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MareSloCam
August 6, 2012, 20:05:08
Hello,


I have the next problem:

When I want to use Trigger example or Trigger IMAQ example with external trigger I cant get my Grab value to change inside event structure. So that means that when using external trigger I cant get my image inside LabVIEW to update. The IC reference does update but the picture (Trigger example) IMAQ picture (IMAQ trigger example) does not update.

If I am triggering the vi manualy by clicking the grab button then my picture inside LabVIEW updates with no problem.

How can I update that picture or how can I make a value change to the Grab value ?

I dont see why is there a trigger example if you cant realize a external trigger in it!

Feedback pls.

Stefan Geissler
August 7, 2012, 10:33:53
Marko,

I am not sure, which trigger sample is meant, because I simply do not have all of them in mind :-)

However, using an external trigger is tricky in LabVIEW, because you need to add the ImageAvailable event handler to the LabVIEW event list (or what it is named. (I am not a LabVIEW expert, please excuse me)).

In the event handler, something like the IC_Grab*VIs must be implemented. The only difference is, the "MemorySnapImage" call must be removed, because the filled image buffer is already available as property node "ImageActiveBuffer" of IC Imaging Control. The IC_Grab*.VIs must not be used, if the ImageAvailable event is used.

Also, the property node "LiveCaptureContinuous" must be set to true, so all incoming images are saved in the ring buffer of IC Imaging Control automatically.

In general, if trigger is in used, use the ImageAvailable event, because the IC_Grab* will block the program, if they miss the image. The IC_Grab* will wait for the next complete image. That means, if they are called to late and the triggered image is already in delivery, this image will be discarded and the IC_Grab waits for the next image. This is the basic functionality of the used "MemorySnapImage" method of IC Imaging Control.

Related links:
ImageAvailable Event:
http://www.imagingcontrol.com/en_US/support/documentation/activex/event_descICImagingControl_ImageAvailable.htm
ImageActiveBuffer:
http://www.imagingcontrol.com/en_US/support/documentation/activex/prop_descICImagingControl_ImageActiveBuffer.htm
MemorySnapImage:
http://www.imagingcontrol.com/en_US/support/documentation/activex/meth_descICImagingControl_MemorySnapImage.htm