Automatic alignment of video frames for image processing
First Claim
1. A method for aligning image frames, comprising steps of:
- selecting a reference image;
selecting a sample image to be aligned to the reference image;
Fourier-transforming the reference image to obtain a Fourier transform of the reference image;
Fourier-transforming the sample image to obtain a Fourier transform of the sample image;
coordinate-transforming an absolute value of the Fourier transform of the reference image to obtain a coordinate-transformed Fourier transform of the reference image;
coordinate-transforming an absolute value of the Fourier transform of the sample image to obtain a coordinate-transformed Fourier transform of the sample image;
obtaining a first phase shift from the coordinate-transformed Fourier transform of the reference image and the coordinate-transformed Fourier transform of the sample image;
inverse-Fourier-transforming the first phase shift to obtain an inverse Fourier transform of the first phase shift;
finding a first transformation factor from the inverse Fourier transform of the first phase shift;
transforming the sample image by the first transformation factor to obtain a first-transformed sample image;
Fourier-transforming the first-transformed sample image to obtain a Fourier transform of the first-transformed sample image;
obtaining a second phase shift of the Fourier transform of the reference image and the Fourier transform of the first-transformed sample image;
inverse-Fourier-transforming the second phase shift to obtain an inverse Fourier transform of the second phase shift;
finding a second transformation factor from the inverse Fourier transform of the second phase shift; and
transforming the first-transformed sample image by the second transformation factor.
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Abstract
The provided is a method that can automatically align image frames in recorded video clips. Individual frames in video may shift and rotate due to shaking or vibration of a video camera. Unaligned frames make some imaging processing techniques difficult or infeasible. One example of image processing techniques is to isolate, recognize, and/or quantitatively analyze vapor plume images captured by an Infrared (IR) camera. Such techniques have a great potential to be used to automatically detect volatile organic compounds (VOC) leaked from process equipment at refineries and chemical plants. This invention is a technique for various subsequent image processing techniques. The invention uses spatially based Fast Fourier Transforms (FFT) to determine amount of shift, rotation, and scaling to align image frames, and uses a digital filtering technique to improve the alignment.
22 Citations
19 Claims
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1. A method for aligning image frames, comprising steps of:
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selecting a reference image; selecting a sample image to be aligned to the reference image; Fourier-transforming the reference image to obtain a Fourier transform of the reference image; Fourier-transforming the sample image to obtain a Fourier transform of the sample image; coordinate-transforming an absolute value of the Fourier transform of the reference image to obtain a coordinate-transformed Fourier transform of the reference image; coordinate-transforming an absolute value of the Fourier transform of the sample image to obtain a coordinate-transformed Fourier transform of the sample image; obtaining a first phase shift from the coordinate-transformed Fourier transform of the reference image and the coordinate-transformed Fourier transform of the sample image; inverse-Fourier-transforming the first phase shift to obtain an inverse Fourier transform of the first phase shift; finding a first transformation factor from the inverse Fourier transform of the first phase shift; transforming the sample image by the first transformation factor to obtain a first-transformed sample image; Fourier-transforming the first-transformed sample image to obtain a Fourier transform of the first-transformed sample image; obtaining a second phase shift of the Fourier transform of the reference image and the Fourier transform of the first-transformed sample image; inverse-Fourier-transforming the second phase shift to obtain an inverse Fourier transform of the second phase shift; finding a second transformation factor from the inverse Fourier transform of the second phase shift; and transforming the first-transformed sample image by the second transformation factor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A non-transitory machine readable storage medium providing instructions that cause the machine to perform operations to align image frames, the operations comprising:
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selecting a reference image that is represented in Cartesian coordinates; selecting a sample image to be aligned to the reference image, the sample image being represented in Cartesian coordinates; Fourier-transforming the reference image to obtain a Fourier transform of the reference image; Fourier-transforming the sample image to obtain a Fourier transform of the sample image; coordinate-transforming an absolute value of the Fourier transform of the reference image from Cartesian coordinates to log-polar coordinates to obtain a coordinate-transformed Fourier transform of the reference image; coordinate-transforming an absolute value of the Fourier transform of the sample image from Cartesian coordinates to log-polar coordinates to obtain a coordinate-transformed Fourier transform of the sample image; obtaining a rotational phase shift from the coordinate-transformed Fourier transform of the reference image and the coordinate-transformed Fourier transform of the sample image; inverse-Fourier-transforming the rotational phase shift to obtain an inverse Fourier transform of the rotational phase shift; finding a rotational shift from the inverse Fourier transform of the rotational phase shift; rotating the sample image by the rotational shift to obtain a rotated sample image; Fourier-transforming the rotated sample image to obtain a Fourier transform of the rotated sample image; obtaining a translational phase shift of the Fourier transform of the reference image and the Fourier transform of the rotated sample image; inverse-Fourier-transforming the translational phase shift to obtain an inverse Fourier transform of the translational phase shift; finding a translational shift from the inverse Fourier transform of the translational phase shift; and translating the rotated sample image by the translational shift. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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Specification