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On-Screen Pre-Deblurring of Digital Images Using the Wavefront

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Florida International University FIU Digital Commons FIU Electronic Theses and Dissertations University Graduate School 4-4-2003 On-screen pre-deblurring of digital images using the wavefront aberration function of the human eye to improve computer access for the visually impaired Miguel Alonso Florida International University DOI: 10.25148/etd.FI13101605 Follow this and additional works at: https://digitalcommons.fiu.edu/etd Part of the Computer Engineering Commons Recommended Citation Alonso, Miguel, "On-screen pre-deblurring of digital images using the wavefront aberration function of the human eye to improve computer access for the visually impaired" (2003). FIU Electronic Theses and Dissertations. 1111. https://digitalcommons.fiu.edu/etd/1111 This work is brought to you for free and open access by the University Graduate School at FIU Digital Commons. It has been accepted for inclusion in FIU Electronic Theses and Dissertations by an authorized administrator of FIU Digital Commons. For more information, please contact [email protected]. FLORIDA INTERNATIONAL UNIVERSITY Miami, Florida ON-SCREEN PRE-DEBLURRING OF DIGITAL IMAGES USING THE WAVEFRONT ABERRATION FUNCTION OF THE HUMAN EYE TO IMPROVE COMPUTER ACCESS FOR THE VISUALLY IMPAIRED A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in COMPUTER ENGINEERING by Miguel Alonso Jr. 2003 To: Dean Vish Prasad College of Engineering This thesis, written by Miguel Alonso Jr., and entitled On-Screen Pre-Deblurring of Digital Images Using the Wavefront Aberration Function of the Human Eye to Improve Computer Access for the Visually Impaired, having been approved in respect to style and intellectual content, is referred to you for judgment. We have read this thesis and recommend that it be approved. Malek Adjouadi Frank Candocia Armando Barreto, Major Professor Date of Defense: April 4, 2003 The thesis of Miguel Alonso Jr. is approved. Dean Vish Prasad College of Engineering Dean Douas Wartzok University Graduate School Florida International University, 2003 ii DEDICATION I dedicate this thesis to my family. Without the support of my Mother, Father, Sister, Grandmother, and my Girlfriend, this work would not have been possible. iii ACKNOWLEDGMENTS This thesis was supported by NSF grant EIA-9906600. I would like to acknowledge my thesis committee members, Dr. Armando Barreto, Dr. Malek Adjouadi, and Dr. Frank Candocia. They provided much insight and ideas which contributed to the development of my thesis. Without their help, I would not have been able to complete my Master's degree. iv ABSTRACT OF THE THESIS ON-SCREEN PRE-DEBLURRING OF DIGITAL IMAGES USING THE WAVEFRONT ABERRATION FUNCTION OF THE HUMAN EYE TO IMPROVE COMPUTER ACCESS FOR THE VISUALLY IMPAIRED by Miguel Alonso Jr. Florida International University, 2003 Miami, Florida Professor Armando Barreto, Major Professor Traditional Optics has provided ways to compensate some common visual limitations (up to second order visual impairments) through spectacles or contact lenses. Recent developments in wavefront science make it possible to obtain an accurate model of the Point Spread Function (PSF) of the human eye. Through what is known as the "Wavefront Aberration Function" of the human eye, exact knowledge of the optical aberration of the human eye is possible, allowing a mathematical model of the PSF to be obtained. This model could be used to pre-compensate (inverse-filter) the images displayed on computer screens in order to counter the distortion in the user's eye. This project takes advantage of the fact that the wavefront aberration function, commonly expressed as a Zernike polynomial, can be generated from the ophthalmic prescription used to fit spectacles to a person. This allows the pre-compensation, or on- screen deblurring, to be done for various visual impairments, up to second order (commonly known as myopia, hyperopia, or astigmatism). The technique proposed towards that goal and results obtained using a lens, for which the PSF is known, that is v introduced into the visual path of subjects without visual impairment will be presented. In addition to substituting the effect of spectacles or contact lenses in correcting the low- order visual limitations of the viewer, the significance of this approach is that it has the potential to address higher-order abnormalities in the eye, currently not correctable by simple means. vi TABLE OF CONTENTS CHAPTER PAGE 1 Introduction................................................................................................................. 1 1.1 Problem Overview .............................................................................................. 1 1.2 Problem Statem ent.............................................................................................. 3 1.3 Im age D ata....................................................................................................... 4 1.4 Pre-com pensation...........................................................................6 1.5 Testing M ethods.............................................................................................. 7 1.6 Thesis O verview ............................................................................................. 8 2 H um an V ision ...................................................................................................... 9 2.1 A natom ical D escription of the Hum an Eye .................................................... 9 2.2 Optical System of the H um an Eye.................................................................... 12 2.3 Im age Form ation for Optical System s ........................................................... 15 2.3.1 Classical Optics.........................................................................................16 2.3.2 W ave Theory of Im age Form ation......................................................... 19 2.3.3 Fourier Optics ...................................................................................... 23 2.4 H um an Eye as an Im aging System ............................................................... 25 2.5 Wavefront Aberrations and Zernike Polynomials ......................................... 28 2.6 Second Order A berrations.............................................................................. 30 2.6.1 Em m etropia ............................................................................................... 31 2.6.2 Hyperopia .................................................................................................. 32 2.6.3 M yopia .................................................................................................. 33 2.6.4 A stigm atism ........................................................................................... 34 2.7 High O rder A berrations ................................................................ ....... 36 2.8 Obtaining the Analytical PSF ...................................................................... 37 3 Clinical V isual Optics ...................................................................... ........ 39 3.1 V isual A cuity ................................................................................................ 39 3.2 Eye Chart D escriptions .................................................................................. 41 3.3 Evaluation of V isual Perform ance ................................................................ 44 4 D econvolution...........................................................................................................49 4.1 V an Cittert's M ethod .................................................................................... 50 4.2 N on-N egative Least Squares......................................................................... 51 4.3 Minimum Mean Square Error Filtering ............................................................ 52 5 Experim ent D escription ............................................................................ .......... 55 5.1 O verview ....................................................................................................... 55 5.2 System Elem ents............................................................................................... 57 5.2.1 M onitor .................................................................................................. 57 5.2.2 Cam era.................................................................................................. 58 5.2.3 Lens....................................................................................................... 60 vii 5.2.4 Personal Com puter................................................................................ 61 5.3 Introduction of W avefront Aberration ........................................................... 61 5.3.1 Scaling.......................................................................................................62 5.3.2 D eterm ining the true W avefront Aberration......................................... 63 5.4 Eye Chart Im plications .................................................................................. 71 5.4.1 Resolution of the Minimum Angle .......................... 71 5.5 Testing Procedure ......................................................................................... 72 6 Results and D iscussion ......................................................................................... 77 6.1 Simulated Experiment for -6.00 Diopter Sphere Lens..................................
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