Achieving Seamlessness in Multi-Projector based Tiled Display using Camera Feedback Pranav Kant Gaur * , Dinesh M. Sarode * , Pritam P. Shete * , Venkata P.P.K * , S.K. Bose * * Computer Division, Bhabha Atomic Research Centre {pranav,dinesh,ppshete,panikv,bose}@barc.gov.in Abstract—High resolution displays utilizing an ar- ray of commodity projectors are becoming popular approach(also called tiled displays) for visualizing high resolution content like scientific data-sets. These systems provide a relatively cheaper and flexible alternative to displays based on single high resolu- tion monitor or projector. This approach inherently provides a method to create displays with resolution much higher than that possible by using a single high resolution display device. However, bezels in monitor based tiled displays obstruct the geometric continuity of the rendered content. In this paper, we describe the algorithms for geometric alignment of projection regions of an array of arbitrarily placed projectors and attenuation of projected intensities in the over- lapping regions of multiple projectors using camera as a feedback device. Combination of these algorithms help us achieve a seamless high resolution display. We have observed improvements in fidelity of the rendered content by utilizing collinearity constraint in geometric alignment calculations. We also propose a novel technique based on cross-ratio invariant for utilizing full projection region of individual projectors which was limited by the size of features used for geometric alignment in the earlier approaches for pla- nar displays. This also results in more imperceptible edge blending artifacts for same physical setup of projectors. Index Terms—geometric alignment, edge blending, collinearity, cross-ratio, multi-projector display I. I NTRODUCTION Tiled displays provide an alternative to the vi- sualization of high resolution content over single large scale high resolution monitor(or projector) by attaining comparable performance using combina- tion of low cost and low resolution commodity displays. Tiled displays have been realized either using grid of monitors[2], [3] or projectors[1], [5], [6], [7]. Using LCD monitors provides a compact, relatively cheaper and readily configurable high res- olution visualization solution, though it still cannot completely imitate a single high resolution display because bezels of monitors obstruct the geometric continuity of the rendered content. Whereas in a multiprojector system, projectors may be arbitrarily placed and they inherently do not enforce any limitations of physical seams. Our work addresses seamless rendering of the content using projectors. Projectors will have quad shaped projection re- gion without necessarily ensuring geometric conti- nuity over the projected content. Manual keystoning to geometrically align content from multiple projec- tors on the screen is time consuming and tedious. Further, it can easily become impractical for large number of projectors. Brown’s[1] approach relaxes that assumption and instead allows for a casual positioning of projectors. It aims to create geomet- rically seamless and rectangular image in camera- space which guarantees geometrical seamlessness on the screen. But it does not guarantee rectangular output on the screen. Further, the usable projection region is limited by the size of features used for geometric alignment. Our contribution through this work is to remove the above mentioned limitations in [1] for the case when projection screen is planar. Further, by utilizing the collinearity constraint in geometric alignment calculations we have observed more accurate final rendering. 293 978-1-4799-6629-5/14/$31.00 c 2014 IEEE