Thesis (PhD (Electronic Engineering))--University of Stellenbosch, 2009. / The downloading of images is a bottleneck in the image acquisition chain
for low earth orbit, remote sensing satellites. An on-board image quality assessment
system could optimise use of available downlink time by prioritising
images for download, based on their quality.
An image quality assessment system based on measuring image degradations
is proposed. Algorithms for estimating degradations are investigated.
The degradation types considered are cloud cover, additive sensor noise and
the defocus extent of the telescope.
For cloud detection, the novel application of heteroscedastic discriminant
analysis resulted in better performance than comparable dimension reducing
transforms from remote sensing literature. A region growing method, which
was previously used on-board a micro-satellite for cloud cover estimation, is
critically evaluated and compared to commonly used thresholding. The thresholding
method is recommended. A remote sensing noise estimation algorithm
is compared to a noise estimation algorithm based on image pyramids. The
image pyramid algorithm is recommended. It is adapted, which results in
smaller errors. A novel angular spectral smoothing method for increasing the
robustness of spectral based, direct defocus estimation is introduced. Three
existing spectral based defocus estimation methods are compared with the
angular smoothing method.
An image quality assessment model is developed that models the mapping
of the three estimated degradation levels to one quality score. A subjective
image quality evaluation experiment is conducted, during which more than
18000 independent human judgements are collected. Two quality assessment
models, based on neural networks and splines, are tted to this data. The
spline model is recommended.
The integrated system is evaluated and image quality predictions are shown
to correlate well with human quality perception.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1436 |
| Date | 03 1900 |
| Creators | Marais, Izak van Zyl |
| Contributors | Steyn, W. H., Du Preez, J. A., University of Stellenbosch. Faculty.of Engineering. Dept. of Electronic Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
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