Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: Diabetic- and hypertensive retinopathy are two common causes of blindness
that can be prevented by managing the underlying conditions. Patients suffering
from these conditions are encouraged to undergo regular examinations
to monitor the retina for signs of deterioration.
For these routine examinations an ophthalmoscope is used. An ophthalmoscope
is a relatively inexpensive device that allows an examiner to directly
observe the ocular fundus (the interior back wall of the eye that contains the
retina). These devices are analog and do not allow the capture of digital imagery.
Fundus cameras, on the other hand, are larger devices that o er high
quality digital images. They do, however, come at an increased cost and are
not practical for use in the eld.
In this thesis the design and implementation of a system that digitises imagery
from an ophthalmoscope is discussed. The main focus is the development
of software algorithms to increase the quality of the images to yield results of
a quality closer to that of a fundus camera. The aim is not to match the
capabilities of a fundus camera, but rather to o er a cost-e ective alternative
that delivers su cient quality for use in conducting routine monitoring of the
aforementioned conditions.
For the digitisation the camera of a mobile phone is proposed. The camera
is attached to an ophthalmoscope to record a video of an examination. Software
algorithms are then developed to parse the video frames and combine
those that are of better quality. For the parsing a method of rapidly selecting
valid frames based on colour thresholding and spatial ltering techniques
are developed. Registration is the process of determining how the selected frames t together. Spatial cross-correlation is used to register the frames.
Only translational transformations are assumed between frames and the designed
algorithms focuses on estimating this relative translation in a large set
of frames. Methods of optimising these operations are also developed. For the
combination of the frames, averaging is used to form a composite image.
The results obtained are in the form of enhanced grayscale images of the
fundus. These images do not match those captured with fundus cameras in
terms of quality, but do show a signi cant increase when compared to the
individual frames that they consists of. Collectively a set of video frames
can cover a larger region of the fundus than what they do individually. By
combining these frames an e ective increase in the eld of view is obtained.
Due to low light exposure, the individual frames also contain signi cant noise.
In the results the noise is reduced through the averaging of several frames that
overlap at the same location. / AFRIKAANSE OPSOMMING: Diabetiese- en hipertensiewe retinopatie is twee algemene oorsake van blindheid
wat deur middel van die behandeling van die onderliggende oorsake voorkom
kan word. Pasiënte met hierdie toestande word aangemoedig om gereeld
ondersoeke te ondergaan om die toestand van die retina te monitor.
'n Oftalmoskoop word gebruik vir hierdie roetine ondersoeke. 'n Oftalmoskoop
is 'n relatiewe goedkoop, analoë toestel wat 'n praktisyn toelaat om die
agterste interne wand van die oog the ondersoek waar die retina geleë is. Fundus
kameras, aan die ander kant, is groter toestelle wat digitale beelde van 'n
hoë gehalte kan neem. Dit kos egter aansienlik meer en is dus nie geskik vir
gebruik in die veld nie.
In hierdie tesis word die ontwerp en implementering van 'n stelsel wat
beelde digitaliseer vanaf 'n oftalmoskoop ondersoek. Die fokus is op die ontwikkeling
van sagteware algoritmes om die gehalte van die beelde te verhoog.
Die doel is nie om die vermoëns van 'n fundus kamera te ewenaar nie, maar
eerder om 'n koste-e ektiewe alternatief te lewer wat voldoende is vir gebruik
in die veld tydens die roetine monitering van die bogenoemde toestande.
'n Selfoonkamera word vir die digitaliserings proses voorgestel. Die kamera
word aan 'n oftalmoskoop geheg om 'n video van 'n ondersoek af te neem.
Sagteware algoritmes word dan ontwikkel om die videos te ontleed en om videogrepe
van goeie kwaliteit te selekteer en te kombineer. Vir die aanvanklike
ontleding van die videos word kleurband drempel tegnieke voorgestel. Registrasie
is die proses waarin die gekose rame bymekaar gepas word. Direkte
kruiskorrelasie tegnieke word gebruik om die videogrepe te registreer. Daar word aanvaar dat die videogrepe slegs translasie tussen hulle het en
die voorgestelde registrasie metodes fokus op die beraming van die relatiewe
translasie van 'n groot versameling videogrepe. Vir die kombinering van die
grepe, word 'n gemiddeld gebruik om 'n saamgestelde beeld te vorm.
Die resultate wat verkry word, word in die vorm van verbeterde gryskleur
beelde van die fundus ten toon gestel. Hierdie beelde is nie gelykstaande aan
die kwaliteit van beelde wat deur 'n fundus kamera geneem is nie. Hulle toon
wel 'n beduidende verbetering teenoor individuele videogrepe. Deur dat 'n
groot versameling videogrepe wat gesamentlik 'n groter area van die fundus
dek gekombineer word, word 'n e ektiewe verhoging van data in die area van
die saamgestelde beeld verkry. As gevolg van lae lig blootstelling van die individuele
grepe bevat hul beduidende ruis. In die saamgestelde beelde is die ruis
aansienlik minder as gevolg van 'n groter hoeveelheid data wat gekombineer is
om sodoende die ruis uit te sluit.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/85633 |
| Date | 12 1900 |
| Creators | Van der Westhuizen, Christo Carel |
| Contributors | Blanckenberg, M. M., Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xviii, 140 p. : ill. |
| Rights | Stellenbosch University |
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