Dynamic Shadow Removal from Front Projection Displays

A technique and system for detecting a radiometric variation/artifacts of a front-projected dynamic display region under observation by at least one camera. The display is comprised of one or more images projected from one or more of a plurality of projectors; the system is preferably calibrated by using a projective relationship. A predicted image of the display region by the camera is constructed using frame-buffer information from each projector contributing to the display, which has been geometrically transformed for the camera and its relative image intensity adjusted. A detectable difference between a predicted image and the display region under observation causes corrective adjustment of the image being projected from at least one projector. The corrective adjustment may be achieved by way of pixel-wise approach (an alpha-mask is constructed from delta pixels/images), or bounding region approach (difference/bounding region is sized to include the area of the display affected by the radiometric variation). Also: a technique, or method, for detecting a radiometric variation of a display region under observation, as well as associated computer executable program code on a computer readable storage medium, therefor

Real-time shadows in OpenGL caused by the presence of multiple light sources

U suvremenoj računalnoj grafici naglasak je na detaljima prizora, a uzimajući u obzir poboljšanja hardverskih svojstava, nije dopušteno raditi kompromise kada je riječ o stvarnosti scena. Svaki odraz, sjena, zaobljeni kut ili prozirnost mora biti doveden do savršenstva i prikazan u cilju da se scena koja se oslikava učini što realističnijom. U jednom od najšire rabljenih API-ja za renderiranje 3D objekata, OpenGL-u, ne postoji nešto poput knjižnice za dodavanje ovih pojava koje postoje u stvarnosti. Ako se razmatra mogućnost postojanja više izvora svjetlosti, renderiranje svih ovih detalja postaje pravi izazov. Cilj ovog rada je obezbjeđivanje metoda za generiranje sjene na efikasan način, za objekte često rabljene kao komponente složenih 3D objekata, u uvjetima prisutnosti više svjetlosnih izvora s mogućnošću kretanja.In modern computer graphics, the emphasis is on the details of the scene, and taking into account the improvements in hardware performances, it is not allowed to make compromises when it comes to the reality of scenes. Each reflection, shadow, rounded corner and transparency must be brought to perfection and presented in order to make a depicted scene more realistic. In one of the most widely used API for rendering 3D objects, OpenGL, there is nothing similar to a library for adding those phenomena that exist in reality. If the possibility of existence of multiple light sources is considered, rendering all these details becomes a real challenge. The aim of this paper is to provide a method for generating shadows in an efficient way, for the objects commonly used as components of complex 3D objects, in conditions of the presence of moving light sources

Dynamic shadow elimination for multi-projector displays

A major problem with interactive displays based on front-projection is that users cast undesirable shadows on the display surface. This situation is only partially-addressed by mounting a single projector at an extreme angle and pre-warping the projected image to undo keystoning distortions. This paper demonstrates that shadows can be muted by redundantlyilluminating the display surface using multiple projectors, all mounted at different locations. However, this technique does not eliminate shadows: multiple projectors create multiple dark regions on the surface (penumbral occlusions). We solve the problem by using cameras to automatically identify occlusions as they occur and dynamically adjust each projector’s output so that additional light is projected onto each partially-occluded patch. The system is self-calibrating: relevant homographies relating projectors, cameras and the display surface are recovered by observing the distortions induced in projected calibration patterns. The resulting redundantly-projected display retains the high image quality of a single-projector system while dynamically correcting for all penumbral occlusions. Our initial two-projector implementation operates at 3 Hz. c○Compaq Computer Corporation, 2001 This work may not be copied or reproduced in whole or in part for any commercial purpose. Permission to copy in whole or in part without payment of fee is granted for nonprofit educational and research purposes provided that all such whole or partial copies include the following: a notice that such copying is by permission of the Cambridge Research Laboratory of Compaq Computer Corporation in Cambridge, Massachusetts; an acknowledgment of the authors and individual contributors to the work; and all applicable portions of the copyright notice. Copying, reproducing, or republishing for any other purpose shall require a license with payment of fee to the Cambridge Researc

Distortion Correction for Non-Planar Deformable Projection Displays through Homography Shaping and Projected Image Warping

Video projectors have advanced from being tools for only delivering presentations on flat or planar surfaces to tools for delivering media content in such applications as augmented reality, simulated sports practice and invisible displays. With the use of non-planar surfaces for projection comes geometric and radiometric distortions. This work dwells on correcting geometric distortions occurring when images or video frames are projected onto static and deformable non-planar display surfaces. The distortion-correction process involves (i) detecting feature points from the camera images and creating a desired shape of the undistorted view through a 2D homography, (ii) transforming the feature points on the camera images to control points on the projected images, (iii) calculating Radial Basis Function (RBF) warping coefficients from the control points, and warping the projected image to obtain an undistorted image of the projection on the projection surface. Several novel aspects of this work have emerged and include (i) developing a theoretical framework that explains the cause of distortion and provides a general warping pattern to be applied to the projection, (ii) carrying out the distortion-correction process without the use of a distortion-measuring calibration image or structured light pattern, (iii) carrying out the distortioncorrection process on a projection display that deforms with time with a single uncalibrated projector and uncalibrated camera, and (iv) performing an optimisation of the distortioncorrection processes to operate in real-time. The geometric distortion correction process designed in this work has been tested for both static projection systems in which the components remain fixed in position, and dynamic projection systems in which the positions of components or shape of the display change with time. The results of these tests show that the geometric distortion-correction technique developed in this work improves the observed image geometry by as much as 31% based on normalised correlation measure. The optimisation of the distortion-correction process resulted in a 98% improvement of its speed of operation thereby demonstrating the applicability of the proposed approach to real projection systems with deformable projection displays

Abstract Dynamic Shadow Elimination for Multi-Projector Displays

A major problem with interactive displays based on frontprojection is that users cast undesirable shadows on the display surface. This situation is only partially-addressed by mounting a single projector at an extreme angle and prewarping the projected image to undo keystoning distortions. This paper demonstrates that shadows can be muted by redundantly-illuminating the display surface using multiple projectors, all mounted at different locations. However, this technique does not eliminate shadows: multiple projectors create multiple dark regions on the surface (penumbral occlusions). We solve the problem by using cameras to automatically identify occlusions as they occur and dynamically adjust each projector’s output so that additional light is projected onto each partially-occluded patch. The system is self-calibrating: relevant homographies relating projectors, cameras and the display surface are recovered by observing the distortions induced in projected calibration patterns. The resulting redundantly-projected display retains the high image quality of a single-projector system while dynamically correcting for all penumbral occlusions. Our initial two-projector implementation operates at 3 Hz. 1