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- HOW: Dark field imaging technique. Put a variable iris with a center stop in F. plane. It blocks transmitted light to obtain an image of the scattered light.
Fractional derivatives - analysis and experimental implementation |
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< | Jeffrey Davis, David Smith, Dylan McNamara, Don Cottrell, Juan Campos
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> | Jeffrey Davis, David Smith, Dylan McNamara, Don Cottrell, Juan Campos
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| | Applied Optics 2001
Forward References: 7
http://www.opticsinfobase.org/abstract.cfm?URI=ao-40-32-5943
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- HOW: To encrypt the image, multiply the image with a random noise phase mask, n, in the input plane. Then put another random noise phase mask, b, in the Fourier plane. The output is an encrypted complex image with amplitude and phase. To decrypt the image, put the encoded complex image in the input plane and the random noise phase mask, b, in the F. plane. The output when imaged onto a CCD is the decrypted image since the CCD will capture the squared magnitude of the output beam.
- OPINION: This paper is truly a significant and influential paper in this field. 89 forward references! It has become a standard in the field of optical encryption.
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> | Email from Tom Grycewicz (Jan 17, 2008)
Tom Grycewicz is currently at The Aerospace Corporation in the Sensor Engineering and Exploitation Dept. His work is in optical engineering with quite a bit of work on optical correlators and more generally, optical system modeling and design (image chain analysis), and pattern recognition. I had asked him what he thought were some significant and preferably recent contributions in Fourier optics applied to image processing. This is part of his email response.
Here is the basic problem with image processing: in order to pass data through an optical processing system, the data first needs to be transferred to a spatial light modulator, and this bottleneck is about ten Mpixels per second. Reading the answer requires a camera--another ~ten Mpixel per second bottleneck. A good math coprocessor can handle a Mpixel FFT faster than the data transfer rate to or from the optical system. Add to this all of the advantages a programmable processor has over analog hardware for computing.
Fingerprint recognition was an "almost ran" application. A company in Canada developed and marketed a product which used an optical processor (using an optical binary phase-only Fourier-plane filter) for a commercial system in ~1993. I don't remember the company, the key engineer was Colin Soutar. He published a few SPIE conference papers. But the technology was quickly surpassed by all-digital processing, like the recognition system included in the IBM ThinkPad laptop.
The closest successful application of Fourier optical processing to image analysis I can think of is Fourier transform infrared (FTIR) spectroscopy This process allows a two-dimensional focal plane to capture a three-dimensional hyperspectral data cube. Many instruments of this type have been built, but I don't have references at my fingertips. A good example of the technology is the SPIRE instrument on the ESA Hershel space telescope.
An implementation of wavefront sensing used for Extreme Adaptive Optics (ExAO) uses a pinhole to spatially filter the input wavefront so that high-spatial frequency modes are not sent to the Shack-Hartmann wavefront sensor. The idea first surfaced around 2004. I think the inventor was Lisa Poyneer at Lawrence Livermore National Lab. Of course, this is considered an application of simple optics, not optical processing. Applications of holography to optical memory shows a lot of promise. Readout of a multilayer disk is essentially a holographic process. But of course no good engineer would mention optical disk readout and optical processing in the same breath. Optical processing is the technology of the future....and by unwritten agreement always will be.
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