eyegaze report revised
TRANSCRIPT
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EYEGAZE SYSTEMS
Dept. Of EEE, KLEIT, HUBLI. 1 | P a g e
1. INTRODUCTION
The Eyegaze System is a communication and control system for people with complex physical
disabilities. You run the system with your eyes. By looking at control keys displayed on a
screen, a person can synthesize speech, control his environment (lights, appliances, etc.), type,
operate a telephone, run computer software, operate a computer mouse, and access the Internet
and e-mail. Eyegaze Systems are being used to write books, attend school and enhance the
quality of life of people with disabilities all over the world.
Imagine yourself being a intelligent, motivated, and working person in the fiercely
competitive market of information technology, but just one problem You can't use your
hands. Or you can't speak. How do you do your job? How do you stay employed? You can,
because of a very good gift from computer Industry: The Eyegaze, a communication &
control system you run with your eyes.
The Eyegaze System is a direct-select vision-controlled communication and control system. It
was developed in Fairfax, Virginia, by LC Technologies, Inc., An Eyegaze Desktop system is
shown in Fig 1.
Fig 1 Eyegaze System
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EYEGAZE SYSTEMS
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2. WHO's USING THE EYEGAZE SYSTEM?
This system is mainly developed for those who lack the use of their hands or voice. Only
requirements to operate the Eyegaze are control of at least one eye with good vision & ability
to keep head fairly still. Eyegaze Systems are in use around the world. Its users are adults and
children with cerebral palsy, spinal cord injuries, brain injuries, ALS, multiple sclerosis,
brainstem strokes, muscular dystrophy, and Werdnig-Hoffman syndrome. Eyegaze Systems
are being used in homes, offices, schools, hospitals, and long-term care facilities. By looking at
control keys displayed on a screen, a person can synthesize speech, control his environment
(lights, appliances, etc.), type, operate a telephone, run computer software, operate a
computer mouse, and access the Internet and e-mail. Eyegaze Systems are being used to write
books, attend school and enhance the quality of life of people with disabilities all over the
world.
2.1 THE SKILLS NEEDED BY THE USER:
2.1.1 GOOD CONTROL OF ONE EYE:
The user must be able to look up, down, left and right. He must be able to fix his gaze on all
areas of a 15-inch screen that is about 24 inches in front of his face. He must be able to focus
on one spot for at least 1/2 second.
1. Several common eye movement problems may interfere with Eyegaze use. These include:Nystagmus (constant, involuntary movement of the eyeball):
The user may not be able to fix his gaze long enough to make eyegaze selections.
Alternating strabismus(eyes cannot be directed to the same object, either one deviates):
The Eyegaze System is constantly tracking the same single eye. If, for example, a user with
alternating strabismus is operating the Eyegaze System with the right eye, and that eye begins
to deviate, the left eye will take over and focus on the screen. The Eyegaze camera, however,
will continue to take pictures of the right eye, and the System will not be able to determine
where the user's left eye is focused.
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EYEGAZE SYSTEMS
Dept. Of EEE, KLEIT, HUBLI. 3 | P a g e
When the left eye deviates and the right eye is again fixed on the screen the Eyegaze System
will resume predicting the gazepoint. Putting a partial eye patch over the nasal side of the eye
not being observed by the camera often solves this tracking problem. Since only the
unpatched eye can the screen, it will continuously focus on the screen. By applying only a
nasal-side patch to the other eye, the user will retain peripheral vision on that side.
2.1.2 ADEQUATE VISION:
Several common vision problems may affect a user's ability to see text clearly on the Eyegaze
monitor. These include the following:
INADEQUATE VISUAL ACUITY:
The user must be able to see text on the screen clearly. If, prior to his injury or the onset of
his illness he wore glasses, he may need corrective lenses to operate the Eyegaze System. If
he's over 40 years old and has not had his vision checked recently, he might need reading
glasses in order to see the screen clearly.
In most cases, eyetracking works well with glasses. The calibration procedure accommodates
for the refractive properties of most lenses. Hard-line bifocals can be a problem if the lens
boundary splits the image of the pupil, making it difficult for the system's image processing
software to determine the pupil center accurately. Graded bifocals, however, typically do not
interfere with eyetracking.
Soft contact lenses that cover all or most of the cornea generally work well with the Eyegaze
System. The corneal reflection is obtained from the contact lens surface rather than the
cornea itself. Small, hard contacts can interfere, if the lens moves around considerably on the
cornea and causes the corneal reflection to move across the discontinuity between the contact
lens and the cornea.
BLURRED VISION:
Another occurrence associated with some brain injuries, as well as a side effect of
medications, a blurred image on the screen decreases the accuracy of eye fixations.
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EYEGAZE SYSTEMS
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DIPLOPIA(DOUBLE VISION):
Diplopia may be the result of an injury to the brain, or a side effect of many commonly
prescribed medications, and may make it difficult for the user to fix his gaze on a given point.Partially patching the eye not being tracked may alleviate double vision during Eyegaze
System operation.
