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Mesh-based piecewise planar motion compensation and optical flow clustering for ROI codingholger meuel, marco munderloh, matthias reso and jörn ostermann For the transmission of aerial surveillance videos taken from unmanned aerial vehicles (UAVs), region of interest (ROI)-based coding systems are of growing interest in order to cope with the limited channel capacities available. We present a fully automatic detection and coding system which is capable of transmitting high-resolution aerial surveillance videos at very low bit rates. Our coding system is based on the transmission of ROI areas only. We assume two different kinds of ROIs: in order to limit the transmission bit rate while simultaneously retaining a high-quality view of the ground, we only transmit new emerging areas (ROI-NA) for each frame instead of the entire frame. At the decoder side, the surface of the earth is reconstructed from transmitted ROI-NA by means of global motion compensation (GMC) . In order to retain the movement of moving objects not conforming with the motion of the ground (like moving cars and their previously occluded ground), we additionally consider regions containing such objects as interesting (ROI-MO). Finally, both ROIs are used as input to an externally controlled video encoder. While we use GMC for the reconstruction of the ground from ROI-NA, we use meshed-based motion compensation in order to generate the pelwise difference in the luminance channel (difference image) between the mesh-based motion compensated and the current input image to detect the ROI-MO. High spots of energy within this difference image are used as seeds to select corresponding superpixels from an independent (temporally consistent) superpixel segmentation of the input image inorder to obtain accurate shape information of ROI-MO. For a false positive detection rate (regions falsely classified as containing local motion) of less than 2 we detect more than 97 true positives (correctly detected ROI-MOs) in challenging scenarios. Furthermore, we propose to use a modified high-efficiency video coding (HEVC) video encoder. Retaining full HDTV video resolution at 30 fps and subjectively high quality we achieve bit rates of about 0.6-0.9 Mbit/s, which is a bit rate saving of about 90 compared to an unmodified HEVC encoder.

For aerial surveillance systems two key features are important. First they have to provide as much resolution as possible, while they secondly should make the video available at a ground station as soon as possible. Recently so called Unmanned Aerial Vehicles (UAVs) got in the focus for surveillance operations with operation targets such as environmental and disaster area monitoring as well as military surveillance. Common transmission channels for UAVs are only available with small bandwidths of a few Mbit /s. In this paper we propose a video codec which is able to provide full HDTV (1920 × 1080 pel) resolution with a bit rate of about 1-3 Mbit /s including moving objects (instead of 8-15 Mbit /s when using the standardized AVC codec). The coding system is based on an AVC video codec which is controlled by ROI detectors. Furthermore we make use of additional Global Motion Compensation (GMC). In a modular concept different Region of Interest (ROI) detectors can be added to adjust the coding system to special operation targets. This paper presents a coding system with two motion-based ROI detectors; one for new area detection (ROI-NA) and another for moving objects (ROI-MO). Our system preserves more details than an AVC coder at the same bit rate of 1.0 Mbit /s for the entire frame.