The Threshold effect determines how much contrast there is between neighboring pixels for the sharpening to affect them. The higher setting exclude more and more pixels.
In the Properties Window you can change the effect properties. The following properties of the Threshold effect are available for setting: Level and Grayscale. The Grayscale box is checked by default, you can uncheck it, if you want to add colors to your video.
On the figures below you can see the video picture before and after applying the Threshold effect:
Before applying the Threshold effect
After applying the Threshold effect