How to force frame rate in MAX or Labview with 1394 camera

[ejb3439]

I am very new to the imaging capabilities in Labview and am having a difficlut time forcing a frame rate for my cameras.  I am using (2) Pixelink PL-A741 cameras and both appear in MAX.  However, the frame rate is not an attribute that I am able to set.  I need to be able to force a frame rate of 30-50 and either need to be able to do this in MAX or in Labview.  Please help!

Emily

[Vladimir_Drzik]

Hi Emily

You can set the frame rate of FireWire cameras with internal triggering by the "packet size" value. Keep in mind that "packet size" value is the size of one data packet on the FW bus in bytes. The bus always transfers 8000 packets per second. For transmission of one image from the camera, you need exactly width*height bytes, provided that the image is 8-bit. Thus, if you want to achieve FPS frames per second, then

packet_size =  FPS*width*height/8000

Vladimir

[ejb3439]

I try to do this in MAX, but am unable to change the packet size.  If my cameras are set to the Legacy NI-IMAQ IEEE 1394 driver, I update the video mode to format 7 and change the region of interest to 640x480.  However, the packet size is locked in at 4092.  If I update the driver to NI-IMAQdx, however, the packet size is locked in at 2320 with a 640x480 image, again in format 7.

Is this something i can change in my VI rather than in MAX and if so, any suggestions for code?

Emily

[Vladimir_Drzik]

You are right that you can only change the packet size for Format7 acquisition. Other video modes have predefined FPS.

I'm not sure why you are not able to change the packet size. It definitely can be done from MAX. Keep in mind two things. The default packet size value is the maximum, so you can only go to lower values. And you cannot change the packet size while the acquisition is active.

[iZACHdx]

Hello,

You can change the attributes of the camera file programmatically as outlined in this document: http://sine.ni.com/devzone/cda/epd/p/id/1212 . This involves parsing through the camera file and setting the appropriate attribute. Do you have the most recent version of the firmware for your camera? Some details of your operating system may be helpful as this could be the problem as well: http://ae.natinst.com/operations/ae/public.nsf/web/searchinternal/2243D57B9EEF22B686256FB7005E23C1 .

-Zach