Upload
hillary-joleen-melton
View
231
Download
1
Tags:
Embed Size (px)
Citation preview
Outline
• Basic Idea of 3D
• Projections
• What are some things we didn’t have to worry about before?
• What are some new things we can do?
Viewing a 3D world
We have a model in this world and would like to view it from a new position.
We’ll call this new position the camera or eyepoint. Our job is to figure out what the model looks like on the display plane.
+X
+Y
+Z
How to make a 2D image appear as 3D!
• Output is typically 2D Images
• Yet we want to show a 3D world!
• How can we do this?– We can include ‘cues’ in the image that give
our brain 3D information about the scene– These cues are visual depth cues
Visual Depth Cues
• Monoscopic Depth Cues (single 2D image)
• Stereoscopic Depth Cues (two 2D images)
• Motion Depth Cues (series of 2D images)
• Physiological Depth Cues (body cues)
Monoscopic Depth Cues• Interposition
– An object that occludes another is closer• Shading
– Shape info. Shadows are included here• Size
– Usually, the larger object is closer• Linear Perspective
– parallel lines converge at a single point• Surface Texture Gradient
– more detail for closer objects• Height in the visual field
– Higher the object is (vertically), the further it is
• Atmospheric effects – further away objects are blurrier
• Brightness– further away objects are dimmer
Stereoscopic Display Issues
• Stereopsis
• Stereoscopic Display Technology
• Computing Stereoscopic Images
• Stereoscopic Display and HTDs.
• Works for objects < 5m. Why?
StereopsisThe result of the two slightly different views of the external world that our laterally-displaced eyes receive.
Time-parallel stereoscopic images
• Image quality may also be affected by– Right and left-eye images do not match in
color, size, vertical alignment.– Distortion caused by the optical system– Resolution– HMDs interocular settings– Computational model does not match viewing
geometry.
Disparity
• If an object is closer than the fixation point, the retinal disparity will be a negative value. This is known as crossed disparity because the two eyes must cross to fixate the closer object.
• If an object is farther than the fixation point, the retinal disparity will be a positive value. This is known as uncrossed disparity because the two eyes must uncross to fixate the farther object.
• An object located at the fixation point or whose image falls on corresponding points in the two retinae has a zero disparity.
Convergence Angles
i
f2
f1
D1
D2a b
c d
1
+a+c+b+d = 180
+c+d = 180
- = a+(-b) = 1+2 = Retinal Disparity
2
Stereoscopic Display
• Stereoscopic images are easy to do badly, hard to do well, and impossible to do
correctly.
Stereoscopic Displays
• Stereoscopic display systems create a three-dimensional image (versus a perspective image) by presenting each eye with a slightly different view of a scene.– Time-parallel– Time-multiplexed
Time Parallel Stereoscopic Display
Two Screens• Each eye sees a
different screen• Optical system directs
each eye to the correct view.
• HMD stereo is done this way.
Single Screen• Two different images
projected on the same screen
• Images are polarized at right angles to each other.
• User wears polarized glasses (passive glasses).
Passive Polarized Projection Issues
• Linear Polarization– Ghosting increases when you tilt head– Reduces brightness of image by about ½– Potential Problems with Multiple Screens (next
slide)
• Circular Polarization– Reduces ghosting but also reduces brightness
and crispness of image even more
Problem with Linear Polarization
• With linear polarization, the separation of the left and right eye images is dependent on the orientation of the glasses with respect to the projected image.
• The floor image cannot be aligned with both the side screens and the front screens at the same time.
Time Multiplexed Display
• Left and right-eye views of an image are computed and alternately displayed on the screen.
• A shuttering system occludes the right eye when the left-eye image is being displayed and occludes the left-eye when the right-eye image is being displayed.
Motion Depth Cues
• Parallax created by relative head position and object being viewed.
• Objects nearer to the eye move a greater distance
Pulfrich Effect
• Neat trick• Different levels of illumination require
additional time (your frame rates differ base of amount of light)
• What if we darken one image, and brighten another?
• http://dogfeathers.com/java/pulfrich.html• www.cise.ufl.edu/~lok/videos/pulfrich.avi
Physiological Depth Cues
• Accommodation – focusing adjustment made by the eye to change the shape of the lens. (up to 3 m)
• Convergence – movement of the eyes to bring in the an object into the same location on the retina of each eye.
Summary
• Monoscopic – Interposition is strongest.
• Stereopsis is very strong.
• Relative Motion is also very strong (or stronger).
• Physiological is weakest (we don’t even use them in VR!)
• Add as needed– ex. shadows and cartoons
What are some new things we can do?
• Lighting and Shading!
• Texturing!
• Stereo
• Surfaces– Normals– Materials