Shadow-based Illusion of Depth and Transparency in Printed Images

Abstract

A cast shadow is one of the visual features that serve as a perceptual cue to the three-dimensional (3D) layout of objects. Although it is well known that adding cast shadows to an object produces the illusion that the object has a 3D layout, investigations into this illusion have been limited to virtual objects in a display. Using a light-projection technique, we show that it is possible to create a similar 3D layout illusion for real two-dimensional objects. Specifically, we displayed spatial patterns that look like cast shadows in the vicinity of an object depicted as a printed image. The combination of the cast shadow patterns with the printed object made it appear as if the printed object hovered over its original location even though the object was physically two-dimensional. By using this technique, we demonstrated that the shadow-induced layout illusion resulted in printed images having novel perceptual transparency. Vision researchers may find our technique useful if they want to extend their studies on the perception of cast shadows and transparency with real objects.