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Title: Re-evaluation of illuminant estimation algorithms in terms of reproduction results and failure cases
Author: Zakizadeh, Roshanak
ISNI:       0000 0004 6059 930X
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2017
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Illuminant estimation algorithms are usually evaluated by measuring the recovery angular error, the angle between the RGB vectors of the estimated and ground-truth illuminants. However, this metric reports a wide range of errors for an algorithm-scene pair viewed under multiple lights. In this thesis, a new metric, “Reproduction Angular Error”, is introduced which is an improvement over the old metric and enables us to evaluate the performance of the algorithms based on the reproduced white surface by the estimated illuminant rather than the estimated illuminant itself. Adopting new reproduction error is shown to both effect the overall ranking of algorithms as well as the choice of optimal parameters for particular approaches. A psychovisual image preference experiment is carried out to investigate whether human observers prefer colour balanced images predicted by, respectively, the reproduction or recovery error metric. Human observers rank algorithms mostly according to the reproduction angular error in comparison with the recovery angular error. Whether recovery or reproduction error is used, the common approach to measuring algorithm performance is to calculate accurate summary statistics over a dataset. Mean, median and percentile summary errors are often employed. However, these aggregate statistics, by definition, make it hard to predict performance for individual images or to discover whether there are certain “hard images” where some illuminant estimation algorithms commonly fail. Not only do we find that such hard images exist, based only on the outputs of simple algorithms we provide an algorithm for identifying these hard images (which can then be assessed using more computationally complex advanced algorithms).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available