Method and apparatus for embedding a watermark into a digital image or image sequence

• US 6,037,984 A
• Filed: 12/24/1997
• Issued: 03/14/2000
• Est. Priority Date: 12/24/1997
• Status: Expired due to Term

• Current Assignee: Hanger Solutions, LLC (IP Investments Group LLC)
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: Musgrave, Clyde, Isnardi, Michael Anthony
• Primary Examiner(s): Harvey, David E.
• Application Number:
  US08/997,965
• Time in Patent Office: 811 Days
• Field of Search: 348/403, 348/408, 348/473, 380/5, 380/10, 380/23, 380/49, 380/54
• US Class Current: 375/240.21
• CPC Class Codes: G06T 1/0035 Output size adaptive watermarking
• 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: H04N 19/00 Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/132 Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/18 the unit being a set of transform coefficients
• CPC Class Codes: H04N 19/467 characterised by the embedded information being invisible, e.g. watermarking
• CPC Class Codes: H04N 19/59 involving spatial sub-sampling or interpolation, e.g. alteration of picture size or resolution
• 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 5/913 for scrambling ; for copy protection

Abstract

A method and apparatus for watermarking an image or sequence of images without limiting the watermark signal. The watermarking apparatus includes a conventional DCT unit and quantizer for generating an array of quantized DCT coefficients. The array is watermarked by masking the array to select certain ones of the DCT coefficients that are then replaced by zero values to form a masked array. The masked array is further processed by a watermark inserter that replaces the zero valued coefficients with predefined watermark coefficients to form a watermarked array of DCT coefficients, e.g., a watermarked image. A decoder for decoding the bitstream thusly generated and for removing the embedded watermark is also taught.

Claims

1. An image encoder for inserting a watermark into an image containing a plurality of pixels, where the pixels are encoded using discrete cosine transform (DCT) coefficients, comprising:

a watermark mask for masking an array of DCT coefficients representing said image and setting select ones of said DCT coefficients in said array to a zero value; and

a watermark inserter, coupled to said watermark mask, for inserting watermark values into locations in said DCT coefficient array where said DCT coefficients were masked and set to a zero value.

2. The apparatus of claim 1 further comprising a watermark generator for producing said watermark coefficients as quantized DCT coefficients of a predefined character string.

3. The apparatus of claim 1 further comprising a watermark generator for producing said watermark values are pseudo-randomly generated.

4. A DCT based image encoder for inserting a watermark into an image containing a plurality of pixels, where the pixels are encoded using discrete cosine transform (DCT) coefficients, comprising:

a watermark mask for selecting certain ones of said DCT coefficients representing said image and changing the value of the selected DCT coefficients to zero to form a masked array of DCT coefficients;

an image decoder, coupled to said watermark mask, for generating a predicted image from said masked array of DCT coefficients;

a watermark inserter, coupled to said watermark mask, for replacing the selected DCT coefficients with watermark values to produce a watermarked array of DCT coefficients;

an output processor, coupled to said watermark inserter, for losslessly coding said watermarked array of DCT coefficients to form a bitstream.

5. The apparatus of claim 4 further comprising a watermark generator for producing said watermark coefficients as quantized DCT coefficients of a predefined character string.

6. The apparatus of claim 4 further comprising a watermark generator for producing said watermark values are pseudo-randomly generated.

7. The apparatus of claim 6 wherein said watermark generator is coupled to said output processor and supplies said output processor with certain information useful in decoding said watermark values, where the output processor inserts the certain information into said bitstream.

8. The apparatus of claim 7 wherein said certain information is a seed for decoding said pseudo-randomly generated watermark values.

9. A method of inserting a watermark into an image containing a plurality of pixels, where the pixels are encoded using discrete cosine transform (DCT) coefficients, comprising the steps of:

masking an array of DCT coefficients representing said image and setting select ones of said DCT coefficients in said array to a zero value; and

inserting watermark values into locations in said DCT coefficient array where said DCT coefficients were masked and set to a zero value.

10. A method of extracting a watermark from a bitstream comprising the steps of:

extracting, from the bitstream, DCT coefficients that contain watermark values;

comparing the watermark values to reference watermark values;

producing an authentication signal if the watermark values match the reference watermark values;

if said authentication signal is produced, setting said watermark values in said DCT coefficients of said bitstream to zero to remove the watermark from the DCT coefficients in the bitstream, whereby an image is decoded without the appearance of a watermark.

11. The method of claim 10 further comprising the step of recalling said reference watermark values from memory.

12. The method of claim 10 further comprising the step of:

decoding information within said bitstream to produce said reference watermark values.

13. The method of claim 12 wherein said information is a seed for a pseudorandom code that forms the basis for the reference watermark values.