CATARACTS (CLOUDING OF THE LENS OF THE EYE):
If a cataract has formed on the portion of the lens that covers the pupil, it may prevent light
from passing through the pupil to reflect off the retina. Without a good retinal reflection the
Eyegaze System cannot accurately predict the user's eye fixations.
The clouded lens may also make it difficult for a user to see text on the screen clearly.
Surgical removal of the cataracts will normally solve the problem and make Eyegaze use
possible.
HOMONYMOUS HEMIANOPSIA (blindness or defective vision in the right or left halves
of the visual fields of both eyes):
This may make calibration almost impossible if the user cannot see calibration points on one
side of the screen.
2.2 ABILITY TO MAINTAIN A POSITION IN FRONT OF THE
EYEGAZE MONITOR:
It is generally easiest to run the System from an upright, seated position, with the head
centered in front of the Eyegaze monitor. However the Eyegaze System can be operated from
a semi-reclined position if necessary.
Continuous, uncontrolled head movement can make Eyegaze operation difficult, since the
Eyegaze System must relocate the eye each time the user moves away from the camera's field
of view and then returns. Even though the System's eye search is completed in just a second
or two, it will be more tiring for a user with constant head movement to operate the System.
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EYEGAZE SYSTEMS
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1. ABSENCE OF MEDICATION SIDE EFFECTS THAT AFFECT EYEGAZEOPERATION:
Many commonly prescribed medications have potential side effects that can make it difficult
to operate Eyegaze. Anticonvulsants (seizure drugs) can cause: nystagmus, blurred vision,
diplopia, dizziness, drowsiness, headache and confusion. Some antidepressants can cause
blurred vision and mydriasis (abnormally dilated pupil.) And Baclofen, a drug commonly
used to decrease muscle spasms, can cause dizziness, drowsiness, headache, disorientation,
blurred vision and mydriasis. Mydriasis can be severe enough to block eyetracking. If the
retinal reflection is extremely bright, and the corneal reflection is sitting on top of a big,
bright pupil, the corneal reflection may be indistinguishable and therefore unreadable by the
computer.
2.3 MENTAL ABILITIES THAT IMPROVE THE PROBABILITY FOR
SUCCESSFUL EYEGAZE USE:
2.3.1 ABILITY TO READ:
At present, the Eyegaze System is configured for users who are literate. The System is text-
based. A young child with average intelligence may not be reading yet, but probably has the
capability to learn to read at an average age. He may be able to recognize words, and may be
moving his eyes in a left to right pattern in preparation for reading. As an interim solution
many teachers and parents stick pictures directly onto the screen. When the child looks at the
picture he activates the Eyegaze key that is located directly underneath it.
2.3.2 MEMORY:Memory deficits are a particular concern in considering the Eyegaze System for someone
with a brain injury. A user who can't remember from one day to the next how to operate the
system may find it too difficult to use effectively.
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3. EYEGAZE SYSTEM WORKING
3.1 WORKING:
As a user sits in front of the Eyegaze monitor, a specialized video camera mounted below the
monitor observes one of the user's eyes. Sophisticated image- processing software in the
Eyegaze System's computer continually analyzes the video image of the eye and determines
where the user is looking on the screen. Nothing is attached to the user's head or body. The
Eyegaze system working principle can be understood by the Eyegaze System Architecture
shown in Fig 2 clearly.
Fig 2 Eyegaze System Architecture
In detail the procedure can be described as follows: The Eyegaze System uses the pupil-
center/corneal-reflection method to determine where the user is looking on the screen. An
infrared-sensitive video camera, mounted beneath the System's monitor, takes 60 pictures per
second of the user's eye. A low power, infrared light emitting diode (LED), mounted in the
center of the camera's lens illuminates the eye. The LED reflects a small bit of light off the
surface of the eye's cornea. The light also shines through the pupil and reflects off of the
retina, the back surface of the eye, and causes the pupil to appear white. The bright-pupil
effect enhances the camera's image of the pupil and makes it easier for the image processing
functions to locate the center of the pupil. The computer calculates the person's gazepoint,
i.e., the coordinates of where he is looking on the screen, based on the relative positions of
the pupil center and corneal reflection within the video image of the eye. Typically the
Eyegaze System predicts the gaze-point with an average accuracy of a quarter inch or better.
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EYEGAZE SYSTEMS
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Prior to operating the eyetracking applications, the Eyegaze System must learn several
physiological properties of a user's eye in order to be able to project his gazepoint accurately.
The system learns these properties by performing a calibration procedure. The user calibrates
the system by fixing his gaze on a small yellow circle displayed on the screen, and following
it as it moves around the screen. The calibration procedure usually takes about 15 seconds,
and the user does not need to recalibrate if he moves away from the Eyegaze System and
returns later.
EYE TRACKER/EYEGAZE COMPONENTS:
An eye tracker consists of several parts; a general overview of these is provided in Figure 3.
A video-based eye tracker obtains its information from one or more cameras (Image Data).
