Error resilient digital video scrambling
View Patent ↗A method and an apparatus for error resilient, digital image scrambling are disclosed. Error resilience scrambling is produced by shuffling transform coefficients between arrays of coefficients arranged along an axis substantially orthogonal to the axis along which packetization of the coefficients proceeds. Scrambling transform coefficients requires a reasonable level of processing resources and has minimal impact on the efficiency of the compression process. Shuffling can be performed in a number of ways to provide good access security and a variety of security. Scrambling the image data in a direction substantially orthogonal to the direction of packetization of the transform coefficients distributes any transmission error in the image reducing the effects of data error or loss on the displayed image.
1. A method of scrambling a sequence of digital images comprising the steps of:
(a) selecting at least one said image for coding as a discrete image;
(b) transforming respective values of said pixels of said discrete image to a plurality of arrays of transform coefficients;
(c) selecting a plurality of said arrays arranged with respect to each other along a first axis of said image;
(d) transposing selective one or more coefficients of a first of said selected arrays with selective one or more coefficients of a second of said selected arrays, wherein every step by which a coefficient is transposed, transposes said coefficient in at least a direction along the direction of said first axis, and being identified by a cryptographic key; and
(e) packetizing said coefficients of said plurality of arrays along a second axis orthogonal to said first axis.
2. The method of claim 1 wherein said coefficient of said second selected array occupies a same position in said second selected array as said replaced coefficient occupies in said first selected array.
3. The method of claim 1 wherein a luminance representation of said pixels is transformed to said array of transform coefficients.
4. The method of claim 1 wherein a chrominance representation of said pixels is transformed to said array of transform coefficients.
5. The method of claim 1 further comprising the step of altering a value of coefficient of said second of said selected arrays.
6. The method of claim 1 wherein said selected plurality of arrays arranged along a first axis of said image includes a first and a second pluralities of said arrays, said first and said second pluralities aligned with said first axis but displaced from each other along said second axis.
7. The method of claim 1 further comprising the steps of:
(a) selecting at least one image for prediction from said discrete image;
(b) determining a difference between said predicted image and said discrete image;
(c) transforming pixels of said difference to a plurality of arrays of transform coefficients;
(d) selecting a plurality said arrays arranged along a first axis of said image;
(e) replacing a coefficient of a first of said selected arrays with a coefficient of a second of said selected arrays, said coefficients of said first and said second arrays being identified by a cryptographic key; and
(f) packetizing said coefficients of said plurality of arrays along a second axis orthogonal to said first axis.