A Virtual Retinal Display For Augmenting Ambient Visual Environments
by Michael Tidwell
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Chapter 1: Introduction
1.1 Introduction to the Thesis
The goal of this project is to design, build, and characterize
a full color, monocular, see-through, virtual image display which
scans light directly onto the retina of the eye. The display resolution
is equivalent to VGA graphics resolution of 640 horizontal by
480 vertical picture elements. The display is suitable for helmet
mounted display (HMD) applications where overlay of virtual information
onto the real world is desirable. The display is termed an augmented
vision display connoting the user's ability to see through
the device (to the outside world) with no additional optical power
and thereby view the computer generated video superimposed onto
the real world environment.
An augmented vision display has many unique applications. Other
occluded virtual image and real image displays give information
decoupled from the physical environment. Information coupling
between virtual and physical reality conveys, in some cases, more
information than the sum of the two independent realities. For
example, alphanumeric or graphical assembly information could
be superimposed onto an assembly line in a manufacturing application.
The assembler gains more information by seeing the solution (where
X goes!) and the problem (where does X go?) at the same point
in space and time. In a medical application, an anesthesiologist
views vital signs and instrument readings and never looks away
from the patient. The anesthesiologist reads facts from the display
and from the patient's appearance, condition, and movement and
utilizes both sources of information simultaneously to make decisions.
The display designed and built for this thesis is a version of
the Virtual Retinal Display (VRD) [1] developed at the Human Interface
Technology Laboratory at the University of Washington. The VRD
scans collimated light in a raster fashion directly onto the retina
of the eye. The angular extent of the scan determines the field
of view, or perceived size, of the display. The light is intensity
modulated and synchronized with the scan to generate the desired
image for the viewer.
1.2 Introduction to Chapters
Chapter 2 provides background information on characteristics of
the human eye. Field of view, resolution, limitations to resolution,
and display characteristics related to the human eye such as contrast,
contrast ratio, and contrast modulation are discussed here. Chapter
3 describes the ideal augmented vision display in terms of resolution,
field of view, color, and other important characteristics. A survey
of current helmet mounted display technology is given in Chapter
4 and two applications for an augmented vision display are discussed
in Chapter 5. Chapter 6 discusses the general theory of building
an augmented vision Virtual Retinal Display. The discussion in
Chapter 6 centers on the Optical Invariant and how it relates
to the scanning device used for this project. Chapter 7 provides
the system design and related issues while Chapter 8 reports the
measured performance of this display. Finally, Chapter 9 describes
future work to solve remaining technical challenges.
Human Interface Technology Laboratory