A Real-Time and Portable Bionic Eye Simulator - Biomedical Engineering Systems and Technologies - page 38

An initial solution to this problem was to allow the user to adjust thresholding levels
manually via the remote control. This however, proved rather tedious. Furthermore, it
was observed that users seemed to move back and forth between a range of thresholds
in order to obtain more structural information about a scene. Based on this observation,
an automatic threshold ramping function has been developed.
The function makes use of a histogram in order set upper and lower threshold bounds
to move between. This is done in real-time and is dependent on current frame pixel data.
After the bounds have been established, the threshold values are then incremented or
decremented at set time intervals and following either a saw-tooth or triangular ramping
pattern. The preferred pattern can be chosen by the user and the time interval can be
adjusted so that a faster or slower ramp can be achieved.
Although effective in certain situations, this function was also found to induce nausea
occasionally and so has been excluded from evaluation in the preliminary testing we
present.

3.7 Extra Functions

Additional functions have been implemented in our system, such as edge detection, his-
togram assisted threshold selection and dead electrode simulation. These features have
not been evaluated in the preliminary testing we present in this paper; however, would
be of importance for future psychophysical research we intend to carry out. Figure 9
demonstrates edge detection and dead electrode simulation.

Fig. 9. Edge detection: full resolution (top left), binary thresholding (top middle), edge detection
(top right). Dead electrode simulation: 0% (bottom left), 10% (bottom middle), 50% (bottom
right).

4 Experimental Setup

After the HatPack was constructed, three different psychophysical preliminary testing
experiments were devised by the authors and conducted by a number of Monash Vision
Group staff and post-graduate students as volunteers. These experiments were not for-
malised clinical trials, but rather preliminary trials to test the effectiveness of the system