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Monoscopic Depth Cues
Monoscopic Depth Cues
Retinal Disparity
Retinal Disparity
Convergence Angles
Convergence Angles
Convergence Angles
Convergence Angles
Convergence Angles
Convergence Angles
Convergence Angles
Convergence Angles
Passive Polarized Projection Issues
Passive Polarized Projection Issues
Problem with Linear Polarization
Problem with Linear Polarization
Stereographics Shutter Glasses
Stereographics Shutter Glasses
Screen Parallax
Screen Parallax
Screen Parallax (cont
Screen Parallax (cont
Stereoscopic Voxels
Stereoscopic Voxels
Screen Parallax and Convergence Angles
Screen Parallax and Convergence Angles
Point of fixation
Point of fixation
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Seeing 3D from 2D Images

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1Seeing 3D from 2D Images. William and 23distance to screen. Different convergence
Craig 115 - 164. angles can all have the same screen
2How to make a 2D image appear as 3D! parallax. Also depends on assumed eye
Output is typically 2D Images Yet we want separation.
to show a 3D world! How can we do this? We 24How to create correct left- and
can include ‘cues’ in the image that give right-eye views. To specific a single view
our brain 3D information about the scene in almost all graphics software or
These cues are visual depth cues. hardware you must specify: Eyepoint
3Visual Depth Cues. Monoscopic Depth Look-at Point Field-of-View or location of
Cues (single 2D image) Stereoscopic Depth Projection Plane View Up Direction.
Cues (two 2D images) Motion Depth Cues 25Basic Perspective Projection Set Up
(series of 2D images) Physiological Depth from Viewing Paramenters. Y. Z. X.
Cues (body cues). Projection Plane is orthogonal to one of
4Monoscopic Depth Cues. Interposition the major axes (usually Z). That axis is
An object that occludes another is closer along the vector defined by the eyepoint
Shading Shape info. Shadows are included and the look-at point.
here Size Usually, the larger object is 26What doesn’t work. Each view has a
closer Linear Perspective parallel lines different projection plane Each view will
converge at a single point Surface Texture be presented (usually) on the same plane.
Gradient more detail for closer objects 27What Does Work.
Height in the visual field Higher the 28Setting Up Projection Geometry. No.
object is (vertically), the further it is Look at point. Eye Locations. Yes. Eye
Atmospheric effects further away objects Locations. Look at points.
are blurrier Brightness further away 29Screen Size. The size of the window
objects are dimmer. does not affect the retinal disparity for
5Stereoscopic Display Issues. a real window. Once computed, the screen
Stereopsis Stereoscopic Display Technology parallax is affected by the size of the
Computing Stereoscopic Images Stereoscopic display screen.
Display and HTDs. Works for objects < 30Visual Angle Subtended. Screen
5m. Why? parallax is measured in terms of visual
6Stereopsis. The result of the two angle. This is a screen independent
slightly different views of the external measure. Studies have shown that the
world that our laterally-displaced eyes maximum angle that a non-trained person
receive. can usually fuse into a 3D image is about
7Retinal Disparity. If both eyes are 1.6 degrees. This is about 1/2 the maximum
fixated on a point, f1, in space, then an amount of retinal disparity you would get
image of f1 if focused at corresponding for a real scene.
points in the center of the fovea of each 31Accommodation/ Convergence. Display
eye. Another point, f2, at a different Screen.
spatial location would be imaged at points 32Position Dependence (without
in each eye that may not be the same head-tracking).
distance from the fovea. This difference 33Interocular Dependance. True Eyes.
in distance is the retinal disparity. Modeled Eyes. Projection Plane. Perceived
8Disparity. If an object is closer than Point. Modeled Point. F.
the fixation point, the retinal disparity 34Obvious Things to Do. Head tracking
will be a negative value. This is known as Measure User’s Interocular Distance.
crossed disparity because the two eyes 35Another Problem. Many people can not
must cross to fixate the closer object. If fuse stereoscopic images if you compute
an object is farther than the fixation the images with proper eye separation!
point, the retinal disparity will be a Rule of Thumb: Compute with about ? the
positive value. This is known as uncrossed real eye separation. Works fine with HMDs
disparity because the two eyes must but causes image stability problems with
uncross to fixate the farther object. An HTDs (why?).
object located at the fixation point or 36Two View Points with Head-Tracking.
whose image falls on corresponding points True Eyes. Modeled Eyes. Projection Plane.
in the two retinae has a zero disparity. Perceived Points. Modeled Point.
9Convergence Angles. ?+a+c+b+d = 180 37Maximum Depth Plane.
?+c+d = 180 ?-? = a+(-b) = ?1+?2 = Retinal 38Can we fix this? Zachary Wartell,
Disparity. ?2. ?1. f1. a. D1. f2. b. a. "Stereoscopic Head-Tracked Displays:
D2. b. c. d. i. Analysis and Development of Display
10Miscellaneous Eye Facts. Stereoacuity Algorithms," Ph.D. Dissertation,
- the smallest depth that can be detected Georgia Institute of Technology, August
based on retinal disparity. Visual 2001. Zachary Wartell, Larry F. Hodges,
Direction - Perceived spatial location of William Ribarsky. "An Analytic
an object relative to an observer. Comparison of Alpha-False Eye Separation,
11Horopters. Corresponding points on the Image Scaling and Image Shifting in
two retinae are defined as being the same Stereoscopic Displays," IEEE
vertical and horizontal distance from the Transactions on Visualization and Computer
center of the fovea in each eye. Horopter Graphics, April-June 2002, Volume 8,
- the locus of points in space that fall Number 2, pp. 129-143. (related tech
on corresponding points in the two retinae report is GVU Tech Report 00-09 ( Abstract
when the two eyes binocularly fixate on a , PDF , Postscript .) Zachary Wartell,
given point in space (zero disparity). Larry F. Hodges, William Ribarsky.
