1. CHAPTER 4 DISPLAY DEVICES

2. Understanding Display Devices
The primary method of getting information out of a computer is to use a computer video display unit (VDU)
Display systems convert computer signals into text and pictures and display them on a TV‐like screen.

3. How Displays work
First computer sends signal to Video Adapter (an expansion board) telling it to display an image or character
Adapter then renders the image/character for the display i.e. converts the above instruction into several instructions that tell the display device (monitor, projector, TV) how to draw the image
Finally the adapter sends the instruction to the display
**Video adapters are either digital or analog
The legacy digital transistor‐transistor logic (TTL) and the analog technologies that began with video graphics array (VGA) were once the two broad categories of video technologies.
These categories have nothing to do withnthe makeup of the VDU but instead with how the graphics adapter communicates with theVDU

4. Types of Video Display Unit (VDU)
Display Components
Applications
LCD (Liquid Crystal Display)
Liquid Crystal molecules
Watches, digital clocks, microwave and household appliance displays, laptops and modern monitors
Plasma
Ionized charged particles
Plasma Display panels (PDPs), TVs
OLED (Organic Light Emitting Diode)
Organic light emitting compound
Home interior, car interior, headlamps, flashlights
Projection System

5. 1. Liquid Crystal Display (LCD)
liquid crystals are basically liquid chemicals whose molecules can be aligned precisely when an electrical current is introduced. Think of how metal shavings line up when a magnet is nearby.
an inventor found that when he passed an electrical current through a semi‐crystalline liquid, the crystals aligned themselves with the current
When properly aligned they allow light to pass through hence the LCD
Require backlighting
The first application of these liquid crystal displays (LCDs) was the LCD watch
The application was expanded to work on monitors hence reducing the weight of luggable computers by almost 30 pounds.

6. Liquid Crystal Display (LCD)
LCDs have both analog and digital interfaces– VGA or DVI-A and DVI-D or HDMI
Analog: PC digital signals are rendered by the video card and sent out as analog signals via a cable connected to the display (modulation); the analog signal is then converted to digital signal by the display device (Demodulation). This process is known as modulation
Digital: Modern LCDs have a digital interface hence require no modulation/demodulation and therefore don’t suffer any signal loss (DVI-D and HDMI supported Video Cards)

7. LCD Construction Two Methods:
Pros
Cons
TN – Twisted Nematic
Two electrodes placed on opposite sides of a liquid crystal layer
Faster response rate – suitable for gamers
Color shifting in angled view (negative effect)
React to pressure (blanching)
IPS – In-Plane Switching
The electrodes that are positioned parallel to one another on the same side of the liquid crystal panel
Colors are more accurate in angled viewing
Do not react to pressure; best for touchscreens
Slow response and lusterless or dull display of black hues
Expensive

8. TN vs. IPS

9. LCD Pixel Addressing
Pixel is a “dot” or the smallest addressable area of illumination, usually a square

10. Active‐matrix vs. Passive‐matrix screens
An active‐matrix screen is made up of several independent LCD pixels. A transistor at each pixel location, when switched among various levels, activates two opposing electrodes that align the pixel’s crystals and alter the passage of light at that location to produce hundreds or thousands of shades.
crisp and easy to look at through nearly all oblique angles
179 degree viewing angle – screen doesn’t turn dark at tight angles like in Passive matrix
does not require constant refreshing
Disadv - Requires large amounts of power to operate all transistors

11. Active‐matrix vs. Passive‐matrix screens
A passive‐matrix display does not have a dedicated transistor for each pixel
Uses a matrix of conductive traces instead
Disadv –poor rate of response (computer takes hundreds of millions of seconds to change a pixel as opposed to tens of millions of seconds in Active matrix)
An effect called Submarining occurs – mouse moved rapidly it disappears and reappears on new location

12. For a single pixel, when the display is instructed to change the crystalline alignment of a particular pixel, it sends a signal across the x‐ and y‐coordinate traces that intersect at that pixel, thus turning it on.

13. Dual scan Dual scan is a variation of the passive‐matrix display.
The classic passive matrix screen is split in half to implement a dual‐scan display.
Each half of the display is refreshed separately
Increased quality of passive‐matrix displays, but still not as good as active matrix.

