3/23/2005 © Dr. Zachary Wartell 1 “Dynamic Adjustment of Stereo Display Parameters” Colin Ware, Cyril Gobrecht, and Mark Andrew Paton IEEE Transactions on Systems, Man and Cybernetics—Part A: Systems and Humans, vol. 28, no. 1, January 1998, pg Presentation: Revision 1.0

3/23/2005 © Dr. Zachary Wartell 2 Introduction reviewed depth cues: –retinal disparity, diplopia, panum’s fusion area –occlusion –SFM –need to reduce/control screen parallax Warning: –[Ware] “virtual eye separation” = [Class] model eye separation –doesn’t distinguish measurement in scaled space Accommodation/vergence conflict

3/23/2005 © Dr. Zachary Wartell 3 SFM: Motion Parallax optic flow

3/23/2005 © Dr. Zachary Wartell 4 screen wireframe cube (backlit) SFM: Kinetic Depth Effect

3/23/2005 © Dr. Zachary Wartell 5 Modeled versus True Eye Separation -

3/23/2005 © Dr. Zachary Wartell 6 Experiment 1: Rate of Change of Eye Separation Cyberscope

3/23/2005 © Dr. Zachary Wartell 7 Experiment 1: Rate of Change of Eye Separation ●plane infinite field of truncated pyramids moving towards viewer ●plane tilted 70 o from screen

3/23/2005 © Dr. Zachary Wartell 8 Varying Eye Separation –IV: amplitude variation: 10%, 20%, 30% –IV: separations: 6.3, 4.2, 2.1 cm Ex: 6.3 cm with 10% yields [5.67,6.3] –3 x 3 conditions –DV: sinusoidal variation frequency increased until subjects noticed it –within subjects, fully randomized –9 subjects, each subject sees all conditions

3/23/2005 © Dr. Zachary Wartell 9 Results - detectable frequency varies inversely with amplitude of oscillation -no significant interaction between amplitude and model eye sep. -worst case: average detectable frequency is 0.3 Hz occurs at max. amp. & max. e.s.

3/23/2005 © Dr. Zachary Wartell 10 Examine Peak Velocity significant effects of amplitude and model e.s. on V p so peak velocity not primary determinant of response thresholds should keep rate of change of model e.s. < 0.2 cm/s

3/23/2005 © Dr. Zachary Wartell 11 Experiment 2 subjects adjust model e.s. until diplopia occurs than back to comfortable value: find “max. comfortable value” Hypothesis: Sub’s will vary max. model e.s. based on scene depth

3/23/2005 © Dr. Zachary Wartell 12 Exp 2: Method vary scene depth via angle of “moving carpet”: 10 through 80 degrees sub’s make two e.s. settings per angle (diplopia & back to comfortable value) 12 subjects randomized, within-subjects

3/23/2005 © Dr. Zachary Wartell 13 Results considerable sub. variation high neg. correlation (r 2 =0.99) E v = 18.5 – θ Implications: drive algorithm to adjust e.s.; expect sub. variation

3/23/2005 © Dr. Zachary Wartell 14 Algorithm for Dynamic Disparity Adjustment two stages –cyclopean scale –modeled eye separation adjustment purpose: reduce a/c conflict and optimize stereo depth effectiveness use experimental result to control stereo adjustment

3/23/2005 © Dr. Zachary Wartell 15 Cyclopean Scale determine near point scale about eye center to bring near point to screen (equivalent of changing virtual e.s. in our term.)

3/23/2005 © Dr. Zachary Wartell 16 Dynamic Implementation

3/23/2005 © Dr. Zachary Wartell 17 Dynamic Implementation P P'P' PlPl PrPr

3/23/2005 © Dr. Zachary Wartell 18 Adjustment of Eye Separation optional addition to cyclopean scale model e.s. function from lower 95 th percentile of exp. 2 (model e.s. varies 14cm through 4 cm) E v = – θ , θ = arctan ( dz/dh ) E v = – arctan ( dz/dh )

3/23/2005 © Dr. Zachary Wartell 19 Adjustment of Eye Separation How to transform results from “magic carpet” to general scene? E v = arctan ( Z max /S h )+14.0 Z max : zbuffer max S h : screen height Z max ShSh θ

3/23/2005 © Dr. Zachary Wartell 20 Properties of Algorithm Z max from 0 to ∞ → modeled e.s. 14 cm to 4 cm

3/23/2005 © Dr. Zachary Wartell 21 Properties of Algorithm relate max. displayed depth after m.e.s. adjustment to max. depth before ( Z max ) assume modeled depth is infinite:

3/23/2005 © Dr. Zachary Wartell 22 Individual Differences customize with MaxSep ( E v = arctan ( Z max /S h )+14.0)

3/23/2005 © Dr. Zachary Wartell 23 Controlling Rate of Change Options: leave m.e.s. uncontrolled use running average last 5 of model e.s. to smooth change use threshold 0.2 cm/s for m.e.s. problem: sudden changes in scene depth cause diplopia for some period Tradeoff: anecdotally its better to allow abrupt m.e.s. change than allow diplopia

3/23/2005 © Dr. Zachary Wartell 24 Experiment 3: Distortion with Changes in M.E.S. investigate perceived distortion: How much do users notice distortion? How do users rate it compared to diplopia? Method: –terrain map, 80 x 80 grid height field colored by height, shaded, shadows –pre-set flyby path: downlooking flying in, rotate to horizontal view, flyout –Goal: large changes in view distance and relative depths

3/23/2005 © Dr. Zachary Wartell 25 6 Conditions no algorithm – m.e.s. = 6.4 cm cyclopean scale only dynamic adjustment – max m.e.s. 6.4 cm dynamic adjustment – max m.e.s cm dynamic adjustment – max m.e.s cm dynamic adjustment – max m.e.s cm

3/23/2005 © Dr. Zachary Wartell 26 Measurements sub’s report perception of double images and note “overall shape of surface appeared to change” Rate distortion (0-4) Rate eye strain (0-4) 7 subjects, within subjects, randomized presentation of all cond.’s

3/23/2005 © Dr. Zachary Wartell 27 Results: Diplopia “no algorithm” – all sub’s report double images when scene was distant “dynamic adj. with max 25 cm” – 2 / 7 reported double images indicates support for algorithm’s ability to control diplopia

3/23/2005 © Dr. Zachary Wartell 28 Results: Distortion See chart one report of eye strain but exp. Only lasted 20 minutes

3/23/2005 © Dr. Zachary Wartell 29 Conclusions dynamic disparity adjustment used in terrain vis. app. algorithm provides; –strong depth cues & minimize diplopia compare Williams & Parrish: –old alg. always maps modeled space to fixed depth range in display space –new alg. limits exaggeration of shallow scenes (factor of 2) SFM cues still dominate in giving sense of “flying”

3/23/2005 © Dr. Zachary Wartell 30 Future Work investigate penalty from distortion when depth judgements are important improve depth buffer sampling; small # of sample points: –works best for large extended surfaces –missing small/narrow features alternative: use bounding boxes, but more complex implemention

3/23/2005 © Dr. Zachary Wartell 31 Questions, Comments long term (> 20 min.) study of eye strain affect (subjective questionnaire versus A/V ratio test) user study comparing Will. and Parrish. technique why test angle of magic carpet? not direct depth? better way to rate distortion (tease out diplopia effect in cond. #1) use near point from previous frame & scale about cyclopean eye battery of tests for best way to get zbuffer info.—GPU solution?