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(2) Tri A Visual Ergonomics > Week 3- Visual display devices > Flashcards

Week 3- Visual display devices Flashcards

1
Q

Visual display devices facts:-

A

• Hardware used for displaying visual media using graphics, texts, images
• Consists of components such as monitor, video adapter card, video cable
• Devices include Cathode ray tubes (CRT): Colour CRT, Direct View storage Tube (DVST): resembles CRT

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2
Q

What is a monitor?

A

•Monitor or VDU (Display), electronic display for computers
- Example: liquid crystal display
• Quality depends on: monitor/video controller

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3
Q

Monitor types:- (3)

A

• Monochrome
• Greyscale
• Colour

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4
Q

Monochrome monitor:-

A

• “Green screen”
• Oldest type of CRT display: 1960’s-1980’s
•Still used in visual psychophysics laboratories

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5
Q

Greyscale monitors:-

A

• “Black and white” monitors
• Special type of monochrome display able to show different shades of grey
• sixteen different shades

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6
Q

Colour monitors:-

A

• Displays many different colours
• Work like monochrome - except have three electron beams instead of one
• Three guns representing red, green and blue
• Each pixel includes three phosphors: red, green and blue; arranged in triangle
• Beams can combine different combinations lighting up phosphors

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7
Q

How do CRT’s work?

A

• Using electromagnetic coils in vacuum tubes
• Due to negative charge on particles, the electrons can be manipulated

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8
Q

How do monitors work?

A

• Cathode ray-tube as display device
• CRT: Glass tube that is narrow at one end, and opens to flat screen at other end
- Electrons travel through vacuum sealed container from cathode (negative) to anode (positive)
• Ray can be manipulated by magnet due to negative charge using COILS

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9
Q

How do cathode ray tube(CRT) monitors work?

A

• CRT monitors contain millions of tiny red, green and blue phosphor dots that glow when struck by electron beam
• CRT tube: the cathode is a heated filament
• Heated filament is in vacuum inside glass tube
• Electron beams hitting anode screen produce image by making screen glow

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10
Q

Explain Basic Cathode ray tube:-

A

• Electrons excite phosphor to glow (anode)
• Electrons fired from back (cathode)
• Phosphor is arranged in dots called Pixels
• Dot mask ensures proper pixel is lit

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11
Q

What is phosphor:-

A

• Semi-conductor which emits visible radiation in response to impact of electrons
• Due to sudden change in electron beam, light emission does not fall instantaneously; there is gradual reduction called “Fluorescence”

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12
Q

What is the scanning pattern of CRT electron gun?

A

• Electron gun scams beam left to right AND top to bottom
• This refreshes every phosphor in zig zag pattern

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13
Q

Advantages of CRTs:- (Old facts - not true anymore)

A

• Easy to increase brightness using CRT
• Produced more colours than newer LCD or Plasma screens
• Image quality also of cathode ray also higher than LCD or Plasma Screens
• Contrast feature of cathode ray considered excellent

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14
Q

Disadvantages of CRT (6)

A

• Large back + takes up space
• Heavy to pick up + move around
• Electromagnetic fields constitute health hazard to living cells
• Also emit x-rays which may institute health hazard
• Refresh rate of CRT produces headaches
• CRT’s operators at high voltage: overheating + exploding
- This is exaggerated due to vacuum seal

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15
Q

Liquid Crystal Display Monitors are:-

A

• Flat panel displays, electronic or video displays that use light modulating properties of liquid crystals (LCs)
• LC’s don’t emit light directly
• Were offered as replacement to CRT

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16
Q

CRT compared to LCD:-

A

• CRT
- Bulky, heavy, use vacuum tube technology.
- Using technology that was developed in the 19th century.
• LCD
- First LCD laptop monitors were very small due to manufacturing costs but now are available in a variety of sizes.
- Light, sleek, energy-efficient, have sharp picture.

17
Q

Two categories of LCD’s:-

A

• Passive matrix
• Active matrix

18
Q

How do Passive Matrix LCD work?:-

A

•Monochrome passive-matrix LCD’s were standard in most early laptops
- Consists of grid of horizontal and vertical wires
- At intersection each grid is LCD element constituting a single pixel, either by letting light through or blocking it
•Passive matrix LCD
- Pixels arranged in grid
- Pixels activated indirectly : rows/columns activated
- Animation can be blurry

19
Q

Active Matrix LCD’s:-

A

• Depend on Thin-film transistors
- TFT’s are tiny switching transistors and capacitors
• Arranged in matrix on a glass substrate
• Each pixel is activated directly
- Pixel have 4 transistors, one for red, green, blue
- One for opaqueness
• Animation is crisp and clean

20
Q

Advantages of LCD:-(6)

A

• LCD display may be tweaked maximally to give a sharp image.
• High peak intensity produces very bright images.
• Screens are perfectly flat.
• Thin, with a small footprint. little electricity and produce little heat
• Lightweight
• Lack of flicker and low glare reduce eyestrain.

