Subjective Assessment of Image Compression Artefacts on Stereoscopic Display

Image and video quality are important to depict any pictorial information vividly and correctly. With the advancement of technology, we can produce high-quality images and can display those in advanced high-resolution displays. But as high-quality images continue to increase in size, transmitting these exceeds the limited bandwidth of display links. To cope, we need to compress the images but desire that the user cannot perceive any difference between the compressed and uncompressed images. In my thesis, psychophysical experiments with a flicker paradigm were undertaken to do a subjective assessment of the visibility of compression artefacts of two sets of images with two codecs viewed on a stereoscopic display. For one set of images the result shows that artefacts can be silenced in some stereo images relative to 2D while testing with the other set of images was inconclusive. This thesis documented evidence for silencing of artefacts in 3D displays. Other differences between stereoscopic and 2D presentation can be predicted but were not observed here (perhaps due to floor effects). Further large-scale subjective assessment with challenging images may help to get a concrete conclusion

I expect, therefore I see: individual differences in visual awareness

Predictive processing theories posit that awareness of the visual world emerges as the brain engages in predictive inference about the causes of its sensory input. At each level of the processing hierarchy top-down predictions are corrected by bottom-up sensory prediction error to form behaviourally optimal inferences about the state of the visual world. Research suggests there may be individual differences in predictive processing mechanisms such that some individuals are more reliant on prior knowledge, whereas others assign more weight to sensory evidence. Predictive processing biases are thought to manifest in a range of typical and atypical perceptual experiences including proneness to perceptual illusions, sensory sensitivity in autism, and hallucinations in psychosis. The overarching aim of this thesis was to investigate whether in the general population predictive processing biases predict individual differences in visual awareness. Change blindness was selected as the central paradigm of investigation, as it can be conceptualised as a failure to incorporate a novel change into the current prediction about the state of the visual world. The empirical work in Chapter 2 aimed to characterise individual differences in visual change detection using naturalistic scenes and to identify the perceptual and cognitive measures that predict noticing ability. There were reliable individual differences in change detection that generalised to ecologically valid displays. The ability to notice visual changes was predicted by the strength and stability of perceptual predictions, as measured by the accuracy of visual short-term memory and attentional control in the face of distractors. In Chapter 3 I used voxel-based-morphometry to investigate whether inter-individual variability in brain structure predicts individual differences in visual awareness. The latter was assessed by the change blindness task as well as its strongest predictor measures (visual short-term memory, attentional capture, and perceptual rivalry). Regions of interest (ROIs) were selected in the parietal and visual cortices based on previous evidence that these areas are causally involved in the awareness of visual stimuli. This study aimed to discover whether the average grey matter density in the ROIs predict susceptibility to CB. The ROI-based analyses revealed the average grey matter density in left posterior parietal cortex predicted visual short-term memory accuracy but none of the other hypothesised relationships were significant. Chapter 4 aimed to measure individual differences in the reliance on prior knowledge by employing the Mooney face detection task. In this task participants disambiguated faces in two-tone degraded images before and after the presentation of the original versions of the images. Better change detection was predicted by Mooney face detection without any prior knowledge of the images, a measure of ‘perceptual closure’ or an ability to generate a gestalt of a scene. The attention to detail subscale of the autism spectrum also predicted superior change detection. Reliance on prior knowledge in visual perception (assessed by improvement in Mooney face detection after seeing original images) did not consistently predict atypical perceptual experiences associated with the autism spectrum or schizotypy. Chapter 5 was an investigation into, firstly, whether there is a general predictive processing bias, which manifests across different methods of inducing prior knowledge, or whether such a bias is paradigm-specific and, secondly, whether reliance on priors predicts perceptual experiences and traits. All prior manipulations in this study lead to an increased tendency to see the expected stimulus in a binocular rivalry display, except adaptation, which lead to a suppression of visual awareness. Attentional control, perceptual priming, expectancy, and imagery loaded onto a common factor, suggesting that the strength of selective attention is closely linked with the facilitatory effect of expectation. The strength of adaptation predicted superior change detection and perceptual priming predicted the propensity to experience perceptual illusions. Taken together, these findings suggest that there are reliable individual differences in visual change detection, and these are predicted by the strength of visual short-term memory representations, attentional control, perceptual closure ability, as well as the strength of low-level adaptation. Possessing expectations facilitates the entry of the corresponding percept into awareness, irrespective of the method of prior induction. The facilitatory effect that priors exert on visual awareness across different methods is closely linked with the ability to exert attentional control. This suggests that the effects of expectations on awareness may be attentional. However, predictive processing biases were method-specific in that a facilitatory effect using one prior induction method will not necessarily predict the magnitude of the effect using a different method. Some prior effects (e.g., perceptual priming, imagery, and adaptation) yielded correlations with perceptual experiences and traits in the general population. As the research in this thesis is correlational, future studies will need to delineate the effects of expectation, attention, and adaptation on visual awareness and explore the neural representations of these mechanisms

