Method and apparatus for discerning image distortion by reference to encoded marker signals
First Claim
1. A method of image processing that includes encoding the image with additional data that, when represented in the spatial frequency domain, includes a pattern of spot-like orientation markers, said pattern permitting subsequent distortion of the processed image to be characterized, said distortion being scaling or rotation, said encoding being essentially imperceptible to human viewers of the image.
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Abstract
To permit scaling or rotation of an image to be discerned—even if the original image is not available—certain marker signals are steganographically encoded in the image. In one particular implementation, encoding is effected by adding an overlay signal to the image. The overlay signal—when represented in the spatial frequency domain—includes a pattern of spots. If the image is scaled or rotated, this pattern changes in known ways. By examining the change in this pattern, the distortion (i.e., scale/rotation) of the image can be inferred. This technology finds particular application in conjunction with watermarking systems, permitting recovery of watermark data from images that have been scaled or rotated subsequent to watermarking.
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Citations
26 Claims
- 1. A method of image processing that includes encoding the image with additional data that, when represented in the spatial frequency domain, includes a pattern of spot-like orientation markers, said pattern permitting subsequent distortion of the processed image to be characterized, said distortion being scaling or rotation, said encoding being essentially imperceptible to human viewers of the image.
- 8. A method of processing an input image to yield an encoded image, the encoded image being essentially human-indistinguishable from the input image, the method comprising adding an additional signal to said input image, wherein a frame of difference data obtained by subtracting the input image from the encoded image yields a pattern that, when transformed into the spatial frequency domain, includes plural spot features.
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11. A computer having a memory, the memory having both an image processing program and an image stored therein;
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the image having earlier been encoded with additional data that is essentially imperceptible to human viewers of the image and that, when represented in the spatial frequency domain, includes a pattern of spot-like orientation markers;
the image processing program being adapted to discern from said additional data a distortion of said image subsequent to the time of its encoding, said distortion being scaling or rotation.
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12. An image processing method that includes encoding an image to secretly convey plural bits of auxiliary data that is essentially imperceptible to human viewers, characterized in that the auxiliary data can be recovered from an encoded image without reference to an unencoded image, the method comprising:
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during encoding;
modifying data related to the image so as to yield modified image data that exhibits a characteristic pattern in a transform domain; and
during decoding;
finding a pattern in the transform domain that corresponds to said characteristic pattern, and discerning a transformation of said found pattern from said characteristic pattern.- View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20)
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- 21. An image processing method that includes encoding an image to secretly convey plural bits of auxiliary data that is essentially imperceptible to human viewers, characterized in that the auxiliary data can be recovered from an encoded image without reference to an unencoded image, the method including modifying data related to the image so as to yield modified image data that exhibits a characteristic pattern in a transform domain, said characteristic pattern being useful in decoding to discern scaling or rotation of the encoded image.
Specification