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- Eriksson, Anders P
(författare)
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Optimization Methods for Large Scale Combinatorial Problems and Bijectivity Constrained Image Deformations
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis treats two separate but connected themes. This affiliation originates in optimization being the common choice of method for solving most of the occurring challenges. The first theme of the thesis is image segmentation. This is usually defined as the task of distinguishing objects from background in unseen images. This visual grouping process is typically based on low-level cues such as intensity, homogeneity or image contours. Popular approaches include thresholding techniques, edge based methods and region-based methods. Regardless of the method, the difficulty lies in formulating and describing the perception of what constitutes foreground and background in an arbitrary image. Furthermore, such a grouping is also highly contextually driven, certain image regions may be labeled differently depending on the task at hand - are we looking for people, buildings or trees? If one also allows for more labels than only foreground and background, the problem becomes increasingly harder and requires a much higher level of scene understanding. Once a formulation of the problem has been established and properly stated the question of how to efficiently solve it still remains. The complexity of this task and the size of most natural images typically leads to very large and difficult optimization problems. It is these issues we make an attempt at addressing in this thesis. We are interested in how to efficiently find visually relevant image partitions as well as how prior information can be included into the segmentation process. The second theme of this thesis concerns non-linear deformations of images and its applications. Functions that map $R^2$ onto itself are widely used in computer vision, medical imaging and computer graphics. What is common to all three is that mappings are used to model deformation occurring in natural images. As such deformations are highly complex they are near impossible to characterize. A reasonable and widely accepted assumption, or approximation, is that as the overall structure of the objects depicted will remain intact after deformation, hence folding or tearing of the images should never occur. Under these premises there must exist a dense mapping that is both one-to-one and onto. The deformations must be bijective. This is not entirely correct as for instance self-occlusion can not be described by bijective mappings. There exist an abundance of methods for parameterizing non-linear deformations. This part of the thesis concerns conditions for bijectivity of, perhaps the most commonly used method of describing non-linear deformations, the thin-plate spline mapping and its applications in computer vision.
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| 2. |
- Eriksson, Erik J., 1978-
(författare)
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That voice sounds familiar : factors in speaker recognition
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Humans have the ability to recognize other humans by voice alone. This is important both socially and for the robustness of speech perception. This Thesis contains a set of eight studies that investigates how different factors impact on speaker recognition and how these factors can help explain how listeners perceive and evaluate speaker identity. The first study is a review paper overviewing emotion decoding and encoding research. The second study compares the relative importance of the emotional tone in the voice and the emotional content of the message. A mismatch between these was shown to impact upon decoding speed. The third study investigates the factor dialect in speaker recognition and shows, using a bidialectal speaker as the target voice to control all other variables, that the dominance of dialect cannot be overcome. The fourth paper investigates if imitated stage dialects are as perceptually dominant as natural dialects. It was found that a professional actor could disguise his voice successfully by imitating a dialect, yet that a listener's proficiency in a language or accent can reduce susceptibility to a dialect imitation. Papers five to seven focus on automatic techniques for speaker separation. Paper five shows that a method developed for Australian English diphthongs produced comparable results with a Swedish glide + vowel transition. The sixth and seventh papers investigate a speaker separation technique developed for American English. It was found that the technique could be used to separate Swedish speakers and that it is robust against professional imitations. Paper eight investigates how age and hearing impact upon earwitness reliability. This study shows that a senior citizen with corrected hearing can be as reliable an earwitness as a younger adult with no hearing problem, but suggests that a witness' general cognitive skill deterioration needs to be considered when assessing a senior citizen's earwitness evidence. On the basis of the studies a model of speaker recognition is presented, based on the face recognition model by V. Bruce and Young (1986; British Journal of Psychology, 77, pp. 305 - 327) and the voice recognition model by Belin, Fecteau and Bédard (2004; TRENDS in Cognitive Science, 8, pp. 129 - 134). The merged and modified model handles both familiar and unfamiliar voices. The findings presented in this Thesis, in particular the findings of the individual papers in Part II, have implications for criminal cases in which speaker recognition forms a part. The findings feed directly into the growing body of forensic phonetic and forensic linguistic research.
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| 4. |
- Svensson, Christina, 1964-
(författare)
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Ultrasound Assessment and Vascular Mechanics in Takayasu Arteritis and Systemic Lupus Erythematosus
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Takayasu arteritis (TAK) and systemic lupus erythematosus (SLE) are inflammatory diseases that primarily affect young women. TAK is a rare vasculitis that affects the aorta and its main branches, whereas SLE is a chronic autoimmune disease that effects multiple organs. Both diseases are associated with premature cardiovascular disease (CVD), and a wish to understand these associations prompted the studies of this thesis.The macrocirculation, microcirculation and vascular haemodynamics were studied in patients with TAK (N=25 in Paper I, N=17 in Paper II) and SLE (N=60 in Papers III and IV), and compared with age- and gender-matched controls. Vessel wall thickness (intima-media thickness (IMT)), vessel wall appearance, and occurrence of atherosclerotic plaques were evaluated in multiple vascular areas using high-frequency ultrasound (US). Microcirculation in the skin was studied after induced ischaemia employing a new method that combines laser Doppler flowmetry (LDF) and diffuse reflectance spectroscopy (DRS). The measured microcirculatory value was defined as the peak oxygen saturation (OxyP). Pulse wave analysis was used for calculation of the central augmentation index (AIx). Cerebrovascular reserve capacity (CVR) was analysed using transcranial Doppler (TCD).Paper IIn this study, TAK patients were examined with US, including follow-up studies. Clinically active cases of TAK showed significantly increased IMT compared to stable patients with TAK and healthy controls. The arteries of patients with active disease showed signs of intra-mural micro-vessels, oedema, or increased vessel diameter, whereas these signs were not seen in cases of stable disease. The Takayasu US index (based on the summation of the IMT in three arterial areas) was higher in active disease than in stable disease, and was valuable for the assessment of relapse.Paper IIIn this study of vascular haemodynamics in patients with TAK we observed impaired microcirculation, as compared with controls. CVR was preserved regardless of proximal arterial stenosis. The AIx, reflecting arterial stiffness, was increased, also in the arms without proximal stenosis or occlusion.Papers III and IVIncreased IMT with predominantly medium echogenicity was observed in multiple arteries of the 60 patients with SLE, predominantly in vascular areas that are not usually part of the IMT measurements. The patients with SLE developed plaques more frequently and earlier in life compared to the controls. Correlation with traditional cardiovascular risk factors was observed, indicating atherosclerotic mechanisms rather than inflammation. The patients with SLE had higher AIx values and lower OxyP levels, even at younger ages, and both these methods correlated with the IMT and plaque occurrence.ConclusionsFor patients with TAK, US can be valuable both for the diagnosis of the disease and for distinguishing between the active and stable disease forms. The microcirculation and degree of arterial stiffness in the arms are affected also in patients with TAK without proximal stenosis/occlusion, indicating a more widespread arterial wall dysfunction.In patients with SLE, increased IMT, an affected microcirculation, increased arterial stiffness, and premature atherosclerotic plaques indicate vascular affection coupled with increased risk for cardiovascular disease. All these evaluated methods may be used for longitudinal studies with or without intervention.
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