Colour videos with depth : acquisition, processing and evaluation

The human visual system lets us perceive the world around us in three dimensions by integrating evidence from depth cues into a coherent visual model of the world. The equivalent in computer vision and computer graphics are geometric models, which provide a wealth of information about represented objects, such as depth and surface normals. Videos do not contain this information, but only provide per-pixel colour information. In this dissertation, I hence investigate a combination of videos and geometric models: videos with per-pixel depth (also known as RGBZ videos). I consider the full life cycle of these videos: from their acquisition, via filtering and processing, to stereoscopic display. I propose two approaches to capture videos with depth. The first is a spatiotemporal stereo matching approach based on the dual-cross-bilateral grid – a novel real-time technique derived by accelerating a reformulation of an existing stereo matching approach. This is the basis for an extension which incorporates temporal evidence in real time, resulting in increased temporal coherence of disparity maps – particularly in the presence of image noise. The second acquisition approach is a sensor fusion system which combines data from a noisy, low-resolution time-of-flight camera and a high-resolution colour video camera into a coherent, noise-free video with depth. The system consists of a three-step pipeline that aligns the video streams, efficiently removes and fills invalid and noisy geometry, and finally uses a spatiotemporal filter to increase the spatial resolution of the depth data and strongly reduce depth measurement noise. I show that these videos with depth empower a range of video processing effects that are not achievable using colour video alone. These effects critically rely on the geometric information, like a proposed video relighting technique which requires high-quality surface normals to produce plausible results. In addition, I demonstrate enhanced non-photorealistic rendering techniques and the ability to synthesise stereoscopic videos, which allows these effects to be applied stereoscopically. These stereoscopic renderings inspired me to study stereoscopic viewing discomfort. The result of this is a surprisingly simple computational model that predicts the visual comfort of stereoscopic images. I validated this model using a perceptual study, which showed that it correlates strongly with human comfort ratings. This makes it ideal for automatic comfort assessment, without the need for costly and lengthy perceptual studies

The influence of environmental conditions on volcanic processes on the terrestrial planets

This thesis aims to identify what environmental conditions are most influential on volcanic processes on the terrestrial planets. The research primarily focuses on intermediate-sized volcanoes on Venus and Mars; complete surveys of these planets have been performed in order to compile a new catalogue of all such features that lists morphological and locational information for each one. This has yielded three key findings: evolutionary precursors of large volcanoes and several morphologies of steep-sided domes have been identified on Venus, and low-relief shields with very similar morphologies have been identified on Venus and Mars. In each case, morphological differences and similarities are interpreted with respect to the changing configuration of magma within the edifices, differences in surface environment, and magma properties and supply rate. The research topic is also approached from two other aspects. Data obtained by the MARSIS radar sounder have been scrutinized in order to identify aquifers in the shallow Martian crust, and from this gauge the potential for crustal water to have influenced past volcanic activity. However, MARSIS has not succeeded in resolving Martian aquifers, leading to an independent estimate of its aquifer detection depth, and the conclusion that this instrument is insufficient to significantly constrain estimates of the crustal water budget. In addition, ground-penetrating radar surveys have been performed on Icelandic rootless cones, a category of small volcanic feature, in order to determine how their environments have affected their morphologies and interior structures during formation and subsequent modification. Five Icelandic cones have been surveyed, and three classes of cone morphology have been identified. Analogous cone morphologies are observed on Mars, and have been correlated to their interpreted modification environments using the results of the Icelandic surveys as a basis

