HL Grab Update IMAQ Property

[Michelle_N]

If you've ever played with IMAQ camera settings in MAX during an acquisition (grab) you'll notice that the acquisition keeps humming along while these settings are updated. But if you try this in LabVIEW by slipping an IMAQ property node inside an acquisition you'll notice two things:
1.) The properties do not get updated and 2.) You get an error (-1074397151) stating LabVIEW cannot perform request; acquisition currently in progress:

What gives? Is MAX doing magic behind the scenes? As cool as it would be to have magic calling the shots it is just not happening. What is happening is everytime a user changes an setting, such as Acquisition Window, Reference Level, and Frame Timeout, during an acquisiton wintin MAX, the acquisition is actually stopped, the setting is updated and then the acquisition is started again. Really. No really. It happens fast enough that you don't notice.

So to do the same thing programmatically within LabVIEW you actually have to stop the acquisition as well. This example does just that:

This particular example uses White Reference and Black Reference voltage properties (analog properties) but this principle will work with any IMAQ property. Simply go to the True case of the case structure and change the property to the one of interest. Also, there are other ways to do this - if you like Event Structure feel free to swap the Case Structure out.

Wow! Look! It's a code snippet! If you have LV 2009 you're in luck as you can drag and drop this into your block diagram! First make sure you're using Internet Explorer and then drag and drop the snippet onto your block diagram. Amazing!

Note: You may have to click on the snippet to enlarge it before dragging and dropping.

If you don't have 2009, don't fret. Below you can download a version saved in LabVIEW 8.0.

For a more information check out this KnowledgeBase:
Why Can't I Update IMAQ Properties During a Grab Acquisition in LabVIEW but I Can in MAX?