The first step of an eye tracker is to find the initial eye position (Detection component) in the
images. The position is used for initializing the Eye Tracking component, which, in turn,
aims at following the eye over time. Based on information obtained from the eye region and
possibly head pose, the Gaze Estimation component will then determine where the user is
looking. This information is then used in the gaze-based application.
The objective is to review all possible feature combinations and to evaluate the ability of the
resulting models to estimate gaze.
Fig 3: Eye Tracker Components
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Eye tracker software components were analysed in deliverable D5.2 Report on new
approaches to Eye Tracking (Daynys et al. 2006). The focus of the current deliverable is
mainly on the hardware components of the system. The hardware components must ensure
good quality image data with required features such as the eye pupil and the glints produced
by infrared light sources. The main hardware component of an eye tracker is the camera.
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4. HOW TO RUN THE EYEGAZE SYSTEM?
A user operates the Eyegaze System by looking at rectangular keys that are displayed on the
control screen. To "press" an Eyegaze key, the user looks at the key for a specified period of
time. The gaze duration required to visually activate a key, typically a fraction of a second, is
adjustable. An array of menu keys and exit keys allow the user to navigate around the Eyegaze
programs independently.
1. The Edge Analysis System uses the Pupil-Center/Corneal-Reflection method todetermine the eye's gaze direction.
2. A video camera located below the computer screen remotely and unobtrusivelyobserves the subject's eye.
3. No attachments to the head are required.4. A small, low power, infrared light emitting diode (LED) located at the center of the
camera lens illuminates the eye. The LED generates the corneal reflection and causes
the bright pupil effect, which enhances the camera's image of the pupil.
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EYEGAZE SYSTEMS
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5. USES OF EYEGAZE
Every year more than 100 000 people are diagnosed with motor neurone diseases. Typically,
even when all other ways of communicating are either severely damaged or completely lost,
the eyes still function. Communication by Gaze Interaction (COGAIN) is a Network of
Excellence designed specifically to help people with these disabilities to communicate more
effectively with eye gaze. At the COGAIN stand you can see how this technology is used by
a person who relies on it.
Current eye tracking equipment allows users to generate text on a computer by using eye
gaze. Users are able to select letters and numbers by looking at a keyboard on a screen withtheir eyes, and can construct words and sentences that can be spoken aloud by the system.
Using these systems both empowers and enables people with disabilities as they can now
communicate without the need for an assistant or helper, giving the users greater freedom in
their lives.
Eye tracking systems that allow text entry by eye gaze have been in existence for about two
decades, but the technology is still only available to a small portion of the potential user
population. Obstacles for more wide-spread use currently include: the high cost of eye
tracking equipment, the limitation that gaze communication applications may only work with
a particular dedicated eye tracking device, and finally that eye tracking devices are often hard
to use and require experts to operate them.
5.1 The Basic Eyegaze Can:
1. ADJUST TO A NEW USER in about 15 seconds. (Calibration)2. TYPE with one of four keyboards, then print or speak. (Typewriter)3. TURN pages on the computer screen by looking at "up" or "down". (Read Text)4. PLAY games, two "Paddle" games, plus Solitaire and Slot Machine.5. TEACH new users with simplified screens. (Teach Screens)
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EYEGAZE SYSTEMS
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5.2 With Options the Eyegaze Can:
1. BE AT TWO SITES!!Portable computer has a handle to hand-carry between twosites. Two sets of other components and cables for access to Eyegaze System at
schools, work or home. Dimensions 9"x5'txl7'1, weight approximately 16 lbs.
(Transportable Computer)
2. BE A KEYBOARDto a second computer to run any keyboard-controlled software,by means of the T-TAM connector. (Second Computer Mode)
3. SPEAK 100"canned phrases" through a speech synthesizer, with a single glance ofthe eye. Phrases can be changed by caregiver or user. (Phrases)
4. CONTROL appliances anywhere in the home or office from one Eyegaze screen.No special wiring. (Lights and Appliances)
5. DIAL and answer a speaker phone from one screen. "Phone Book" stores 16frequently used numbers. (Telephone)
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6. MENUS OF EYEGAZE SYSTEM
THE MAIN MENU:
The Main Menu appears on the screen as soon as the user completes a 15-second calibration
procedure. The Main Menu shown in Fig 4 presents a list of available Eyegaze programs. The
user calls up a desired program by looking at the Eyegaze key next to his program choice.
Fig 4 Main Menu Screen
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EYEGAZE SYSTEMS
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MAIN MENU OPTIONS:
6.1 THE PHRASE PROGRAM:
The Phrases program, shown in Fig 5 along with the speech synthesizer, provides quick
communications for non-verbal users. Looking at a key causes a preprogrammed message to
be spoken. The Phrases program stores up to 126 messages, which can be composed and
easily changed to suit the user.
Fig 5 Phrases Screen
6.2 TYPEWRITER PROGRAM:
Simple word processing can be done using the Typewriter Program. The user types by
looking at keys on visual keyboards. Four keyboard configurations, simple to complex, are
available. Typed text appears on the screen above the keyboard display.
