Human Visual Foveation Model
The photoreceptors
(cones and rods) and ganglion cells are non-uniformly distributed in the retina
in the human eye as shown in the left figure below. The density of cone receptors
and ganglion cells play important roles in determining the ability of our eyes
to resolve what we see. Spatially, the resolution has the highest value at the
point of the fovea and drops rapidly away from that point as a function of
eccentricity. When a human observer gazes at a point, a variable resolution
image is transmitted through the front visual channel into the high level
processing units in the human brain. The region around the point of fixation
(or foveation point) is projected into the fovea, sampled with the highest
density, and perceived with the highest sensitivity. The right image below
simulates the foveation process of the human eye.
|
|
|
The human visual
system's foveation feature has two different effects:
- At a certain eccentricity, the highest
spatial frequency that can be resolved by the human eye without aliasing
is limited by the corresponding sampling density in the human visual
system. This feature frequency is usually called the local cutoff
frequency.
- Within the frequency band that can be resolved
by the human eye, the visual error sensitivity varies as a function of
eccentricity.
The
following figures demonstrate our visual sensitivity model, where brightness
indicates the normalized strength of visual error sensitivity. The top-left,
top-right, bottom-left and bottom-right figures are for image size 512 by 512
and viewing distance v = 1, 3, 6 and 10 times of the image width,
respectively. The white curves show the foveated cutoff frequency.
Back to Embedded Foveation Image Coding (EFIC)
Back to Foveation Scalable Video Coding (FSVC)
Back to Foveated Wavelet Image Quality Index (FWQI)
Back to Zhou Wang's Research Work
Back to Zhou Wang's Homepage
Back to LIVE
Last
updated Mar. 5, 2001