Grab
Grab
User-Specific Functions
Close