Since lossless compression can only achieve two to four times data compression, it may not be efficient to deploy lossless compression in bandwidth constrained applications. Instead, it would be more economical to adopt perceptually lossless compression, which can attain ten times or more compression without loss of important information. Consequently, one can transmit more images over bandwidth limited channels. In this research, we first aimed to compare and select the best compression algorithm in the literature to achieve a compression ratio of 0.1 and 40 dBs or more in terms of a performance metric known as human visual system model (HVSm) for maritime and sonar images. Our second objective was to demonstrate error concealment algorithms that can handle corrupted pixels due to transmission errors in interference-prone communication channels. Using four state-of-the-art codecs, we demonstrated that perceptually lossless compression can be achieved for realistic maritime and sonar images. At the same time, we also selected the best codec for this purpose using four performance metrics. Finally, error concealment was demonstrated to be useful in recovering lost pixels due to transmission errors.
All three components of the current density are required to compute the heating rate due to free magnetic energy dissipation. Here we present a first test of a new model developed to determine if the times of increases in the resistive heating rate in active region (AR) photospheres are correlated with the subsequent occurrence of M and X flares in the corona. A data driven, 3 D, non-force-free magnetohydrodynamic model restricted to the near-photospheric region is used to compute time series of the complete current density and the resistive heating rate per unit volume (Q(t)) in each pixel in neutral line regions (NLRs) of 14 ARs. The model is driven by time series of the magnetic field B measured by the Helioseismic & Magnetic Imager on the Solar Dynamics Observatory (SDO) satellite. Spurious Doppler periods due to SDO orbital motion are filtered out of the time series for B in every AR pixel. For each AR, the cumulative distribution function (CDF) of the values of the NLR area integral Q i (t) of Q(t) is found to be a scale invariant power law distribution essentially identical to the observed CDF for the total energy released in coronal flares. This suggests that coronal flares and the photospheric Q i are correlated, and powered by the same process. The model predicts spikes in Q i with values orders of magnitude above background values. These spikes are driven by spikes in the non-force free component of the current density. The times of these spikes are plausibly correlated with times of subsequent M or X flares a few hours to a few days later. The spikes occur on granulation scales, and may be signatures of heating in horizontal current sheets. It is also found that the times of relatively large values of the rate of change of the NLR unsigned magnetic flux are also plausibly correlated with the times of subsequent M and X flares, and spikes in Q i . 96.60.Mz, 96.60.qe, 95.30.Qd, 52.30.Cv PACS numbers Research Article ContentsMichael L. Goodman, Chiman Kwan, Bulent Ayhan, and Eric L. Shang, Front. Phys. , () Research Article IntroductionFlares are concentrated in neutral line regions (NLRs) of active regions (ARs). NLRs are sites of relatively large current densities that represent free magnetic energy available for conversion into particle energy during the flaring process (Hagyard et al. 1984;Schrijver 2009;Fletcher et al. 2011;Hudson 2011;Georgoulis et al. 2012;Wang & Liu 2015). Coronal observations show that for M and X flares, smaller pre-cursor flares occur in the same region within ∼ 24 hours prior to the main flares (Gyenge et al. 2016), and that there are temporal and spatial correlations between consecutive flares (Balázs et al. 2014). These facts suggest that, in the corona, the NLR current system evolves towards a large flaring event, and that this evolution involves smaller scale energy releases via current dissipation. Observations of quiet Sun network magnetic fields in the transition region indicate the appearance and intensification of non-potential magnetic fields, and hence of curre...
We present a video compression framework that has several components. First, we aim at achieving perceptually lossless compression. Several well-known video codecs in the literature have been evaluated and the performance was assessed using several well-known performance metrics. Second, we investigated the impact of error concealment algorithms for handling corrupted pixels due to transmission errors in communication channels. Extensive experiments using actual videos have been performed to demonstrate the proposed framework.
We present a video compression framework that has two key features. First, we aim at achieving perceptually lossless compression for low frame rate videos (6 fps). Four well-known video codecs in the literature have been evaluated and the performance was assessed using four well-known performance metrics. Second, we investigated the impact of error concealment algorithms for handling corrupted pixels due to transmission errors in communication channels. Extensive experiments using actual videos have been performed to demonstrate the proposed framework.
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