Quadtree Driven Lossy Event Compression

Event cameras are emerging bio-inspired sensors that offer salient benefits over traditional cameras. With high speed, high dynamic range, and low power consumption, event cameras have been increasingly employed to solve existing as well as novel visual and robotics tasks. Despite rapid advancement in event-based vision, event data compression is facing growing demand, yet remains elusively challenging and not effectively addressed. The major challenge is the unique data form, \emph{i.e.}, a stream of four-attribute events, encoding the spatial locations and the timestamp of each event, with a polarity representing the brightness increase/decrease. While events encode temporal variations at high speed, they omit rich spatial information, which is critical for image/video compression. In this paper, we perform lossy event compression (LEC) based on a quadtree (QT) segmentation map derived from an adjacent image. The QT structure provides a priority map for the 3D space-time volume, albeit in a 2D manner. LEC is performed by first quantizing the events over time, and then variably compressing the events within each QT block via Poisson Disk Sampling in 2D space for each quantized time. Our QT-LEC has flexibility in accordance with the bit-rate requirement. Experimentally, we show results with state-of-the-art coding performance. We further evaluate the performance in event-based applications such as image reconstruction and corner detection.