What's the best way to control frame rate?

[marinvms]

I am trying to acquire a sequence of images using LabWindows/CVI version 5.0 and IMAQ 2.5, device PXI-1422. The fps of my camera (Pulnix 9701) is 30. I want to be able to specify a lower value than that, say 15 fps.

ImgSequenceSetup doesn't seem to provide that functionality. What is the best way to control the frame rate in that case? (1) Is there a way to specify frame rate directly before acquiring a whole sequence with the supplied sequence acquisition functions or (2)is it a better idea to use some sort of snap functions in a loop to get each frame individually?

Thanks for any help given.

[Kyle_V]

If you leave your camera in free run mode (no asynchronous triggering), then the most exact way to lower the frame rate will be with a skip count. The imgSequenceSetup function has an input array called Skip Count[] that specifies the number of frames to skip before acquiring an image. So if you had a sequence that was three buffers long, and you wanted to acquire at 15fps, then you would enter skip counts of 1 for the first three values of the array. For 100 buffers, you'll need 100 elements to the skip count array.

A snap in a loop with a time delay value will also give you the same effect, but it will be timed in software and won't be as exact as the skip count, which is timed in hardware.

Kyle V
Applications Engineer
National Instruments
www.ni.com/ask