Irfan Essa’s Academic Activities

Gabriel Brostow (2004), “Novel Skeletal Representation for Articulated Creatures” PhD Thesis, Georgia Institute of Technology, College of Computing. (Advisor: Irfan Essa) [PDF] [URI]AbstractThis research examines an approach for capturing 3D surface and structural data of moving articulated creatures. Given the task of non-invasively and automatically capturing such data, a methodology and the associated experiments are presented, that apply to multiview videos of the subjects motion. Our thesis states: A functional structure and the timevarying surface of an articulated creature subject are contained in a sequence of its 3D data. A functional structure is one example of the possible arrangements of internal mechanisms (kinematic joints, springs, etc.) that is capable of performing the motions observed in the input data. Volumetric structures are frequently used as shape descriptors for 3D data. The capture of such data is being facilitated by developments in multi-view video and range scanning, extending to subjects that are alive and moving. In this research, we examine vision-based modeling and the related representation of moving articulated creatures using Spines. We define a Spine as a branching axial structure representing the shape and topology of a 3D objects limbs, and capturing the limbs correspondence and motion over time. The Spine concept builds on skeletal representations often used to describe the internal structure of an articulated object and the significant protrusions. Our representation of a Spine provides for enhancements over a 3D skeleton. These enhancements form temporally consistent limb hierarchies that contain correspondence information about real motion data. We present a practical implementation that approximates a Spines joint probability function to reconstruct Spines for synthetic and real subjects that move. In general, our approach combines the objectives of generalized cylinders, 3D scanning, and markerless motion capture to generate baseline models from real puppets, animals, and human subjects.

Gabriel J. Brostow and  Irfan Essa (2001) “Image-based motion blur for stop motion animation” In Proceedings of the 28th annual conference on Computer graphics and interactive techniques (ACM SIGGRPH) Pages: 561 - 566 August 2001, ISBN:1-58113-374-X ACM New York, NY, USA (DOI|PDF|Video|Project Site)

ABSTRACT

Stop motion animation is a well-established technique where still pictures of static scenes are taken and then played at film speeds to show motion. A major limitation of this method appears when fast motions are desired; most motion appears to have sharp edges and there is no visible motion blur. Appearance of motion blur is a strong perceptual cue, which is automatically present in live-action films, and synthetically generated in animated sequences. In this paper, we present an approach for automatically simulating motion blur. Ours is wholly a post-process, and uses image sequences, both stop motion or raw video, as input. First we track the frame-to-frame motion of the objects within the image plane. We then integrate the scene’s appearance as it changed over a period of time. This period of time corresponds to shutter speed in live-action filming, and gives us interactive control over the extent of the induced blur. We demonstrate a simple implementation of our approach as it applies to footage of different motions and to scenes of varying complexity. Our photorealistic renderings of these input sequences approximate the effect of capturing moving objects on film that is exposed for finite periods of time.