Progressive watermark decoding on a distributed computing platform

• US 6,724,914 B2
• Filed: 10/16/2001
• Issued: 04/20/2004
• Est. Priority Date: 10/16/2001
• Status: Expired due to Term

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Brundage, Trent J., Hannigan, Brett T.
• Primary Examiner(s): Patel, Jayanti K.
• Assistant Examiner(s): CARTER, AARON W
• Application Number:
  US09/978,332
• Publication Number:
  US 20030072467A1
• Time in Patent Office: 917 Days
• Field of Search: 382/100, 382/232, 380/51, 380/54, 713/176
• US Class Current: 382/100
• CPC Class Codes: G06T 1/005 Robust watermarking, e.g. average attack or collusion attack resistant
• CPC Class Codes: G06T 2201/0065 Extraction of an embedded watermark; Reliable detection

Abstract

The disclosure describes a method of progressively decoding a digital watermark on a distributed computing platform. A client device equipped with a digital camera, such as a PDA or cell phone, captures a digital image of a watermarked object, and pre-filters the image to isolate a portion of the image data suspected of containing a digital watermark. The pre-filter de-correlates a portion of the image data suspected of containing a digital watermark from the remaining host image signal using a predictive filter. The client then quantizes the filtered data and progressively transmits the quantized data to a watermark decoder. The progressive transmitter sends image data as necessary to achieve a valid decoding operation. To reduce bandwidth requirements, the transmitter starts with the most highly quantized version of the filtered image, and sends lesser quantized versions until the watermark decoder completes a successful decoding operation.

Claims

1. A method of decoding a digital watermark comprising:

receiving an image frame captured of a watermarked object;

pre-filtering the image frame to derive an estimate of a digital watermark signal;

quantizing the estimate of the digital watermark signal into two or more levels of detail; and

progressively sending the quantized estimate to a watermark decoding process for extraction of a digital watermark message, starting with the lowest level of detail.

2. A computer readable medium on which is stored instruction for performing the method of claim 1.

3. The method of claim 1 wherein the pre-filtering includes band pass filtering the image frame to isolate image content having a higher watermark signal to host image signal ratio.

4. The method of claim 1 wherein the pre-filtering includes de-correlating a digital watermark signal from a host image signal to compute the estimate of the digital watermark signal.

5. The method of claim 4 wherein the de-correlating includes performing a predictive filtering to estimate the digital watermark signal.

6. The method of claim 1 wherein the quantizing comprises reducing bit depth of the estimate of the digital watermark signal.

7. The method of claim 1 wherein the estimate of the digital watermark is represented as an estimate of positive and negative adjustments to a host image that has been embedded with the digital watermark;

and the positive and negative adjustments are quantized by reducing the bit depth used to represent the amount of the adjustments.

8. The method of claim 1 including:

receiving feedback about results of a watermark decoding operation on the quantized data, and response to the feedback, controlling the progressive transmission of additional watermarked data to the watermark decoding process.

9. A method of progressive digital watermark decoding comprising:

in a client, receiving a watermarked media signal;

quantizing the watermark media signal into two or more levels of detail;

progressively sending the quantized media signal to a watermark decoding server, starting with sending quantized data represented with a first set of quantization levels, and progressively sending more detailed versions of the quantized media signal represented with increasingly more quantization levels than the first set to reduce the bandwidth needed between the client and server to decode a digital watermark message successfully from the media signal on the server.

10. The method of claim 9 including:

isolating an estimate of a digital watermark signal in the watermarked media signal, wherein the quantizing comprises quantizing the isolated estimate of the digital watermark signal.

11. A computer readable medium on which is stored instruction for performing the method of claim 9.

12. The method of claim 9 wherein the client and server comprise remote devices interconnected via a communication link.

13. A method of efficient digital watermark decoding comprising:

receiving a watermarked media signal;

performing a lossy compression of the watermarked media signal that discards part of the media signal information, yet leaves a residual media signal from which the digital watermark is decoded;

progressively sending the residual media signal at successively higher levels of detail to a watermark decoder for extracting the digital watermark until the digital watermark is successfully extracted from the residual media signal.

14. A watermark decoding server method comprising:

receiving a pre-filtered image block and a watermark decoding request from a client, where pre-filtering on the client has reduced an image to an estimate of a digital watermark signal; and

performing watermark detection on the pre-filtered block, including reporting a detection result to the client to regulate requests for decoding additional blocks from the client.

16. The method of claim 14 including:

receiving a plurality of pre-filtered image blocks and watermark decoding requests from different clients;

and managing watermark decoding operations for each of the pre-filtered image blocks.

15. A watermark decoding server method comprising:

receiving a pre-filtered image block and a watermark decoding request from a client, where pre-filtering on the client has reduced an image to an estimate of a digital watermark signal;

receiving quantized versions of the prefiltered block, starting with lower level of detail, and increasing with each; and

performing watermark detection on the pre-filtered block, including reporting a detection result to the client to regulate requests for decoding additional blocks from the client.

17. A method of efficient digital watermark decoding from a watermarked media signal that has been created by embedding a digital watermark into a host media signal, the method comprising:

receiving the watermarked media signal;

performing a lossy compression of the watermarked media signal that discards part of the media signal information, yet leaves a residual media signal from which the digital watermark is decoded, wherein the lossy compression is performed at a receiver to isolate a portion of the watermarked media signal likely to have a higher watermark signal to host media signal ratio;

sending the isolated portion from the receiver to a watermark decoder;

extracting a digital watermark message from the residual media signal at the watermark decoder.