21
Q

Disadvantages of LCD:- (5)

A

• After a while some pixels on an LCD display will die
- This is seen as discoloured spots or a black spot on the display.
• LCDs are expensive.
• The display response times are slow.
• An LCD display has a fixed resolution display and cannot be changed.
• The viewing angle of a LCD display is very limited.

22
Q

Other types of display monitors:-

A

• Paper-white displays
- High contrast between fore and background
• Electro-luminescent displays (ELD)
- Similar to LCD
- Uses phosphor to produce light
• Plasma monitor
- Gas is excited to produce light

23
Q

Monitor specifications include:-

A

Monitor Specifications can be judged by:
- Size
- Resolution
- Refresh rate
- Dot pitch

24
Q

Monitor size facts:-

A

•Determines how well images can be seen
• Larger monitor = Larger images
• Monitors measured diagonally
- A 17-inch monitor measures 17 inches from the lower left to the upper right corner.
• In contrast, a CRT monitor’s viewing area was smaller than the monitor’s overall size.

25
Q

Monitor resolution facts:-

A

• The term resolution refers to the sharpness and clarity of an image.
- A monitor resolution is determined by the number of pixels on the screen. It is expressed as a Matrix.
• Monitor made up of video controller
• Images made up of pixels
• More pixels = higher image quality
- For example, 640 X 480 resolution meant that there were 640 pixels horizontally across the screen and 480 pixels vertically down the screen.

26
Q

Refresh rate facts:-

A

• How many times per second display refreshes its image
• Refresh rate places hard cap on frame rate thats visible
• Refresh rate and frame rate are not the same
- Refresh rate = Monitor, frame rate = info sent to it
•

27
Q

Refresh rate in CRT:-

A

• In a CRT, monitor refresh rate = Number of times electron gun scanned every pixel
• Refresh rate Important due to fading of phosphor dots
• If the screen is not refreshed, it will appear to flicker.
• Refresh rate is measured in Hz or Cycles per second.
- If the monitor refresh rate is 100 Hz, it means that it refreshes its pixels 100 times every second.

28
Q

What are video cards/GPU’s?

A

•Interface between computer and display device
• The CPU sends information from software applications images to GPU - which thens decides how to pixilate the image.

29
Q

How did Video cards work?

A

• At common resolutions, a computer has millions of pixels, and needs to decide how to turn them into an image
- it needs something to take binary data from the CPU and turn it into a picture
• GPU’s do this unless pc has built in GPU in motherboard
• These days all computers have GPUs built into them.
• This all reduces workload of CPU

30
Q

Some uses of GPU’s:-

A

•Operations: Bitmaps, painting, window resizing, repositioning, line drawing, polygon rendering
• Some GPU’s have image enhancements algorithms

31
Q

Video cards - Memory: what is it?

A

• Uses RAM - Random access memory
• GPU can have its own ram, called VRAM (Video ram)
- Ranges from 125mb-800mb
• Has clock rates of 300Mhz-1.7Ghz
•Z-buffer is important as takes care of depth coordinates in 3D graphics

32
Q

What is ergonomics relation to monitors?

A

• Eyestrain
- It is the fatigue of the eyes
• Steps to avoid
- Choose a good monitor
- Place the monitor 2 - 3 feet away
- Centre of screen below eye level
- Avoid reflected light

33
Q

Hazards of Monitors?

A

• Electronic magnetic fields (EMF)
- Generated by all electronic devices
-EMF may be detrimental to health
Steps to avoid
• Keep the computer at arms length
• Take frequent breaks
• Use an LCD monitor

34
Q

What is a data projector?

A

• A video projector is an image projector that receives a video signal and projects the corresponding image on a projection screen using a lens system.

35
Q

Optometry aids with VDU’s:-

A

• Energy contact lenses from cooper vision
• VDU spectacles - a varifocal for young folk

(2) Tri A Visual Ergonomics (11 decks)

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