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Matrox guide to digital and analog display technology
Purchasers of new display technology
are often faced with deciding between digital display technology and analog
display technology. Matrox makes a variety of graphics
hardware to support both digital and analog displays. This guide explains
the basics of digital and analog displays, and compares the advantages of each
technology.
The basics
Monitor technology is often distinguished
based on the type of signal it receives from a computer. A digital signal is
sent as a series of very rapid electrical pulses interpreted as a series of
1's and 0's, and which encode information. By contrast, an analog signal has
a continuous nature rather than a pulsed or discrete nature. Information within
a computer is generally processed digitally and, to support an analog monitor,
graphics hardware converts display information using a DAC (Digital-to-Analog
Converter). Because digital and analog outputs are handled differently by graphics
hardware, the level of hardware support for each may differ, most notably with
regards to display resolution.
A failure in a digital transmission usually results in missing data. With a
digital monitor, this may appear as missing (black) pixels or as no screen image
at all. With an analog signal, many factors can slightly or severely affect
the quality of the signal and these quality issues may appear as blurring or
ghosting. With both digital and analog monitor signals, problems with the signal
can be caused by poor quality graphics hardware. However, Matrox graphics hardware
is renowned for its high image quality and is made using high-quality parts
and manufacturing.
From the user's point of view, the difference between these two types of signals
is less important than the type of monitor usually associated with each type
of signal. Digital computer monitors are generally flat panel monitors using
LCD (Liquid Crystal Display) technology and analog monitors are generally CRT
(Cathode-Ray Tube) monitors.
First there was analog
 A
CRT is a specialized vacuum tube in which images are produced when an electron
beam strikes a phosphorescent surface. This technology was invented over 100
years ago and was later used in the first TVs and computer monitors. Typically,
CRT monitors connect to a computer using an HD-15
(VGA) monitor connector. This type of connector was first introduced in
1987 with the VGA
standard developed by IBM. The signal used with a "VGA" connector
is always analog and the female connector is usually blue.
And then there was digital
An LCD, like a computer, is
an inherently digital device. An LCD consists of crystals in a liquid suspension
between two glass or plastic panels. When electric current is applied to a localized
area of the display, the crystals change orientation and block light instead
of allowing it pass through. LCDs have been around since 1970 and, with subsequent
improvements to the technology, they have become pervasive in devices like calculators,
cell phones, digital cameras, laptops, and flat panel monitors.
There are other types of flat panel monitors, most notably plasma displays.
This type of display has gas-filled cells coated with phosphorescent material.
When an electric current charges the cell, the coating glows. Compared to LCDs,
Plasma displays offer brighter colors and cost less at larger sizes but, like
CRTs, they consume more power and have shorter life spans. Given the characteristics
of plasma displays, they're more often used for entertainment systems, public
displays, and control rooms than for computer desktops.
 Digital
monitors typically have a DVI
(Digital Visual Interface) connector. However, there are flat panel monitors
that use analog (HD-15) connectors. When an analog connector is used with a
flat panel monitor, the monitor itself converts the analog signal it receives
to a digital signal. As with any conversion of an analog signal, there may be
some degradation depending on the quality of the hardware involved. Given the
same monitor, the difference between using a digital or analog signal may or
may not be noticeable. The high-quality of Matrox graphics hardware may make
such differences less noticeable.
LCD advantages
The following lists advantages
that LCD monitors have over CRT monitors:
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Use less space:
This is the most obvious advantage and can be critical in space-constrained
environments. This also makes using more than one monitor at a time more
practical. Matrox is an industry leader in multi-display
technology. |
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Consume less
energy: This is important for the environmentally conscious but
it also reduces the total cost of ownership. |
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Emit less heat:
In environments with many monitors in a confined space, this can be an important
issue. Less heat emission reduces the need for extra cooling and can thus
reduce costs. Electronic parts also tend to last longer in cooler environments. |
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Capable of
sharper image quality: LCDs at native resolution generally have
sharper image quality than CRTs at any resolution. The highest resolution
supported by an LCD monitor is often called its "native
resolution". At this resolution, each pixel is individually rendered
and clearly defined, and this results in a sharper, clearer screen image.
