19-03-2014, 03:07 PM
Human body 3D imaging by speckle texture projection photogrammetry
Human body 3D imaging.pdf (Size: 1.18 MB / Downloads: 62)
Abstract
Describes a non-contact optical sensing technology called
C3D that is based on speckle texture projection
photogrammetry. C3D has been applied to capturing all-
round 3D models of the human body of high dimensional
accuracy and photorealistic appearance. The essential
strengths and limitation of the C3D approach are
presented and the basic principles of this stereo-imaging
approach are outlined, from image capture and basic 3D
model construction to multi-view capture and all-round 3D
model integration. A number of law enforcement, medical
and commercial applications are described briefly including
prisoner 3D face models, maxillofacial and orofacial cleft
assessment, breast imaging and foot scanning. Ongoing
research in real-time capture and processing, and model
construction from naturally illuminated image sources is
also outlined.
INTRODUCTION
3D image sensing[1] is rapidly coming of age,
maturing from a laboratory curiosity to being
a driving force behind new and exciting
applications. 3D imaging devices promise to
open a very wide variety of applications,
particularly, those involving a need to know
the precise 3D shape of the human body, e.g.
e-commerce (clothing), medicine
(assessment, audit, diagnosis and planning),
anthropometry (vehicle design), post-
production (virtual actors) and industrial
design (workspace design). In short, any
situation where you want to get the 3D shape
of a person into the computer.
Background
C3D was chosen by the 3D-MATIC Faraday
Partnership (see[2]) for our research work on
human body imaging as it affords a number of
advantages over other non-contact optical
measurement techniques. The geometric
simplicity of the capture hardware and well-
understood calibration methods employed
ensure that the accuracy can be superior to
more optically complex techniques which can
be more difficult to engineer. Perhaps more
importantly, the technique is also a full field
one, producing three-dimensional information
from the whole scene without the need for
scanning. In applications where data acquisition
speed is critical, such as in the measurement of
live subjects, this can be fundamental to the
success of the data acquisition technique.
How it works
Triangulation and stereo
C3D relies on camera-camera base line
triangulation (Figure 1c) to perform depth
sensing. Most people have two eyes and can
perceive depth cues from the slight parallaxes
(or disparities) present between the views
observed in each eye. C3D takes these same
parallaxes, as captured by a stereo pair of
cameras, and decodes them to produce an
explicit depth map. Convergent geometry has
been adopted to maximise the depth coverage
obtained over the field of view of the cameras.
As can be seen from Figure 2, a point P in
space will project to two slightly different
locations on the imaging plane of each camera
and the difference in location is termed
parallax or disparity. This disparity increases
as the imaged point P in the world is
translated further in the depth axis from the
convergence point C of the camera stereo-pair
(the sign of the disparity is reversed
depending on whether the imaged world
point lies in front or behind C). Accordingly,
the magnitude and sign of the disparity values
can be decoded to produce depth values if the
geometry of the camera configuration is
known (this is found by means of calibration).
Conclusions
3-D human body imaging applications are an
important sector of the 3-D image capture
market. By affording quasi-instantaneous
capture to deliver accurate 3D photorealistic
body models, the speckle texture projection
stereo-photogrammetry approach is uniquely
suited to imaging the human form.
Furthermore, as the principal ingredients of
this approach are simply cameras and
software, it also has the potential to become a
very low-cost technology.