Researchers have developed a new method that can automatically produce clear
images through murky water. The new technology could be useful for searching
for drowning victims, documenting submerged archaeological artifacts and
monitoring underwater farms.
Imaging clearly underwater is extremely challenging because the water and
the particles in it tend to scatter light. But, because scattered light is
partially polarized, imaging using a camera that is sensitive to
polarization can be used to suppress scattered light in underwater images.
"Our new method overcomes the limitations of traditional polarimetric
underwater imaging, laying the groundwork for taking this method out of the
lab and into the field," said research team leader Haofeng Hu from Tianjin
University in China. "Unlike previous methods, there's no requirement for
the image to include a background area to estimate the backscattered light."
In The Optical Society (OSA) journal Optics Express, the researchers
demonstrate their method's ability to enhance image contrast while
preserving image details without introducing considerable noise. The new
method even works in dense turbid water, which is so cloudy it is almost
impossible to see through.
"Our polarimetric imaging method can improve the image quality in various
scattering media, not just turbid water," said Hu. "We think the principle
we used might be extendable to imaging through other scattering media such
as fog, haze and smoke."
Practical underwater imaging
Traditional approaches to underwater imaging use either prior knowledge of
the imaging area or the background of an image to calculate and remove
scattered light. These methods have limited utility in the field because
they typically require manual processing, images do not always have visible
backgrounds, and prior information is not always available.
To overcome these challenges, the researchers combined a traditional
polarized imaging setup with a new algorithm that automatically finds the
optimal parameters to suppress the scattering light. This not only
significantly improves image contrast to achieve clear imaging but can be
used without any prior knowledge of the imaging area and for images with or
without background regions.
"Our approach represents a distinct improvement that could enable practical
application of underwater polarimetric imaging beyond the 'ideal' underwater
environment found in the laboratory," said Hu. "It could be adapted for a
variety of applications in which clear vision is critical but where image
quality is usually poor due to turbid water."
Seeing through murky water
The researchers tested their new technique by acquiring images in turbid
liquid mixtures in the laboratory. They started with a transparent tank
filled with water and then blended in different amount of milk to mimic an
underwater environment with different turbidities. They imaged various
objects made from a variety of materials, such as wood, plastic and ceramic.
"Our experimental results show that our method has distinct advantages in
terms of suppressing scattering, recovering details and reducing noise when
imaging different objects in water with various turbidities," said Hu.
"While background regions are often not visible in dense turbid water, our
method was able to accomplish clear vision in this environment."
Now that the method has been demonstrated in the lab, the researchers plan
to test it in a practical underwater environment such as in the ocean. They
also plan to improve the imaging distances to make it more useful in a
real-world underwater environment.
Reference:
Hongyuan Wang et al, Automatic underwater polarization imaging without
background region or any prior, Optics Express (2021).
DOI: 10.1364/OE.434398
Tags:
Physics