The Next Wave of 3-D – Light-Field Displays
by Nikhil Balram
In May of 2013, for our last special issue on 3-D, I wrote a guest editorial with the title “Is 3-D Dead (Again)?” The 3-D in question was stereoscopic 3-D for consumers. In that editorial, I focused on a fundamental limitation of stereoscopic 3-D – the vergence-accommodation conflict. This conflict is caused by the fact that presentation of stereoscopic images on a single plane results in an unnatural decoupling of vergence (the point at which our two eyes converge) and accommodation (the point at which our two eyesfocus), in contrast to real-world viewing where these two are always closely coupled.
This conflict has been shown to cause viewer discomfort that manifests itself in different ways such as nausea, headaches, and tiredness. In that editorial, and the two articles that accompanied it, the hypothesis put forward was that the likely path toward a natural 3-D experience was through volumetric displays, with light-field displays in particular being the closest to first commercial implementation. In this issue, I want to build further on that hypothesis by providing an update on the exciting developments in light-field displays and a vision of what lies ahead. Holographic displays are the other major category of volumetric displays. But, in my opinion, the state of the art, while continuing to advance impressively, is a decade or more away from a first significant commercial deployment. So, I chose to focus again on light-field displays.
The most fundamental segmentation in the design of display systems is between displays designed for group or multi-user viewing and those designed for personal or portable use. The critical issues and the approaches to solving them are very different for these two categories. Hence, they are discussed separately in the two invited articles in this issue.
The first article is from Professor Xu Liu and his colleagues at Zhejiang University, who have produced an impressive body of work in different types of group-viewable or multi-user light-field displays. “The Progress of Light-Field 3-D Displays” starts by providing a reminder of the fundamental definition of the light field and the basic principles of light-field displays. This is an important starting point because there have been some inconsistencies and ambiguities in how various authors have used the term in the literature. The article goes on to present the two main types of approaches for multi-view/multi-user light-field displays – time sequential (temporal multiplexing) using various types of scanning systems and spatial multiplexing using arrays of projectors or panels – and to discuss the state of the art and the tradeoffs.
The second article is from Dr. Kathrin Berkner and her colleagues at Ricoh Innovations Corporation in Silicon Valley. Their piece, “Personal Near-to-Eye Light-Field Displays,” takes a different approach from the first paper, arriving at portable, personal (single-user), near-to-eye light-field displays from the point of view of mobility. This work arises from a project initiated by me 3 years ago that sought to define the next-generation mobile platform after the smartphone. We came to the realization that this next-generation platform, which we call the Mobile Information Gateway (MIG), would need a near-to-eye light-field display to satisfy the big gaps in the human interface offered by the current mobile platform. This article lays out the logic leading to the definition of the requirements of this system and provides an overview of the state of the art in the various approaches that have been taken thus far. Here as well the approaches can be separated into those that use temporal multiplexing (time sequential) and those that use spatial multiplexing. Each type of approach has some advantages and disadvantages, and it appears that the best choice depends on the attributes of the target application.
These two articles remind us of the rich diversity and potential that light-field displays offer, with parallel paths taking us toward group/multi-user and personal/portable systems. In my opinion, the prospect of developing useful real (natural) 3-D displays within the next 5 years is very bright. I confidently predict that these will first see use in a set of applications before the year 2020. •