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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
       to an ADC
       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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