Points on the horopter appear at the same "Balancing Fusion, Image Depth, and
depth as the fixation point. Vieth-Mueller Distortion in Stereoscopic Head-Tracked
Circle. Displays." SIGGRAPH 99 Conference
12Stereoscopic Display. Stereoscopic Proceedings, Annual Conference Series. ACM
images are easy to do badly, hard to do SIGGRAPH, Addison Wesley, August 1999,
well, and impossible to do correctly. p351-357. (Paper: Abstract , PDF ,
13Stereoscopic Displays. Stereoscopic Postscript ; SIGGRAPH CD-ROM Supplement,
display systems create a three-dimensional supplement.zip, supplement.tar.Z ).
image (versus a perspective image) by 39Point of fixation. Change in eyepoint
presenting each eye with a slightly separation with change in point of
different view of a scene. Time-parallel fixation. Centers of rotation of the eyes
Time-multiplexed. are assumed to be 6.4 centimeters apart.
14Time Parallel Stereoscopic Display. 40Position and Eyepoint Dependence! If
Two Screens Each eye sees a different you use an eye separation distance that is
screen Optical system directs each eye to not exactly the eye separation of the user
the correct view. HMD stereo is done this then, with head-tracking, the image is
way. Single Screen Two different images going to be unstable. BUT, if you use the
projected on the same screen Images are real eye separation in computing the
polarized at right angles to each other. screen parallax most users will not be
User wears polarized glasses (passive able to fuse the stereoscopic image.
glasses). 41Ghosting. Affected by the amount of
15Passive Polarized Projection Issues. light transmitted by the LC shutter in its
Linear Polarization Ghosting increases off state. Phosphor persistence Vertical
when you tilt head Reduces brightness of screen position of the image.
image by about ? Potential Problems with 42Ghosting (cont.). Extinction Ratio =.
Multiple Screens (next slide) Circular Image Position Red White Top 61.3/1 17/1
Polarization Reduces ghosting but also Middle 50.8/1 14.4/1 Bottom 41.1/1 11/1.
reduces brightness and crispness of image Luminance of the correct eye image
even more. ------------------------------------------
16Problem with Linear Polarization. With ----------------- Luminance of the
linear polarization, the separation of the opposite eye ghost image.
left and right eye images is dependent on 43Ghosting (cont.). Factors affecting
the orientation of the glasses with perception of ghosting Image brightness
respect to the projected image. The floor Contrast Horizontal parallax Textural
image cannot be aligned with both the side complexity.
screens and the front screens at the same 44Time-parallel stereoscopic images.
time. Image quality may also be affected by
17Time Multiplexed Display. Left and Right and left-eye images do not match in
right-eye views of an image are computed color, size, vertical alignment.
and alternately displayed on the screen. A Distortion caused by the optical system
shuttering system occludes the right eye Resolution HMDs interocular settings
when the left-eye image is being displayed Computational model does not match viewing
and occludes the left-eye when the geometry.
right-eye image is being displayed. 45Motion Depth Cues. Parallax created by
18Stereographics Shutter Glasses. relative head position and object being
19Screen Parallax. The screen parallax viewed. Objects nearer to the eye move a
is the distance between the projected greater distance.
location of P on the screen, Pleft, seen 46Pulfrich Effect. Neat trick Different
by the left eye and the projected levels of illumination require additional
location, Pright, seen by the right eye time (your frame rates differ base of
(different from retinal disparity). amount of light) What if we darken one
20Screen Parallax (cont.). p = i(D-d)/D image, and brighten another?
where p is the amount of screen parallax http://dogfeathers.com/java/pulfrich.html
for a point, f1, when projected onto a www.cise.ufl.edu/~lok/multimedia/videos/pu
plane a distance d from the plane frich.avi.
containing two eyepoints. i is the 47Physiological Depth Cues.
interocular distance between eyepoints and Accommodation – focusing adjustment made
D is the distance from f1 to the nearest by the eye to change the shape of the
point on the plane containing the two lens. (up to 3 m) Convergence – movement
eyepoints d is the distance from the of the eyes to bring in the an object into
eyepoint to the nearest point on the the same location on the retina of each
screen. eye.
21Screen Parallax. Zero parallax at 48Summary. Monoscopic – Interposition is
screen, max positive parallax is i, strongest. Stereopsis is very strong.
negative parallax is equal to I halfway Relative Motion is also very strong (or
between eye and screen. stronger). Physiological is weakest (we
22Stereoscopic Voxels. don’t even use them in VR!) Add as needed
23Screen Parallax and Convergence ex. shadows and cartoons.
Angles. Screen parallax depends on closest
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