Shadows Can Change the Shape Appearances of Real and Virtual Objects

The human visual system can estimate the shape of an object casting a shadow. The principle has been widely studied, and utilized in 3D scanners. However, estimating the shape of an object on which a shadow is casted ("screen object") was rarely investigated. In this study, we show that the casted shadow distorts the perceived shape of a screen object in a class of virtual and physical scenes. In addition, we utilized the principle to create variations of Cafe-wall illusion. The principles can be utilized to control the perceived shapes without changing the structure of the screen object.