The ecology and conservation of hotspots for Hector’s dolphin

Many species of marine top-predator have ‘hotspots’ in their distribution. Hotspots can be defined as areas within the distribution of a population that are used disproportionately more than other locations. Usually identified as consistent, high density aggregations, hotspots are generally locations that are important for certain life history processes or key behaviours such as foraging. Knowledge on what drives the existence of hotspots is crucial for the conservation of species and for understanding ecosystems. New Zealand’s only endemic cetacean, Hector’s dolphin, is endangered and sparsely distributed. This thesis investigates hotspots in the distribution of Hector’s dolphins at Banks Peninsula in order to determine what makes these locations unique and thus to appraise how human disturbance may threaten the ecology of these areas. Three simple questions were considered: Where and when do hotspots exist? Why do the dolphins use these areas? What habitat features make these locations unique? Hotspot locations were defined using Kernel density analysis (KDe) of a visual sightings database from standardized, boat-based surveys. The analyses showed that fifty percent of sightings, made over 29 years and weighted by search effort, were clustered into only 21% of the study area. The seasonal pattern of hotspots strongly reflected summer distribution patterns, but several hotspots were also important in spring and autumn. Locations of hotspots were consistent over almost three decades. Passive acoustic monitoring showed the highest rates of foraging buzzes at hotspots; suggesting that foraging opportunities shape distribution in this species. The temporal distribution of foraging was complex, with substantial differences among locations over seasonal, diel and tidal cycles. Data from hydro-acoustic surveys of epipelagic fish showed strong overlap between dolphins and their prey. The depth of prey schools was also important. Prey were generally more abundant, and shallower, at hotspots compared to reference areas. A broad range of habitat variables were pooled from several sources to determine the best predictors of habitat use and the characteristics of hotspots. Covariates were considered that define the physical and biological features of habitat that may be correlated with distribution. Variables significantly related to the relative abundance of dolphins included prey abundance, mud coverage, reef coverage, depth, current velocity, salinity, fluorescence and thermocline depth. However, only the preferred values of prey, depth, dominant habitat type, and to a lesser extent, reef coverage were more common at hotspots. Confirmation of the locations of hotspots, their stability over time and their importance for foraging provides candidates for areas deserving more protection. Hector’s dolphins in this area face threats associated with fisheries bycatch, vessel strike and noise pollution. Further, information on the characteristics of hotspots provides management with opportunities to prevent degradation of the features that make good quality habitat. With spatially explicit management that focusses on the full range of threats, populations of this ecologically important, taonga species may recover to previous, un-impacted levels

Psr1p interacts with SUN/sad1p and EB1/mal3p to establish the bipolar spindle

Regular Abstracts - Sunday Poster Presentations: no. 382During mitosis, interpolar microtubules from two spindle pole bodies (SPBs) interdigitate to create an antiparallel microtubule array for accommodating numerous regulatory proteins. Among these proteins, the kinesin-5 cut7p/Eg5 is the key player responsible for sliding apart antiparallel microtubules and thus helps in establishing the bipolar spindle. At the onset of mitosis, two SPBs are adjacent to one another with most microtubules running nearly parallel toward the nuclear envelope, creating an unfavorable microtubule configuration for the kinesin-5 kinesins. Therefore, how the cell organizes the antiparallel microtubule array in the first place at mitotic onset remains enigmatic. Here, we show that a novel protein psrp1p localizes to the SPB and plays a key role in organizing the antiparallel microtubule array. The absence of psr1+ leads to a transient monopolar spindle and massive chromosome loss. Further functional characterization demonstrates that psr1p is recruited to the SPB through interaction with the conserved SUN protein sad1p and that psr1p physically interacts with the conserved microtubule plus tip protein mal3p/EB1. These results suggest a model that psr1p serves as a linking protein between sad1p/SUN and mal3p/EB1 to allow microtubule plus ends to be coupled to the SPBs for organization of an antiparallel microtubule array. Thus, we conclude that psr1p is involved in organizing the antiparallel microtubule array in the first place at mitosis onset by interaction with SUN/sad1p and EB1/mal3p, thereby establishing the bipolar spindle.postprin

Removal of antagonistic spindle forces can rescue metaphase spindle length and reduce chromosome segregation defects

Regular Abstracts - Tuesday Poster Presentations: no. 1925Metaphase describes a phase of mitosis where chromosomes are attached and oriented on the bipolar spindle for subsequent segregation at anaphase. In diverse cell types, the metaphase spindle is maintained at a relatively constant length. Metaphase spindle length is proposed to be regulated by a balance of pushing and pulling forces generated by distinct sets of spindle microtubules and their interactions with motors and microtubule-associated proteins (MAPs). Spindle length appears important for chromosome segregation fidelity, as cells with shorter or longer than normal metaphase spindles, generated through deletion or inhibition of individual mitotic motors or MAPs, showed chromosome segregation defects. To test the force balance model of spindle length control and its effect on chromosome segregation, we applied fast microfluidic temperature-control with live-cell imaging to monitor the effect of switching off different combinations of antagonistic forces in the fission yeast metaphase spindle. We show that spindle midzone proteins kinesin-5 cut7p and microtubule bundler ase1p contribute to outward pushing forces, and spindle kinetochore proteins kinesin-8 klp5/6p and dam1p contribute to inward pulling forces. Removing these proteins individually led to aberrant metaphase spindle length and chromosome segregation defects. Removing these proteins in antagonistic combination rescued the defective spindle length and, in some combinations, also partially rescued chromosome segregation defects. Our results stress the importance of proper chromosome-to-microtubule attachment over spindle length regulation for proper chromosome segregation.postprin