# CM0304 Graphics Overview Mouse

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```					                                  CM0304 Graphics

I Graphics Hardware
I.3 Input Devices

Xianfang Sun

F. C. Langbein

School of Computer Science
Version 2.3
Cardiff University

Overview
Interactive input devices
Mouse
Graphics tablet
Data glove
Haptic devices
Digitiser
2D scanner
Sensors: PMT, CCD, CMOS
3D scanner

Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices                   1

Mouse
Mouse measures velocity vx, vy of x-, y-movement
Integrating the velocity over time (or summation over
small time steps) gives relative change in position:

∆x =        vx dt ≈               vx(t)∆t,             ∆y =           vy dt ≈       vy(t)∆t
t                                                 t

Keeping track of relative changes by software allows to
track absolute x, y position
Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices                   2
Mechanical Mouse

Movement rotates ball inside mouse
Ball rotates two wheels with radial slots cut in them
Gives rotation around two orthogonal axes
Speed of a wheel is measured by photo sensor pair, which
gives the speed in x- and y- direction

Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices       3

Mechanical Mouse

clockwise rotation ⇒                            ⇐ anti-clockwise rotation

How to determine the direction of movement with two
sensors?
Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices       4

Mechanical Mouse

clockwise rotation ⇒                            ⇐ anti-clockwise rotation

Rotation direction detected by time delay between signals
Measure LED1 when LED2 goes from light to dark
If LED1 is light, wheel rotates clockwise
Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices       4
Optical Mouse
Use a small camera instead of mechanical parts
Light from a red LED is reﬂected by surface onto a
Complementary Metal-Oxide Semiconductor sensor
CMOS sensor converts light into electrons and has a
transistor at each pixel to amplify and move the charge
Sensor takes snapshots of surface (≥ 1500 images/s)
Changes in snapshots translated into movement
(measured by image correlation at ≥ 18MIPS)
Yields smoother, more precise movement
(but has problems with regular surface patterns and
reﬂective surfaces)

Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices   5

Graphics Tablet
A graphics tablet is a small, rectangular tablet
User can move a pen over tablet
Absolute position on tablet transmitted using switch on
pen
Typical way of determining pen position
Grid of horizontal and vertical
wires underneath tablet surface
Electro-magnetic   interaction
between pen and signals send
through wire used to identify
position

Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices   6

Data Glove
Records position and orientation
of hand and ﬁnger movements
Operating principle:
Short ﬁbre-optic sensors ar-
ranged along hand/ﬁngers
Each sensor has a LED and a photo-transistor
Fibre-optic cable is roughened in area where it should
be sensitive to bending
When ﬁbre-optic cable is bend light is lost or reduced
Additional sensor for absolute hand position/orientation

Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices   7
Haptic Devices
Haptics : apply tactile sensation to human interaction with
computers

Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices   8

2D Scanner
Converts images on paper to high-resolution raster images
Operating principle:
Shine bright white light on paper
Light is reﬂected on sensor (single sensor or whole row)
Either paper is moved along sensor (drum scanner) or
sensor is moved over paper (ﬂatbed scanner)
Different sensor technologies:
PMT (photo-multiplier tube)
CCD (charge coupled device)
CIS (contact image sensor / CMOS sensor)

Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices    9

PMT
Photo-multiplier tubes used by old, high-end drum scanners
Mount photo on rotating drum
and move along sensor
Reﬂected light is split into
three beams (RGB)
Light intensity measured by
PMT
Higher sensitivity to light and lower noise level than CCD
Excellent tonal resolution
Less errors due to refraction or focus when compared to
ﬂatbed scanners
Expensive

Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices   10
CCD
A charge-coupled device semiconductor sensor converts
light into charges
When light hits the CCD, electrons are released
Depending on intensity light builds up a local charge
Charges are transported to output and converted
pixel by pixel to digital representation by
analog-to-digital converter
Measurements take place at regular time intervals
(per exposure of CCD)
Colour recorded by using RGB ﬁlters
Beam-splitter with multiple CCDs
Rotating ﬁlter or RGB grid ﬁlter in front of one CCD

Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices            11

CCD
Charges transported of CCD and measured in sequence

Used in digital scanners, cameras and camcorders
Good quality, fast

Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices            12

CIS / CMOS Image Sensor
Similar to CCD, but based on CMOS technology
Each pixel has its own conversion circuit
Less pixels available, but each pixel can be read
individually

CCD                             CMOS
Quality                          high, low-noise                 noisy
Light sensitivity                high                            low to medium
Power                            lots                            little (≈ 1/100 of CCD)
Price                            medium                          cheap

Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices            13
3D Scanner
Captures 3D point set representing surface of an object
Distance between a sensor and a point on the object is
measured ( range data ) and converted to 3D position
Some also capture colour / images

Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices   14

Optical Triangulation, 3D View
To measure distance triangulate position of a laser beam

Alternatives like acoustic, tactile, magnetic methods exist
Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices   15

Optical Triangulation, 2D View

Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices   16
Summary
How does a mechanical / optical mouse, graphics tablet,
data glove work?
What are haptic devices?
What is the operating principle of a 2D scanner?
Which sensors types can be used?
What is a CCD?
How does it capture photos and videos?
How can it be used to capture colour images?
How does a 3D scanner capture data from an object?
Explain optical triangulation

Xianfang Sun F. C. Langbein, CM0304 Graphics – I Graphics Hardware; I.3 Input Devices   17

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Description: CM0304 Graphics Overview Mouse