With CRT monitors, each pixel is rendered by multiple phosphor dots and
thus the sharpness of each pixel is subject to the distance between these
dots. |
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Fewer problems
with eyestrain due to screen flickering: This is because the light
emitted from LCD monitors is of a more continuous nature. Less likelihood
for eyestrain is important for users who have to look at their displays
for long periods of time. Eyestrain can lead to head aches and other symptoms. |
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Pivoting is
more feasible: Because LCD monitors are lighter and more compact,
they're easier to physically pivot. With pivoting, the display orientation
can be changed to and from portrait and landscape orientations. Displays
that are taller than they are wide have a "portrait" orientation
and those that are wider than they are tall have a "landscape"
orientation. Display rotation is more practical with a monitor that specifically
supports this with its mounting. Graphics hardware that supports this feature
is also required. Pivoting is useful for users viewing different types of
information that fit better in different orientations. Several Matrox
products support this feature. |
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Monitor is
more esthetic: This is debatable, but many find flat panel monitors
themselves (as opposed to what's on their screens) more pleasing to look
at. Since many put a lot of attention into how their environments appear,
it's not surprising that this would be a consideration. |
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Generally contain
less hazardous waste material: By contrast, CRTs contain hazardous
materials, including large quantities of lead, phosphor, cadmium, barium,
and mercury. Improperly disposed of monitors are a large source hazardous
waste in land fills and many countries have laws restricting the disposal
of products containing such materials. |
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Image "burn-in"
less likely: "Burn-in" can occur when static images stay
on screen for long periods of time. The problem appears as a permanent faint
outline of the image in the screen. The Windows taskbar at the bottom of
a screen is an example of a static image that can, over time, can be burnt
into a screen. The use of screen savers makes this problem less likely. |
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Less electromagnetic
radiation: Such radiation can interfere with other electronic devices.
This can be an important consideration in mission-critical environments
like emergency dispatch centers or military control rooms. |
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No distortion
due to screen shape: As the name suggests, the screens of digital
flat panels are completely flat and rectangular. By contrast, the screens
of CRTs are slightly curved and this causes minor image distortion. This
distortion can be an issue in applications where precision is essential,
for example, in medical imaging. |
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Longer monitor
lifespan: Generally, LCD monitors last longer than CRTs. A typical
LCD lifespan is 50,000 hours of use compared to 15,000 to 25,000 for a CRT.
A longer monitor lifespan can provide a better return on investment. |
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Higher resolution
versions available: Some super high-resolutions are only supported
by LCD monitors. For example there are the monitors supported by the Matrox
Parhelia
DL256 and Parhelia
HR256 graphics cards. Such super high-resolution monitors are useful,
for example, for viewing satellite imagery. |
CRT advantages
The following lists advantages
that CRT monitors have over LCD monitors.
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Wider viewing
angle: This allows users to see the screen clearly from more positions. |
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Capable of
showing a variety of resolutions at similar quality: While the
display of an LCD may look better at its native resolution, there's less
difference in quality between the different resolutions that a given CRT
monitor may support. This is because of the analog nature of CRTs. |
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Capable of
showing more colors: Being able to show a greater range of colors
is important in applications like image editing and medical imaging. The
Matrox GigaColor feature (1 billion simultaneous colors) available with
certain Parhelia graphics
cards requires a CRT. |
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Faster screen
redraw / less latency: Many CRTs are capable of updating the screen
at 85 Hz (cycles per second) or more, compared to the 60 Hz or less rate
typical of LCDs. More frequent screen updates can result in noticeably smoother
display for fast-paced, real-time simulations or games. |
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Less expensive:
While LCDs have been dropping in price, CRTs are still generally less expensive
than comparable LCDs. Price often supersedes all other considerations. |
LCD versus CRT summary
The following is a summary of the
advantages of LCD monitors versus CRT monitors.
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LCD
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CRT
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Use less space
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Consume less energy
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Emit less
heat
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Capable of sharper image quality
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Fewer problems with eyestrain
due to screen flickering
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Pivoting is more feasible
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Monitor is more esthetic (arguably)
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Generally contain less hazardous
waste material
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Image "burn-in" less
likely
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Less electromagnetic radiation
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No distortion due to screen shape
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Longer monitor lifespan
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Higher resolution versions available
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Wider viewing angle
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Capable of showing a variety of
resolutions at similar quality
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Compatible with a wider range
of graphics hardware
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Capable of showing more colors
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Faster screen redraw / less latency
(traditionally)
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Less expensive (traditionally)
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LCD versus plasma summary
The following is a summary of the advantages
of LCD monitors versus Plasma monitors.
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LCD
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Plasma
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Less expensive at smaller sizes
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Higher resolution versions available
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Image "burn-in" less
likely
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Don't weigh as much
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Longer monitor lifespan
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Consume less energy
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Less expensive at larger sizes
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Brighter image
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Wider viewing angle (traditionally)
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Faster screen redraw / less latency
(traditionally)
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