A short presentation about history and technology of computer monitors.

1. Computer Monitors
Mr. SAGAN Bruno
Mr. MAURICARD François-Xavier

2. Why monitors ?
• The monitors are display devices. Display
is the most-used output device on a
computer.
• Display provides instant feedback by
showing you text and graphic images as
you work or play.

3. Common definitions
• pixel : A pixel is a dot of color, the smallest part of a
display.
• resolution : The resolution is the number of pixels on
the display area. It is expressed like « height » x
« width ».
For example : 1024x768 stands for an area of 1024
horizontal pixels high and 768 vertical pixels wide, in
other words the area contains 1024 columns and 768
lines.
• aspect ratio : The aspect ratio is the ratio between the
number of horizontal pixels and the number of vertical
pixels.

4. Common definitions
• color depth : It is the number of bit that are used to
describe a color.
There are three components: RGB : Red / Green / Blue,
each component is described by a tier of the color depth.
Sometimes there is a fourth component called Alpha
Channel that describe the transparency level of the color.
Color Depth Number of displayable colors
8 bits 256 colors
15 bits 32768 colors
16 bits 65536 colors
24 bits 16 777 216 colors
32 bits 4 294 967 296 colors

5. Standard Resolution Aspect Ratio
VGA Video Graphics Array 640 x 480 4:3
SVGA Super Video Graphics Array 800 x 600 4:3
XGA eXtended Graphics Array 1024 x 768 4:3
SXGA Super eXtended Graphics Array 1280 x 1024 5:4
SXGA+ Super XGA plus 1400 x 1050 4:3
UXGA Ultra XGA 1600 x 1200 4:3
QXGA Quad XGA 2048 x 1536 4:3
QSXGA Quad SXGA 2560 x 2048 4:3
QUXGA Quad UXGA 3200 x 2400 4:3
WXGA Wide XGA 1280 x 800 16:10
WSXGA Wide SXGA 1600 x 1024 ~ 16:10
WSXGA+ Wide SXGA plus 1680 x 1050 16:10
WUXGA Wide Ultra XGA 1920 x 1200 16:10

6. Display Technologies
• There is many technologies available such as :
– Cathode Ray Tube (CRT)
– Liquid Crystal Display (LCD)
– Plasma
– Read projection
– Projector
• Only CRT and LCD are used in computer
monitors (Plasma is used only in large screen
size >40 inches).

7. Cathode Ray Tube
• Cathode Ray Tube was the first technology originally used.
• The cathode (negative electrode) is a heated filament that
is in a vacuum created inside a glass tube.
• The ray is a stream of electrons generated by an electro
gun that naturally pour off a heated cathode into the
vacuum.
• Because the electrons are negative they are attracted by
the anode (positive electrode).
• The screen is coated with phosphor, an organic material
that glows when struck by the electron beam.

8. Cathode Ray Tube

9. Cathode Ray Tube
• There is multiple way to filter the electron
beam in order to have the correct picture on
the screen :
• shadow mask : it is a thin metal screen with
very small holes. Three electron beams pass
through the holes to focus on a single point.
The mask helps to control the electron beams
so that the beams strike the correct phosphor
at just the right intensity to create the desired
colors on the display. The unwanted beams
are blocked or « shadowed ».

10. Cathode Ray Tube
• aperture grille : it consists of tiny vertical
wires. Electron beams pass through the
aperture grille to illuminate the phosphor on
the faceplate. This technology was used on
Sony Trinitron® and Mitsubishi Diamondtron®
tubes.
• slot mask : it uses a combination of shadow
mask and aperture grille technologies. Rather
than the round perforations found in shadow
mask displays, a slot mask uses vertically
aligned slots. This technology was used on
NEC Cromaclear® tubes.

11. Liquid Crystal Diode
• Liquid Crystal Diode (LCD) works by blocking light.
• An LCD display is made of two pieces of polarized glass
that contain a liquid crystal material between them.
• A backlight creates light that passes through the first
substrate.
• At the same time, electrical currents cause the liquid
crystal molecules to align to allow varying levels of light to
pass through to the second substrate and create the colors
and images that you see.

12. Liquid Crystal Diode
Light passing through the first
polarized glass.
Light passing through the second
polarized glass.
Only the light components that have oscillation parallel to the
grooves can pass through.

13. Liquid Crystal Diode
• Passive matrix : In passive matrix displays pixels
are controlled by row and by column. The pixel
switch on when it is addressed and then switch off
between each refresh. Passive matrix screen
have usually low contrast and luminosity.
• Active matrix : In active matrix displays each pixel
is controlled individually and can save his own
state. Thanks to that the pixel can leave on
between two refreshes. Active matrix screen have
a better luminosity.

14. CRT vs LCD
CRT LCD
Power - +
Size / Weigh - +
Response time + -
Color fidelity + -
Price + -

15. CRT vs LCD
• Illustrate the impact of response time :
perfect display simulated ghosting effects of 3 frames
actual fastest LCD
typical CRT

16. Conclusion
• Today, two monitor technologies coexist, the CRT that is
less and less used, and the new king of the hill, the LCD.
• Each technologies have they pros and cons, but the lower
power consumption and the reduced size of the LCD has
got the opinion preference.
• But the future of LCD maybe compromised, by SED and
OLED that the road ! Each promises you high quality
display with reduced size. So wait and see… ;-)