14. Screen Filters
A privacy filter is a panel that fits over the front of a display; it intentionally limits the viewing angle of the monitor through polarization.
Antiglare filters, brightening and clarifying the image appearing on the monitor’s screen

15. Backlight Sources
FYI – LED displays are LCD panels with Light Emitting Diodes as opposed to classic fluorescent bulbs. The name is good for marketing
Backlight source is LED instead of fluorescent
LED provide intelligent backlighting since there are many “controlled” LEDs in an LED display
Fluorescent bulbs require AC to power while LEDs work on DC power, therefore laptops with LED displays do not require inverter board for DC-AC conversion
LEDs have high contrast ratio rivaling plasma displays

16. 2. Plasma Displays
plasma refers to a cloud of ionized (charged) particles—atoms and molecules
Plasma display panels (PDPs) create this cloud from an inert gas, such as neon – same technology in neon signs
This process is similar to CRTs (cathode ray tubes) which use Phosphors
Disadv - These chemicals can be used up resulting in reduced quality over time
Disadv – Heat generated can result in image burn on the screen

17. Plasma contd..
No backlight required in plasma displays because each pixel produces their own light
Plasma have fluid video motion at 600Hz refresh rate – this high rate on LCDs causes the soap opera effect
Soap opera effect (high refresh rates and intentional quality enhancement aka motion smoothing that results in non-cinematic look but instead the crisp soap opera/documentary look)
More popular in larger-monitor market over LCD because of cost effectiveness

18. 3. Organic Light Emitting Diode (OLED) Displays
Unlike LED displays, the image producing parts of the display, not just the light source are made up of organic light emitting compounds
The compound is placed between an anode and a cathode
When current is passed through the compound it emits light
OLEDs create the image in an OLED display and supply light source, hence no need for backlighting as LCDs do
Higher contrast ration than LCD
OLEDs are self‐contained cells that use the same principle to create light

19. OLED continued.. Can be classifies as AMOLED and PMOLED
Active Matrix organic LED (AMOLED) have better quality that Passive Matrix Organic LED (PMOLED)
Materials used in OLED construction demonstrate shorter life-spans than those in LCD and Plasma displays

20. AMOLED enhancement
Thanks to Samsung -1. Super AMOLED and 2. Super AMOLED Plus display
Super AMOLED replaces the standard touch sensor panel (TSP) found in LCDs with a thinner flatter on-cell TSP resulting in more visible screen in all lighting conditions and increased sensitivity in touch panels
Super AMOLED uses the on-cell TSP with 1.5 times as many subpixels in each pixel – crisper display and 18% more energy effecient

21. 3. Projection Systems
Projectors projects the VDU’s image onto a screen or other flat surface for group viewing
Interactive allow presenters to project an image onto the board as they use virtual markers to draw electronically on the displayed image
Focus lens, keystone, image rotation and other features are included to allow viewing in multiple angles

22. Rear projection TVs
Projector built into a TV cabinet with reverse image projection
A projector is built into a cabinet behind a screen onto which a reverse image
is projected so that an observer in front of the TV can view the image correctly

23. DLP Projectors
Digital Light Processing (DLP) technology allows projectors to be extremely small by using DLP chips called optical semiconductors
DLP chips have as many rotatable mirrors on their surface as pixels in the display resolution
A colored filter wheel switches rapidly among primary and secondary colors thousands of times per second

24. DLP Projection https://www.youtube.com/watch?v=CI0cwk25CAs
DMD – Digital Micromirror device (optical semiconductor that enables light to be modulated digitally)
Signal is sent to the DMD and DMD mirrors switch on and off thousands of times per second reflecting up to 1024 shades of gray
Monochrome to color - Color is added by placing a light filter called a color wheel in between the DMD and a light source

25. Brightness Measured in Lumens (lm)
Lumen is the total amount of visible light that the projector gives off
Based on what the human eyes can see and not visible wavelengths
Lux – derivative of lumens is how much a projector lights up a surface it is given. As you move the projector further away from a surface lux decreases
Ambient light – Light in the room from other sources such as bulbs, windows

26. Adjusting Display Settings
Refresh rate
Frame rate
Resolution
Multiple Displays

27. Refresh Rate
how many times in one second the image on the screen can be completely redrawn, if necessary.
Measured in screen draws per second, or hertz (Hz),
It indicates how much effort is being put into checking for updates to the displayed image.
Refresh rate is selected for the monitor but must be supported by the graphics card

28. Refresh rate continued
LCD TVs have a fixed refresh rate
PC monitor refresh rates are adjustable
As you increase the resolution higher refresh rates become unavailable
Therefore to get the highest refresh rate you may have to settle for lower resolution

29. Frame Rate
Measure of how many unique screens of content were recorded per second.
Video recordings can be done in different frames per second (fps)
Most common – 30fps, 24fps
Refresh rate chosen on playback device must be compatible with the recorded video frame rate
30fps video plays well at 60Hz refresh rate but not 24fps

30. Resolution
How many software picture elements (pixels) are used to draw the screen.
Higher resolutions means more information can be displayed in the same screen area.
Higher resolution also means smaller and harder to see images

31. Resolution continued
Resolution describes visible image’s dimensions, i.e how many rows and columns of pixels are used to draw the screen.
Resolution of 1024×768 means 1024 pixels across (columns) and 768 pixels down (rows) were used to draw the pixel matrix.
1024 × 768 =786,432 pixels to draw the screen.

