filename : Papas12.pdf entry : toappear conference : ACM SIGGRAPH ASIA 2012, Singapore, Singapore, 28 November - 1 December, 2012 pages : to appear year : 2012 month : December title : The Magic Lens: Refractive Steganography subtitle : author : Marios Papas, Thomas Houit, Derek Nowrouzezahrai, Markus Gross and Wojciech Jarosz booktitle : ISSN/ISBN : editor : publisher : ACM publ.place : Singapore volume : issue : language : English keywords : Steganography, Image Morphing, Lens Fabrication abstract : Motivated by classical steganography techniques we construct Magic Lenses, composed of refractive lenslet arrays, to reveal hidden images when placed over potentially unstructured printed or displayed source images. We determine the refractive geometry of these surfaces by formulating and efficiently solving an inverse light transport problem, taking into account additional constraints imposed by the physical manufacturing processes. We fabricate several variants on the basic magic lens idea including using a single source image to encode several hidden images which are only revealed when the lens is placed at prescribed rotational orientations or viewed from different angles. We also present an important special case, the universal lens, that forms an injection mapping from the lens surface to the source image grid, allowing it to be used with arbitrary source images. We use this type of lens to generate hidden animation sequences. We validate our simulation results with many real-world manufactured magic lenses, and experiment with two separate manufacturing processes.