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