Why is trigger time less than exposure time when using a GenTL adapter?

I have noticed that when I set the exposure time for the camera to 1 second, and then trigger image acquisition of 1 frame. The image acquisition takes significantly less time than what the exposure rate is set to. 

Why is this happening?

For reference, I am using the following two camera for image acquisition:

1) FLIR Blackfly S BF5-U3-200S6M-C

2) Matrix Vision BF3-2124G-1211

Answer 1

[MathWorks Support Team]

Based on the information provided above, the reason this happens is due to the way the image acquisition engine works under the hood.

When you start a 'videoinput' object in MATLAB, the camera begins streaming frames constantly, even if they are not being recorded/logged by MATLAB. When the 'trigger' function is called, the next frame that is delivered from the camera is added to the MATLAB buffer, which is then returned by 'getdata'. In the situations where you see image acquisition of less than 1 second, it is likely due to MATLAB receiving the trigger after a frame has already started being acquired, meaning that the total time since the call to trigger is less than 1 second, but the frame actually took the full second to acquire as expected.

One way you can verify that the exposure is set correctly is by configuring the camera to take significantly more than one frame per trigger (preferably 10+ minimum). Then, use the methods described on the documentation page

here

to determine frame time differences and the average frames per second. This will verify that the camera is correctly acquiring the images with the specified exposure.