To save manufacturing cost, most color digital video cameras employ a single-sensor technology with a red-green- blue (RGB) color filter array (CFA) to capture real-world scenes. Due to only one primary color measured at each pixel location, the captured videos are usually referred to as the mosaic videos. For the purposes of economical storage and transmission, it is very important to achieve a good tradeoff between the quality and bitrate when compressing mosaic videos with different RGB-CFA structures. In this paper, based on mathematical optimization technique, a novel chroma subsampling strategy is presented for compressing mosaic videos with arbitrary RGB-CFA structures in H.264/AVC and High Efficiency Video Coding (HEVC). For each 2 × 2 YUV block to be subsampled with 4:2:0 format, the proposed strategy determines the proper sampled U and V components by minimizing, prior to compression, the quality distortion between the original colocated mosaic block and the mosaic block conversed from the current subsampled YUV block. Through the mathematical optimization formulated in the proposed strategy, the significance of the sampled U and V components for reconstructing R, G, and B pixels can be simultaneously taken into consideration. The experimental results demonstrate that the proposed chroma subsampling strategy has the best quality and bitrate tradeoff at a similar execution time requirement for compressing mosaic videos with arbitrary RGB-CFA structures in H.264/AVC and HEVC compared with the state-of-the-art ones by Chen et al. and Yang et al. as well as the three commonly used ones.

Wireless sensor networks (WSNs) are one of the most important ingredients in the Internet of Things. Thus it is vital to design a good power saving protocol, which operates at the medium access control (MAC) layer, for a WSN since sensors are generally battery-powered. On the other hand, organizing a WSN into coronas centered at the sink is a simple effective technique to achieve low-overhead routing where every sensor needs neither to broadcast beacons nor to maintain routing/neighbor tables. Hence in this paper, we propose an optimal and maximized configurable power saving protocol, named Green-MAC, for a corona-based WSN, which has the following attractive features. (i) By using the generalized Chinese remainder theorem, Green-MAC guarantees that any two sensors in the neighboring coronas can simultaneously wake up in bounded time regardless of their schedule offset as well as their respective cycle lengths. (ii) Given the cycle length, the ATF-ratio (i.e. the fraction of awake time frames in a cycle) of each sensor reaches the theoretical minimum. (iii) Under the minimum ATF-ratio constraints, the number of configurable ATF-ratios of each sensor reaches the theoretical maximum. (iv) An ATF-ratio configuration scheme is proposed for Green-MAC such that the power consumption of a WSN can be minimized while the worst event-to-sink delay requirement can be fulfilled with high probability. Both theoretical analysis and simulation results demonstrate that Green-MAC greatly outperforms existing power saving protocols for corona-based WSNs, including Q-MAC and Queen-MAC, in terms of ATF-ratio, configurability, network lifetime, delay violation ratio, and event-to-sink throughput.