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
