Regarding slave mode on the quad capture card for Zedx, how are the camera capture time, exposure start/end times, and image timestamps related to the input trigger?
With the master mode, it is clearly documented that The output trigger signals are two square waves, with their rising edges synchronized with the end of the exposure phase of the CMOS sensors.
My assumption is that the end of exposure time on the slave cameras is also synced with the rising edge - given the statement hereNow, all the cameras connected to the ZED Link Quad will have synchronized frame acquisition with 15µs precision. Is the assumption correct? Is this true also for triggers generated externally (not by Zed)?
Does that mean that the exposure phase start after it recieved the rising edge. If yes in that case the images would be out of sync since the master camera outputs a sync pulse with the edge synced to the end of exposure.
The behavior is much more complex.
The end of the capture is synchronized with the rising edge, so the beginning of the exposure is calculated according to the “exposure time setting” such that this behavior is guaranteed.
For example, in the following picture, the purple signal is the trigger, while the blue signal is the exposure.
Just to be clear, when you say the end of the capture is synchronized with the rising edge you are referring to the slave right ?
This would also mean that in case the trigger is generated usign a master Zed camera, then end of exposure of both the slave and master is synced with the rising edge of the trigger.
@Myzhar, I tried using the slave mode on Zedx, but when I follow this link and restart the computer, I can still see that ZED_Explorer continues to capture images without an external trigger. Please see this screen recording showing the same, where I confirm that the slave mode has been configured and the ZED_Explorer can still collect images.
I am running SDK 5.2 and Quad card drivers 1.4
Is this the expected behaviour?
If not, can you please investigate and help with what is going wrong?
If yes, then this seems wrong since for other cameras in the industry, slave mode means no image capture if no trigger is sent.
Have you rebooted after installing the new (old) driver or after applying the slave mode config?
It does not look like you did it from the video that you shared.
I am seeking confirmation on the timing logic for the ZED X in Slave Mode with an external sync. For an example lets take the camera framerate to be 30fps (period 33.33 ms) and exposure time 10ms.
My understanding is that the camera aligns the end-of-exposure with the rising edge of the sync signal.
This implies the camera ‘anticipates’ the pulse by starting the exposure 23.33ms after the previous trigger. So ZED X uses the previous pulse to predict the next one and time the start of the exposure window accordingly.
If above two are correct, to find mid-exposure-time I just deduct half of my exposure-time from my trigger-time. In this case - exposure starts 23.33ms after the previous trigger, 5ms later at 28.33ms we are mid-exposure, and frame ends 33.33ms at which point new raising edge from trigger comes in.
In case the exposure time is not fixed, the camera calculates exposure time for the next frame (say it gets darker and exposure will be 20ms). So the camera starts exposure at 13.33ms after the previous trigger, 10ms later we are mid exposure and the frame ends 20ms after, at which time next trigger comes in.
