DIGITAL HOLOGRAPHY AND IMAGE PROCESSING

Beam spatial filter Collimator Lens Digital Photographic camera
Laser Object table
Microscope
Computer
Digital Reconstruction of Holograms (Equivalent optical setup)
Hologram
Hologram sensor
Computer Analog-todigital conversion Preprocessing of digitized hologram Image reconstruction (DFT/DFrT) Image processing Output image
Yes
Continue iterations ? No
Comparing reconstructed and initial wave fronts; computing and accumulation of noise statistical parameters Output data
Simulating wave front reconstruction (IDFT, IDFrT)
Hologram
First focal plane
Fourier Plane
Second focal plane
Digital Holography: Digital Reconstruction of Holograms
M.A. Kronrod, N.S. Merzlyakov, L.P. Yaroslavsky, Reconstruction of a Hologram with a Computer, Soviet Physics-Technical Physics, v. 17, no. 2, 19lected wave front Hologram Reconstructed image
Statistical characterization of speckle noise in coherent imaging
L. Yaroslavs ky, A. Shefler, Statistical characterization of speckle noise in coherent imaging systems, in: Optical Measurement Systems for Industrial Inspection III, SPIE’s Int. Symposium on Optical Metrology, 23-25 June 2003, Munich, Germany, W. Osten, K. Creath, M. Kujawinska, Eds., SPIE v. 5144, pp. 175-182
Generating 2-D array of pseudo-random numbers that specify the phase component of the object wave front
Computing object’s wave front
Simulating wave front propagation (DFT, DFrT)
Digital holography and image processing: twins born by the computer era
Digital holography: - computer synthesis, analysis and simulation of wave fields Digital image processing: - digital image formation; - image perfection; - image enhancement for visual analysis; - image measurements and parameter estimation; - image storage; image visualization
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In the same way as in economics currencies are general equivalent, digital signals are general equivalent in information handling. A digital signal within the computer that represents an optical one is, so to say, purified information carried by the optical signal and deprived of its physical integument. Thanks to its universal nature, the digital signal is an ideal means for integrating different informational systems.
Computer model
Illustrative examples of simulated images: a) - original image; b) - image reconstructed in far diffraction zone from 0.9 of area of the wave front; c) - image reconstructed in far diffraction zone from 0.5 of area of the wave front; d) image reconstructed in far diffraction zone after limitation of the wave front orthogonal components in the range.
DIGITAL HOLOGRAPHY AND IMAGE PROCESSING
L. Yaroslavsky,
Ph.D., Dr. Sc. Phys&Math, Professor Dept. of Interdisciplinary Studies, Faculty of Engineering, Tel Aviv University, Tel Aviv, Israel www.eng.tau.ac.il/~yaro
Digital computers integrated into optical information processing systems enable them to perform arbitrary signal transformations Acquiring and processing quantitative data contained in optical signals, and integrating optical systems into other informational systems and networks is most natural when data are handled in digital form.
Computer simulation of coherent imaging
Case study: Speckle noise in coherent imaging systems
Diffusely reflecting object
Hologram sensor
Measuring hologram orthogonal/ amplitude-phase components: - Limitation of the hologram size - Limitation of the hologram component dynamic range - Hologram signal quantization Reconstruction of the hologram
2-D array that specifies amplitude component of the object wave front
Introducing signal distortions: -Array size limitation -Dynamic range limitation -Quantization
Digital Holographic/Interferometric Microscopy
One of the main drawbacks of microscopy: the higher is the spatial resolution, the lower is depth of focus. This problem can be resolved by holography. Holography is capable of recording 3-D information. Optical reconstruction is then possible with visual 3-D observation. Drawbacks of optical holography: -Intermediate step (photographic development of holograms) is needed. -Quantitative 3-D analysis requires bringing in additional facilities Radical solution: optical holography with hologram recording by electron means (digital photographic cameras) and digital reconstruction of holograms. This is the principle of digital holographic microscopy.