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Why do I often get blank frames while acquiring images using external trigger under Windows 7?

I'm using Windows 7, the latest LabVIEW and IMAQdx right now. The program was developed based on the example provided by LabVIEW. Everything ran well on Windows XP using internal trigger or external trigger. But when I wanted to run the program on a desktop with Win 7, I just cannot get the images continuously using the external trigger. Although I can get the images, the blank frames showed up very often. When I chose the internal trigger, there was no problem.

Once I thought there might be something wrong with my program. But I tried the LabVIEW example to select the internal trigger mode and external trigger mode, it had the same problem.

Is there anyone could give me some suggestions to solve this problem?

Thanks!

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Hi Hubert,

 

Could you please provide some further information? Which specific example are you referring to? There are many IMAQ and IMAQdx triggering examples provided in the LabVIEW Example Finder. Does the Windows 7 machine have the same LabVIEW and Vision Acquisition Software versions as the XP computer? Just to clarify, the images are still acquired at the correct time, the problem is that they are blank (all black), correct? It will also be helpful if you can provide what camera you are working with.

 

Thanks and sorry for the barrage of questions.

Matt
NI Community Team
National Instruments
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Hi Matt,

 

Thanks for your reply.

I was using the "Triggered Grab.vi" to test the camera.

The Windows 7 desktop runs LabVIEW 2010 and Vision Acquisition Software 2009.

The XP computer runs LabVIEW 8.2.1 and Vision Acquisition Software 8.2.

I used a function generator to trigger the camera externally at 5 fps. The amplitude of the trigger signal is about 8 V. I set the trigger mode as "Mode0". Images are acquired at the right time from XP computer without any problems. But when I connected the camera to the Windows 7 computer, it just captured all black frames sometimes during the acquisition. I mean I still can acquire the images at 5 fps, but not all the images acquired were useful, some of which were black frames. And it occurred very often. 

 

Thanks again for you help!

 

Hubert

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I'm sorry I forgot to mention the camera.

I'm using DMK21BF04 firewire CCD camera. You could find the information here:http://www.theimagingsource.com/en_US/products/cameras/firewire-ccd-mono/dmk21bf04/

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Hi Hubert,

 

Are the images always either "all blank" or "all good" or are they sometimes good images with black bands across them or scrambled images? The hardware setup (camera, function generator, etc) is the exact same with each computer, correct? Does there seem to be any pattern to how often blank images vs. good images are acquired?

 

Have you checked if similar results are seen when you acquire images in Measurement and Automation Explorer? Try beginning your triggering via the function generator and then performing a grab in MAX and let us know how it goes. Are blank images acquired or does the display properly update with a new image every trigger pulse?

Matt
NI Community Team
National Instruments
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Hi Matt,

 

The images are either "all blank" or "all good".

The hardware setup is exactly the same.

The blank images are not acquired periodically.

Similar results were also seen when using MAX to control the camera.

 

We found a solution to this problem. But we don't know how to explain it. When we were using the 5-Hz external trigger, we thought the video mode would not affect the image acquisition and therefore we left the video mode option as default (15 fps). But when we change the video mode to 7.5 fps or 30 fps, the problem disappeared. So now if we want to get rid of the blank frames while using the external trigger, we just need to choose the video mode other than 15 fps. Interestingly, when we switch back to the XP system, the camera also acquried inconsistent blank frames if we set the video mode at 15 fps.

 

Thanks again for your help.

 

Hubert 

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Hi Hubert,

 

Thanks for the information and I'm glad to hear you were able to get things working! That's definitely surprising that just15 fps was not functioning. I'm curious if the issue is related more to the camera and the video mode rather than triggering, but I'm happy you found a workaround.

Matt
NI Community Team
National Instruments
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