1,720,986 research outputs found
Objective assessment of the WebP image coding algorithm
No full textResearch on multimedia data coding is allowing for better performance in terms of compression ratio, coding features, and robustness against transmission errors. While rate-distortion performance is being improved at a slower pace if compared to what we were used to up to a decade ago, remarkable advances are being made by adding complex features, such as fast adaptive transforms, lossy to lossless coding, compressed domain processing, etc. One of the latest codec which is expected to improve on the state of the art is the WebP algorithm released by Google. In this paper we provide an objective evaluation of WebP, by comparing it with the JPEG family algorithms. From the results it appears that the performance of the proposed codec is in line with that of the alternative methods, without achieving any major improvement and lacking several features
JPEG2000-coded image error concealment exploiting convex sets projections
No full textTransmission errors in JPEG2000 can be grouped into three main classes, depending on the affected area: LL, high frequencies at the lower decomposition levels, and high frequencies at the higher decomposition levels. The first type of errors are the most annoying but can be concealed exploiting the signal spatial correlation like in a number of techniques proposed in the past; the second are less, annoying but more difficult to address; the latter are often imperceptible. In this paper, we address the problem of concealing the second class or errors when high bit-planes are damaged by proposing a new approach based on the theory of projections onto convex sets. Accordingly, the error effects are masked by iteratively applying two procedures: low-pass (LP) filtering in the spatial domain and restoration of the uncorrupted wavelet coefficients in the transform domain. It has been observed that a uniform LP filtering brought to some undesired side effects that negatively compensated the advantages. This problem has been overcome by applying an adaptive solution, which exploits an edge map to choose the optimal filter mask size. Simulation results demonstrated the efficiency of the proposed approach
Property protection and user authentication in IP networks through challenge-response mechanisms: Present, past and future trends (Chapter V)
No full textStreaming video over wireless channels: Exploiting reduced-reference quality estimation at the user-side
No full textWe propose a source rate control scheme for streaming video sequences over wireless channels by resorting on a reduced-reference (RR) quality estimation approach. It works as follows: the server extracts important features of the original video, which are coded and sent through the channel along with the video sequence and then exploited at the decoder to compute the actual quality; the observed quality is analyzed to obtain information on the impact of the source rate at the given system configuration; at the receiver, decisions are taken on the optimal source rate to be applied next at the encoder to maximize the quality as perceived at the user-side. The rate is adjusted on a per-window basis to compensate low-throughput periods with high-throughput periods so as to avoid abrupt video quality changes, which can be caused by sudden variations in the channel throughput. The use of the RR quality estimation represents the main novelty of the proposed work. This has the advantage of allowing the rate control to optimize the user-perceived video quality after all the streaming system impairments have affected the signal, including actual channel errors, playback buffer starvation occurrences and error concealment. This approach is new in this context, since in the past proposals video models are used to predict the relationships of the quality with the coding rate, channel errors and starvation occurrences. Numerical simulations show how the proposed approach is able to achieve results similar to those obtained with model-based approaches, but with the significant benefit of not requiring any knowledge on the signal and channel characteristics
Quality perception when streaming video on tablet devices
No full textThe proposed work aims at analyzing the quality perceived by the user when streaming video on tablet devices. The contributions of this paper are: (i) to analyze the results of subjective quality assessments to determine which Quality of Service (QoS) parameters mainly affect the users' Quality of Experience (QoE) in video streaming over tablet devices; (ii) to define a parametric quality model useful in system control and optimization for the considered scenarios; (iii) to compare the performance of the proposed model with subjective quality results obtained in alternative state-of-the-art studies and investigate whether other models could be applied to our case and vice versa
Addressing un-Interoperability Issues in QoE Models: Is a Layered Modelling Effective?
No full textUn-interoperability issue is herein defined as the unfeasibility (or at least difficulty) of integrating the results of different modelling activities to broaden the range of scenarios where the integrated model can be applied. Given the huge number of parameters to be considered when defining a Quality of Experience (QoE) model, many different QoE models have been proposed in the literature. Each involves different scenarios and parameters, and specifies how such features are combined. In order to solve un-interoperability issues, we propose a layered modelling approach, which follows the well-known model for interoperable systems in the networking field. Each layer of the model is devoted to a specific quality domain and the interfaces with the other domains are well-defined in order to further simplify the combination of models related to different domains. Such model could be the reference for a general-purpose QoE management system. Experimental results for validating the proposed model are provided
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