Slower frame rate than expected using NI 1427

[Omer]

Hello,

I'm using NI 1427 cameralink card to acquire and save images with CCAM cmos camera.

Using ROI I can increase the camera frame rate up to hunderds frames per second (FPS).

When I use the IMAQ sequence.vi to acquire a sequence of frames, the resulted FPS is much less than expected (i.e. 230 instead of 370). I'm using a flat sequnce structure with 2 clocks to estimate the acquired FPS.

When openning the camera in MAX I checked that indeed the camera works at the high FPS.

I'm working on PC with AMD Athlon64 x2 Dual 3800+, windows xp pro, 1Gb RAM, Labview7.1.1, vision acq. software 8.2.1

Can anyone spot the problem?

thanks

Omer

[Jasper S]

Omer,

There is nothing functionally different between the two methods you are grabbing frames, and they should be able to acquire at the same rate.  How are you calculating the frame rate in the Sequence in LabVIEW?  Also, try running a Grab example in LabVIEW, and see what frame rate you can achieve there.

Regards,

Jasper S

[Omer]

Hi Jasper, thank you for your respose.

I'm using a flat sequence structure to calculate the frame rate. I put clocks at the 1st and 3rd frames of the sequence structure and the IMAQ sequence.vi at the middle (2nd frame). I calculate the difference between the 2 clocks and divide the result by the number of acquired frames to get the number of frames per second. 

I couldn't find a grab example that calculates frame rate. Using continous grab and calculating the frame rate (again elapsed time divided by number of frames) I get pretty much the same result as with the sequence.

I attached the sub-vi I'm using for the acquisition, as it might help.

Thanks,

Omer

[BruceAmmons]

My guess is that you are including acquisition setup time in your calculations.  It takes some time to set up the buffers, initialize the camera, etc.  You would get more accurate results if all the setup steps were before your timing structure.

My favorite way to measure frame rates is to start a continuous acquisition, then record the frame number and start time.  As time goes on, I compare the current frame number and time with the initial values and calculate the frame rate.  This converges very rapidly to the actual frame rate.

Bruce