Abstract
Observing dynamic micro-scale phenomena occurring at millisecond time scales, such as organism activity, micron particle flows, or any opaque object observation, requires volumetric microscopy techniques able to achieve high data acquisition rates while maintaining contrast so that measurement of fine micro-scale features is possible. In realizing this purpose, the light-field (LF) technique has already been used on three-dimensional (3D) scene capturing and even for microscopic visualizations. In studying the ability and feasibility of 3D surface morphology reconstruction via LF microscopy, we adopted a lab-made LF microscope and integrated a four-dimensional Fourier slice algorithm and a Markov random field propagation algorithm. Furthermore, for numerical comparison and quantized analysis, the Tenengrad function was utilized to calculate the average contrast of the region of interest. Reflective US Air Force targets and 3D photolithography-made micro-scaffolds coated with 50 nm nickel thin films were adopted for system alignment and calibration. The experimental results demonstrate that the developed LF microscope with the signal processing algorithms can observe the 3D surface morphology of opaque microstructures with one snapshot, and has been preliminary applied to Brownian motion observation with 30 Hz volumetric image rate.
Highlights
Three-dimensional (3D) micro-surface morphology measurement is currently used in many fields, such as dynamics of micro-electro-mechanical systems, biomedical applications for label-free live cells, and detection of hydrodynamic flow of micron-size particles, among others[1,2,3,4,5,6,7]
We demonstrate that calculation of the 3D surface geometry of an opaque can be approached via refocused images of LF microscopy, after a computer vision method is used to estimate depth image
To evaluate a depth image from LF microscopy, the 4D Fourier slice algorithm is used to obtain a series of digitally refocused images that allow the defocused and correspondence image to be calculated from those images
Summary
Three-dimensional (3D) micro-surface morphology measurement is currently used in many fields, such as dynamics of micro-electro-mechanical systems, biomedical applications for label-free live cells, and detection of hydrodynamic flow of micron-size particles, among others[1,2,3,4,5,6,7]. DHM has greater potential for wide-field image observation, and can increase the data recording rate Techniques for such measurement include DHM, laser scanning microscopy for 3D topography, and quantitative phase microscopy for transparent samples. DHM allows a full 3D registration with wide-field exposure to be obtained, but without any of the vertical displacement that occurs, for instance, in vertical laser scanning interferometry, according to white light sources and phase shifting interferometry[1] These techniques involve complex optical setups with two-beam interference optical designs, where one beam is the object beam and the other is the reference beam, which necessitates a very coherent light source. In this work, we investigate and demonstrate the feasibility of utilizing LF microscopy to reconstruct the 3D micro-morphology of opaque objects and observe the 3D Brownian motion of polystyrene microspheres
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