What is the Threshold setting (THR), and how does adjusting it impact tracking?

The Threshold setting is an image processing setting that determines a minimum brightness of a pixel for it to be considered in the calculation of a 2D object. All pixels with a brightness below the Threshold setting are ignored. Increasing the Threshold value can help filter interference from non-markers in the camera view (e.g. reflections and external light sources), while lowering the Threshold value can allow less visible markers (e.g. small markers, worn markers, and markers at longer distances from the camera) to be seen by the camera.

The Threshold value can range from 1 to 255. The Pixel Inspector is used to find an optimal Threshold setting by examining the brightness of pixels from each camera on the 2D view port. The Pixel Inspector can be enabled from the Application Settings pane.

Threshold value set to 255. Pixel Inspector in precision mode (left) and segment mode (right)