A carregar...
14 resultados
Resultados da pesquisa
A mostrar 1 - 10 de 14
- Retargeting UHD 4k Video for SmartphonesPublication . Kumar, Rohit; Navarro, António; Assunção, Pedro; Ferreira, LinoThis paper evaluates a new video-retargeting algorithm jointly with two others previously published in the literature. Four Ultra High Definition (UHD) 4K resolution video sequences were used for subjective assessment. Subjective testing results show that the proposed algorithm yields the best performance when UHD 4K video is retargeted to 1920 × 1080 resolution. The main application of these retargeting algorithms is to increase the quality of experience (QoE) provided to consumers when playing UHD videos on small screen devices like smartphones.
- Towards key-frame extraction methods for 3D video: a reviewPublication . Ferreira, Lino; Luis A. da Silva Cruz; Assunção, PedroThe increasing rate of creation and use of 3D video content leads to a pressing need for methods capable of lowering the cost of 3D video searching, browsing and indexing operations, with improved content selection performance. Video summarisation methods specifically tailored for 3D video content fulfil these requirements. This paper presents a review of the state-of-the-art of a crucial component of 3D video summarisation algorithms: the key-frame extraction methods. The methods reviewed cover 3D video key-frame extraction as well as shot boundary detection methods specific for use in 3D video. The performance metrics used to evaluate the key-frame extraction methods and the summaries derived from those key-frames are presented and discussed. The applications of these methods are also presented and discussed, followed by an exposition about current research challenges on 3D video summarisation methods.
- Video summary generation and coding using temporal scalabilityPublication . Ferreira, Lino; Cruz, Luís; Assunção, Pedro A. AmadoIn this paper two algorithms for video summary generation and coding are proposed. Two distortion metrics used in the video summary generation algorithm are compared and an algorithm with reduced computational complexity is presented. The paper also proposes two frame structures in the temporal domain suitable for coding using temporal scalability of the H.264/SVC.
- H.264/SVC ROI encoding with spatial scalabilityPublication . Ferreira, Lino; Cruz, Luís; Assunção, Pedro A. AmadoThis paper proposes two H.264/AVC compliant methods for encoding Regions-of-Interest (ROI) with spatial scalability and evaluates their respective rate-distortion-complexity performance. The base layer is kept unchanged and provides lower resolution images with roughly constant quality, without identification of the ROI. In the proposed methods there is no need to encode contour information because the ROI is implicitly defined in the upper layer of the spatial resolution in a transparent way by using different encoding parameters for the ROI and its complementary region. It is shown, that spatial scalability in ROI can be efficiently used to enhance specific regions of an image sequence in both spatial resolution and quality with low coding complexity. The proposed encoding scheme is suitable for remote surveillance, medical applications and entertainment, where higher resolution and higher quality ROI is a useful functionality for object/face recognition, selective encryption, detail analysis, etc.
- Sistema de aquisição e registo de sinais biomédicos baseado numa plataforma de desenvolvimento open-source de baixo custoPublication . Jardan, Daniel; Gil, João; Martins, Fernando; Ferreira, Lino; Fonseca-Pinto, RuiEste artigo apresenta um sistema de aquisição e registo de sinais biomédicos baseado na plataforma desenvolvimento open-source Arduino. O sistema tem associado um cartão de memória para registo de dados, bem como um acelerómetro que indica a atividade/postura do paciente. É utilizado um módulo de comunicação Blue- tooth para ligação a um dispositivo móvel (smartphone e tablet) de forma a permitir a parametrização, o comando do sistema de aquisição e a monitorização em tempo real dos dados adquiridos. Estes dados foram usados para calcular o balanço vago-simpático associado a tarefas específicas do dia-a-dia.
- An improved sub-optimal video summarization algorithmPublication . Coelho, Luís; Cruz, Luis A. da Silva; Ferreira, Lino; Assunção, Pedro A.During the last few years the amount of digital video content has been increasing exponentially as a result of the proliferation of media sources like digital TV, streaming video internet sites like YouTube and wider availability of digital video cameras. The video data volume is so large that the only way a user can browse these libraries is through the use of timecondensation techniques. Video summarization achieves timecondensation by choosing a sub-set of frames of the original video creating a summary hopefully representative of the source video. The frame selection process can be directed according to different principles, based on either subjective or objective frame-relevance measures. Previous works have used dynamic programming (DP) and greedy approaches to choose the frames that make up the video summary. We present an algorithm that performs better than the greedy solution achieving a performance closer to DP's while keeping the greedy solution's simplicity.