Fig 6Alpha Keyboar
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The user may "speak" or print what he has typed. He may also store typed text in a file to be
retrieved at a later time. The retrieved text may be verbalized, edited or printed. The Alpha
Keyboard is used for typing purpose shown in the Fig 6.
6.3 THE TELEPHONE PROGRAM:
The telephone program allows the user to place and receive calls. Frequently used numbers
are stored in a telephone "book". Non-verbal users may access the speech synthesizer to talk
on the phone. The telephone control screen is shown in Fig 6.
Fig 7 Telephone Control Screen
6.4 RUN SECOND PC:
The Run Second PC program permits the Eyegaze Communication System to act as a
peripheral keyboard and Mouse interface to a Windows computer. The user can run any off-
the-shelf software he chooses on the second computer. He can access the Internet, and send e-
mail by looking at keyboard and mouse control screens on the Eyegaze monitor.
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The programs being run are displayed on the second computer's monitor. Typed text appears
simultaneously on the Eyegaze and second pc's screens. For children, two new Eyegaze
programs have been added to the Eyegaze System. Both run with the Second PC option. Eye
Switch is a big, basic on-screen switch to run "cause & effect" software programs on a
Second PC. Simple Mouse is an easy mouse control program to provide simplified access to
educational software on a Second PC.
Figs 8 and Fig 9 shows the Keyboard and Mouse control screens used in the Eyegaze systems
respectively.
Fig 8 Frequency Keyboard
Fig 9 Mouse Control Screen
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6.5 PADDLE GAMES & SCORE FOUR:
These are the visually controlled Games.
6.6 READ TEXT PROGRAM:
The Read Text Program allows the user to select text for display and to "turn pages" with his
eyes. Any ASCII format text can be loaded for the user to access. Books on floppy disk are
available from Services for the Blind.
6.7 TELEVISION:
Television programs can be displayed directly on the desktop Eyegaze System screen. On-
screen volume and channel controls provide independent operation. (Not available on the
Portable Eyegaze System.
6.8 THE LIGHTS & APPLIANCES PROGRAM:
The Lights & appliances Program which includes computer-controlled switching equipment,
provides Eyegaze control of lights and appliances anywhere in the home or office. No special
house wiring is necessary. The user turns appliances on and off by looking at a bank of
switches displayed on the screen. For controlling the Lights and other equipments the
eyegaze system uses a Light and Appliances screen as shown in Fig 9.
Fig 10 Lights And Appliances Screen
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7. FOR PEOPLE WITH LIMITED EYE CONTROL
Scanning Keyboard is the new row/column keyboard with an on-screen eye "switch" for
people with limited eye movement. The switch can be placed on either side, above, or below
the keyboard to accommodate users with only horizontal movement, or only vertical
movement. The user may "speak" what he has typed.
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8. ENVIRONMENT REQUIRED FOR AN EYEGAZE SYSTEM
Environment required for an Eyegaze system are as follows:
1. Because eye-tracking is done using infrared light, Eyegaze system must take care oflight sources in the room in order to ensure the best accuracy.
2. The Eyegaze System must be operated in an environment where there is limited ofambient infrared light.
3. Common sources of infrared light are sunlight and incandescent light bulbs. TheSystem makes its predictions based on the assumption that the only source of infrared
light shining on the user's eye is coming from the center of the camera.
4. Therefore, stray sources of infrared may degrade the accuracy or prevent Eyegazeoperation altogether. The System works best away from windows, and in a room lit
with fluorescent or mercury-vapor lights, which are low in infrared.
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EYEGAZE SYSTEMS
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9. NEW PORTABLE EYEGAZE SYSTEM
The Portable Eyegaze System, as in Fig 10 and Fig 11, can be mounted on a wheelchair and
run from a 12-volt battery or wall outlet. It weighs only 6 lbs (2.7 kg) and its dimensions are
2.5"x8"x9" (6.5cm x20cm x23cm). The Portable Eyegaze System comes with a flat screen
monitor and a table mount for its monitor. The monitor can be lifted off the table mount and
slipped into a wheelchair mount.
Fig 10 Portable Eyegaze System Mounted On Wheelchair
Fig 11 Monitor Of Portable Eyegaze System
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10. EYEGAZE SYSTEM PERFORMANCE SPECIFICATIONS
10.1 SPECIFICATIONS:
10.1.1 Accuracy
Eyegaze Measurement
Angular Gaze
Orientation
Spatial Gaze Point
(with head 20" (51 cm) from
camera)
Typical Average Bias Error*
(over the monitor screen range)
0.45 degree 0.15 inch (0.38 cm)
Maximum Average Bias Error*
(over the monitor screen range)
0.70 degree 0.25 inch (0.63 cm)
Frame-to-frame variation+
(1-sigma variation with eye fixed
on a point)
0.18 degree 0.06 inch (0.15 cm)
Table 1 Accuracy Of The System
* Bias errors result from inaccuracies in the measurement of head range, asymmetries of the
pupil opening about the eye's optic axis, and astigmatism. They are constant from frame to
frame and cannot be reduced by averaging or smoothing.
