WATS Presentation

Multi-projector displays using commercial of the shelf (COTS) projectors

Andrew JamisonCEO, Scalable Display Technologies

Example Case: 50 COTS HD projectors on a 40’ dome

Message: “It’s all about the system solution”…

The system as a “pixel pipeline”

COTS “home cinema” projectors Color correction/control Light/black levels Color depth (10 bit)

Geometry correction Accuracy & warp location A word on texture filtering

ImageGenerator

Warping Function

Projector Screen

Color Correction/Control

Projector color calibration is a requirement

Projector must have Ethernet connection & knobs to turn

Serial connections work but require more parts in the system

Set projector in “cinema mode” Two approaches to calibrate color

Shaders – send corrected pixels to the projector “input”

Correct the projectors “output” – modify settings of the projector

“Input” onlyCorrection

Projector “output”Corrected

1 2 3 1 2 3Available dynamic range

Three projector illustration

Color Calibration Trade-offs

Input side Offers opportunity for localized correction of “hot

spots” and other aberrations Faster to calibrate One weak lamp can drag down the performance of

the entire array “Lowest common denominator”

Output side Maximizes dynamic range of array More difficult to execute

Requires communication with each individual projector make and model

Takes longer to calibrate

“Output” approach considerations

There are two typical methods to control projectors remotely “menu based” control

Mimic a remote control – Slow and subject to missed commands

“value based” control Can receive specific values Much faster and more accurate

Ask your vendor to provide “value based” control

Light/black levels First consider impact of screen shape/finish

Part 60 4.d – surface contrast ratio – 5:1 cross reflectance…1 lux of ambient light (i.e. a small

candle), the max perceivable contrast ratio is 500:1. A dimly lighted room with 30 lux of lighting would squash the maximum perceivable contrast ratio to 50:1

– “Black Level” – no more than .015 candelas/square meter (cd/m²) in an unlit portion of a displayed scene as measured from the pilot eye-point.

Contrast ratio of projectors Low contrast results in low resolution but high contrast

does not necessarily mean high resolution High CR is a good goal but be careful of marketing

numbers…did it say ANSI? Look for iris and iris controls

Brightness 4.e - Not less than six (6) foot-lamberts (20 cd/m2).

Black level challenge

Area of maximum shared light

Edge-blended “tiled” example

High contrast ratio projectors are required for good blends

Projector 1

Projector 3 Projector 4

Projector 2

Shared pixels and elevated black here

Color depth

10 Bit color through the entire pipeline makes for brilliant displays

Geometry Calibration

Objective is to align the pixels and blend the edges

Manual calibration Practical and cost-effective for some scenarios

Small arrays and flat screen Advanced tools are available but challenges persist

Fully automatic calibration Domes, cylinder and other complex geometries

are very difficult to correct manually Fast, reliable and flexible

Geometric Accuracy

4.c - System Geometry – 5° even angular spacing within ±1° as measured from either

pilot eye point and within 1.5° for adjacent squares. Uniformity of a grid as measured by theodolite

6.e - The visual system must be free from optical discontinuities and artifacts that create non-realistic cues. Geometric mesh must be free of aberrations or

discontinuities Some manual approaches suffer from this…

Geometric warping location

Three places to execute geometric warping Projector External box IG

External box and projector warping “application independent” Can be fully automatic Possibility for good filtering

IG warping “application dependent” – requires SDK integration Truly zero latency since warp is within the 16ms

render cycle – (typically .15ms) Also consider aliasing artifacts

Texture Filtering Basics

• Better quality re-sampling = better quality images

Nearest neighbor Polynomial interp.Linear interpolation

F

Horizontal Field Of View ~ 143 degrees

Comparable to 50mm lens

(8,400 arc minutes) 4,200 unique pixels needed

~ 5,000 projected pixels Including overlap

1 arc minute = .3 milliradiansEach pixel = .6milliradians

A view on resolution

4.f – Not greater than two (2) arc minutes (per pixel).

Sony – 4K pixels / 100°

One radian is the angle subtended at the center of a circle by an arc that is equal in length to the radius of the circle.

1 radian = 57.3°

Graphic Cards Allow for Resolution Higher

Multi-GPU technology (Vista only) nVidia's 'SLI' ATI's 'Crossfire‘

Quad output cards Pixel shader abilities

It’s a system

Points of failure are: Cables Connectors Power supplies

Simulators/FTD are controlled environments Know screens, IGs, projectors These are repeatable environments

4 Projector Dome, 220 Degrees.

Thank you