Image Acquisition triggering

[Andruha]

Hello. I'm using an image acqusition board PCI - 1411 with external trigger line. Programing language is Labview 7.0.

When I try to acquire 25 fps by external trigger 0 with option ,trigger start of each buffer list, I succeed to acquire all 25 fps. But when I use option ,trigger each buffer, I succeed to acquire only about 12 fps or less. I attempted to generate the external trigger by two ways: co pulse ticks (from DAQ board) and frequency generation alone.

Can you explain me, please, what is the problem?

Thank you ,Andrey.

[DJ_L.]

Hey Andrey,

First, it would be a good starting point to determine the difference between the two options that you are speaking of.

The first option, Trigger Start of Each Buffer List, means that "When the assertion edge of a trigger is received, the buffer list is acquired. If the acquisition is continuous, buffer index 0 always waits on a trigger before acquiring." In summary, you provide the acquisition with a trigger and when that trigger is received, the frame grabber acquires a list of images and stores them into a buffer list. This is like triggering the start of a grab, which is why you are seeing all 25 fps, because it is not triggering each buffer, just the start of the buffer list.

Now the second option, Trigger Each Buffer, means that "Each buffer waits for a trigger before acquiring an image into the buffer." In summary the frame grabber will acquire an image on each trigger edge and store it into one of the buffers that you have set up. The reason that you are seeing only 12 fps might be due to the frequency of your trigger source. Try to increase the frequency of your trigger source, no matter what it may be, and you should see your frame rate increase. Also, maybe try decreasing the size of your image if you don't see any improvement when you increase your trigger frequency.

You can find more information and details on the functions by using the Context Help on the function. Then you can click on the "click here for more help" link, which will take you to the VI Reference Help where you can find more details on all of the options, such as the definition of the options described above.

I hope this helps. Please let me know if you have any questions or concerns. Thanks and have a great day.

Regards,

DJ L.

[Andruha]

Thank you , DJ L. for your help. I tested the posibility of a trigger rate increasing, but I see only about 12 fps maximum. If I decrease the trigger rate I acquire less then 12 fps as was expected.

Best regards, Andrey

[DJ_L.]

Hey Andrey,

What size images are you acquiring? Have you tried to decrease the size of your images when you increased the trigger rate? What mode are you running in? There can be a lot of things that cause your frame rate to level off at the 12 fps that you are seeing, but in order to help you out, if you are wanting to acquire at a higher rate than 12 fps, then you will have to provide more information about your overall system, such as bit depth, etc. Please provide as much information as possible. Thanks.

Regards,

DJ L.

[Andruha]

Hello DJ L.

I acquire images as 8 bit in png format. The average size of image is about 350 Kb. My computer is 512Mb, 3Ghz, 80Gb.

I also attached a part of my program that is corresponded to a noted problem above. Here you can see number of ticks that I wait to acquire an images is 200, but in an original program this number varies according to DAQ sample rate.

The decreasing of the images size didn't solve the problem.

Thank you, Andrey.

[DJ_L.]

Hey Andrey,

I was wondering what camera you are using? And, in your camera's user manual, does it say that it supports the 30 fps in triggered mode? Also, how are you determining what frame rate that you are acquiring at, in MAX, or some other way? Thanks.

Regards,
DJ L.

[Andruha]

Hello,DJ L.

Camera that I use is Pulnix TMC-6. My camera supports 25 fps, and I can acquire this quantity by nontriggered continous mode. As  I undrestand camera constantly generated 25 fps as analog signal and there isn't any connection to trigger. Only by setting up the input trigger at image acqusition board I can acquire from 0 up to 25 fps (I take the proper frames that I need and miss not relevant for me, this option I implement by using daq counter and co ticks function as was described at the beggining of our forum). In MAX I can see that camera constantly generates 25 fps I have no control to this number.

Thank you, Andrey

[DJ_L.]

Hey Andrey,

The reason that you are not able to get the full 25 fps when you run in a triggered mode is because you are really not triggering the acquisition. The analog camera you have is constantly sending images to the board, and if you are triggering the 1411, you are really just telling your program when to acquire an image, and this is not a hardware triggered acquisition. Since the camera is constantly sending images, and you trigger at a certain frequency, you might be triggering at a time when a frame is currently being sent to the board, and you have to wait for that frame to finish sending its signal before you can acquire the next frame. This in turn is slowing down the images that you are acquiring. So you are doing more of a software triggering, and this is causing you to miss frames that are being sent to the frame grabber. So your best option is to acquire in a nontriggered continuous mode if you need the 25 fps frame rate that you mentioned. Another option you have is to get a new frame grabber and a new camera that has triggering capabilities, and then you can get a true hardware triggered acquisition. Last, in MAX you can change the 25 fps option if your camera has the option to do so. If the camera doesn't have that option, then you can't change it in MAX.

I hope this clarifies things for you. Let me know if you have any questions. Thanks, and have a great day.

Regards,

DJ L.

[Andruha]

Hello, DJ L.

Thank you very much for your advising. Now I understand what's happaned.