Stereoscopic & Collimated Display Requirements

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2 Stereoscopic & Collimated Display Requirements October 3, 01 Charles J. Lloyd President, Visual Performance LLC

3 Overview Introduction Stereoscopic displays Antialiasing and pixel pitch Collimated displays Motion induced blurring 3

4 Goals Training system acquisitions professionals must follow a highly regulated process that averages 3 years in duration With this fragile process, unachievable, inappropriate, or missing requirements too often cause delays and cost overruns Improved requirements are needed to: Increase the probability the delivered system meets the training need Reduce the duration and cost of the acquisition process Allow the development/selection of solutions with the highest benefit/cost ratio, without over-constraining suppliers 4

5 Attributes of a Good Requirement Addresses system attributes that support training needs Correlate with training task performance Objective, quantitative, measurable Unambiguous, well-described, accessible to supplier community Easily measured, using affordable devices, with little training Measurable for sub-systems as well as completed system Demonstrable prior to source selection Lloyd (011) Towards a decision support system for simulation training display requirements. Interservice/Industry Training, Simulation, and Education Conference (I/ITSEC) 5

6 Stereoscopic Displays The consideration of stereoscopic displays is expected to increase for training applications due to significant cost reduction and their (predicted) adoption in entertainment markets The simulation training industry has little experience specifying and acquiring these systems Previous attempts at stereoscopic boom operator displays did not go well: KDC-10 (Dutch tanker, 1996) exaggerated the stereopsis cue 64 times to make it useable Couvillion, W. C., A. J. Roberts, et al. (003). KC-135 Boom Operator Training Hi-Fidelity Stereoscopic Display Technology Demonstrator, I/ITSEC: System did not work, no data were collected. KC-135 BOWST ( ), never considered stereoscopic, were convinced it would provide no benefit Air National Guard (010-11) Attempted a stereoscopic system: Abandon the requirement for stereo 6

7 Stereoscopic Utility Vision science sets the threshold for normal observers to be 3 to 10 arcsec, about 4 to 1 inches at a 0 m working distance Experienced display engineers and some papers from the VR community concluded stereoscopic displays are not useful beyond about 10+ ft Lloyd, C. J. & Nigus, S. G (01) Effects of stereopsis, collimation, and head tracking on air refueling boom operator performance, Proceedings of the IMAGE Society Annual Conference, Scottsdale 7

8 Evaluation Results Measured a large, reliable improvement in distance discrimination performance with stereoscopic display Better performance with collimated than direct view 3.5 Stereoscopic 3.5 Collimation Mean 1.5 Mean

9 Assuring Successful Implementation Develop and support the essential practical requirements that mediate success: Resolution x Antialiasing Dipvergence Crosstalk (leakage) Disparity Range Accommodation-Vergence Mismatch 9

10 Effects of Antialiasing and Pixel Pitch Used mirror stereoscope that set accommodation and vergence distance to 0 m 10 10

11 Results: Disparity Thresholds Model summarizing 600 threshold measurements from four observers R = 0.88, p < , 35 df Threshold Disparity, arcsec AA kern width, pix Pitch, arcmin AA kern width, pix arcsec Pitch, arcmin 30 R =

12 Results: Viewing Comfort Ratings: 1 = comfortable 5 = very uncomfortable R = 0.96, p < , 35 df Comfort Rating AA kern width, pix AA kern width, pix Pitch, arcmin R = Pitch, arcmin 1 1

13 Conclusions, Second Evaluation Eye-limited stereoscopic depth discrimination performance can be obtained using currently available and affordable display technology ONLY if we get spatial sampling artifacts are under control The typical hardware antialiasing solution of the past few years is expected to be insufficient for this application 13 13

14 Quantifying Spatial Sampling Artifacts Radial test patterns have been used for years for subjective tests Simultaneously evaluate all resolutions and angles Developing Procedure: Create polygonal pattern and display Photograph from the eyepoint Process image to quantify magnitude of sampling artifacts 14

15 Initial Spatial Sampling Artifact Metric Results Correlation with disparity thresholds for 1.5 arcmin pitch: R = 0.98 (p < 0.001, 7 df) Metric Response Antialiasing Kernel Width

