DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Viewing environment
Max. luminance,
cd·m –2
Typical simul.
contrast ratio L* range
Cinema 40 80:1 11…100
Television (living room) 100 20:1 27…100
Office 200 5:1 52…100
Table 19.1 Typical simultaneous contrast ratios in image display are summarized.
Y0 : Adaptation (surround)
luminance
Y: Test luminance
∆Y: Increment in test luminance
Figure 19.3 Contrast sensitivity
test pattern is
presented to an observer in
an experiment to determine
the contrast sensitivity
of human vision. The
experimenter adjusts ∆Y;
the observer reports
whether he or she detects
a difference in lightness
between the two patches.
During the course of the day we experience a wide
range of illumination levels; adaptation adjusts accordingly.
But in video and film, we are nearly always
concerned with viewing at a known adaptation state, so
a simultaneous contrast ratio of 100:1 is adequate.
Contrast sensitivity
Within the two-decade range of luminance that is
useful for image reproduction, vision has a certain
threshold of discrimination. It is convenient to express
the discrimination capability in terms of contrast sensitivity,
which is the ratio of luminances between two
adjacent patches of similar luminance.
Figure 19.3 below shows the pattern presented to an
observer in an experiment to determine the contrast
sensitivity of human vision. Most of the observer’s field
of vision is filled by a surround luminance level, Y 0 ,
which fixes the observer’s state of adaptation. In the
central area of the field of vision are placed two
adjacent patches having slightly different luminance
Y 0
Y Y+∆Y
198 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES