Percorrer por autor "Assuncao, P."
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- Dynamic Motion Vector Refreshing For Enhanced Error Resilience In HevcPublication . Carreira, J.; Silva, V. de; Ekmekcioglu, E.; Kondoz, A.; Assuncao, P.; Faria, S.The high level of compression efficiency achieved by HEVC coding techniques decreases the error resilience performance under error prone conditions. This paper addresses the error resiliency of the HEVC standard, focusing on the new motion estimation tools. It is shown that the temporal dependency of motion information is comparatively higher than that in the H.264/AVC standard, causing an increase in the error propagation. Based on this evidence, this paper proposes a method to make intelligent use of temporal motion vector (MV) candidates during the motion estimation process, in order to decrease the temporal dependency, and improve the error resiliency without penalising the rate-distortion performance. The simulation results show that the proposed method improves the error resilience under tested conditions by increasing the video quality by up to 1.7 dB in average, compared to the reference method that always enables temporal MV candidates.
- Enhancement method for multiple description decoding of depth maps subject to random lossPublication . P. Correia; Marcelino, S.; Assuncao, P.; Faria, S.; S. Soares; C. Pagliari; E. da SilvaThis paper proposes a method to improve the quality of depth maps transmitted in multiple descriptions through multipath error prone networks. Whenever a single description is lost, the remaining ones are still able to provide a coarsely decoded version of the depth map. While in multiple description video, such coarse decoding is still acceptable for display, in the case of depth maps the additional decoding distortion propagates through the corresponding view synthesis. The proposed method is capable of enhancing low quality depth maps decoded from one single description, based on geometric information available in coarsely decoded slices, combined with higher quality depth values in adjacent slices decoded from both descriptions. In comparison with existing MDC decoders, the enhancement method achieves quality gains in synthesised views up to 1.69dB for packet loss rates of 10%.
- A robust video encoding scheme to enhance error concealment of intra framesPublication . Carreira, J; Assuncao, P.; Faria. S; Ekmekcioglu, E.; Kondoz, A.In this paper a robust encoding scheme is proposed to improve the visual quality of HEVC decoded video when intra frames are lost along the streaming path. For this purpose, the encoding process includes frame loss simulation and subsequent error concealment, to find the most efficient method that should be used by a decoder to recover lost intra frames. In this novel scheme, each image is divided into partitions, which are associated with the error concealment method that achieves the lowest distortion. Then this information is signalled to the decoder through SEI messages in the coded stream. In order to efficiently use the signalling overhead, rate-distortion optimisation is used to achieve the best trade-off between the number of transmitted symbols and distortion of reconstructed frames. Experimental results show the effectiveness of the proposed method to enhance the quality of reconstructed intra frames under different packet loss ratios (PLR). For PLR=10%, the robust coding scheme is able to improve the average PSNR of all frames affected by errors, up to 1.50 dB and 3.44 dB in Low-Delay and Random-Access configurations respectively, at a maximum overhead cost of 0.24%.
- Selective motion vector redundancies for improved error resilience in HEVCPublication . Carreira, J.; Ekmekcioglu, E; Kondoz, A.; Assuncao, P.; Faria, S.; Silva, V. DeThis paper addresses the problem caused by motion vector coding dependencies on the error resilience performance of the emergent High Efficiency Video Coding (HEVC) standard. We propose a method based on the prediction dependency of motion vectors (MV) to select the most relevant ones for redundant coding with reduced overhead. The spatial dependencies are analysed in the encoder to prioritise the MVs that should be selected for redundancy, based on the number of subsequent dependent coding units. Then, a subset of prioritised MVs is transmitted as redundancy (referred to as side information in the paper), to reduce the use and propagation of mismatched MV predictions in case of transmission errors or data loss. The simulation results show that the proposed MV selection method can effectively identify the most relevant motion field, achieving improved error robustness with a reduced redundancy overhead. Exploiting only 30% of the generated MVs for redundancy, average quality gains of up to 1 dB are achieved compared to a uniform MV selection scheme, and up to 2 dB compared to the original HEVC standard with no redundant encoded information.
- Subjective assessment of frame loss concealment methods in 3D videoPublication . Carreira, J.; Pinto, L.; Rodrigues, N.; Faria, S.; Assuncao, P.This paper investigates the subjective impact resulting from different concealment methods for coping with lost frames in 3D video communication systems. It is assumed that a high priority channel is assigned to the main view and only the auxiliary view is subject to either transmission errors or packet loss, leading to missing frames at the decoder output. Three methods are used for frame concealment under different loss ratios. The results show that depth is well perceived by users and the subjective impact of frame loss not only depends on the concealment method but also exhibits high correlation with the disparity of the original sequence. It is also shown that under heavy loss conditions it is better to switch from 3D to 2D rather than presenting concealed 3D video to users.