Common NI-IMAQ VI Parameters

IMAQ Session is a unique identifier that specifies the interface file used for the acquisition. This identifier is produced by the IMAQ Init VI and used as an input to all other NI-IMAQ VIs. The NI-IMAQ VIs use IMAQ Session Out, which is identical to IMAQ Session, to simplify dataflow programming. IMAQ Session Out is similar to the duplicate file sessions provided by the file I/O VIs. The high-level acquisition VIs—IMAQ Snap, IMAQ Grab Setup, and IMAQ Sequence—require you to wire IMAQ Session In only if you are using an interface other than the default img0, if you are using multiple devices, or if you need to set IMAQ properties before the acquisition.

Many acquisition VIs require that you supply an image buffer to receive the captured image. You can create this image buffer with the IMAQ Create VI. Refer to Managing Buffers in LabVIEW for more information. The input that receives the image buffer is Image in. The Image out output returns the captured image.

During development, it may be useful to examine the contents of your image at run-time. With LabVIEW 7.0 or later, you can use a LabVIEW image probe to view the contents of your image during execution. Right-click your image wire and select Probe.

The acquisition VIs use the Region of Interest input to specify a rectangular portion of an image frame to be captured. You can use Region of Interest to reduce the size of the image you want to capture. Region of Interest is an array of four elements with the elements defined as Left, Top, Right, Bottom. If Region of Interest is not wired, the entire image acquisition window is captured. You configure the default acquisition window using MAX.

The acquisition VIs use the Step x and Step y inputs to specify a horizontal and vertical sampling step. The sampling step causes a reduction in spatial resolution.