Optical correlator
First Claim
Patent Images
1. A method of optical correlation between an input image and a reference image, including the steps of:
- Optically performing a joint transform correlation between an input image and a reference image;
displaying the two images side by side as a binary phase image;
modulating the resulting binary phase image with a phase-encoded checkerboard pattern;
displaying the modulated image on a spatial light modulator;
illuminating by a constant light source the spatial light modulator; and
performing a joint transform correlation on the displayed image, the correlation including binarising an intermediate image by thresholding each pixel using values of its surrounding pixels.
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Abstract
A method is described of optically performing a joint transform correlation starting from images displayed side-by-side on a spatial light modulator illuminated by a collimated light source. The image is focused by a lens onto a camera, the image is recorded by a frame grabber, and processed by a computer. By using a two pass process, the result is a measure of the correlation of the images. The images may be preprocessed in a phase-encoded chequerboard pattern and binarised by thresholding based on the average value of neighbouring pixels.
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Citations
18 Claims
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1. A method of optical correlation between an input image and a reference image, including the steps of:
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Optically performing a joint transform correlation between an input image and a reference image;
displaying the two images side by side as a binary phase image;
modulating the resulting binary phase image with a phase-encoded checkerboard pattern;
displaying the modulated image on a spatial light modulator;
illuminating by a constant light source the spatial light modulator; and
performing a joint transform correlation on the displayed image, the correlation including binarising an intermediate image by thresholding each pixel using values of its surrounding pixels. - View Dependent Claims (2, 3, 4, 5)
obtaining the joint power spectrum (JPS) corresponding to the Fourier transform of the input and reference images, and then obtaining a correlation image containing information about the correlation between input and reference images by taking the Fourier transform of the JPS.
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3. A method according to claim 1, wherein the step of performing a joint transform correlation comprises:
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shining collimated light onto the spatial light modulator;
forming an intermediate image of the modulated image on the spatial light modulator through a lens;
recording and processing the intermediate image;
displaying the result on a spatial light modulator;
shining collimated light onto the latter spatial light modulator; and
recording a resulting correlation image of the spatial light modulator through a lens.
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4. A method according to claim 1, further comprising the steps of:
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forming the intermediate image of the displayed modulated image and recording it with a camera;
processing the intermediate image;
displaying the processed intermediate image on the same spatial light modulator; and
recording the correlation image with the camera to give an indication of the correlation between the input and reference images.
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5. A method according to claim 4, further including a step of binarising the intermediate image by thresholding each pixel on the basis of the average value of the surrounding pixels.
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6. A method of optical correlation for obtaining a correlation image corresponding to the correlation between an input and a reference image by displaying the input and reference images on a spatial light modulator, and performing a joint transform correlation, including the steps of:
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shining collimated light onto the spatial light modulator;
forming an intermediate image of the spatial light modulator through a lens;
recording the intermediate image electronically as a plurality of pixels;
binarising the intermediate image by thresholding each pixel using a value of the surrounding pixels;
displaying the binarised intermediate image on a spatial light modulator; and
shining collimated light onto the spatial light modulator, to obtain the correlation image being the image through a lens of the intermediate image on the latter spatial light modulator. - View Dependent Claims (7)
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8. A joint transform correlator comprising:
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an electrically addressed spatial light modulator (SLM) for modulating collimated input light by an input image and a reference image;
a lens;
a camera for capturing modulated light after it has passed through the lens and for producing a signal corresponding thereto; and
a control means for recording the captured image from the modulator and for addressing the spatial light modulator;
wherein the correlator is adapted to operate in a two-pass process to produce a correlation image from the input image and the reference image;
characterized in that the control means is adapted to phase-encode the input image and the reference image using a checkerboard pattern before displaying them on the spatial light modulator. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15)
recording images of the individual products passing the video camera;
displaying pairs of recorded images as input and reference images on a correlator according to claim 8; and
outputting the correlation between the pair of the recorded images as a measure of disturbances in the products.
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16. A joint transform correlator comprising:
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an electrically addressed spatial light modulator (SLM) for modulating collimated input light by an input image and a reference image;
a lens;
a camera for capturing modulated light after it has passed through the lens and for producing a signal corresponding thereto; and
a control means for recording the captured image from the modulator and for addressing the spatial light modulator;
wherein the correlator is adapted to operate in a two-pass process to produce a correlation image from the input image and the reference image;
characterised in that the control means is further adapted to binarise the intermediate image by thresholding each pixel on the basis of the mean value of the eight surrounding pixels.
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17. A joint transform correlator comprising:
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an electrically addressed, binarising, ferroelectric liquid crystal modulator with a plurality of pixels each of which can switch between two states outputting light in antiphase with respect to each other for modulating collimated input light by an input image and a reference image;
a lens;
a camera for capturing modulated light after it has passed through the lens and for producing a signal corresponding thereto; and
a control means for recording the captured image from the modulator and for addressing the ferroelectric liquid-crystal spatial light modulator;
wherein the correlator is adapted to operate in a two-pass process to produce a correlation image from the input image and the reference image;
characterized in that the control means is adapted to phase-encode the input image and the reference image using a checkerboard pattern before displaying them on the spatial light modulator.
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18. A joint transform correlator comprising:
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an electrically addressed spatial light modulator (SLM) for modulating collimated input light by an input image and a reference image;
a lens;
a camera for capturing modulated light after it has passed through the lens and for producing a signal corresponding thereto; and
a control means for recording the captured image from the modulator and for addressing the ferroelectric liquid-crystal spatial light modulator, the control means being adapted to take the recorded image, to process it and to display the processed image on the spatial light modulator in a second pass, and in turn to output the correlation image;
wherein the correlator is adapted to operate in a two-pass process to produce a correlation image from the input image and the reference image;
characterized in that the control means is adapted to phase-encode the input image and the reference image using a checkerboard pattern before displaying them on the spatial light modulator.
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Specification