Method and apparatus for watermarking video images

• US 6,229,924 B1
• Filed: 08/21/1998
• Issued: 05/08/2001
• Est. Priority Date: 05/16/1996
• Status: Expired due to Term

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Rodriguez, Anthony, Rhoads, Geoffrey B., Davidson, Clay
• Primary Examiner(s): Couso, Jose L.
• Application Number:
  US09/138,061
• Time in Patent Office: 991 Days
• Field of Search: 382/100, 382/232, 382/280, 382/284, 382/287, 395/135, 380/4, 380/23, 380/25, 380/51, 380/54, 283/6, 283/93, 283/94, 348/475, 235/494, 358/448, 358/450, 358/454, 358/124, 358/142
• US Class Current: 382/232
• CPC Class Codes: G06T 1/0035 Output size adaptive watermarking
• CPC Class Codes: G06T 1/0064 Geometric transfor invariant watermarking, e.g. affine transform invariant
• CPC Class Codes: G06T 2201/0051 Embedding of the watermark in the spatial domain
• CPC Class Codes: G06T 2201/0052 Embedding of the watermark in the frequency domain
• CPC Class Codes: G06T 2201/0053 Embedding of the watermark in the coding stream, possibly without decoding; Embedding of the watermark in the compressed domain
• CPC Class Codes: G06T 2201/0061 Embedding of the watermark in each block of the image, e.g. segmented watermarking
• CPC Class Codes: G06V 30/40 Document-oriented image-based pattern recognition
• CPC Class Codes: G10L 19/018 Audio watermarking, i.e. embedding inaudible data in the audio signal
• CPC Class Codes: G11B 20/00884 involving a watermark, i.e. a barely perceptible transformation of the original data which can nevertheless be recognised by an algorithm
• CPC Class Codes: G11B 2020/10537 Audio or video recording
• CPC Class Codes: H04N 1/00005 relating to image data
• CPC Class Codes: H04N 1/00037 Detecting, i.e. determining the occurrence of a predetermined state H04N1/00031 takes precedence
• CPC Class Codes: H04N 1/00079 remotely
• CPC Class Codes: H04N 1/32122 in a separate device, e.g. in a memory or on a display separate from image data
• 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 1/32187 with selective or adaptive application of the additional information, e.g. in selected frequency coefficients
• CPC Class Codes: H04N 1/32277 Compression
• CPC Class Codes: H04N 1/32352 Controlling detectability or arrangements to facilitate detection or retrieval of the embedded information, e.g. using markers for decoding, detection or retrieval operations H04N1/32149 and subgroups take precedence
• CPC Class Codes: H04N 19/467 characterised by the embedded information being invisible, e.g. watermarking
• CPC Class Codes: H04N 19/48 : using compressed domain processing techniques other than decoding, e.g. modification of transform coefficients, variable length coding [VLC] data or run-length data motion estimation in a transform domain H04N19/547; processing of decoded motion vectors H04N19/513
• CPC Class Codes: H04N 19/60 : using transform coding
• CPC Class Codes: H04N 19/61 : in combination with predictive coding
• CPC Class Codes: H04N 2005/91335 : the copy protection signal being a watermark
• CPC Class Codes: H04N 21/23892 : involving embedding information at multiplex stream level, e.g. embedding a watermark at packet level
• 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 2201/3205 : of identification information, e.g. name or ID code H04N2201/3209 takes precedence
• CPC Class Codes: H04N 2201/3207 : of an address
• 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 5/913 : for scrambling ; for copy protection

Abstract

Embedding a watermark in an image by changing selected DCT coefficients in the blocks and macro blocks of coefficients which represent the image. The changes in the blocks that comprise each macro block are done in a coordinated manner so that the phase of the watermark signal is preserved across the block boundaries. By preserving the phase across block boundaries, a detectable grid is formed which can be used as an orientation and scaling grid. Furthermore, by preserving the phase across block boundaries the visual artifacts introduced by the watermark are minimized. The bit rate of the image signal is preserved by maintaining a count (referred to as the cumulative change count) that represents the amount that the bit rate has been increased by changes in coefficients less the amount that the bit rate has been decreased by changes in the coefficients. If at any time the cumulative change count exceeds a pre-established limit, coefficient changes that decrease the cumulative change count continue; however, coefficient changes that increase the cumulative change count are suspended. The suspension of coefficient changes that increase the cumulative change count continues until the cumulative change count falls below the pre-established limit.

Claims

1. A method for adding a multibit watermark to an image comprising,

generating DCT (Discrete Cosine Transform) coefficients representing said image, said coefficients being arranged in blocks, said blocks being arranged into macro blocks,

each of said macro blocks containing a block one, a block two, a block three and a block four, and the coefficients in each block being arranged in rows and columns, alternate of said rows and columns being designated even and odd rows and columns, adjusting said coefficients as follows:

the coefficient in block one being changed directly in response to the bits of said watermark, the bits in blocks two, three and four being changed in accordance with the following rules;

Block two;

invert the direction of the change if the coefficient is in an odd row,

Block three;

invert the direction of the change if the coefficient is in an odd row column

Block four;

invert the direction of the change if the coefficient is in an odd row or if it is in and odd column, but do no invert the direction of the change if the coefficient is in both and odd row and in an odd column,

whereby the sinusoids generated by said adjustments are in phase across block boundaries in each macro block.

2. A system for adding a multibit watermark to an image comprising,

means for generating DCT (Discreet Cosine Transform) coefficients representing said image, said coefficients being arranged in blocks, said blocks being arranged into macro blocks,

each of said macro blocks contains four blocks, block one, block two, block three and block four, the coefficients in said blocks being arranged in rows and columns, alternate of said rows and columns being designated even and odd rows and columns,

means for adjusting said coefficients in accordance with the bits of said watermark to embed said watermark in said image,

the coefficient in block one being changed directly in response to the bits of said watermark, the bits in blocks two, three and four being changed in accordance with the following rules:

Block two;

invert the direction of the change if the coefficient is in an odd row,

Block three;

invert the direction of the change if the coefficient is in an odd column

Block four;

invert the direction of the change if the coefficient is in an odd row or if it is in and odd column, but do not invert the direction of the change if the coefficient is in both and odd row and in an odd column

whereby the sinusoids generated by said adjustments are in phase across block boundaries in each macro block, and

whereby the same changes which represent said watermark form a grid which can be used to detect the scale and rotation of said watermark.