ITEC 2016 is the annual forum where representatives from across the military, industry and academia connect and share knowledge about military simulation, training and education community. For more information on ITEC 2016, click here.
Geoff’s ITEC 2016 presentation is titled ‘Optical Blending – Difficult yet Essential for Maximising Dynamic Range of Projection Displays’
Here’s a snippet of the abstract…. For full details or to request a copy of the presentation, please contact us
Quality projection displays for visual simulation have evolved to use mainstream commercial projection devices, which, together with automatic alignment solutions, have dramatically reduced time required for their installation, alignment and maintenance. However, one bugbear has remained in the form of projector light leakage when displaying dark scene content.
Electronic blending solutions exist that produce excellent results for bright scenes but, for continuous background intensity levels in dark scenes, one must use infill techniques that sacrifice precious dynamic range. Often, solutions are commissioned that sacrifice up to 75% of the possible dynamic range, on the basis that ‘it’s the best you can get’. Often, this trade-off is not even apparent to the end-user, who therefore understandably assumes that the resulting performance really does represent the state of the art, which in turn limits the useful application scope of an expensive simulation system. Optical solutions to blending multiple channels can solve this problem, offering the promise to increase the utility and hence value of visual simulation training substantially, yet often this option is not even considered – so why is this?
Factors limiting the take-up of optical blending include: –
- Difficulty: implementing optical blending has proven to be surprisingly difficult. While standalone projected image quality of commercially available projectors is often excellent, optical characteristics tend to be unsympathetic to simple solutions. A systematic and well-founded methodology can lower this barrier substantially.
- Higher contrast projectors are available: even displays employing some of the more recent high-contrast projectors would benefit from optical blending – almost to the same degree as lesser contrast examples, owing to the enormous perception range of the human observer over a wide range of viewing conditions.
- Cost: while cost of the display system is certainly increased by the addition of optical blending hardware, it is a low proportion of visual system cost and the performance enhancement can represent value well in excess of this increase. Optical blending implementations – which place physical masks in the projection light paths – have been around for a long time, but a universal solution for all projector types and scene content has yet to become available. Many solutions give relatively poor performance that can be tolerated for dark scenes such as those experienced in night training, so are actuated out of the light paths for use with daytime scenes. These present logistical challenges to simulator users, where a choice must be made as to what ‘mode’ you are training, or some transition must be suffered while the blending system switches mode. Other solutions cannot withstand sustained light flux without degradation, so again must be actuated, while yet others may cause image sharpness degradation in the blend regions, so must be designed very carefully to limit this impact, particularly with high-resolution projectors.
The purpose of this paper is to inform the simulator operator and trainee community of this key area of visual system optimisation, including its cost-benefit analysis. Included in this will be a review of the mainstream projection technologies and their respective pros & cons, particularly with regard to scene dynamic range and blend implications. This in turn leads to a detailed review of optical blending options, presenting their operating theories and application scope. Finally, a new active optical blend technology is introduced that widens the range of display types that can benefit from high quality optical blending.