32. Multiple Displays
Simultaneous use of 2 or more monitors (external displays)
Dual view – Extended desktop option or desktop cloning
Windows Vista’s Windows Display Driver Model (WDDM) version 1 requires same driver to be used for all adapters in multiple monitor setup

33. Practice Exercise
perform Exercise 4.1 and 4.2

34. Video Standards
5 Major Groups
Monochrome
CGA
EGA
VGA
DVI, HDMI

35. Pre-VGA Technologies (Monochrome, CGA and EGA):
Fixed memory meaning fixed resolution and number of supported colors
VGA and Current
Have adapters with expandable memory, therefore selectable resolution and color palettes such as 24 bit/True color with 17 million colors

36. Monochrome Black and white – Latin mono (one) and Chroma (color)
The first adapter, developed by IBM, was known as the Monochrome Display Adapter (MDA).
Hercules computer could display graphics (graphics mode) as well as text (text mode) at 720 X 350 resolution

37. CGA (Color Graphics Adapter)
Added a splash of color – introduced by IBM
Displays 16-color text at 320 X 200 and 640 X 200 res and graphics at 320 X 200 with 4-color per mode

38. EGA (Enhanced Graphics Adapter)
IBM response to demand for more color
EGA – 16 colors at a higher resolution of 640 X 350
Marks the end of classic digital-video technology, analog VGA sprung and lasted until the advent of DVI and HDMI

39. VGA (Video Graphics Array)
Analog technology
Starting point for computer video
Initially had 256KB of video memory on board
Displayed 16 colors at 640x480, 640x350 and 320x200 or
256 colors at 320x200 using VGA BIOS

40. Advanced Video Resolutions and Concepts
These came up as a result of improvements of VGA adapter, both firmware and memory.

41. Super VGA
XGA

42. Aspect Ratio Calculation
Example 1
Example 2
4:3
4÷3 =
1024÷768 =
(1024÷4) x 3 =768
5:4
5÷4 = 1.25
1280÷1024 = 1.25
(1280÷5) x 4 = 1024
16:9
16÷9 =
1920÷1080 =
(1920÷16) x 9 = 1080
16:10
16÷10 = 1.6
1920÷1200 = 1.6
(1920÷16) x 10 = 1200
If you don’t have a calculator it’s easier to use the method shown in example 2 above by breaking 16 into (8x2). For example,
What is the aspect ratio for 8K resolution 7680 x 4800?
Test for 16:10 by dividing 7680/16 or 7680 ÷ 16 =7680/(8 𝑥 2)
………………………………. 7680÷8 = 960
……………………………….960÷2 = 480
Then multiply your answer x10
……………………………….480 x 10 = 4800
Answer: Aspect Ratio = 16:10

43. Video Standard
Resolution
Calculation/Notes
SVGA/XGA
800 x 600 and 1024 x 768
Same resolution but increased colors i.e. 16/256 and 65k/256 respectively.
WXGA
1280 x 800
W stands for increased Horizontal(+200) and same or near same Vertical (+32)
SXGA
1280 x 1024
Memorize this resolution!!!!!!!
QXGA
2048 x 1536
(1024x2) x (768x2) = 2048 x 1536
Q stands for double (X2) the Horiz. and Vertical resulting in Quadruple the resolution
WQXGA
2560 x 1600
W stands for increased Horizontal(+512) and same or near same Vertical (+64)
SXGA+
WSXGA+
1400 x 1050
1680 x 1050
The pluses (+) have x1050 vertical resolutions
UXGA
WUXGA
1600 x 1200
1920 x 1200
The Us have resolution x1200 with WUXGA being the closest to 1080

44. High Definition (HD) Standards
Video Standard
Resolution
Calculation/Notes
ATSC 720p
ATSC 1080p, 1080i
1280 x 720
1920 x 1080
These resolutions are most common with broadcast TVs especially 1080p. Vertical correspond with the standard x720 and x1080
UHD 4K (16:9)
3840 x 2160
4K standard is the new standard that’s not yet mainstream. YouTube/Netflix have some 4K content though
WQUXGA 4K (16:10)
3840 x 2400
This resolution allows for 16:10 aspect ratio on 4K
WHUXGA 8K
(16:10)
7680 x 4800
8K has double the resolution of 4K

45. Nonadjustable characteristics
Native Resolution – LCD, Plasma, OLED have single fixed none adjustable resolution. Avoid distortion when using these displays with a PC by sticking to this native resolution
Contrast Ratio – ratio of luminance of the brightest color to that of the darkest color. It is not contrast. It is generally fixed, contrast on the other hand is adjustable. There is no vendor neutral measurement, therefore one vendor may use variables not used by another and claim higher contrast ratio
Ratios for smaller LCD monitors and televisions typically start out around 500:1.
Common ratios for larger units range from 20,000:1 to 100,000:1. In the early days of
monitors that used LEDs as backlights, 1,000,000:1 was exceedingly common. Today,
vendors advertise 10,000,000:1 and “infinite” as contrast ratios