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Neuronal encoding of natural imagery in dragonfly motion pathways

Vision is the primary sense of humans and most other animals. While the act of seeing seems easy, the neuronal architectures that underlie this ability are some of the most complex of the brain. Insects represent an excellent model for investigating how vision operates as they often lead rich visual lives while possessing relatively simple brains. Among insects, aerial predators such as the dragonfly face additional survival tasks. Not only must aerial predators successfully navigate three-dimensional visual environments, they must also be able to identify and track their prey. This task is made even more difficult due to the complexity of visual scenes that contain detail on all scales of magnification, making the job of the predator particularly challenging. Here I investigate the physiology of neurons accessible through tracts in the third neuropil of the optic lobe of the dragonfly. It is at this stage of processing that the first evidence of both wide-field motion and object detection emerges. My research extends the current understanding of two main pathways in the dragonfly visual system, the wide-field motion pathway and target-tracking pathway. While wide-field motion pathways have been studied in numerous insects, until now the dragonfly wide-field motion pathway remains unstudied. Investigation of this pathway has revealed properties, novel among insects, specifically the purely optical adaptation to motion at both high and low velocities through motion adaptation. Here I characterise these newly described neurons and investigate their adaptation properties. The dragonfly target-tracking pathway has been studied extensively, but most research has focussed on classical stimuli such as gratings and small black objects moving on white monitors. Here I extend previous research, which characterised the behaviour of target tracking neurons in cluttered environments, developing a paradigm to allow numerous properties of targets to be changed while still measuring tracking performance. I show that dragonfly neurons interact with clutter through the previously discovered selective attention system, treating cluttered scenes as collections of target-like features. I further show that this system uses the direction and speed of the target and background as one of the key parameters for tracking success. I also elucidate some additional properties of selective attention including the capacity to select for inhibitory targets or weakly salient features in preference to strongly excitatory ones. In collaboration with colleagues, I have also performed some limited modelling to demonstrate that a selective attention model, which includes switching best explains experimental data. Finally, I explore a mathematical model called divisive normalisation which may partially explain how neurons with large receptive fields can be used to re-establish target position information (lost in a position invariant system) through relatively simple integrations of multiple large receptive field neurons. In summary, my thesis provides a broad investigation into several questions about how dragonflies can function in natural environments. More broadly, my thesis addresses general questions about vision and how complicated visual tasks can be solved via clever strategies employed in neuronal systems and their modelled equivalents.Thesis (Ph.D.) -- University of Adelaide, Adelaide Medical School, 201

Flicker perception on digital videos

As digital videos are tremendously pervasive in our daily life, developing accurate and automatic video quality assessment (VQA) tools is highly desirable to help optimize video processing systems that provide more satisfactory levels of quality of experience to the end user. One potentially important aspect in the design of VQA models that remains poorly understood is the effect of temporal visual masking on the visibility of temporal distortions. Interestingly, the mere presence of spatial or temporal distortions does not imply a corresponding degree of quality degradation, since the visibility of distortions can be strongly reduced or completely eliminated by visual masking. In this dissertation, I study flicker perception on digital videos. The contributions of this dissertation are fourfold. I find two unknown mechanisms underlying the motion silencing phenomenon as temporal visual masking using human psychophysical studies. I develop a flicker video database to understand flicker visibility on naturalistic videos. Finally, I propose a perceptual flicker visibility index and a new VQA model accounting for temporal flicker masking. First, I discover a lawful relationship between motions and object changes when motion silencing happens as a function of objects’ velocity, flicker frequency, and spacing by conducting psychophysical human experiments. From spectral analysis of visual stimuli, I develop a simple filter-based, spatiotemporal flicker detector model as a working hypothesis of motion silencing. The proposed model successfully captures the psychophysical data over a wide range of velocities and flicker frequencies. Second, I find the effect of eccentricity and spatiotemporal energy on motion silencing. From human psychophysics, I measure the amount of motion silencing as a function of eccentricity, where the threshold velocity for motion silencing almost linearly decreases against log eccentricity. I propose a plausible explanation that as eccentricity increases, the combined motion-flicker signal falls outside the narrow spatiotemporal frequency response regions of the receptive fields, thereby reducing flicker visibility. Third, I investigate the influence of motion and eccentricity on the visibility of flicker distortions in naturalistic videos. I develop a LIVE Flicker Video database by executing a series of human subjective studies to understand flicker distortions as a function of object motion, eccentricity, flicker frequency, and video quality. I describe the motion silencing effects on flicker distortions in naturalistic videos and propose a model of flicker visibility on naturalistic videos using backward visual masking. Lastly, I propose a new VQA model, called Flicker Sensitive – MOtion-based Video Integrity Evaluation (FS-MOVIE), accounting for temporal flicker masking. I augment the MOVIE Index by combining motion tuned video integrity with a new perceptual flicker visibility index on natural videos. FS-MOVIE captures the local spectral signatures of flicker, predicts perceptually suppressed flicker, and evaluates video quality. FS-MOVIE not only substantially improves the MOVIE index, but is also highly competitive with top performing VQA models tested on the LIVE VQA database.Electrical and Computer Engineerin

