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There are different types of display devices

Raster or Refresh scan display

Random or Calligraphic display

Color CRT Monitor Direct view storage tube

Flat panel display

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Used in television screens

It is based on CRT.

It is a point-plotting device

Raster displays store the display primitives (lines,characters, shaded and patterned areas) in a refresh

buffer.

Refresh buffer (also called frame buffer) stores the

drawing primitives in terms of points and pixelscomponents

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Raster: is a rectangle array of dots.

Pixel(picture element): is one dot.

Scan line: is a row of pixels.

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To refresh the picture, the electron beam scans the

entire screen as follows:

1.It starts from the top left corner.

2.Scan row by row 3.Once it reaches the bottom right corner, it jumps

to the top left corner.

4.go to step 1and start the process again

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Quality of images depends on

Resolution: total number of pixels.

Amount of bits per pixels (number of colours).

Raster images cannot be scaled to higher resolutionwithout loss of apparent quality.

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Also called Vector, Stroke, Line drawing displays.

StrokeCharacters are also made of sequences of

strokes (or short lines)

Vector

electron beam is deflected from end-point toend-point

Electron beam is directed only to those parts of the

screen where picture is displayed.

Random scan

picture can be drawn and refreshed by arandom-scan in any order.

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It is a line drawing application (engineering)

Draw one line at a time.

Cannot draw realistic shaded pictures scene. Picture is stored as a line drawing command in a memory

area called:

Display list, Refresh display file, Vector file, or

Display program To display a picture, the system will cycle through the set

of line-drawing commands in the display list.

After all line-drawing commands are drawn, the system

cycle back to the first line-drawing command in the list.

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It has higher resolution than the raster system.

It produces smoother line than raster system

Smaller file size to store images, e.g. to draw a

circle,Radius,Center point, Outline Colour. On zooming in or out, quality of picture remains high

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They are divided into two main categories

Emissive Display: convert electrical energy into light.

Examples:

Plasma Panels Thin-Film electroluminescent displays.

Light emitting diode (LED).

Flat CRTs.

Non-Emissive displays: use optical effects to convertsunlight or light into graphic patterns.

Examples:

Liquid Crystal Display (LCD).

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A layer of gas (usually neon) is sandwiched

between two glass plates.

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A matrix of diode is arranged to form the pixel position

in the display. The picture is stored as usual in the

frame buffer.

Information is read from the refreshed buffer and

converted to voltage levels that are applied to the

diodes to produce the light patterns in the display.

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Used in small systems, such as calculators, laptop

computers.

Produce a picture by passing polarized light (from the

surrounding or from an internal light source) through a

liquid-crystal material that can be aligned to either

block or transmit the light

Liquid crystal: These compounds have a crystalline

arrangement of molecules, yet they flow like a liquid

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It is basically a piece of interface or

program which sits between user and

graphics application progam

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