164 research outputs found

    Outdoor computer vision and weed control

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    Characterisation of a multispectral digital camera System for quantitatively comparing complex animal Patterns in natural environments.

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    Animal coloration can be described by complex colour patterns including elements of varying size, shape and spectral profile which commonly reflect energy outside the spectral range visible for humans. Whilst spectrometry is currently employed for the quantitative study of animal coloration, it is limited on its ability to describe the spatial characteristics of spectral differences in patterns. Digital photography has recently been used as a tool for measuring spatial and spectral properties of patterns based on quantitative analysis of linear camera responses recovered after characterising the device. However current applications of digital imaging for studying animal coloration are limited to image recording within a laboratory environment considering controlled lighting conditions. Here a refined methodology for camera characterisation is developed permitting the recording of images under different illumination conditions typical of natural environments. The characterised camera system thus allows recording images from reflected ultraviolet and visible radiation resulting in a multispectral digital camera system. Furthermore a standardised imaging processing workflow was developed based on specific characteristics of the camera thus making possible an objective comparison from images. An application of the characterised camera system is exemplified in the study of animal colour patterns adapted for camouflage using as a model two Australian, endemic lizard species. The interaction between the spectral and spatial properties of the respective lizards produces complex patterns than cannot be interpreted by spectrophotometry alone. Data obtained from analysis of images recorded with the characterised camera system in the visible and near-ultraviolet region of the spectrum reveal significative differences between sex and species and a possible interaction between sex and species, suggesting microhabitat specialisation to different backgrounds

    Using an illumination discrimination paradigm to investigate the role of illumination priors in colour perception

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    PhD ThesisPrevious studies suggest human colour constancy is optimised for natural daylight illuminations - a \blue bias" for colour constancy - but it is unclear how such a bias is encoded in the visual system. We use an illumination discrimination task to test two hypothesised mechanisms. Both hypotheses suggest that the human visual system has a prior expectation that illuminations are more likely to vary in a bluer region of chromaticity space. One hypothesis (the nature hypothesis) suggests this has developed in the human visual system through evolution, with selection of colour mechanisms that have reduced sensitivity to global bluer changes across a scene (a species prior). The second hypothesis suggests that the prior is learnt through experience with illuminations (the nurture hypothesis - an individual prior). In Chapter 3 we expand on previous results showing a \blue bias" for colour constancy when the illumination varies from a neutral reference, to show that the \blue bias" prevails in variants of the task where the illuminations are all chromatically biased. This result supports the nature hypothesis. However, depending on the chromatic bias, di erent biases can emerge in the threshold data that are more supportive of the nurture hypothesis. In Chapter 4 we explore individual di erences in illumination discrimination ability, compare illumination discrimination ability with chromatic contrast detection ability, and develop ideal observer models for the task. The results in this Chapter are mostly in support of the nurture hypothesis. In Chapter 5 we show that illumination priors may play a role in the recent visual illusion of a dress photograph that appeared blue and black to some observers but white and gold to others. Finally, in Chapter 6, we search for evidence that observers can learn an illumination prior during a psychophysical task. We conclude that the \blue bias" is likely governed by both a learnt prior over the characteristics of daylight illuminations (the nurture hypothesis) and a generic reduction in sensitivity to bluer changes in an illumination (the nature hypothesis)

    Colour Constancy: Cues, Priors and Development

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    Colour is crucial for detecting, recognising, and interacting with objects. However, the reflected wavelength of light ("colour") varies vastly depending on the illumination. Whilst adults can judge colours as relatively invariant under changing illuminations (colour constancy), much remains unknown, which this thesis aims to resolve. Firstly, previous studies have shown adults can use certain cues to estimate surface colour. However, one proposed cue - specular highlights - has been little researched so this is explored here. Secondly, the existing data on a daylight prior for colour constancy remain inconclusive so we aimed to further investigate this. Finally, no studies have investigated the development of colour constancy during childhood so the third aim is to determine at what age colour constancy becomes adult-like. In the introduction, existing research is discussed, including cues to the illuminant, daylight priors, and the development of perceptual constancies. The second chapter contains three experiments conducted to determine whether adults can use a specular highlight cue and/ or daylight prior to aid colour constancy. Results showed adults can use specular highlights when other cues are weakened. Evidence for a daylight prior was weak. In the third chapter the development of colour constancy during childhood was investigated by developing a novel child-friendly task. Children had higher constancy than adults, and evidence for a daylight prior was mixed. The final experimental chapter used the task developed in Chapter 3 to ask whether children can use specular highlights as a cue for colour constancy. Testing was halted early due to the coronavirus pandemic, yet the data obtained suggest that children are negatively impacted by specular highlights. Finally, in the general discussion, the results of the six experiments are brought together to draw conclusions regarding the use of cues and priors, and the development of colour constancy. Implications and future directions for research are discussed

    Proceedings experiencing light 2009 : international conference on the effects of light on welbeing

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    Proceedings experiencing light 2009 : international conference on the effects of light on welbeing

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