16 Vertical Disparity (Dipvergence) Dipvergence errors have been with us for years with collimating mirrors Stereoscopic displays introduce a new source of dipvergence when an observers rolls their head relative to the display system Published evaluations recommend keeping dipvergence at or below 5 arcmin for long term viewing situations Moffitt, K. (1997). Designing HMDs for viewing comfort. Head Mounted Displays. J. E. Melzer and K. Moffitt, McGraw-Hill, New York. Task, H. L. and D. F. Kocian (1995). Design and integration issues of visually-coupled systems, AFRL. Walker, B. H. (000). Optical design for visual systems, SPIE Press. 16

17 Crosstalk (Leakage) Quantifies the separation of the right and left eye images Simple in concept: Command black and white for each eye Measure black and white for each eye position Compute ratio of unintended / intended luminance Proposed metric: Keep crosstalk <= 3% Complications: Autostereoscopic: Crosstalk can depend on viewer position and angles Color affects results for systems that discriminate via wavelength Head Roll can strongly affect results Polarization: Crosstalk can be gray scale dependent with some display types 17

18 Disparity Range Range of disparities presented on the display system shall not exceed 1 deg If you must present objects at infinity, the nearest object you can simultaneously present would be at 3.5 m from the observer 18

19 Accommodation-Vergence Mismatch Accommodation = Focus (viewing) Distance Vergence = Binocular vergence distance Diopter = 1/meter Guideline: Keep the mis-match below about 1/3 rd diopter If you must present objects at infinity (0 diopters), the display should be at least 3 meters from the observer 19

20 Collimated Systems Four types of geometry error occur in common collimated displays, categorized along two dimensions: Global to Local Stationary to non-stationary (depend on observer position) The local non-stationary distortions are the most insidious: Most disruptive to training Cannot be corrected by any alignment system Fundamental attribute of mirror quality Some mirrors are much better than others 0

21 Metric of Mirror Quality Change in geometry (arcmin) / change in position (inches) UEP 1 LEP 1 UEP LEP UEP 3 LEP 3 Long, J. L., Lloyd, C. J. & Beane, D. A. (010) Practical geometry alignment challenges in flight simulation display systems, Proceedings of the IMAGE Society Annual Conference, Scottsdale 1

22 Measurement Procedure Photograph many alignment marks Move camera inches between photos Superimpose the measurements Summarize the localized changes

23 Measurement Results ImageA: 376 ImageB: Elevation, deg th percentile: 0.37 arcmin/inch 99th percentile: arcmin/inch 98th percentile: 1.16 arcmin/inch 95th percentile: 7.3 arcmin/inch 90th percentile: 3.44 arcmin/inch 80th percentile: 1.87 arcmin/inch 50th percentile: 0.88 arcmin/inch Azimuth, deg 3

24 Metric Results Measured 1 mirrors thus far 10:1 difference between mirrors Quality Rating R = Metric Value Histogram of Metric Values 4

25 Motion Induced Blurring Pixel hold time has been identified as a major source of blur for moving images Single point measurement using a photodiode and an oscilloscope Amount of blur depends on object velocity Lloyd, C. J., Williams, L., and Pierce, B. (011) A model of the relative effects of key task and display design parameters on training task performance. Proceedings of the IMAGE Conference, Scottsdale 5

26 Effect on Target Identification Range How much hold time is tolerable? Depends heavily on how fast the targets move and the resolution you need to achieve Conducted two evaluations of effect of hold time, target velocity, resolution, luminance, and contrast: 40 combinations of these design variables 6

27 Results: Hold Time and Pixel Pitch Angular Velocity = 0 deg/sec Angular Velocity = 15 deg/sec Target Identification Distance, m Hold Time, ms Pitch, arcmin Target Identification Distance, m Hold Time, ms Pitch, arcmin 7

28 Results: Contrast and Luminance Target background 85% of peak display luminance Target background 5% of peak display luminance Display Contrast Ratio Display Luminance, Fl Display Contrast Ratio Display Luminance, Fl 8

29 Conclusions A quantitative model is now available that indicates the relative effects of key design variables on identification range: Pixel pitch Pixel hold time (motion blur reduction) Display system contrast Peak display luminance Pitch and hold time offer a larger potential for improving identification range than do contrast and luminance 9

30 More Information Many of the supporting papers can be downloaded from: Please make contact with your ideas for improved display system metrics and measurements Visual Performance would like to collaborate with stakeholders on evaluations and the preparation of papers 30

31 01 Thank you. Questions?