Image processing methods using reversible watermarking
The ability to remove a watermark from an encoded image opens the possibility of various novel applications. Several such applications are detailed. One employs a reversible watermark in conjunction with a second (robust) watermark. In this arrangement, the payload of the reversible watermark conveys information about the robust watermark (e.g., encoding parameters, or an error signal), permitting removal of the robust watermark from an uncorrupted encoded image. By such arrangements, the encoded image can be fully restored to its pristine, unencoded state even if several different watermarks have been applied.
1. A method comprising:
encoding a content object with a first, robust digital watermark, the first watermark conveying a first payload of one or more digital symbols, the first watermark being decodable notwithstanding at least certain corruptions of the encoded object;
encoding the content object with a second digital watermark, the second watermark conveying a second payload of one or more digital symbols, the second watermark being encoded using a process that is reversible given an uncorrupted encoded content object and the second payload;
wherein the second payload conveys data enabling substantial removal of the robust digital watermark from an uncorrupted version of the encoded content object.
2. The method of claim 1 wherein the second payload conveys data enabling complete removal of the first digital watermark from an uncorrupted version of the encoded content object.
3. The method of claim 2 wherein the second payload conveys an error signal characterizing how the encoded first digital watermark varies from an estimated value thereof.
4. The method of claim 2 wherein the second payload conveys encoding data related to the first digital watermark.
5. A method comprising:
receiving a content object encoded with first and second digital watermarks, the first and second watermarks conveying first and second payloads, respectively;
decoding the first watermark to obtain the first payload, the first payload including first data;
decoding the second watermark to obtain the second payload;
processing the content object to remove the first watermark therefrom, yielding an intermediately-processed content object;
through use of the first data, processing the intermediately-processed content object to remove the second watermark therefrom, yielding a processed content object;
wherein said processed content object corresponds to the received content object without any watermarks.
6. The method of claim 5 wherein the second watermark is robust to certain object corruptions.
7. The method of claim 5 that includes:
generating an intermediate watermark by reference to the decoded second payload;
scaling the intermediate watermark by reference to an encoding mask characterized by encoding mask parameters included in the first data, yielding a reconstruction of the second watermark; and
removing said scaled watermark from the intermediately-processed content object.
8. The method of claim 7 that includes subtracting the scaled intermediate watermark from the intermediately-processed content object to yield the processed content object.
9. The method of claim 5 that includes:
generating an intermediate watermark by reference to the decoded second payload;
processing the intermediate watermark in accordance with error signal data included in the first data; and
compensating the intermediately-processed content object in accordance with said processed intermediate watermark to effect removal of the second watermark from the content object.
10. The method of claim 5 wherein one of said first or second payloads includes a first hash corresponding to the content object prior to watermarking, and the method includes:
generating a second hash from the processed content object; and
comparing the first and second hashes to confirm accurate restoration of the content object to an original form.
11. The method of claim 5 wherein the content object comprises samples, and the first watermark provides an average payload capacity of more than 1 bit per sample.
12. The method of claim 5 wherein the content object comprises samples of N-bits each, and the first watermark provides an average payload capacity of more than N/8 bits per sample.
13. The method of claim 5 wherein the content object comprises samples, and the first watermark provides an average payload capacity of more than 2 bits per sample.
14. The method of claim 5 wherein the content object comprises samples of N-bits each, and the first watermark provides an average payload capacity of more than N/4 bits per sample.
15. A method of processing a content object encoded with frail and robust digital watermarks, each watermark conveying a data payload, the robust watermark being adapted to survive at least certain object corruptions, the method comprising:
removing the robust watermark from the content object to provide an intermediate object; and
decoding, from the intermediate object, the payload conveyed by the frail watermark.
16. The method of claim 15 that further comprises removing the frail watermark from the intermediate object, thereby yielding a content object without any watermarking artifact.