Accessing camera image in Unity - OnTrackablesUpdated

Hi everyone,

I've followed this tutorial provided by Vuforia on how to access the camera image in Unity. In the tutorial it's recommended to access the camera image from the OnTrackablesUpdated() callback as "that way you can ensure that you retrieve the latest camera image that matches the current frame".

I have a couple of questions regarding this:

1. If instead of wanting to access the camera image that matches the current frame I'm interested in accessing the camera image as fast as possible (i.e. accessing as many frames as possible), even if that means it's not the frame currently being displayed, how would I go about it? Should I simply access the camera image in Unity's Update() function?

2. When is OnTrackablesUpdated() actually called? If the event "all trackables updated" is registered, is the function called right before the following Update()? (This would match the way current Input Events in Unity are handled, according to the execution order)

Thank you very much in advance for your help!