3D

BinocularCombina0onofImages

3D

USER/GGLASSES

Whatcanhappenwhenimagesarecombinedbythetwoeyes?

•  Fusion-whenimagesaresimilaranddisparityissmall

•  MonocularSuppression/Rivalry-whenimagesarequitedifferentbutdisparityissmall

•  Diplopia-whenimagesaresimilarbutdisparityislarge

•  Summa0on(superposi0on)-whencontrastisloworpresenta0onisbrief.

Rivalryfromcrossedgra0ngs

Rivalry

Summa0on

Suppression

Rivalry:factorscontrollingdominanceandsuppression

•  Inthestrugglefordominance...– Winners:Highcontrast,mo0on,paRernswith�lotsofcontour�

– Losers:Lowcontrast,sta0c,sparsepaRerns

LWWWWWWWWWWWWWWWW

VisualConfusionVisual confusion arises when different images combine in the same visual direction, and may include rivalry, suppression, fusion and summation.

Dynamicsofrivalry

Blakewebpage:hRp://psych-s1.psy.vanderbilt.edu/faculty/blaker/rivalry/BR.htmlRecentBlakefollowupar0cle:hRp://www.journalofvision.org/9/2/8/ar0cle.aspx

Fusion•  Panum�sFusionalArea:Forasinglepointinoneeye,thereisanareaintheothereyewheretargetswillfusewiththatpoint.

•  FusionRange:radiusofPFAApointinthele\

eyeAnareainthe

righteye

F F

6-10min

10-15min

FovealsizeofPFAforasinglepoint

From:Mitchell,DE(1966)Areviewoftheconceptof�Panum�sFusionalAreas�AmJOptom41387-401

�D.T.D.�referstodisparitythresholdfordiplopia.

Fusionrangedependsoneccentricity

7%

Fusion:rangedependsonspa0alfrequency

Schor,C.M.,Wood,I.C.andOgawa,J.(1984)Binocularsensoryfusionislimitedbyspa0alresolu0on.VisionRes24:661-665.

Summa0on-dichop0cplaidsIAtlowcontrast,rivalrytakesmanysecondstokickin.

Liu,Tyler7Schor(1992).Failureofrivalryatlowcontrast…VisionResearch32,1471-1479

LR

Luminancesumma0onFechner�sparadox

Le\ Right

Stereopsis- overview

•  What is Stereopsis?•  Kinds of Stereograms•  History- da Vinci, Wheatstone, Brewster,

etc•  Stimuli used•  some fundamental data•  models of stereopsis

What is Stereopsis?Stereopsis- n. The perception of depth

based on horizontal, relative, retinal disparity.

Perception of Depth•  The perception of depth depends on the

combination of several factors:– Binocular Retinal Disparity– Motion– Shading– Interposition– Size / Perspective – Blur

Horizontal, not Vertical disparity

Calculating disparity

How much depth is 3 arc sec?

•  Compared to 6 meters, – 3 arc sec = 1 cm – Thickness of a finger

•  Compared to .6 meters (arms length)– 3 arc sec = .1 millimeters–  ridges in your fingerprint

How Stereograms are made•  photograph or construct two pictures from

different viewpoints•  present them separately to the two eyes–  stereoscope–  anaglyph (red/green glasses)–  polaroid glasses–  free fusion–  phase haploscope– VR goggles–  auto stereograms

Anaglyph (red/green) glasses

Free Fusion•  Helmholtz:

"Itisveryimportantforanyonewhointendstomakeinves0ga0onsinphysiologicalop0cstolearnhowtoconvergethelinesoffixa0onoftheeyesortomakethemparallelatanymoment,withouthavingtouseanycorrespondingvisualobject;he[orshe]shouldprac0cedoingthis."(PhysiologicalOp0csVIIIp57,Southalltransla0on)

E E

EE

History•  Galen (AD 200) Alhazen (AD 1000), Leonardo da

Vinci (1500), Aguilonius (1600), all wrote about binocular parallax and double vision. Leonardo knew that binocular parallax contributed to depth, and Aguilonius worked out the geometric horopter. But none of these thinkers understood depth from disparity.

•  Wheatstone (1802-1875) invented the mirror and the lenticular stereoscopes in 1832. His device allowed him to experiment systematically with image differences and to firmly establish disparity as a basis for depth perception.

•  Brewster (1781-1868) re-invented lenticular stereoscope in 1849, claimed credit, and fought with Wheatstone for years.

•  1860�s to 1890�s 3-D photography craze takes over world

Wheatstone Stereoscope (1838)•  �mirror

haploscope�

�Brewster� Stereoscope 1849•  Lens / Prism Combination

More on Wheatstone•  The process of discovery:

–  Recognized an anomaly: depth in glint from shiny metal–  Invented a tool to investigate it: the stereoscope–  Started a whole new field of study with his observations.

•  Some of Wheatstone�s observations:–  Disparity, with no other cue, yields a percept of depth.–  Disparity can override perspective and other depth cues.–  Vergence movements are not required for stereopsis:

afterimages with disparity yield stereoscopic depth–  Fusion and stereo can tolerate large differences in image

size.

Stereoscopic Stimuli•  Three classes of stimuli: – 1) dots & lines (�local� targets)• used for most fundamental, early work

– 2) random dots (visual noise)• revealed sophistication of system

– 3) gratings (narrow band)• attempt to unite stereopsis and spatial vision

StereoscopicS0muliinVisionScience•  Threecommonkindsofs0muliusedformeasuringstereopsis:

•  1)dots&lines(“local”targets)Firstexperimentsusedthese,s0llusedforbasicstereotes0ng

•  2)randomdotstereograms

•  Tests“globalstereopsis.”

•  Usedinsomeclinicaltests

•  andformaking“MagicEye”

•  Pictures.

•  3)sinewavegra0ngs

•  Usedfortes0ngstereopsiswithfine,medium,

•  andcoursescalepaRerns

Complex Stereogram•  Takes time to

appear•  Experience with

looking at the patterns makes the time shorter.

Some fundamental results•  Stereoscopic acuity (disparity threshold)

can be as low as 3 arc seconds, in some cases.

•  Stereo judgments can be made for disparities as large as 10 degrees, in some cases (upper disparity limit).

•  Stereo gets worse with eccentricity, short duration, low contrast, etc.

•  Stereopsis gets worse away from the horopter

•  Stereo depends on spatial frequency, to a point.

Stereoacuity depends on…•  Duration Contrast

Stereoacuity depends on…Eccentricity Disparity Pedestal

Stereoacuity depends on…

SameSFDifferentSF

Stereo

acuity

Stereoacuityisbestwithhighspa0alfrequenciesandisverybadwheneacheyeseesadifferentfrequency.(Schoretal.1984)

•  Spatial Frequency Spatial Frequency Difference