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Why Is My Camera Link Image Acquisition Slower Than Expected?



Primary Software: Driver Software>>NI-IMAQ
Primary Software Version: 2014
Primary Software Fixed Version: N/A
Secondary Software: Driver Software>>Vision Acquisition Software
Hardware:

Problem:
I am using triggered acquisition with a Camera Link camera and an NI frame grabber. It seems to be working fine at low trigger rates. However when I increase the trigger rate past a certain point, the acquired frames per second drops to approximately half of the trigger rate. What is causing this?

Solution:
This can be caused by triggering the camera and the frame grabber simultaneously.

Typically you will only need to trigger the camera or the frame grabber. Here are the two recommended ways of triggering your system:
  1. Triggering the camera only.
    When only triggering the camera, the frame grabber continuously tries to acquire images. Whenever you trigger the camera, the camera exposes an image and sends it to the frame grabber, which receives the data. When the FVAL line goes high, the frame grabber reads this data as a new image.

    You can typically use Measurement & Automation Explorer or the camera's configuration software to set the camera's triggered mode. You should not need to modify the image acquisition code in LabVIEW.

  2. Triggering the frame grabber only.
    When triggering only the frame grabber, the camera will operate in free-run mode. The camera will constantly collect and send images to the frame grabber. When the frame grabber is triggered, it waits until the next time the FVAL line goes high and then reads the next image from the camera. When all of the image data has been sent from the camera, the FVAL line will go low and the frame grabber will wait until triggered again. While waiting for the next trigger, the frame grabber will not respond to the FVAL line.

    To configure the trigger in LabVIEW, use the IMAQ Configure Trigger VI.

The problem with triggering the camera and the frame grabber simultaneously is that the frame grabber cannot respond to new trigger pulses while it is receiving data or sending the image from the frame grabber to the computer's memory.

So, if a new trigger pulse is sent while the frame grabber is receiving data, the camera will expose a new image but the frame grabber will ignore the trigger. Since the frame grabber ignores the trigger, it also ignores the new image data that is being sent from the camera to the frame grabber. Therefore, it must wait until the next trigger is sent. This effectively makes the frame grabber miss every other image.



Related Links:
KnowledgeBase 2ARDFUOA: Line Scan Triggering Modes

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Report Date: 10/31/2012
Last Updated: 01/12/2015
Document ID: 62UB6AM7

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