Scientists Develop Lensless Computational Microscopy

Tuesday, August 15, 2017 - 03:02

Researchers of ITMO University and Tampere University of Technology have improved computational imaging of optical signals in lens-less microscopes.

Phys.org reported that this device makes it possible to visualize transparent objects or measure their shape in three dimensions. There are no lenses or objectives that focus light on an image sensor. Instead, lensless microscopes rely on measuring diffraction patterns that result from illuminating an object with laser or LED light.

The image obtained from these patterns is generated by using a computational approach. Special algorithms allow generating an optical image and improving the optical signal itself. It thus produces images with higher resolution using only mathematical methods without any physical changes to microscopes.

An international team of scientists from Russia and Finland turned to computational methods in order to expand the field of view, a crucial feature of any microscope. In traditional microscopy, an objective focuses light from a small object area to a bigger area where the image is captured. Thus, the image size appears to be increased. It is impossible, however, to change the size of the image sensor itself. This is where computational means come into play, allowing researchers to overcome this physical limitation and expand the field of view.

"We used the mathematical method of sparse representation of signal. A simple example may help understand how it works. Imagine that you have a grid paper and you choose a square area of eight by eight. If you register the signal in this eight by eight square, then the retrieved image will be discretized in the same way. But if the signal meets certain requirements of sparsity, you can potentially use the same eight by eight signal to restore all the missing information regarding the same object, but with a smaller discrete mesh of 16x16 or even 32x32. At the same time, the resolution will increase twofold or fourfold correspondingly. Moreover, our computational algorithm expands the signal beyond the registration area. This essentially implies the appearance of extra pixels around our eight by eight square, which therefore expands the field of view," says Nikolay Petrov, one of the authors of the study and head of the Laboratory of Digital and Display Holography at ITMO University.

The new approach enables scientists to improve image resolution without any modifications in the quality of the image sensor and other microscope components. This, in turn, suggests significant economy and cheaper microscopes in the future.

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