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]

introductionVision 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

displaydevice, 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 displayThis device has multiple layer of Liquid Crystal

whichgenerates 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 EyeII. ProjectionIII. 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.

ProjectionThe 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'salgorithm. 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]

PrefilteringThis projection matrix P is saved after the projection phase. they expands theinput image G to a one dimensional vector b and they denote the transformedimage to be x. So the prefiltering equation be: P * x = bThe 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 systemdoes not have a possible solution. A small positive value called (lamda) isdefined 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 willnot be singular anymore. Instead of solving the system directly, Huang'salgorithm changes it into a optimization problem with the target: Minimize: (H’ x - P T b) T * (H’x - P T b) [2]

Disadvantages1. 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]

Simulation code

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

Future of work1: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]

conclusionBy 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]

reference1. 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