Information Technology Reference
In-Depth Information
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Fig. 1
Figure showing a
scatter plot between MOS
from the VQEG dataset and
an FR VQA algorithm's
scores. A non-linear cor-
relation is evident. Figure
also shows a best-fit-line
through the scatter obtained
using the logistic function
proposed in [6].
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Objective Score
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A Brief Foray into the Human Visual System
You are currently staring at these words on a sheet of paper. Due to acquired fluency
in English, it takes you a fraction of a second to view, process, understand and
proceed along this page. But it is not language alone that guides you along. The
human visual system (HVS) which processes all of the information incident upon
the eye and renders it into a form recognizable by higher areas of the human brain
for cognitive processes to occur has been one of the most actively researched areas
of neuroscience.
The first stage of visual processing in the human are the eyes. This spherical mass
is home to different kinds of photoreceptors - receptors that produce a response when
incident with photons. The response of these receptors is fed through the retinal gan-
glion cells and then to the Lateral Geniculate Neucleus (LGN) which resides in the
thalamus. The LGN is analogous to an 'active' switch - receiving and processing both
feed-forward and feedback information. LGN responses are passed on to area V1 of
the primary visual cortex (situated at the back of your head) which then connects to
area V2, V4 as well as area V5/Middle-temporal (MT) and other higher areas in the
brain. This kind of hierarchical structure is common in neural processing.
Each of the above described units is an interesting area of study, however we shall
not pursue them in detail here. The interested reader is referred to [2] for overviews
and descriptions. Here we shall look at these regions of processing using a system-
design perspective. The first stage of processing is the human eye. The eye behaves
akin to a low-pass filter since light at frequencies above 60 cycles per degree (cpd)
are not passed on to the receptors at the back of the eye. Current research indicates
that there are two kinds of photoreceptors - rods and cones, based on their response
characteristics [3]. Rods are generally in use in low-light conditions while cones are
used for vision under well-lit conditions and for color vision. There exist 3 types of
cones and depending upon their response characteristics are classified as Long (L),
Medium (M) and Short (S) wavelength cones. Another very important characteris-
tic of the eye is the fact that not every region in the visual field is perceived with
