Posterize
The Posterize effect lets you specify the tonal level (or brightness values) and then maps pixels to the closest matching level.
In the Properties Area of the Video Effect window you can change the effect propertieschange the effect properties.
The only property available for setting is Posterize Level.
In the figures below you can see the video picture before and after applying the Posterize effect:
Before applying the Posterize effect
After applying the Posterize effect