System for generating thermographic images using thermographic signal reconstruction
AssigneeThermal Wave Imagining, Inc.
InventorSteven M. Shepard
Life of this patent
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Abstract
A method and system for non-destructive, reference-free thermographic detection of sub-surface defects uses an infrared camera to capture multiple, spatially different images of a sample that has been heated and allow to cool to equilibrium temperature. The temperature-time data obtained for each pixel in each image is converted into the logarithmic domain and a least squares fit is conducted on the data to generate a polynomial expression corresponding to the temperature-time data for a given pixel. This polynomial expression can be transformed into the original time domain to obtain temperature-time data with improved signal-to-noise characteristics.
Claims47
A system for determining a time response to a monotonically changing characteristic of a sample, comprising:
- a camera that obtains at least two spatially different images of the sample over time, each image having a plurality of pixels, each pixel having an amplitude corresponding to the monotonically changing characteristic of the sample;
- a controller coupled to the camera for moving the camera spatially to obtain said at least two spatially different images of the sample;
- and
- a processor that receives the plurality of images and generates a data array for each of the spatially different images, the data array corresponding to a logarithm of the pixel amplitude at a given time and a logarithm of the given time,
- wherein the processor fits a polynomial representing a reconstructed function to at least a portion of the data array, the polynomial having at least one polynomial coefficient, such that each pixel in said spatially different images is represented by a coefficient array containing said at least one polynomial coefficient, and
- wherein the processor generates from coefficient arrays at least two reconstructed images corresponding to said at least two spatially different images and forms an image mosaic from the reconstructed images.
A system for determining a time response to a temperature change in a sample, comprising:
- means for changing the temperature of the sample;
- a camera that obtains a plurality of spatially different images of the sample over time, each image having a plurality of pixels each having an amplitude corresponding to the temperature of the sample;
- a controller coupled to the camera for moving the camera spatially to obtain said plurality of spatially different images of the sample, and
- a processor that receives the plurality of images and generates a data array for each of said plurality of pixels, the data array corresponding to a logarithm of the pixel amplitude at a given time and a logarithm of the given time, wherein the processor fits a polynomial representing a reconstructed function to at least a portion of the data array, the polynomial being in the logarithmic domain and having at least two polynomial coefficients, such that each pixel in said plurality of pixels is represented by a coefficient array containing said at least two polynomial coefficients, and wherein the processor calculates at least one of an instantaneous first derivative and an instantaneous second derivative of each reconstructed function for a given time value, and
- and wherein the processor generates from the coefficient arrays at least two reconstructed images corresponding to said at least two spatially different images and forms an image mosaic from the reconstructed images.
The system of 18, wherein the processor determines whether the first derivative of the reconstructed function for each pixel over time deviates from −0.5 by a predetermined threshold.
A method for determining a time response to a monotonic change in a characteristic of a sample, comprising the acts of:
- obtaining a plurality of spatially different images of the sample over time, each spatially different image having a plurality of pixels each having an amplitude corresponding to the monotonically changing characteristic of the sample;
- generating a data array for each of the plurality of pixels, the data array corresponding to the logarithm of the pixel amplitude at a given time and the logarithm of the given time;
- fitting a polynomial representing a reconstructed function to the data array associated with at least a portion of the plurality of pixels, the polynomial having at least two polynomial coefficients, such that each pixel in said portion of plurality of pixels is represented by a coefficient array containing said at least two polynomial coefficients;
- generating a plurality of reconstructed images corresponding to the plurality of spatially different images;
- and
- forming an image mosaic from the reconstructed images.
Dependencies are inferred from the claim text.