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- 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.
- 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.
- Retargeting 4K Video for Mobile Access Using Visual Attention and Temporal StabilizationPublication . Kumar, Rohit; Ferreira, Lino; Assunção, Pedro; Navarro, AntónioThis paper presents different methods of retargeting 4K resolution videos for the smaller resolutions of mobile devices. Several methods are investigated using image cropping based on visual attention maps with removal of temporal jitter. Visual comparison between video sequences obtained from the retargeting methods is presented and evaluated through subjective testing. Based on subjective scores, the proposed algorithm shows the best performance for 480p target resolution.
- A method to compute saliency regions in 3D video based on fusion of feature mapsPublication . Ferreira, Lino; Cruz, Luis A. da Silva; Assunção, PedroEfficient computation of visual saliency regions has been a research problem in the recent past, but in the case of 3D content no definite solutions exist. This paper presents a computational method to determine saliency regions in 3D video, based on fusion of three feature maps containing perceptually relevant information from spatial, temporal and depth dimensions. The proposed method follows a bottom-up approach to predict the 3D regions where observers tend to hold their gaze for longer periods. Fusion of the feature maps is combined with a center-bias weighting function to determine 3D visual saliency map. For validation and performance evaluation, a publicly available database of 3D video sequences and corresponding fixation density maps was used as ground-truth. The experimental results show that the proposed method achieves better performance than other state-of-art models.
- 3D key-frame extraction method based on visual saliencyPublication . Ferreira, Lino; Assunção, Pedro; Cruz, Luis A. da SilvaThis paper presents a method for key-frame extraction from 3D video using visual saliency to weight the 3D content according to a user attention model. Key-frames are found in temporal segments of arbitrary length (i.e., 3D scenes) using a dynamic programming algorithm which minimises the dissimilarity between the reconstructed and the original temporal segment. The dissimilarity measure is based on a combination of frame difference and visual relevance estimated through visual saliency maps. These maps result from attention modeling, taking into account spatial, temporal and depth features of the 3D video content. The results, evaluated using the Shot Reconstruction Degree and the Fidelity measure, show that the proposed method outperforms those obtained from uniform sampling and attention curve methods. This method may be useful for fast browsing of 3D video repositories.
- 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.