Papers by Rafael Rodrigues
ArXiv, 2020
With the coming of age of virtual/augmented reality and interactive media, numerous definitions, ... more With the coming of age of virtual/augmented reality and interactive media, numerous definitions, frameworks, and models of immersion have emerged across different fields ranging from computer graphics to literary works. Immersion is oftentimes used interchangeably with presence as both concepts are closely related. However, there are noticeable interdisciplinary differences regarding definitions, scope, and constituents that are required to be addressed so that a coherent understanding of the concepts can be achieved. Such consensus is vital for paving the directionality of the future of immersive media experiences (IMEx) and all related matters. The aim of this white paper is to provide a survey of definitions of immersion and presence which leads to a definition of immersive media experience (IMEx). The Quality of Experience (QoE) for immersive media is described by establishing a relationship between the concepts of QoE and IMEx followed by application areas of immersive media ex...
ArXiv, 2019
Segmentation of skeletal muscles in Magnetic Resonance Images (MRI) is essential for the study of... more Segmentation of skeletal muscles in Magnetic Resonance Images (MRI) is essential for the study of muscle physiology and diagnosis of muscular pathologies. However, manual segmentation of large MRI volumes is a time-consuming task. The state-of-the-art on algorithms for muscle segmentation in MRI is still not very extensive and is somewhat database-dependent. In this paper, an automated segmentation method based on AdaBoost classification of local texture features is presented. The texture descriptor consists of the Histogram of Oriented Gradients (HOG), Wavelet-based features, and a set of statistical measures computed from both the original and the Laplacian of Gaussian filtering of the grayscale MRI. The classifier performance suggests that texture analysis may be a helpful tool for designing a generalized and automated MRI muscle segmentation framework. Furthermore, an atlas-based approach to individual muscle segmentation is also described in this paper. The atlas is obtained by...
2019 27th European Signal Processing Conference (EUSIPCO), 2019
Muscle texture may be used as a descriptive feature for the segmentation of skeletal muscle in Ma... more Muscle texture may be used as a descriptive feature for the segmentation of skeletal muscle in Magnetic Resonance Images (MRI). However, MRI acquisition is not always ideal and the texture richness might become compromised. Moreover, the research for the development of texture quality metrics, and particularly no-reference metrics, to be applied to the specific context of MRI is still in a very early stage. In this paper, a case study is established from a texture-based segmentation approach for skeletal muscle, which was tested in a thigh Dixon MRI database. Upon the obtained performance measures, the relation between objective image quality and the texture MRI richness is explored, considering a set of state-of-the-art no-reference image quality metrics. A discussion on the effectiveness of existing quality assessment methods in measuring MRI texture quality is carried out, based on Pearson and Spearman correlation outcomes.
2018 Tenth International Conference on Quality of Multimedia Experience (QoMEX), 2018
Multimedia Tools and Applications, 2020
The MPEG-DASH protocol has been rapidly adopted by most major network content providers and enabl... more The MPEG-DASH protocol has been rapidly adopted by most major network content providers and enables clients to make informed decisions in the context of HTTP streaming, based on network and device conditions using the available media representations. A review of the literature on adaptive streaming over mobile shows that most emphasis has been on adapting the video quality whereas this work examines the trade-off between video and audio quality. In particular, subjective tests were undertaken for live music streaming over emulated mobile networks with MPEG-DASH. A group of audio/video sequences was designed to emulate varying bandwidth arising from network congestion, with varying trade-off between audio and video bit rates. Absolute Category Rating was used to evaluate the relative impact of both audio and video quality in the overall Quality of Experience (QoE). One key finding from the statistical analysis of Mean Opinion Scores (MOS) results using Analysis of Variance indicates that providing reduced audio quality has a much lower impact on QoE than reducing video quality at similar total bandwidth situations. This paper also describes an objective model for audiovisual quality estimation that combines the outcomes from audio and video metrics into a joint parametric model. The correlation between predicted and subjective MOS was computed using several outcomes (Pearson and Spearman correlation coefficients, Root Mean Square This research was co-funded by FEDER-PT2020, Portugal partnership agreement, under the project PTDC/EEI-PRO/2849/ 2014-POCI-01-0145-FEDER-016693, Fundação para a Ciência e a Tecnologia (FCT/MCTES) under the project UIDB/EEA/50008/2020 and the Instituto de Telecomunicações-Fundação para a Ciência e a Tecnologia (project UID/EEA/50008/2013) under internal project QoEVIS.
Ultrasound in medicine & biology, Jan 27, 2015
Breast ultrasound images have several attractive properties that make them an interesting tool in... more Breast ultrasound images have several attractive properties that make them an interesting tool in breast cancer detection. However, their intrinsic high noise rate and low contrast turn mass detection and segmentation into a challenging task. In this article, a fully automated two-stage breast mass segmentation approach is proposed. In the initial stage, ultrasound images are segmented using support vector machine or discriminant analysis pixel classification with a multiresolution pixel descriptor. The features are extracted using non-linear diffusion, bandpass filtering and scale-variant mean curvature measures. A set of heuristic rules complement the initial segmentation stage, selecting the region of interest in a fully automated manner. In the second segmentation stage, refined segmentation of the area retrieved in the first stage is attempted, using two different techniques. The AdaBoost algorithm uses a descriptor based on scale-variant curvature measures and non-linear diffu...
Towards breast ultrasound image segmentation using multi-resolution pixel descriptors
ABSTRACT Breast ultrasound images are an important diagnostic factor for breast cancer detection.... more ABSTRACT Breast ultrasound images are an important diagnostic factor for breast cancer detection. However, ultrasound imaging is intrinsically degraded by noise, resulting in a difficult detection of masses or nodules, and, most importantly, the evaluation of their size and shape. Computer-aided diagnosis figures as a major help factor, when it comes to analyzing this type of medical imaging. A fully automated and computationally efficient method for breast ultrasound segmentation is proposed. The algorithm classifies the images, with Support Vector Machines and Discriminant Analysis classifiers, based on a pixel descriptor formed with the information from anisotropic diffusion, band-pass filtering and scale-space curvature. The final segmentation results after the application of a set of heuristic rules for the selection of the classifiers' result, based on the ultrasound image characteristics. The final segmentation results yielded good overall accuracy, precision and also recall rates.
2016 Eighth International Conference on Quality of Multimedia Experience (QoMEX), 2016
The rapid adoption of MPEG-DASH is testament to its core design principles that enable the client... more The rapid adoption of MPEG-DASH is testament to its core design principles that enable the client to make the informed decision relating to media encoding representations, based on network conditions, device type and preferences. Typically, the focus has mostly been on the different video quality representations rather than audio. However, for device types with small screens, the relative bandwidth budget difference allocated to the two streams may not be that large. This is especially the case if high quality audio is used, and in this scenario, we argue that increased focus should be given to the bit rate representations for audio. Arising from this, we have designed and implemented a subjective experiment to evaluate and analyse the possible effect of using different audio quality levels. In particular, we investigate the possibility of providing reduced audio quality so as to free up bandwidth for video under certain conditions. Thus, the experiment was implemented for live music concert scenarios transmitted over mobile networks, and we suggest that the results will be of significant interest to DASH content creators when considering bandwidth tradeoff between audio and video.
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Papers by Rafael Rodrigues