Optical imaging in fields such as medicine (medical diagnosis), marine science as well as security and defense, is quite challenging, particularly if performed through turbid liquid media. Such difficulties are associated with various scattering particles and molecules which lead to strong and multiple scattering effects. These numerous scattering events within such a media degrade image contrast and limit the depth from which hidden objects may be resolved. Moreover, the particles found in such media may absorb the target signal, resulting in substantially reduced visibility and overall image quality. Therefore, the resolution of hidden objects becomes progressively more difficult with increased thickness of turbid media.
Latest research has produced significant breakthroughs in relation to imaging targets within turbid liquid media using light polarization techniques, which increase the visibility range beyond that enabled by direct imaging. That opened the door to studying the properties of polarized light within turbid media in atmosphere, ocean and tissue, have been extensively studied. Nonetheless, counteracting the nontrivial effects of light scattering still remains the primary challenge, limiting the utility of optical imaging within liquid media.
To this note, Israeli researchers led by Professor David Abookasis at Ariel University developed technique to circumvent the optical degradation in turbid liquid media and recover high-quality images of hidden objects by averaging polarized (linear/circular) speckle images projected from several directions through a lens array. Specifically, they designed a simple approach for combining multiple polarized speckle projections using an averaging process based upon a Shift-and-Add (SAA) algorithm to image objects completely embedded within turbid liquid media. Their work is currently published in the research journal, Optics and Lasers in Engineering.
The experimental approach entailed irradiating the media with a laser beam, concurrent to which multiple speckled images from different views were obtained using a lens array and captured by CCD camera. During offline processing, images were shifted to a common center and then superimposed to form a single common image with markedly reduced scattering noise, enabling delineation of the hidden object’s shape. Lastly, quantitative image quality metrics, including SNR, entropy, and sharpness were applied to evaluate quality of the reconstructed images.
The authors were able to confirm the key role of the lens array in improving the resolution of the image reconstructed by fusing multiple low-resolution projections. Most importantly, they were able to successfully demonstrate image reconstruction of two transparent objects of distinct geometrical shapes hidden within turbid liquid media comprising a range of dilutions of commercially available cow’s milk in seawater.
In summary, the study by Ariel University scientists successfully illustrated a different technique for imaging objects hidden within turbid liquid media, by employing an ensemble of multiple speckled polarized (linear/circular polarization) projections. Remarkably, this is the first report to demonstrate successful imaging of hidden object images within turbid liquid media by averaging multiple polarized speckle projections. Altogether, the results presented are promising and advance towards the development of a valuable tool for a range of image recovery applications.
Alex Scherbakov, Konstantin Sheverdin, Galia Chaimov, Mordechai Hakham-Itzhaq, David Abookasis. Experimental demonstration of imaging hidden objects in opaque liquid-based media by fusion of single-shot multiview polarized and unpolarized speckle images. Optics and Lasers in Engineering, volume 113 (2019) page 77-84.Go To Optics and Lasers in Engineering