The Fundamentals of Display Technologies 1579In this chapter we will explore the fundamentals of dis-
play technologies and how each technology does its
work. We will begin by covering display specifications,
video and computer signals, and finally the display
technologies themselves providing the full context of
how an image is produced on screen.44.1 The Effect of Display SpecificationIn most audiovisual systems design, the display is the
key focal point in the room. With this in mind, it is a
requirement to match the display to the environment
and the explicit needs set forth in the original sales pro-
posal and system design. It is necessary to understand
the specifications relating to display technologies, in
order to properly design for individual applications. The
key considerations are:- Brightness.
- Contrast.
•Color. - Resolution.
- Scaling.
Brightness is the element that we are most familiar
with. It is the measurement of light falling on a surface,
or light emitting from a source such as a plasma, LCD,
or OLED flat panel display. It is most commonly stated
in two units of measurement when relating to display
technologies.
44.1.1 Lumens
A lumen is a measurement of light falling on a surface,
such as a projector illuminating a screen. The measure-
ment is taken using a light photometer pointed at the
projector lens thus measuring the light output of the
projector itself.
A lumen is equal to one foot-candle falling on one
square foot of area.
Properly specified, it is referred to as an ANSI
lumen, which infers adherence to the American
National Standards Institute method of measurement
utilizing a nine zone pattern of rectangles and averaging
the light measurement from each of the nine zones.
Since there are no mandatory/standardized methods
of verifying lumen specifications from a given display
manufacturer, the actual light output may vary as much
as 20% less than the published specifications. This
necessitates testing each display for actual lumen light
output prior to specifying a specific projector in each
application.
While lumen light output is the common specifica-
tion, it is really foot Lamberts or the light reflected from
the screen surface to the viewer that is most important.
This necessitates taking the screen surface gain and
ambient light in the room into consideration when spec-
ifying a projector.
Lumen light output will range from 100 lumens in a
tiny pico projector up to over 30,000 lumens in a large
rental and staging or digital cinema projector.44.1.2 Candelas per Meter Squared (cd/m^2 ), or
NitsCandelas per meter squared, or cd/m², is a unit of mea-
sure that may also be referred to as nits and is typically
used in the measurement of light emitting from a flat
panel display such as plasma, LCD, or OLED directly at
the viewer.
Broken down, candela, abbreviated as cd, is a term
that originated in the days when candles were used in
theaters.
For our purposes, candelas per meter squared
measures the light properties radiating from a
one-meter-square surface, providing a technical frame
of reference for the performance of a display’s black
level, peak brightness, grayscale, and gamma readings.
Candelas per meter squared are more accurate than
lumen light output measurements and can be measured
using the same nine zone ANSI pattern. Since the screen
reflectivity or gain is taken out of the equation it is less
complex than a projector and screen combination.
Typical candela per meter squared measurements
vary from 300 cd/m^2 for a 19 inch desktop monitor to
the latest LCD displays providing 1500 cd/m^2 in sizes
up to 108 inches diagonal.
It is generally agreed that contrast is the element in a
picture that provides the appearance of quality in an
image. Poor contrast makes the image appear washed
out while good contrast gives us excellent depth of field
and much more detail in a picture. It also gives us the
appearance of higher resolution while not actually
providing more lines of resolution or more pixel density
in the image.44.1.3 ContrastContrast is the range of light and dark values in a picture.- It is stated as the ratio between maximum and the
minimum brightness values—e.g., 1000:1. - Low contrast is shown mainly in shades of gray.