Robust digital watermarking

• US 6,154,571 A
• Filed: 07/17/1998
• Issued: 11/28/2000
• Est. Priority Date: 06/24/1998
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation, NEC Research Institute, Inc. (NEC Corporation)
• Inventors: Oami, Ryoma, Miller, Matthew L., Cox, Ingemar J.
• Primary Examiner(s): Tadayon, Bijan
• Assistant Examiner(s): NAKHJAVAN, SHERVIN K
• Application Number:
  US09/118,467
• Time in Patent Office: 865 Days
• Field of Search: 382/100, 382/232, 382/250, 382/276, 382/251, 382/252, 382/244
• US Class Current: 382/250
• CPC Class Codes: G06T 1/0028 Adaptive watermarking, e.g. Human Visual System [HVS]-based watermarking
• CPC Class Codes: G06T 1/0064 Geometric transfor invariant watermarking, e.g. affine transform invariant
• CPC Class Codes: G06T 2201/0052 Embedding of the watermark in the frequency domain
• CPC Class Codes: H04N 1/32154 Transform domain methods H04N1/32309 takes precedence
• CPC Class Codes: H04N 1/32165 using cosine transforms
• CPC Class Codes: H04N 1/32192 according to calculated or estimated visibility of the additional information in the image
• CPC Class Codes: H04N 1/32277 Compression
• CPC Class Codes: H04N 1/32304 Embedding different sets of additional information
• CPC Class Codes: H04N 19/467 characterised by the embedded information being invisible, e.g. watermarking
• CPC Class Codes: H04N 21/8358 involving watermark protecting executable software by watermarking G06F21/16; image watermarking in general G06T1/0021; watermarks inserted in still images for transmission purposes H04N1/32144; inserting watermarks during video coding H04N19/467
• CPC Class Codes: H04N 2201/3233 of authentication information, e.g. digital signature, watermark
• CPC Class Codes: H04N 2201/327 which are undetectable to the naked eye, e.g. embedded codes
• CPC Class Codes: H04N 7/24 Systems for the transmission of television signals using pulse code modulation H04N21/00 takes precedence

Abstract

A watermarking procedure that is applicable to images, audio, video and multimedia data to be watermarked divides the data to be watermarked into a set of n×n blocks, such as the 8×8 blocks of MPEG. The same watermark signal can be distributed throughout the set of blocks in a large variety of ways. This allows the insertion algorithm to be changed without affecting the decoders. The decoding procedure first sums together the DCT coefficients of N sets of 8×8 blocks to form a set of N summed 8×8 blocks and then extracts the watermark from the summed block. Since the sum of the DCT blocks is equal to the DCT of the sum of the intensity blocks, efficient decoding can occur in both the spatial and frequency domains. The symmetric nature of the decoding process allows geometric distortions to be handled in the spatial domain and other signal distortions to be handled in the frequency domain. Moreover, insertion of a watermark signal into image data and the subsequent extraction of the watermark from watermarked image data which has been subject to distortion between the times of insertion and extraction involves the insertion of multiple watermarks designed to survive predefined distortions of the image data, such as panscan or letterbox mode transformations. Alternatively, a registration pattern in the image data, after the image data containing the registration pattern is subject to an unknown distortion, is used to compensate for distortion of the watermarked image data.

Claims

1. A method of inserting a watermark signal into video images comprising the steps of:

receiving input video images;

performing discrete cosine transformation (DCT) of said input video images to obtain DCT values of said input video images;

adding watermark signals to said DCT values to obtain DCT values with watermark;

performing an inverse DCT on the DCT values with watermark for generating watermarked images;

subtracting predicted images from said watermarked images for generating residual images;

obtaining the DCT values of residual images and quantizing the DCT values of the residual images;

inverse quantizing the quantized DCT values of the residual images;

performing discrete cosine transformation of the predicted images;

summing the inverse quantized DCT values of the residual images and the DCT of the predicted images for generating DCT coefficients for decoded images;

calculating correction signals from the DCT coefficients of the decoded images and adding the correction signals to the quantized DCT values of the residual images for obtaining an output signal;

inverse quantizing the output signal, inverse DCT the inverse quantized output signal and summing the resultant signal with the predicted images for generating a summed signal;

storing the summed signal in memory for generating the predicted images; and

variable length encoding the output signal for providing a watermarked MPEG video signal of the input video images.

2. A method of inserting a watermark signal into video images as set forth in claim 1, where said calculating step generates a negative value as said correction signal when the extracted value exceeds the corresponding target value, and generates a positive value as said correction signal when the extracted value falls short of the corresponding target value.

3. A method of inserting a watermark signal into video images as set forth in claim 2, where said positive value is +1 and said negative value is -1.

4. A method of inserting a watermark signal into video images as set forth in claim 2, where said calculating step generates a zero value as the correction signal if the corresponding quantized DCT values of residual images are zero.

5. A method of inserting a watermark signal into video images as set forth in claim 4, where said positive value is +1 and said negative value is -1.

6. A method of inserting a watermark signal into video images comprising the steps of:

receiving input video images;

performing discrete cosine transformation (DCT) of said input video images to obtain DCT values of said input video images;

adding watermark signals to said DCT values to obtain DCT values with watermark;

performing discrete cosine transformation on predicted images to obtain DCT values of predicted images;

subtracting DCT values of the predicted images from the DCT values with watermark to obtain DCT values of residual images;

quantizing the difference values to obtain quantized DCT values of residual images;

inverse quantizing the quantized DCT values at residual images and summing the inverse quantized DCT values of residual images with the DCT values of predicted images, for generating DCT coefficients for decoded images,

calculating correction signals from the DCT coefficients for decoded images;

summing the correction signals with the quantized DCT values of residual images to obtain an output signal;

inverse quantizing the output signal and inverse DCT the inverse quantized output signal and summing the resultant signal with predicted images to provide locally-decoded images;

storing the locally-decoded images in memory for generating the predicted images; and

valuable length encoding the output signal to provide a watermarked MPEG video signal of the input video images.

7. A method of inserting a watermark signal into video images as set forth in claim 6, where said calculating step generates a negative value as said correction signal when the extracted value exceeds the corresponding target value, and generates a positive value as said correction signal when the extracted value falls short of the corresponding target value.

8. A method of inserting a watermark signal into video images set forth in claim 7, where said positive value is +1 and said negative value is -1.

9. A method of inserting a watermark signal into video images as set forth in claim 7, where said calculating step generates a zero value as the correction signal if the corresponding quantized DCT values of residual images are zero.

10. A method of inserting a watermark signal into video images as set forth in claim 9, where said positive value is +1 and said negative value is -1.