3/23/2005 © Dr. Zachary Wartell 1 “Dynamic Adjustment of Stereo Display Parameters” Colin Ware, Cyril Gobrecht, and Mark Andrew Paton IEEE Transactions

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 56-65.

Presentation: Revision 1.0


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


SFM: Motion Parallax

optic flow


screen

wireframe cube(backlit)

SFM: Kinetic Depth Effect


Modeled versus True Eye Separation

- v vs

v v v

SE zz

E z E S E z


Experiment 1: Rate of Change of Eye Separation

Cyberscope


Experiment 1: Rate of Change of Eye Separation

●plane infinite field of truncated pyramids moving towards viewer●plane tilted 70o from screen


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


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.


Examine Peak Velocity

• significant effects of amplitude and model e.s. on Vp

• so peak velocity not primary determinant of response thresholds

• should keep rate of change of model e.s. < 0.2 cm/s


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


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


Results

• considerable sub. variation• high neg. correlation (r2=0.99)

Ev = 18.5 – 0.149 θ• Implications:

drive algorithm to adjust e.s.; expect sub. variation


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


Cyclopean Scale

• determine near point• scale about eye center to bring near point to

screen (equivalent of changing virtual e.s. in our term.)


Dynamic Implementation


Dynamic Implementation

PP'

Pl

Pr


Adjustment of Eye Separation

• optional addition to cyclopean scale• model e.s. function from lower 95th percentile of

exp. 2 (model e.s. varies 14cm through 4 cm)

Ev = – 0.144 θ + 14.0,

θ = arctan (dz/dh)

Ev = – 0.144 arctan (dz/dh) + 14.0


Adjustment of Eye Separation

• How to transform results from “magic carpet” to general scene?

Ev = -0.114 arctan (Zmax/Sh)+14.0

Zmax : zbuffer max Sh : screen height

Zmax

Sh θ


Properties of Algorithm

• Zmax from 0 to ∞ → modeled e.s. 14 cm to 4 cm


Properties of Algorithm

• relate max. displayed depth after m.e.s. adjustment to max. depth before (Zmax )

• assume modeled depth is infinite: maxv

a v

SEZ

E E


Individual Differences

• customize with MaxSep

(Ev = -0.114 arctan (Zmax/Sh)+14.0)

max4.0arctan

90.0vh

ZMaxSepE MaxSep

S


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


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


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. 12.8 cm• dynamic adjustment – max m.e.s. 19.2 cm• dynamic adjustment – max m.e.s. 25.6 cm


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


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


Results: Distortion

• See chart• one report of eye strain but exp. Only lasted 20

minutes


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”


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


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?

Documents

3/23/2005 © Dr. Zachary Wartell 1 “Dynamic Adjustment of Stereo Display Parameters” Colin Ware, Cyril Gobrecht, and Mark Andrew Paton IEEE Transactions