What’s on page 13-25?

Tom Butkiewicz

Refresh Rates

• Flicker from shutter systems

• Halve refresh rates

• 2 eyed 120Hz != 1 eyed 60Hz

• Phosphors

• 2 Polarized Monitors + Half Silvered Monitor

Brightness

• Filter glasses – remove frequencies– dim images

• Shutter glasses– Brightness halved over time– Never 100% clear (shutter and polarized)

Example

• Hypothetical stereoscopic display

• Standard CRT

• LCD shutter glasses

• Spatial resolution– Res = 1280 x 1024– Shutter cut vertical in half– Res = 1280 x 512

• Angular resolution– “comfortable viewing distance” = 18 inches– Screen size = 33” x 26”– Φ = 1.9 min x 3.8 min = 1.9’ x 3.8’

• Pixel Pitch– Pitch = (33cm/1280) = (26cm/1024)

= .025cm/pixel

• Field of view– FOV = 40° x 32°

• Depth resolution– (0.00025 x 0.46) / (0.65 – 0.00025) = 0.0018m

• Refresh rate:– 120Hz refresh rate = 60Hz per eye

• Brightness:– LCD shutter transmits 30% of light– Screen seen 50% of the time– Overall: brightness = 15%

Interactive Stereoscopic Display

• Autostereoscopic displays:– Advantages:

• No viewing aids required• Multiple 3D views of the scene

• Interactive systems can achieve this viewpoint-dependence– Head Tracking (HMDs and HTDs)

Example

• Same system as before– Add head tracking

• Interactive• Motion parallax

• Head / Boom system

• Same typical monitor– 1280x1024

• Special optics– 90° field of view for each eye– Partially overlapping– FOV = 135° x 90°– Φ = 90° / 1280 = 4.2’ = 0.0012 radians– Coarse resolution

• Easily change optics to suit different tasks– FOV vs Angular Resolution

• Depth resolution– Must calculate the pitch for infinite-focus

screen at 46cm:• Pitch = 0.0012 x 46cm = 0.056 cm

– D = (0.00056 x 0.46) / (0.065 – 0.00056) = 0.0040 m

Lenticular Screen

• Array of cylindrical lenses– Generates autostereo image– Directs 2D images into viewing subzones– Viewer puts one eye in each subzone

Lenticular Screen

• Horizontal resolution -> one pixel per lenticule

• Vertical resolution -> same as back screen

• N subzones created by N pixels behind each lenticule

Side-Lobes are duplicate sub-zones off to the side of the main centered viewing zone.

Moving out of viewing zone into side-lobes causes pseudoscopic 3D image (right <-> left)

Limitations

• High horizontal resolution required

• Pixel size limits number of views

• Imperfections in lenses focusing abilities– Reduces the directivity– Emerging rays not parallel

• Need to have back screen perfectly aligned with lenticules– Hard because CRTs not flat

• Can be used with multiple projectors

• Diffusing screen

• High horizontal resolution and large number of views possible

• High bandwidth costs

Integral photography

• Similar to lenticular imaging

• Small spherical lenses instead of vertical cylinders

• Up and down in addition to left and right

• Requires more resolution or 2D array of projectors

Example

• Horizontal resolution– Res of each view = screen width / lenticle

width = horizontal res of back screen / number of views

• Horizontal angular resolution = lenticule width / Dscreen

Depth Resolution

• Finite size of horizontal imaging elements

• Limits resolvable depth levels

Depth Resolution

• Subzones may overlap– Due to imperfect direction from lenses– Can degrade depth resolution– Since image space quantized depth res not degrade

until blur angle approaches the angle of the viewing subzones

Depth resolution

– To avoid loss of resolution:

– αc is the spread due to min electron beam width / focal length of lenticules

– αd = 2 asin λ(wavelenght) / pitch

subzonedlc 222

Brightness + Color

• Lenticular screens offer comparatively good brightness to other methods such as parallax barriers.

• Directs only a fraction of the screen, but collects light from a larger area.

• Color can be problem because of CRT phosphor layouts.

Example

• Similar to Hamasaki’s using Braun tube– Allows accurate registration of vertical pixel strips– 8 views– 256 x 256 each– 1 mm lenticules– Focal length 2.25 mm– Horizontal pitch .125 mm– Min electron beam size 0.07 mm– Subzones 35 – 40 mm wide at 750 mm distance