+ Frame-to-frame variations result from image brightness noise and pixel position
quantization in the camera image and may be reduced by averaging or smoothing.
10.1.2 Speed:
Sampling Rate: 60 Hertz
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10.1.3 Angular Gaze-track Range:
Gaze Cone Diameter: 80 degrees
As the eye's gaze axis rotates away from the camera, the corneal reflection moves away from
the center of the cornea. Accurate gaze angle calculation ceases when the corneal reflection
"falls off" the edge of the cornea. The eye's gaze axis may range up to 40 degrees away from
the camera, depending on the arc of the person's cornea. The lower 15 degrees of the gaze
cone, however, is generally clipped due to the upper eyelid blocking the corneal reflection
when the eye is looking down below the camera.
10.1.4 Tolerance To Head Motion (Fixed-camera Eyegaze Systems)
Lateral Range: 1.5 inch (3.8 cm)
Vertical Range: 1.2 inch (3.0 cm)
Longitudinal Range: 1.5 inch (3.8 cm)
Table 2 Tolerance To Head Motion
In fixed-camera Edge Analysis Systems, the eye must remain within the field of view of the
camera. However, if the subject moves away from the camera's field of view, eyetracking
will resume once he returns to a position where his eye is again visible to the camera.
10.1.5 COMPUTER USAGE:
Memory Consumption: 6 MB
CPU Time Consumption: 30-50%
Light Emitting Diode:
Wave Length: 880 nanometers (near infrared)
Beam Width: 20 degrees, between half power points
Radiated Power: 20 milliwatts, radiated over the 20 degree beam width
Safety Factor: 5 -- At a range of 15 inches the LED illumination
on the eye is 20% of the HEW max permissible exposure.
Table 3 Specifications Of LED
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10.2 OPERATIONAL REQUIREMENTS:
Low Ambient Infrared Light:
There must be low levels of ambient infrared light falling on the subject's eye. Stray IR
sources obscure the lighting from the Edge Analysis System's light emitting diode and
degrade the image of the eye. The sun and incandescent lamps contain high levels of infrared
light. The environment may be brightly illuminated with lights such as fluorescent or
mercury-vapor which do not emit in the infrared region of the spectrum. The Edge Analysis
System also works well in the dark.
Eye Visibility:
The camera(s) must have a clear view of the subject's eye(s). If either his pupil or the corneal
reflection are occluded, there may be insufficient image information to make an accurate gaze
measurement. The camera's view of the eye can be obstructed by, for example, 1) an object
between the camera and the eye, 2) the person's nose or cheek if his head is rotated too much
with respect to the camera, or 3) by excessive squinting. Alternative Edge Analysis software
is included to accommodate for an obstructed image of the top of the pupil, usually caused by
a droopy eyelid or an unusually large pupil. The software returns a "false" condition for the
EyeFound flag whenever an adequate image of the eye is not present.
Glasses and Contact Lenses
In most cases, eyetracking works with glasses and contact lenses. The calibration procedure
accommodates for the refractive properties of the lenses. When wearing glasses, the glasses
may not be tilted significantly downward, or the reflection of the LED off the surface of the
glass is reflected back into the camera and obscures the image of the eye. The lens boundary
in hard-line bifocal or trifocal glasses often splits the camera's image of the eye, and the
discontinuity in the image invalidates the image measurements.
Soft contact lenses that cover all or most of the cornea generally work well with the Edge
Analysis System. The corneal reflection is obtained from the contact lens surface rather than
the cornea itself. Small, hard contacts can cause problems, however, if the lenses move
around considerably on the cornea, and the corneal reflection moves across the discontinuity
between the contact lens and the cornea.
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10.3 CAMERAS FOR EYE TRACKING/EYEGAZE
A camera is a key hardware component of an eye tracker. Other technical solutions are
mainly influenced by the choice of a camera. The cameras technical properties have
considerable impact on the performance and stability of the employed algorithms.Furthermore, the influence of several external conditions, e.g. lighting conditions, can be
minimized by a proper choice. The aim of the current section is to share information between
partners about good practice and provide criteria for camera selection.
10.3.1 CLASSES OF CAMERAS
Majority of cameras on market can be classified into 5 classes:1. Machine vision cameras;2. CCTV (Closed Circuit Television) cameras;3. Webcams;4. Camcorders;5. Digital still cameras.
1.
Machine vision cameras:Machine vision cameras are developed for video data transfer to computer for further data
analysis by machine vision algorithms. Machine vision cameras have big variety because of
different frame rate, resolution, connectivity, image sensor type, spectral response.
Functionally machine vision cameras are most suitable for eye tracking, as they transfer
uncompressed digital data. A disadvantage is the high price of such cameras.
