vision correcting display

Vision correcting
display
disha tiwari
btbtc14049
8542(62)

content
 Abstract
 Introduction
 Multilayer display
 Light field display
 Algorithm
Aberration of The Eye
Projection
Prefiltering
 Disadvantage
 Optimization
 Simulation algorithm
 Future work
 Conclusion
 Application
 Reference

abstract
It is estimated that 4 billion people in the world have some sort of
eye aberration disorder. Over 55% of our population currently wear
some form of vision correction to address the issue. [3]
For example, approximately 40% of our population has near-sightedness
(Myopia) and 25% of the our population has far-sightedness ( Hyperopia). There
are many other eye conditions that are caused by optical aberrations in the
human eye.
So MIT Media Lab researchers have
developed a new computational display
technology that automatically corrects
for vision defects. [1]

introduction
Vision Correcting Display (VCD) is an alternative to eyeglasses, contact
lenses , and refractive surgeries for addressing the problem of blurred
human vision. The idea is to “digitally ” modify the content on a display
device, so that when viewed by a particular user, it will appear in sharp
focus for this individual. [4]
Fu-Chung Huang proposed two different solutions in this field.
I. They use a multilayer display
II. They utilize light field display
to generate sharp image out of
the display plane [3].

Multilayer display
This device has multiple layer of Liquid Crystal which
generates 3d effects in a picture without using of glasses [5]

Light fieLd dispLay
• Fu-Chung Huang have created a hardware prototype to
utilize light field technology to generate a sharp image
on the display plane.
• Its special printed transparency is a ray of pinholes that code
the image on the display for human observer
• For this they used a novel Huang’s Prefiltering algorithm
to
sharp The image on the display [5]

aLgorithm
To code the image for the human observer Prefiltering
algorithm have following steps:
I. Aberrations Of The Eye
II. Projection
III. Prefiltering [4]

aberrations of the eye
• Eye aberrations can be categorized into two categories:
lower order and higher order.
• To calculate aberration of the eye we need Zernike
polynomials
• Zernike polynomials are a set of basis functions used to
describe a domain, Z = W(x, y)
a function useful to describe the
wave front surface of rays
entering or exiting the circular
pupil of the eye. [2]

aberrations of the eye
Code used to generate the
wave front and Zernike
coefficients.

projection
The projection relationship is the mapping relationship from the
point on the display plane to the point on the sensor (retina).
The projection relationship is presented by a matrix in Huang's
algorithm. For this he used some symbols like Sh , Sw, a etc.
he assume that resolution of pinhole mask and sensor of
camera is (Sh/a) and (Sw/a) resp.
he transforms the display and
the sensor pixels into two
one-dimensional arrays with
length Ld = Sh * Sw and
Ls = Sh * Sw/a2
, respectively.
and the algorithm builds a
projection matrix [2]

Prefiltering
This projection matrix P is saved after the projection phase. they expands the
input image G to a one dimensional vector b and they denote the transformed
image to be x. So the prefiltering equation be:
P * x = b
The Huang's algorithm transforms P into a square matrix by following step.
The algorithm multiplies the left-hand and right-hand of the equation both by PT
(P T
* P) * x = PT
* b
Define H = (P T
* P). It is very likely that H is singular and this linear system
does not have a possible solution. A small positive value called (lamda) is
defined and added into the system where I is the identity matrix:
H’ <- H + (lamda) * I
(lamda) would introduce error into the system but this error is negligible. H will
not be singular anymore. Instead of solving the system directly, Huang's
algorithm changes it into a optimization problem with the target:
Minimize: (H’ x - P T
b) T
* (H’x - P T
b) [2]

DisaDvantages
1. Huang's algorithm assumes that any point of one screen
pixel can emit all the possible colors. However, that is not
true and each point can only emit one type of color and the
type depends on the location of that point.
2: he uses L-BFGS method
In this prefiltering speed
depends greatly on the
environment settings and
viewer's eye condition, and
the complexity is large
compared to other method. [6]

OPtimizatiOn
In order to improve the speed of the forward method, the
following steps were performed in modifying the code:
• Translation of codebase from Matlab to C++.
• Reducing the number of linear systems to solve from 3 to 1 per
image.
• Computing the pseudo inverse of the projection matrix and caching
it to improve the speed of solving each image.
• Changing the computation from matrix multiplication to direct
assignment. [5]

simulatiOn algOrithm
A computer simulation was developed to model the effectiveness of
various light field displays. they found that the correctness and the
efficiency of them are not the same.. Simulation is essential for making an
accurate design of the physical model, because the experimental setting
in the simulation can be easily changed for testing.[2]

applications
• Tablets / eReaders
• Desktop/ laptops
• Television
• Smart phones
• Automatic display
• Portable media player
• Gaming consoles
• Watches
• GPS Devices
+other device
displays[1]

Future oF work
1:Larger Display: Their current prototype is focused on small screen size. When
considering larger display, for example, computer monitors, many assumptions may
not stand. Larger screens have another set of constrains as well. [6]
2: Eye Tracking : For their current implementation, they assume the eye is perfectly
perpendicular to the display plane. However, this is not true in reality. Some eye
tracking functionalities could be added to evaluate the position of the eye relative to the
display. [2]

conclusion
By the end of 2014 there were 2 billion people worldwide who
owned a Smartphone . It is predicted that by 2017 half of global
population will own a Smartphone . So this technology will helps
billions of people view their smart phones screen without having to
wear eye glasses contact lenses or undergo refractive surgery [1]

reFerence
1. 2020 display technology : Goodbye Glasses! Introducing Smartphone
Screens that will Correct Your Vision http://2020display.com/
2. Investigating Computational Approaches :
http://www2.eecs.berkeley.edu/Pubs/TechRpts/2016/EECS-2016-67.pdf
3. Gordon Wetzstein: "Why should we care about light field displays?“
http://www.youtube.com/watch?v=nF8UDwv7GUU
4. Vision Correcting Displays- 20/20 Display Technologies Inc
http://www.youtube.com/watch?v=6yTCPALXjWw
5. A Computational Light Field Display for Correcting Visual Aberrations
http://www2.eecs.berkeley.edu/Pubs/TechRpts/2013/EECS-2013-206.pdf
6. Eyeglasses-free Display:
http://web.media.mit.edu/~gordonw/VisionCorrectingDisplay/SIG2014-
VisionCorrectingDisplay.pdf

vision correcting display

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