DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Figure 9.1 Surround effect.
The three squares surrounded
by light gray are identical to
the three squares surrounded
by black; however, each of the
black-surround squares is
apparently lighter than its
counterpart. Also, the contrast
of the black-surround series
appears lower than that of the
white-surround series.
DeMarsh, LeRoy E., and Edward
J. Giorgianni, “Color Science for
Imaging Systems,” in Physics
Today, Sept. 1989 , 44–52.
Image-related scattered light
is called flare.
Simultaneous contrast has
another meaning, where it is
a contraction of simultaneous
contrast ratio (distinguished
from sequential contrast ratio).
See Contrast ratio, on page 197.
Surround effect
Human vision adapts to an extremely wide range of
viewing conditions, as I will detail in Adaptation, on
page 196. One of the mechanisms involved in adaptation
increases our sensitivity to small brightness variations
when the area of interest is surrounded by bright
elements. Intuitively, light from a bright surround can
be thought of as spilling or scattering into all areas of
our vision, including the area of interest, reducing its
apparent contrast. Loosely speaking, the visual system
compensates for this effect by “stretching” its contrast
range to increase the visibility of dark elements in the
presence of a bright surround. Conversely, when the
region of interest is surrounded by relative darkness,
the contrast range of the vision system decreases: Our
ability to discern dark elements in the scene decreases.
The effect is demonstrated in Figure 9.1 above, from
DeMarsh and Giorgianni. The surround effect stems
from the perceptual phenomenon called the simultaneous
contrast effect, also known as lateral inhibition.
The surround effect has implications for the display of
images in dark areas, such as projection of movies in
a cinema, projection of 35 mm slides, or viewing of
television in your living room. If an image were reproduced
with the correct relative luminance, then when
viewed in a dark or dim surround, it would appear
lacking in contrast.
82 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES
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