2. CCTV(closed circuit television) cameras:CCTV cameras are mainly used in surveillance systems. They deliver analogue video signal
by NTSC, PAL or SECAM standard. Analogue signal can be transferred by long cables to
monitor or writing devices. Because the target is visual output, CCTV cameras deliver
interlaced frames by frame rate of 30 or 25 fps (frames per second). Most CCTV cameras
operate in low light conditions. They have sensitive sensors. Some cameras are optimised for
near infrared range. The last two features are attractive for eye tracking. Also price are lower
than for machine vision cameras.
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3. Webcams:Webcams were introduced recently. Their purpose is deliver video information through
Internet in real time. Most of web cameras have frame rate of 30 fps. To reduce the data
transfer volume, they deliver compressed video data. Webcams have built in optical lenses.
Inside the cameras there are colour response image sensors. Infrared light is an artefact for
webcams. Usually they have filters to remove infrared illumination. Functionally webcams
are not the best choice for eye tracking. Attractive features include low price, digital output
with (fully available for most PCs) USB connectivity.
4. Camcorders:Camcorders are portable devices for recording video images on an internal storage device.
Nowadays camcorders are digital. Some of them could be used as webcams. Their benefit
against webcams is a better optical system with a possibility of optical zooming. Sony
camcorders also have Night Vision function. In this regime a built in infrared light source
is used for scene lighting. Most camcorders also have Firewire (i-Link for Sony camcorders)
connectivity, which has advantages compared with USB. Though the prices for camcorders
are significantly higher than for webcams, camcorders are more preferable for eye tracking
than webcams because of the above mentioned features. A disadvantage, as for most of all
cameras, is the (low) frame rate of NTSC or PAL video.
5. Digital still cameras:Digital still cameras are devices used to capture and to store photographs in a digital format.
More advanced cameras also have a video function. The benefit of still cameras is their
higher resolution combined with high quality optics. However, the benefit invokes a
disadvantage: a lower frame rate as for camcorders.
10.4 IMAGE SENSOR:
Every camera, which in real time can be connected to a computer, has the following
elements:
1. Optical system;2. Image sensor;3. Interface circuit.
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The optical system projects the scene on image sensor. The function of the image
sensor is to convert the optical image information into electrical signal. The interface
circuit ensures delivering of the electrical signal from the camera to a computer.
Many technical features of a camera are significantly influenced by its image sensor. The
features are: image resolution, windowing, scan type, frame rate, shuttering, responsiveness,
spectral response, dynamic range.
Until recently, charge-coupled devices (CCDs) were the only solid state image sensors used
in digital cameras. In 1993 NASAs Jet Propulsion Laboratory succeeded with a new type of
sensor CMOS image sensor (http://ntrs.nasa.gov). Both image sensors are pixilated metal
oxide semiconductors. They accumulate the signal charge in each pixel, proportional to the
local illumination intensity, serving a spatial sampling function.
When the exposure is complete, a CCD transfers each pixels charge packet sequentially to a
common output structure, which converts the charge to a voltage, buffers it and sends it off-
chip. In a CMOS imager, the charge-to-voltage conversion takes place in each pixel. Such
pixels are called active pixels.
Image resolution corresponds to the size of the image sensor matrix in pixels. Windowing is
the capability to read out a portion of data from the image sensor. There are two methods for
scanning the pixel matrix: progressive scan and interlaced scan. During a progressive scan all
pixels are read in order. In an interlaced scan only every second line of the pixel matrix is
read. In such a case, one frame consists of two frames: one field with odd lines, and a second
field with even lines. CMOS sensors allow windowing. It is possible to read only the selected
region of interest (ROI) from the image sensor. Thus, windowing allows reducing data, which
must be transferred from the image sensor. As a consequence, the frame rate can be
increased.
Shuttering controls the time duration for pixels exposition, during which time, the
conversion of light photons into a charge in pixels occurs. A longer shutter time ensures that
more light is transferred to the sensor in the same illumination conditions. However, long
shutter speeds are problematic if the target moves.
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During a saccade the speed of the eye is high. In that case, long expositions invoke blurring
of a moving object contour in the direction of movement. Hence, the exposition time must be
optimised together with the frame rate and the illumination of the eye.
Responsiveness defines the relation between the incident light energy and the pixel output.
CMOS imagers are marginally superior to CCDs, in general, because the gain elements are
easier to place on a CMOS image sensor. Their complementary transistors allow low-power
high-gain amplifiers, whereas CCD amplification usually comes at a significant power
penalty. Some CCD manufacturers are challenging this conception with new readout
amplifier techniques.
Dynamic range is the ratio of a pixels saturation level to its signal threshold. It gives CCDs
an advantage by about a factor of two in comparable circumstances (Dalsa, 2007). CCDs still
benefit from significant noise advantages over CMOS imagers because of quieter sensor
substrates (less on-chip circuitry), inherent tolerance to bus capacitance variations and
common output amplifiers with transistor geometries that can be easily adapted for minimal
noise. Externally coddling the image sensor through cooling, better optics, more resolution or
adapted off-chip electronics still cannot make CMOS sensors equivalent to CCDs in this
regard. The dynamic range can be defined in decibels or effective number of bits. The
parameter causes number of output bits for pixel; usually it is 8, 10, or 12.
