Acquiring Timestamps From NI-IMAQdx Supported Camera

This article describes how to acquire timestamp data for an NI-IMAQdx supported camera. There are a few methods, but these are dependent on your hardware being used.
 

• The camera may have a built-in timestamp attribute that can be acquired from the custom data.
• Using the NI PXIe-8623, the XNET IP Stack has built in local timestamping which can be used.
• Use the NI-IMAQdx driver's system generated timestamping

It is this final method of the NI-IMAQdx driver timestamping that will be discussed in this article. Unless the NI-IMAQdx camera that you are using explicitly has a timestamp attribute that you can utilize, you will have to use the system generated NI-IMAQdx timestamp. The NI-IMAQdx driver will record a timestamp at the time of the Frame Done Interrupt. This absolute timestamp will represent the timestamp when each frame is acquired by the system based on the system clock. However, it is important to note that this timestamp does not represent the actual time the frame is acquired by the camera and is subject to whatever system jitter is present on the operating system as well as jitter caused by the network or lost packets (if using with GigE camera). 

To set up the NI-IMAQdx driver to generate this absolute timestamp you must configure the camera to do so in NI Measurement & Automation Explorer (MAX):

1.  Within MAX, navigate to your NI-IMAQdx device and click the Camera Attributes tab. Make sure that all of the attributes are exposed by clicking View Options » All Attributes. Scroll down to the Receive Timestamp Mode attribute and select System Time. 
   
   
2. Click on Save and close MAX.

By making this selection the NI-IMAQdx driver will now append the timestamp information as custom data on each acquired frame. The custom data is stored with the NI-IMAQdx image data in the form of two custom data keys, IMAQdxReceiveTimestampHigh and IMAQdxReceiveTimestampLow. A timestamp in LabVIEW consists of 64 bits of data, and both keys represent 32-bits of this information corresponding to the upper and lower halves, respectively. 

In LabVIEW, you can extract these data keys by using the function called IMAQ Get Custom Keys VI found in the Vision and Motion » Vision Utilities » Image Management palette. Once the key has been extracted, you can get the value associated with the key by using the function IMAQ Read Custom Data VI, as shown in the images below. 



Please see the attached VI and LabVIEW Help links for more detailed information on these functions and how to acquire timestamps with the NI-IMAQdx vision driver.
Note that if you do not configure the camera attributes as explained above, error -1074395723 may be generated when trying to retrieve the timestamps with the IMAQ Read Custom Data VI. If this occurs, review the camera configuration in MAX.