It contain description about the display technologies, raster and vector scan, hard copy devices and graphics software.

1. DISPLAY TECHNOLOGIES
RASTER SCAN SYSTEM
RANDOM SCAN SYSTEM
HARD COPY DEVICES
GRAPHICS SOFTWARE
Overview of the Graphics
System

2. Video Display Devices
 The primary output device in a graphics system is a
video monitor.
 The operation of most video monitor is based on the
standard Cathode Ray Tube(CRT)

3. Refresh Cathode Ray Tubes
 Electron are “boiled off” the surface of cathode by
heating it with the help of the heating filament.
 The accelerating voltage is generated with the help of
positively charged metal coating on the inside of CRT
envelope or an accelerating anode can be used.
 The intensity of the electron beam is controlled by
setting the negative voltage of the control grid.
 Focusing system is needed to force the electron beam
to converge into small spot as it strikes the
phosphorous.

4.  Focusing can be implemented with the help of
electric field or the magnetic field.
 As in the case of focusing of the electron, the
deflection of the electron can be controlled by using
either magnetic or the electric field.

8.  Different kind of Phosphors are available for use in
CRT. Beside color major difference between
phosphors is their persistence.
 Persistence is defined as the time it takes for the
emitted light on the screen to decay one-tenth of its
original intensity.
 A phosphors with low persistence is used in
animation while the other one is useful in displaying
highly complex, static pictures.

9.  The maximum number of points that can be
displayed on the screen without overlap is referred to
as the resolution.
 High resolution system are referred to as high-
definition system.
 The physical size of the graphical monitor is given as
the length of the screen diagonal.
 Aspect ratio is the ratio of vertical points to
horizontal points required to produce equal length
lines in both direction on the screen.

10. Raster Scan Display
 The electron beam is swept across the screen one
row at a time top to bottom.
 As the electron beam moves across each row, beam
intensity is turned ON and OFF to create the pattern
of illuminated spots.
 Picture definition is stored in the memory area called
refresh buffer or frame buffer.
 Each screen point is referred to as pixel or
pel(picture element)

11.  On a black white system with one bit per pixel, the
frame buffer is commonly called bitmap.
 For a system with multiple bits per pixel, the frame
buffer is often referred to as pixmap.
 Refreshing on raster scan display is carried out at the
rate of 60 to 80 frames per second.
 On some rater scan system, each frame is displayed
in two passes using an interlaced refresh procedure.

14. Interlaced vs Non-Interlaced Scan
 In interlaced scan, each frame is displayed in two
passes. First pass for odd scan lines and second for
the even.
 In non-interlaced scan, electron beam sweep over all
the scan lines.

15. Question
 Consider a RGB raster system is to be designed using 8
inch by 10 inch screen with a resolution of 100 pixels
per inch in each direction. If we want to store 8 bits per
pixel in the frame buffer, how much storage (in bytes)
do we need for the frame buffer?

16. Question
 Consider 512 pixels X 512 scan lines image with 24-bit
true color. If 5 minutes video is required to capture,
calculate the total memory required?

17. Random scan display
 Electron beam is directed only to part of the screen
where a picture is to be drawn.
 It is also referred to as vector display or stroke-
writing or calligraphic displays.
 The components lines of a picture can be drawn and
refreshed in any specified order.
 Refresh rate depends on the number of lines to be
displayed.
 Picture set is stored as the line drawing commands in
memory called refresh display file or display list or
display program or simply refresh buffer.

18.  It is suited for line drawing application and cannot
display realistic shaded scenes.
 Vector display has higher resolution than raster scan
display.
 Vector display produce smooth line drawing as beam
directly follow the line path.

20. Color CRT Monitors
 Color pictures can be displayed by using a
combination of phosphors that emit different colored
light.
 By combining these different light, range of colors
can be generated.
 Two basic techniques used are:
 Beam Penetration
 Shadow Mask

21. Beam Penetration
 This method is used with random scan monitors.
 Two layers of phosphors, usually red and green are
coated inside CRT.
 The colors are displayed depending on how far the
electron beam penetrates the phosphors layers.
 Beam of slow electrons excite only outer red layer,
fast beam can penetrated deep to excite both layer.
 Only four colors are possible and quality of pictures
is not as good as with other methods.

22. Shadow Mask
 It is used on raster scan system(including color TV).
 It produces much wider range of colors than beam
penetration method.
 It has three phosphor color dots(red, green, blue) at
each pixel position.
 It has three electron gun one for each color dot and
shadow mask grid just behind the phosphors coated
screen.
 The three electron beams are deflected and focused
as group onto shadow mask, which contain series of
holes aligned with phosphors dot pattern.

23.  There are two primary variations
 Stripe Pattern
 Delta Pattern

25. Delta-delta CRT
 When three beam pass through the hole in the
shadow mask, they activate the dot triangle, which
appear as a small color dot on screen.
 Various colors can be generated by varying the
intensity of the three electron guns.
 Difficulties are faced while aligning the shadow mask
hole and respective triads.

27. Precision inline CRT

28. Direct View Storage Tubes(DVST)
 It store the picture information as a charge
distribution just behind the phosphors coated
screen.
 Two electrons gun are used. Primary gun to store
picture pattern and the second flood gun, maintains
the picture display.
 Because no refreshing is needed, very complex
pictures can be displayed at very high resolution
without any flicker.

29.  Disadvantage is that they ordinarily do not display
color and selected part of the pictures can not be
displayed.
 To eliminate the picture section, the entire screen
must be erased and modified picture is redrawn.

30. Flat Panel display
 Flat panel display refers to class of video devices that
have reduced volume, weight and power
requirements compared to CRT.
 They are used in calculators, pocket video games,
laptops, Tv monitors etc.
 We can separate flat panel displays into two
categories:
 Emissive displays
 Non-emissive displays

31.  Emissive display are the devices that convert the
electrical energy into light. Examples are plasma
panel, LED etc.
 Non-emissive display use optical effects to convert
sunlight or light from some other source into
graphical patterns. Example LCD

32. Architecture of Simple Raster Scan System

35. Raster Scan display processor
 Display processor is also called graphics controller or
display coprocessor.
 Its purpose is to free the CPU from the graphics part.
 In addition to the system memory separate display
processor memory can also be provided.
 The major task is to digitize the picture definition
into set of pixel-intensity values for storage in the
frame buffer.
 The digitization process is called scan conversion.

36. Architecture of Raster Scan Display Processor

37. Random Scan System
 An application program is input and store in the
system memory along with graphics package.
 Graphics command in application program are
translated by graphics package and stored in the
display file in the system memory.
 This display file is accessed by the processor to
refresh screen.
 Graphics pattern are drawn by directing electron
beam along components line of the picture.

38. Architecture of Random Scan System

40. Hard-copy devices
 We can obtain hard copy output of the images using
various hard copy devices.
 The quality of the pictures obtain from the device
depends on the dot size and the number of dots per
inch.
 These can be of two types:
 Impact
 Non-Impact

41.  Impact printer pressed the formed character against
the ribbon on to the paper.
 Non-impact system uses the laser technology.
Examples laser printer, plotters etc.

42. Graphics Software
 Two general classification of graphics software:
 General Programming Package
 Special Purpose application package.
 General programming package provides an extensive
set of graphics function that can be used in high level
programming such C or Fortran. Example
GL(Graphics library)
 Special purpose application package is designed for
the non-programmer. Example CAD system