Tech Briefs Magazine - May 2023 - PIT-5

one set of them, two-step iterative shrinkage
thresholding and total variation
(TV), was applied in the present case.
Improvement of sensitivity is accomplished
by using a Fabry-Pérot filter that
randomly modulates the incoming light
in the spatial and spectral dimensions.
Specifically, the averaged transmittance
of a developed filter is about 45 percent
for the visible light. This sensitivity is
about 10 times higher than that of conventional
technology (light use efficiency
less than 5 percent), making it the world's
highest sensitivity for HS imaging. For example,
the developed technology can
clearly capture an object under room illumination
(550 lux), but it is difficult
for the conventional system to recognize
it. The developed HS imaging technology
enables clear shooting without extremely
bright lighting which has been
required in conventional HS imaging.
Acquisition of spectral information
was experimentally demonstrated by dividing
the wavelength range from 450
nm to 650 nm into 20 wavelengths. As
shown in an example using color samples
the spectral information is correctly
obtained via random modulation followed
by image reconstruction. As a result
of the image reconstruction, all pixels
acquire spectral information, and the
number of pixels is preserved in the CSbased
HS imaging. However, this does
not guarantee that each pixel is spatially
separated. To experimentally obtain the
effective spatial resolution, a ladder resolution
chart is photographed and evaluated
by calculating modulation transfer
function (MTF) curves. The MTF curves
show that the spatial resolution of CSbased
HS imaging is comparable to that
of RGB cameras with 3 dB contrast. With
a mm/pixel conversion ratio of 1,150
pixels/130 mm, a spatial resolution of 3
cycles per mm indicates that 3 pixels are
required to separate adjacent lines with
3 dB contrast. This result is reasonable
because edge smoothing occurs in the
CS-based HS imaging during the image
reconstruction process, whereas the
RGB camera with Bayer filter mosaic also
loses spatial information due to 2 × 2 pixel
convolution and inter-pixel crosstalk.
Together with the sensitivity and resolution,
a high frame rate is an essential
factor for high usability. A low frame rate
makes it difficult to perform shooting
procedures smoothly, for example, focusing,
adjusting lighting conditions, and
moving objects into proper positions.
From a usability perspective, video rate
Photonics & Imaging Technology, May 2023
PIT Edmund Optics Ad 0523.indd 1
operation (>30 fps) is an important goal
for HS imaging. The operation speed of
a camera is mainly limited by a shutter
speed and image processing time. The
CS-based HS imaging enables a fast shutter
speed because of the high sensitivity.
High-speed image processing
is
also
achieved by using GPU parallel computing
of the image reconstruction. As a result,
32 fps HS imaging was achieved with
VGA (640 × 480 pixels) resolution.
This article was written by Yako Motoki,
Researcher, Panasonic Applied Materials
Technology Center. For more information,
contact yako.motoki@jp.panasonic.com.
The high usability of the CS-based HS
imaging brings HS imaging in various scenarios,
including not only industrial applications,
but also consumer applications
such as smartphones, drones, and
Internet of Things (IoT) devices.
May 7-12, 2023 | Booth 447
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Tech Briefs Magazine - May 2023

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