FrameRate-Option in MAX

[BeKo]

Hello
I have a question to the camera setting in MAX.
In the register "Acquisition Attributes" can I set the isochronous packet size. This is understandable to me

But in the register "Camera Attributes", I attribute the possibility of a frame rate to (see picture).

What is the difference between the two?


Thanks,
BeKo

[Dippi]

hi BeKo,

What camera are you using? It would be helpful to find documentation on that camera's attributes to make sure, but here's what I can gather without knowing the model.

The DevZone article Acquiring from Firewire Cameras with National Instruments NI-IMAQdx and Legacy NI-IMAQ for IEEE 1394 is a good resource here. Especially see the section called "Configuring Format 7" within it.

When in most modes other than Format 7, "the packet size, framerate, and Region of Interest are fixed depending on the mode that you use within that format". My guess is for these modes, the FrameRate attribute is intended to let you limit the acquisition rate of the camera in order to have some measure of control over bandwidth use - so by setting the framerate attribute low, you reduce the amount of data transferred for a given resolution and the packet size would be fixed (overall, fewer packets would be transferred).

In Format 7, though, "you can modify either the packet size or the Region of Interest to control the amount of bandwidth that will be reserved by the camera and thus controlling the maximum framerate." My impression with this mode is that your camera will generally ignore the FrameRate attribute when in Format 7 and will take the desired packet size and resolution and then automatically allocate a certain amount of bandwidth for acquisitions (which means max framerate is adjusted accordingly)

To summarize, my impression is that formats other than Format 7, it sounds like this particular camera gives you some control over the free-run (non-triggered) frame rate and will adjust packet size accordingly, whereas Format 7 lets you set a packet size and it will adjust frame rate accordingly. Again, this is without knowing what camera the customer is using or what the camera file tells the driver to do when the FrameRate attribute is set or changed. With that information we could probably give a more specific explanation.

Best regards
Dippi

[JohannS]

Beko,

The frame rate camera attribute allows you to tweak the actual frame rate for a given video mode. So if you select 640 x 480 @ 30 fps, then the frame rate attribute will allow you change the specify a lower frame rate (1-30 fps). Note that in most cases, the camera will still use the same ROI and packet size. The only differences is when the camera will actually transmit the packet. This is helpful for free-running applications. This is not very useful for triggered applications.

Hope this helps,

JohannS

[BeKo]

It works. Nice to know.


Thank you very much,

BeKo