Optical ranked-order filtering using threshold decomposition
First Claim
1. A method for performing two-dimensional ranked-order filtering of an image comprising the steps of:
- electronically screening the image;
generating binary threshold images of the electronically screened image;
writing the generated binary threshold images on a first spatial light modulator;
projecting the generated binary threshold images from the first light modulator;
filtering by ranked-order the projected binary threshold images to form multiplexed threshold images;
imaging a composite image of the filtered multiplexed threshold images;
electronically screening the composite image with a constant threshold;
writing the screened composite image onto a second spatial light modulator;
projecting the screened composite image from the second spatial light modulator;
filtering by superposition the projected composite image; and
imaging the superposition filtered composite image.
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Abstract
A hybrid optical/electronic system performs median filtering and related ranked-order operations using threshold decomposition to encode the image. Threshold decomposition transforms the nonlinear neighborhood ranking operation into a linear space-invariant filtering step followed by a point-to-point threshold comparison step. Spatial multiplexing allows parallel processing of all the threshold components as well as recombination by a second linear, space-invariant filtering step. An incoherent optical correlation system performs the linear filtering, using a magneto-optic spatial light modulator as the input device and a computer-generated hologram in the filter plane. Thresholding is done electronically. By adjusting the value of the threshold, the same architecture is used to perform median, minimum, and maximum filtering of images. A totally optical system is also disclosed.
56 Citations
12 Claims
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1. A method for performing two-dimensional ranked-order filtering of an image comprising the steps of:
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electronically screening the image; generating binary threshold images of the electronically screened image; writing the generated binary threshold images on a first spatial light modulator; projecting the generated binary threshold images from the first light modulator; filtering by ranked-order the projected binary threshold images to form multiplexed threshold images; imaging a composite image of the filtered multiplexed threshold images; electronically screening the composite image with a constant threshold; writing the screened composite image onto a second spatial light modulator; projecting the screened composite image from the second spatial light modulator; filtering by superposition the projected composite image; and imaging the superposition filtered composite image. - View Dependent Claims (2, 3, 4, 5)
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6. An apparatus for performing two-dimensional ranked-order filtering of an image comprising:
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a screening means for electronically screening the image and for generating binary threshold images thereof; a first spatial light modulator and a second spatial light modulator; a writing means for writing the binary threshold images on said light modulator; a projecting means for projecting the generated binary threshold images from said first light modulator; a filtering means for ranked-order filtering of the projected binary threshold images to form multiplexed threshold images; an imaging means for imaging a composite image of the multiplexed threshold images; a screening means for electronically screening the composite image with a constant threshold; a writing means for writing the screened composite image onto said second spatial light modulator; a projecting means for projecting the screened composite image from said second light modulator; a filtering means for filtering by superposition the projected composite image; and an imaging means for imaging the superposition filtered composite image. - View Dependent Claims (7, 8, 9, 10, 11)
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12. An optical system for performing ranked-order filtering of an image comprising:
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a first optical thresholding means for generating binary threshold components of the image at a first Fourier plane; a ranked order filtering means located at the Fourier plane for ranked-order optical filtering of the binary threshold components; a second optical thresholding means for generating filtered binary threshold components at a second Fourier plane; a superposition filtering means located at the second Fourier plane for superposition optical filtering of the filtered binary threshold components; and an optical binary means for selecting predetermined ranked-order filter values of the superposition filtered binary threshold components.
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Specification