An important image sensor parameter for selecting the optical system is the sensors format
because lens must produce image of approximately the same size. Format is evaluated from
the sensor width. There are formats of sensors of 1, 2/3, 1/2, 1/3, 1/4, and 1/6. Their
geometrical size is given in Table 4.
Table 4: Geometrical Size Of Image Sensors
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10.5 RESOLUTION AND FRAME RATE
The quality of a digital image depends in part on the number of pixels used to create the
image. The maximum number that one can capture depends on how many pixels there are on
the image sensor used to capture the image.
Resolution can be of two kinds: optical and interpolated. The optical resolution of a camera is
an absolute number because an image sensor's pixels are physical entities that can be counted.
To improve resolution in certain limited respects, the resolution can be increased using
software. This process, called interpolated resolution, adds pixels to the image.
To do so, software evaluates those pixels surrounding each new pixel to determine what its
colours should be. What's important to keep in mind is that interpolated resolution doesn't add
any new information to the imageit just adds pixels and makes the file larger. Interpolation
is often used for coloured images. An example is given in Figure 12 (Micron 2007). The next
algorithm is used:
Have blue, need green and red. G= average of 4 neighbouring greens. R= average of 4
neighbouring reds.
Have green, need blue and red. B= average of 2 neighbouring blues. R= average of 2neighbouring reds.
Have red, need green and blue. G= average of 4 neighbouring greens. B= average of 4
neighbouring blues
Fig 12. Interpolation Of Pixels (Micron, 2007)
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More pixels add detail and sharpen edges. If any digital image is enlarged enough, the pixels will
begin to show-an effect called pixelization. The more pixels there are in an image, the more it can be
enlarged before pixelization occurs.
10.6 RECOMMENDATIONS FOR CAMERA SELECTION:
Native light as well as infrared light approaches have been tested by COGAIN partners.
While the former still poses problems to be solved, the latter (IR) gave promising results. At
partner UNI KO-LD, different cameras were tested for the corneal reflection approach.
1. A FireWire camera from UniBrain, Inc, (Unibrain 2007) named Fire-I, offering640x480 pixel in colour at up to 30 fps at a price of 109.
2. A low cost USB 2 based PC-Camera (web cam) named SN9C201 from an unknownmanufacturer,providing 640x480 at 25 fps for approx. 15.
3. A small high sensitivity camera with a conventional, analogue video output named2005XA from RFConcepts, Ltd. (RF-Concepts, 2007) At approx. 90.
While it is almost impossible to get detailed technical information concerning the low cost
webcam, the other cameras are suitably documented. The Fire-I camera employs a Sony
ICX098BQ sensor chip. The device complies to the IIDC-1394 Digital Camera protocol,
V1.04 (DCAM).
The RF-Concepts 2005XA camera was mainly chosen for its ability to work under weak
illumination conditions. It is based on the Sony CXD2463R controller and a ICX059CL
sensor, which employs Sonys Exview HAD CCD technology. The camera produces images
with a resolution up to 768x576 pixels at a frame rate of 25 fps.
Due to its good image quality and its sensitivity to infrared light the camera was already used
in an earlier project. The standard lens with 3,6mm focal length was replaced with a 8mm
lens. For this camera, an illumination of only 0.003 lux is sufficient to provide images, while
usual cameras need at least 1-2 lux. This sensitivity is of major importance when using
infrared light only.
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Alternatively, a Pan-Tilt-Zoom (PTZ) camera might be considered, however such cameras
need considerably more space, are more expensive and require active control for the
positional parameters by implementing an appropriate head tracking and therefore were not
chosen for our tests. Furthermore, the available models do not meet the sensitivity
requirements which turned out to be crucial.
As tracking in visible light lacks a geometric reference to estimate the gaze direction, it has to
be accompanied by geometrically accurate head pose estimation. While such approaches are
under further investigation, as they don't require an additional infrared light source and thus
perfectly meet the intention to set up a system from COTS hardware, we also tried to setup an
infrared based system using a minimum of extra hardware. This however requires a camera
with a sufficiently high IR sensitivity.
10.7 EYEGAZE SYSTEM FEATURES:
1. Calibration: Fully automated calibration is fast (15 - seconds), easy and long lasting.2. Accuracy: Highly accurate and tolerant to many variations, such as pupil drift and
head range variation - typical average bias error .45 degrees. Good tolerance to
ambient infrared light and to high-speed head motion.
3. Remote Video Tracking: Unobtrusive and non-distracting with nothing attached tothe subject.
4. Accommodates Most Human Eye Variations: Useable by 90% of the people whotry it, functional with most glasses and contacts.
5. Binocular Eye Tracking: Tracks both of the subjects eyes to increase gaze pointaccuracy by adjusting for head rotation.
6. Trace Suite:This suite of programs captures a subjects gaze when presented withstatic or moving images or during computer operations. In addition to generating the
standard data of our Analysis System, the users gaze and the stimulus are linked so
they can be replayed and studied in depth. The observer can view the subjects screen,
eye images and gaze point in real time on a separate monitor.
