Computer graphics: Pictures generated and/or displayed by computers

ruralrompSoftware and s/w Development

Dec 2, 2013 (4 years and 29 days ago)

101 views

Computer Graphics


Page

1

12/02/13



1

Display Hardware


Printers/Plotters




Resolution

Dot Size: dpi

(dot per inch).


300, 600
,
1200, …



Dot Distance:





Type
:



Dot
-
matrix:

Printer head has 7x7 ~ 24x24 pins.




Pen plotter:

Drawing with mechanical pens.


Computer Graphics


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Laser printer
: position
-
charged r
otating drum,
laser beam hits the parts to be white, discharge the
areas, negatively charged powered toner adheres to
the positively charged area.




Ink
-
jet printer
: sprays cyan, magenta, yellow and
black ink onto paper.




Thermal
-
transfer
:

Colored wax
-
pape
r ==> plain paper




Thermal
-
sublimation dye transfer:

256 intensities for each C, M, Y==>16M colors.

Near
-
photographic




Camera




Film recorder




Computer Graphics


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Display Technologies



B/W CRT

(Cathode Ray Tube): Cathode ray hits
phosphor, which in turn emits light.




Phosp
hor Persistence
: time of decay after
electronic excitation.




Critical Fusion Frequency

CFF

> 60 frames/second.

Computer Graphics


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Bandwidth

of a monitor depends on how fast the
electron gun can be turned on and off.

n pixels / scan line ==> on/off n times per scan line

1000

pixels / line * 1000 line /frame * 60 frames / s



16 nanoseconds / switch.




Color CRT



3 guns: RGB



Triad phosphor dots: RGB





LCD: liquid
-
crystal display (light weight)



raster, grid
-
like



lighting at point (x, y) changes when voltage is
applied at the poi
nt.



Active Matrix: emitting light



Passive: reflecting light


Computer Graphics


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Projection CRT (for large
-
screen)


Raster
-
Scan Display Systems



A simple Raster System

System Bus
CPU
System
Memory
Video
Controller
Frame
Buffer
Display
Peripheral
Device




Frame Buffer
:

memory that stores the color data for
each pixel on the screen.



Video controller read
s
the color value for each pixel
and controls the intensity of the display at the pixel.

Video Card

Computer Graphics


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Memory Speed Problem
:

1K pixels / line


1K lines / frame


60frame / second


60 million reads/second ==>16 ns per read

RAM speed ~ 5
0 ns/read

?

Interlacing

odd
and even lines.

VRAM
: Video RAM (TI),

reads all the pixels on a scan line in one cycle.




Frame Buffer Depth



N
umber of bits for each pixel

(n)
.



Also called number of planes.



Number of possible colors: 2
n



VRAM size >= screen resolution * depth



24 bits: 16
M colors,
True Color



1K

1K

3 bytes =3MB VRAM



1K

768

3=2.3MB



800

600

3=1.5MB



640

480

3=1MB



32 bits: RGBA, 16 M colors + Transparency

(“Highest” in Windows)




16 bit:
Pseudo True Color
, 64K

(“Medium” in Windows)




1K

1K

2=2MB VRAM



1K

768

2=1.5MB



800

600

2=
1 MB



640

480

2=0.6 MB

Computer Graphics


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8 bit:
Indexed Color
, 256, SVGA



1K

1K

1=1MB VRAM



800

600

1=0.5MB




Look
-
up Table for Indexed Color

With indexed colors, pixel values represent the index
number into the LUT. The corresponding data value in the
LUT represent the colors
.

8 bits / pixel => 256 colors at a time.

12 bit / entry => 4k colors to chose the 256 from.

Computer Graphics


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GPU (
Graphics Process
ing Unit)

System Bus
CPU
System
Memory
Peripheral
Device
Video
Controller
Display
Processor
Memory
Frame
Buffer
Display
Display
Processor
Graphics
Controller



Specialized hardware to assist graphics display
operations. (scan
-
convert, bitblt)


The Video Controller



The most important ta
sk for the controller is the constant
refresh of the display (60 frame per second)



Interlaced



1
st

field: odd lines



2
nd

field: even lines



Non
-
interlaced: updates every scan
-
line in every field



Output: RGB, monochrome, NTSC (video tape)



Sprites

in animation:

a sequence of fixed
-
size pixel
maps.



Video Mixing:

FB + External Vid
eo
--
> VC
--
> display


Computer Graphics


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9


Input and Interaction

(GUI Design: Look & Feel)




A good user interface allows users to perform interaction
tasks with
ease

and
joy.



WYSIWYG

(What you see is what

you get).



Four basic interaction tasks:

position, text, select, quantify


Input Hardware



Locators
:



relative devices: mice, trackballs, joysticks



absolute devices: data tablets



direct devices: light pens, touch screens



indirect devices: mice, trackballs, j
oysticks



continues devices: mice, trackballs, joysticks



discrete devices: control keys



Keyboards
:



QWERTY(slow down typing)



Dvorak, order by frequency of use



alphabetic order



Valuators
:



bounded: volume control on radio



unbounded: clock



Choice Devices
:



f
unction keys



foot switches

Computer Graphics


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Other Devices
:



voice controls



pressure
-
sensitive stylus



force
-
feedback controls

(Sensable Omni)



3D Interaction Devices



joysticks with a shaft that twists for a third
dimension



Sensable’s Phantom Haptic Device (3D
input
device wi
th force feed
back).



Polhemus 3D sensors

Figure 4B.1





optical sensors (LED)



VR: virtual reality, immersive, head
-
mounted



wands: magnetic, infrared



data glove
s


Computer Graphics


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11




Image Scanners



CCD: Charge
-
Coupled
-
Device



Photo Scanner

Computer Graphics


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12

Basic Interaction Tasks (BITS)



p
osition: by pointing (GRAPHICS)



selection: by name (DB), by pointing



GUI: hierarchical pull
-
down menu
s
,
submenus, page
tabs,
radio
-
buttons
, ch
eck
-
box
e
s
.

e.g. Format
-
>Paragraph…



text interaction: keyboard
--
>text
-
string



quantify interaction: dials, sliders



3D interaction tasks: Z value

multiple views, shift + button
-
down
, projection


Composite Interaction Tasks (CITs)



dialogue boxes

e.g. Format
-
>Paragraph…



rubber
-
banding


Interaction
-
Technique Toolkits



get user input (control) ==>events



graphical output (
feedback) ==>display



graphic device interfaces: GDI

Computer Graphics


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13

o

X Windows Toolkit (UNIX)

o

Windows API (PC)

o

JAVA AWT (Abstract Window Toolkit)

o

JAVA Foundation Class (JFC)

o

JAVA Swing

o

HW
-
independent

Computer Graphics


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Summary



Output:



Printers (YMCK)



CRT (RGB)



Frame Buffer, Depth, Plane
s
, Video Cards,
GPU



Input:




Scanners



Locators



K
eyboard
s



Valuators



Choice Devices



3D Devices



Interactions:



BITS



CITS



ITTS