Tech Briefs Magazine - February 2022 - 33

it converts these changes into both
pulse and respiration rate.
The first version of this system was
trained with a dataset that contained
both videos of people's
faces and
" ground truth " information: each person's
pulse and respiration rate measured
by standard instruments in the
field. The system then used spatial and
temporal information from the videos
to calculate both vital signs. It outperformed
similar machine learning systems
on videos where subjects were
moving and talking. But while the system
worked well on some datasets, it
still struggled with others that contained
different people, backgrounds,
and lighting - a common problem
known as " overfitting. "
The researchers improved the system
by having it produce a personalized
ma chine learning model for each individual.
Specifically, it helps look for
important areas in a video frame that
likely contain physiological features
correlated with changing blood flow in
a face under different contexts such as
different skin tones, lighting conditions,
and environments. From there, it
can focus on that area and measure the
pulse and respiration rate.
While this new system outperforms
its predecessor when given more challenging
datasets, especially for people
Multi-Shot Lensless Camera
The camera could have uses in faster disease diagnosis and thinner cellphones.
The Pennsylvania State University, University Park, PA
type of imaging that does not re -
quire a lens and uses reconfigurable
particle-based masks to take
multiple shots of an object is being
developed. The electric-field directed
self-assembling mask technology was
developed by creating a mask of microscopic
gold wires and placing it near
the object to be imaged. The mask
scatters the light reflected off the
object and an image sensor collects
the light.
An electric
current
rearranges the particles in the mask,
producing a new mask with every iteration
and the system records each new
image. The multiple light captures are
then computationally reconstructed
into the original object image, resulting
in highly improved resolution and
quality.
Typically, one would need to make
multiple masks and physically move
them around to get multiple images.
This becomes bulky and expensive and
negates some of the simplicity that is
the advantage of lens-free imaging.
In typical microscopy, there exists a
tradeoff between the field of view and
the power of the resolution, so a 10x
field is wider than a 100x field. By
using a lens-free imaging technology,
it is possible to combine a wide field of
view with high magnification for lowercost
images and faster diagnosis of disease.
This could be especially useful in
developing countries where high-end
microscopes are not available.
Tech Briefs, February 2022
A
LENSLESS IMAGING
Reconfigurable
Particle Mask
with darker skin tones, there is
still
more work to do. There is still a trend
toward inferior performance when the
subject's skin type is darker, in part
because light reflects differently off of
darker skin, resulting in a weaker signal
for the camera to pick up.
Any ability to sense pulse or respiration
rate remotely provides new opportunities
for remote patient care and
tele medicine. This could include selfcare,
follow-up care, or triage, especially
when someone doesn't have convenient
access to a clinic.
For more information, contact Sarah
McQuate at smcquate@uw.edu; 206-5432580.
Image
Reconstruction
Object
Schematic
of the layout for a lensless camera. (Photo: Keating/Liu Labs, Penn State)
In the case of cellphones, one major
contributor to their bulk is due to the
camera lens needing to be a certain distance
to the detector. A lens-free camera
could help minimize the space requirewww.techbriefs.com
Cov
ToC
ment.
Likewise, a lens-free system added
to a cellphone could turn the cellphone
into a low-power microscope.
For more information, contact Walt Mills
at wem12@psu.edu; 814-865-0285.
33
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Tech Briefs Magazine - February 2022

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