- Efficient scalable coding of video summaries using dynamic GOP structuresPublication . Ferreira, Lino; Cruz, L.; Assunção, PedroA method to efficiently encode an arbitrary video summary with temporal scalability and dynamic Group of Pictures (GOP) structures is proposed in this paper. The video summary is encoded as the base layer of a Scalable Video Coding (SVC) bitstream using a novel approach, which matches the summary frames available in temporal segments onto corresponding dynamic GOP structures. An algorithm is devised to compute variable GOP sizes along with an efficient independent prediction structure for the summary. The results show that the proposed method can be used to encode arbitrary video summaries with increased efficiency in the temporal base layer and negligible loss of R-D performance in the whole scalable sequence
- Optimal priority MDC video streaming for networks with path diversityPublication . Correia, Pedro; Ferreira, Lino; Assunção, Pedro; Cruz, Luis; Silva, VitorThis paper proposes a robust video streaming scheme for priority networks with path diversity, based on a combined approach of multiple description coding (MDC) with optimal picture classification into two priorities. A binary classification algorithm is proposed to define high (HP) and low (LP) priority network abstraction layer units (NALU), which in turn define the packet priorities. An optimisation algorithm is used to find HP pictures, based on dynamic programming and relying on minimisation of the packet loss concealment distortion. The paper shows that the proposed algorithm is able to effectively improve the decoded video without increasing the MDC stream redundancy. The overall performance evaluation, carried out by simulating MDC video streaming over lossy networks with path diversity, demonstrates that the proposed algorithm yields higher video quality for a wide range of packet loss rates (PLR). Comparing with no-priority MDC video streaming schemes, the simulation results show that the proposed algorithm can improve the average PSNR results in 0.7-3.2dB for packet loss rates between 3% and 15%.
- A method for automatic detection of rectangular regions of interest in arbitrary imagesPublication . Martins-Ferreira, Nelson; Ferreira, Lino; Pascoal-Faria, Paula; Cruz, Luis A. da Silva; Assunção, Pedro; Alves, NunoThis paper presents a computational method to extract optimum rectangular Regions of Interest (RoI) in images with an associated saliency map. Although saliency maps provide an individual relevance measure for each pixel, to find the sub-image (i.e., rectangular region) that contains the set of the most relevant pixels requires an optimisation procedure to define the boundaries of the best RoI. This is achieved by the method devised in the paper, by following an approach based on balancing the amount of relevant information that is included and excluded from the RoI. The results show that such method is capable of finding the most relevant rectangular RoI and thus to extract the optimum sub-images according to the relevance measure given by a generic saliency map. Since the method is not tied to any particular type of images, it finds application in quite different fields, such as salient object extraction and processing in industry and surveillance, image compression using attention modelling, biomedical imaging, etc.
- A generic framework for optimal 2D/3D key-frame extraction driven by aggregated saliency mapsPublication . Ferreira, Lino; Cruz, Luis A. da Silva; Assunção, PedroThis paper proposes a generic framework for extraction of key-frames from 2D or 3D video sequences, relying on a new method to compute 3D visual saliency. The framework comprises the following novel aspects that distinguish this work from previous ones: (i) the key-frame selection process is driven by an aggregated saliency map, computed from various feature maps, which in turn correspond to different visual attention models; (ii) a method for computing aggregated saliency maps in 3D video is proposed and validated using fixation density maps, obtained from ground-truth eye-tracking data; (iii) 3D video content is processed within the same framework as 2D video, by including a depth feature map into the aggregated saliency. A dynamic programming optimisation algorithm is used to find the best set of K frames that minimises the dissimilarity error (i.e., maximise similarity) between the original video shots of size and those reconstructed from the key-frames. Using different performance metrics and publicly available databases, the simulation results demonstrate that the proposed framework outperforms similar state-of-art methods and achieves comparable performance as other quite different approaches. Overall, the proposed framework is validated for a wide range of visual content and has the advantage of being independent from any specific visual saliency model or similarity metrics.