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7. Eyegaze Software Development Tool Kit: EgWin API - Eyegaze Function Library(DLL and import library), Gaze Tracking Demonstration Program (executable and C
source code), EgTraceImage and EgTraceText Programs (executable and C source
code), Fixation/Saccade Analysis Function (C source code), EgServer and
EgClientDemo Programs (C source code).
8. NYAN Analysis Tool: NYAN is an analysis tool based on screen recordingtechnology with synchronized gaze and mouse data. It can be used instead of the
Trace Suite to analyze web pages and intranet applications as well as standard
application software and still images.
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11. APPLICATIONS
Every year more than 100,000 people are diagnosed with motor neurone diseases. Typically,even when all other ways of communicating are either severely damaged or completely lost,
the eyes still function. Communication by Gaze Interaction (COGAIN) is a Network of
Excellence designed specifically to help people with these disabilities to communicate more
effectively with eye gaze. At the COGAIN stand you can see how this technology is used by
a person who relies on it.
Current eye tracking equipment allows users to generate text on a computer by using eye
gaze. Users are able to select letters and numbers by looking at a keyboard on a screen with
their eyes, and can construct words and sentences that can be spoken aloud by the system.
Using these systems both empowers and enables people with disabilities as they can now
communicate without the need for an assistant or helper, giving the users greater freedom in
their lives.
A wide variety of disciplines use eye tracking techniques, including cognitive science,
psychology (notably psycholinguistics, the visual world paradigm), human-computer
interaction (HCI), marketing research and medical research (neurological diagnosis). Specific
applications include the tracking eye movement in language reading, music reading, human
activity recognition, the perception of advertising, and the playing of sport. Uses include:
Cognitive Studies
Medical Research
Laser refractive surgeryHuman Factors
Computer Usability
Translation Process Research
Vehicle Simulators
In-vehicle Research
Training Simulators
Virtual RealityAdult Research
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Infant Research
Adolescent Research
Geriatric Research
Primate Research
Sports Training
fMRI / MEG / EEG
Commercial eye tracking (web usability, advertising, marketing, automotive, etc)
Communication systems for disabled
Improved image and video communications
Computer Science: Activity Recognition
Fig 13: Eyegaze System Communication System
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12. THE EYEGAZE SYSTEM: COMPONENTS & PRICES
Desktop Eyegaze System $14,900 US$
Software Programs
Main Menu
Keyboard
Games
Read Text
Teach
Settings Program
Hardware
Desktop computer with Windows 2000, Video frame grabber, sound,
CD and floppy drives
15" LCD Flat Panel Monitor
Adjustable monitor tray with camera bracket
High-speed infrared sensitive camera and lens
Surge protector, cables and connectors
Upgrades and Options
Portable computer (in place of desktop computer)
Computer access (hardware and software to run a PC)
Lights & Appliances
Telephone
Television
$1000
$500
$350
$350
$350
Options for use outside the U.S. are slightly different.
All money is in U.S. Dollars.
The above prices do not include shipping costs or travel-related installation expenses.
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13. ADVANTAGES AND LIMITATIONS OF THE SYSTEM
13.1 ADVANTAGES
1. Easy to Use.2. Enhance the quality of life of people with disabilities all over the world.3. Moving the eyes is natural, requires little conscious effort, and frees the hands for
other tasks.
4. Experiments show that our eye gaze selection technique is faster than selecting with amouse.
13.2 LIMITATIONS
1. The Obvious one is the price.2. Stray sources of infrared may degrade the accuracy or prevent Eyegaze operation
altogether.
3. Not all applications can be controlled using EYEGAZE.
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CONCLUSION
Today, the human eye-gaze can be recorded by relatively unremarkable techniques. This
thesis argues that it is possible to use the eye-gaze of a computer user in the interface to aid
the control of the application. Care must be taken, though, that eye-gaze tracking data is used
in a sensible way, since the nature of human eye-movements is a combination of several
voluntary and involuntary cognitive processes. The main reason for eye-gaze based user
interfaces being attractive is that the direction of the eye-gaze can express the interests of the
user-it is a potential porthole into the current cognitive processes-and communication through
the direction of the eyes is faster than any other mode of human communication. It is argued
that eye-gaze tracking data is best used in multimodal interfaces where the user interacts with
the data instead of the interface, in so-called non-command user interfaces.
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BIBLIOGRAPHY
www.eyegaze.com http://www.diku.dk/~panic/eyegaze/node29.html http://www.gschlosser.de/eyegaze_english.htm www.abilityhub.com/mouse/eyegaze.htm www.eyetechds.com Pullivelli, A. (2005) Low-Cost Digital Cameras: Calibration, Stability
Analysis, and Applications. Thesis. Department of Geomatics
Engineering, University of Calgary. Available online at
http://www.geomatics.ucalgary.ca/Papers/Thesis/AH/05.20216.Anoop
Pullivelli.pdf
RF-Concepts (2007). CCTV cameras. http://www.rfconcepts.co.uk