Film matters: Historical and material considerations of colour, movement and sound in film

The narratives presented in most film histories seem to ignore the essential material components of analogue film stock. Film matters focuses on material components of the film image – specifically colour, movement and sound – with the aim of telling a material history in a contemporary, ‘post-digital’ environment. The aim of this history is to show how film as a material has participated in the building of social and political realities that are still at work today. My practice-led research results in two videos on colour and a 16 mm film on movement and sound. In these works I practice alternative ways of history writing and telling that may not be written, but which leave their sediments in the materialities and projections of film. My research is embedded in a historical framework, but at the same time reflects upon the actuality of the political history of film. History and memory images are disassembled into their components in order to make visible that which the image does not show, but of which it is made. Setting out from this methodology, in Chapter 1 I research the representational and constitutional participation of these material components in film’s different temporalities. Through a close reading of several seminal films and moving image works I focus on the interplay between film, time and certain contexts of social and political structures, in order to understand how these are constructed along with material history. Chapter 2 explores movement, rhythm and physicality in the materiality of film. Setting out from the experimental set-up of the film Fugue (2015), the chapter analyses the relationship between physicality(of a body) and materiality (of the film) founded on movement. I claim that movement on film and movement of film produce involuntary side products, which become readable in film through dance-like movements and rhythms. I discover micromovements and habit-formation in both the movement of the film and the movement of the body and seek to read their political and transformative potential in situations in which they were joined, or when transitions from one to the other took place. In Chapter 3 I analyse the role of colour within film history and collective memory. Colour, as a chemical component of the film emulsion, has a temporal permanence, seeping into the grounds and bodies as chemicality, as toxic substance. Colour as a transtemporal figure is elaborated in the video Red, she said (2011), which focuses on Technicolor, looking at the colonising power of colour film by characterising the film emulsion as an autonomous actor within the rules and boundaries of cinematic space. The research into colour continues with Rainbow’s Gravity (2014) – a cinematic study of the production, use and employment of colour in the Nazi period and the politics of memory it entails. I found that in many historical cases colour can take on an active role in processes of memorisation. The thesis concludes in a reflection on the practice of working with a negative approach. In my search for forms of resistance within the moving image that interrupt constant reproductions of power and its representations, I detect the necessity of working with negativity in a processual way

Smart Sensor Technologies for IoT

The recent development in wireless networks and devices has led to novel services that will utilize wireless communication on a new level. Much effort and resources have been dedicated to establishing new communication networks that will support machine-to-machine communication and the Internet of Things (IoT). In these systems, various smart and sensory devices are deployed and connected, enabling large amounts of data to be streamed. Smart services represent new trends in mobile services, i.e., a completely new spectrum of context-aware, personalized, and intelligent services and applications. A variety of existing services utilize information about the position of the user or mobile device. The position of mobile devices is often achieved using the Global Navigation Satellite System (GNSS) chips that are integrated into all modern mobile devices (smartphones). However, GNSS is not always a reliable source of position estimates due to multipath propagation and signal blockage. Moreover, integrating GNSS chips into all devices might have a negative impact on the battery life of future IoT applications. Therefore, alternative solutions to position estimation should be investigated and implemented in IoT applications. This Special Issue, “Smart Sensor Technologies for IoT” aims to report on some of the recent research efforts on this increasingly important topic. The twelve accepted papers in this issue cover various aspects of Smart Sensor Technologies for IoT