Biomedical Engineering Reference
In-Depth Information
2
Vision Psychology
Vision psychology is very important part of vision (perception) process. The image
attraction plays very important role in the vision process. We measure eye movement
during the image observation on different types of scene that is presented below.
And during the process of HVS modelling we set up a criterion of picture activity
(
PA
) that corresponds with an attraction of the image information [
21
].
2.1
Measuring Eye Movement During Image Observation
For studying visual system function a small experiment was conducted. This
experiment used E.M.AN. for image recording and its modified image analysis.
For this purpose only the distant monitor (PAL television at 3.12 m - given by the
device's construction) was used to stimulate the visual apparatus. It showed images
of the testing scenes. Before the testing scene, the initial shot with the sequence's
serial number was shown for 5 s. The subject focussed on the centre of this image.
After changing the scene on the analysed image, eye movement was recorded after
the scene. The observation period was about 6 s.
Another modification to the equipment took place in the analysis software
part (block scheme of the original image analysis is in Fig.
8
). Analysis of
accommodation was left out and the assessment of the eye's horizontal movement
was also used in an analogous manner for assessing vertical movement. The next
step analysed the shot sequence and assessed eye movement after the observed
scene. The result was a two row matrix with horizontal and vertical vergence values
for the given shot. The result of the analysis was related to the originally observed
centre of the image. A calculation of the trajectory to the monitored image is then
made from the geometric distance of the monitor and the eye. The eye position
values were plotted onto the original fixed image and connected by lines to represent
individual trajectories. Results eye movements during the observation of selected
scenes are in Fig.
18
.
The first point of the eye trajectory is in the middle at the top for the SQUARE
image (marked by the red arrow) followed by movement in the direction of the
lamp and then to the crowd, the church and back to the crowd. In the PORTRAIT
image the situation is different. Observation starts on the left with the hair, followed
by an analysis of the woman's face details then moving to the right analyzing the
hair, part of the sweater and finishing with the face. Between the measured points
(given by a camera frame rate of 360 fps) the saccadic movements are shown, which
often goes very quickly through the areas of constant texture (the background with
low image activity - frequency). It seems from both images that for the observer
the quality of the edges together with sensitivity to face colour (skin tone) play an
important role. Edges often represent areas with high frequencies. If they are low-
quality (blurred) it very often results in poor image quality, more so than distortion
