A technique controls access to a protected resource. The display filter includes: a filter base; an external light-shielding layer comprising a base substrate including a transparent resin and light-shielding patterns spaced apart on a surface of the base substrate at predetermined intervals; and a diffusion layer diffusing a light provided from a panel assembly. Region based information is extracted based on the position error signals, and the region based information is used in conjunction with the position error signals to generate region-based displacement estimates with respect to each null burst.