7,897 research outputs found
Chromatic Illumination Discrimination Ability Reveals that Human Colour Constancy Is Optimised for Blue Daylight Illuminations
The phenomenon of colour constancy in human visual perception keeps surface colours constant, despite changes in their reflected light due to changing illumination. Although colour constancy has evolved under a constrained subset of illuminations, it is unknown whether its underlying mechanisms, thought to involve multiple components from retina to cortex, are optimised for particular environmental variations. Here we demonstrate a new method for investigating colour constancy using illumination matching in real scenes which, unlike previous methods using surface matching and simulated scenes, allows testing of multiple, real illuminations. We use real scenes consisting of solid familiar or unfamiliar objects against uniform or variegated backgrounds and compare discrimination performance for typical illuminations from the daylight chromaticity locus (approximately blue-yellow) and atypical spectra from an orthogonal locus (approximately red-green, at correlated colour temperature 6700 K), all produced in real time by a 10-channel LED illuminator. We find that discrimination of illumination changes is poorer along the daylight locus than the atypical locus, and is poorest particularly for bluer illumination changes, demonstrating conversely that surface colour constancy is best for blue daylight illuminations. Illumination discrimination is also enhanced, and therefore colour constancy diminished, for uniform backgrounds, irrespective of the object type. These results are not explained by statistical properties of the scene signal changes at the retinal level. We conclude that high-level mechanisms of colour constancy are biased for the blue daylight illuminations and variegated backgrounds to which the human visual system has typically been exposed
Review of Person Re-identification Techniques
Person re-identification across different surveillance cameras with disjoint
fields of view has become one of the most interesting and challenging subjects
in the area of intelligent video surveillance. Although several methods have
been developed and proposed, certain limitations and unresolved issues remain.
In all of the existing re-identification approaches, feature vectors are
extracted from segmented still images or video frames. Different similarity or
dissimilarity measures have been applied to these vectors. Some methods have
used simple constant metrics, whereas others have utilised models to obtain
optimised metrics. Some have created models based on local colour or texture
information, and others have built models based on the gait of people. In
general, the main objective of all these approaches is to achieve a
higher-accuracy rate and lowercomputational costs. This study summarises
several developments in recent literature and discusses the various available
methods used in person re-identification. Specifically, their advantages and
disadvantages are mentioned and compared.Comment: Published 201
Colour constancy in simple and complex scenes
PhD ThesisColour constancy is defined as the ability to perceive the surface colours of objects
within scenes as approximately constant through changes in scene illumination.
Colour constancy in real life functions so seamlessly that most people do not realise
that the colour of the light emanating from an object can change markedly throughout
the day. Constancy measurements made in simple scenes constructed from flat
coloured patches do not produce constancy of this high degree. The question that
must be asked is: what are the features of everyday scenes that improve constancy?
A novel technique is presented for testing colour constancy. Results are presented
showing measurements of constancy in simple and complex scenes. More specifically,
matching experiments are performed for patches against uniform and multi-patch
backgrounds, the latter of which provide colour contrast. Objects created by the
addition of shape and 3-D shading information are also matched against backgrounds
consisting of matte reflecting patches. In the final set of experiments observers
match detailed depictions of objects - rich in chromatic contrast, shading, mutual
illumination and other real life features - within depictions of real life scenes.
The results show similar performance across the conditions that contain chromatic
contrast, although some uncertainty still remains as to whether the results are
indicative of human colour constancy performance or to sensory match capabilities.
An interesting division exists between patch matches performed against uniform and
multi-patch backgrounds that is manifested as a shift in CIE xy space.
A simple model of early chromatic processes is proposed and examined in the
context of the results
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