Optical Blending for Maximising Dynamic Range of Projection Displays

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, infill techniques are often applied, which can sacrifice up to 75% of the possible dynamic range. 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?

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.

Included in this presentation 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.

Geoff Blackham, GBVi

Geoff Blackham has worked more than 30 years in the Simulation and Visualisation industries as an engineer and company board-level director. While his major focus has been on simulation display systems engineering and technology development, Geoff was a key contributor to the growth and development of SEOS Ltd. from joining in 1989 up to its acquisition by Rockwell Collins in 2008.  Post-acquisition, Geoff continued with Rockwell Collins in management and then principal engineering roles before leaving to set up GBvi Ltd. in mid-2011.   Geoff is a named inventor on 14 root patents and applications, including established re-modulation projection technology.