3.3
Gabor Patches
Dino, Natalie, Maggi, Jessica, Sarah
Sine Wave Grating
• A sine wave grating is an image in
which light intensity alternates
between its brightest and darkest
values according to a sine
function. The bottom image
illustrates a sine wave function,
and below you see this function
superimposed on the Gabor
patch. As you can see, the
intensity cycles from its brightest
value (white in a high-contrast
grating) through a series of
intermediate grays, to its darkest
value (black in a high-contrast
grating), and then back to white
again.
Gaussian Window
• Sharp edges are formed where the
grating meets the background, and in an
experiment, these sharp edges could
“confuse” a neuron. The edges can be
eliminated by multiplying the grating by
a “Gaussian window,” which causes the
grating to blend in with the background.
The Gaussian function is also known as
the “normal curve” or the “bell curve”.
• You will see that the image’s intensity is
highest in the middle and decreases
towards the edges, just as the Gaussian
function does.
Spatial Frequency
• One important property of a
Gabor patch is the spatial
frequency of its sine wave
grating. Spatial frequency is
usually measured in cycles per
degree: the number of times the
sine wave repeats in one degree
of visual angle. The image at
right illustrates a cycle, and
above, two cycles of the grating
are highlighted in
green. Remember that visual
angle is determined by the size
of an object and the distance of
the object from your eye.
Contrast
• The contrast of a Gabor patch’s
sine wave grating refers to the
intensity difference between
the lightest and darkest
portions of the patch, as
illustrated in the image at
right. In a high contrast patch,
the lightest regions of the
image are white and the
darkest regions are black. In a
low contrast patch, the lightest
regions are light gray and the
darkest regions are dark gray.
Phase
• The phase of a Gabor
patch refers to the
relative position, or
shift, of the sine wave
from left to right. The
image at
right illustrates the
phases of a sine wave,
from 0 degrees through
90, 180, 270, and back
to 0 degrees.