Watermark Placement in Watermarking of Time Varying Media Signals

Abstract

A method of placing a watermark in a video stream estimates motion between frames in the video stream, and computes a representative motion for a frame. Before embedding the watermark in that frame, the method spatially adjusts a digital watermark by the representative motion. This method is particularly suited for embedding a watermark in a video stream compressed using motion estimation. In this case, the method uses the motion vectors in the video stream to compute a dominant motion for a frame, and then shifts the watermark by this dominant motion before embedding it in the frame.

1 . A system for placing a watermark in a video stream comprising:
 memory;   a programmed computer in communication with the memory, the programmed computer for estimating motion between frames in the video stream, for computing a representative motion for at least part of a frame to be embedded with a digital watermark, and for spatially adjusting the digital watermark by the representative motion, wherein the representative motion is derived from motion in the video over time, and the representative motion used to spatially adjust digital watermark is dependent on watermark energy.   
     
     
         2 . The system of  claim 1  wherein the motion is derived from motion data in a compressed video stream. 
     
     
         3 . The system of  claim 2  wherein the motion data comprises motion vectors. 
     
     
         4 . The system of  claim 1  wherein spatially adjusting the digital watermark comprises shifting the digital watermark in a direction specified by the representative motion. 
     
     
         5 . The system of  claim 1  wherein the representative motion comprises a dominant motion in the frame. 
     
     
         6 . The system of  claim 1  wherein the representative motion is derived from statistics of motion data from a plurality of locations in the frame. 
     
     
         7 . The system of  claim 1  wherein the spatially adjusted watermark is embedded into the video such that the watermark is robust to the spatial adjustment. 
     
     
         8 . The system of  claim 1  wherein the memory comprises a computer readable medium having instructions executed by the programmable computer. 
     
     
         9 . A method of placing a watermark in a compressed data stream comprised of frames of time varying data, where the data stream includes frames compressed using motion estimation, the method comprising:
 using a programmed computer to perform the acts of:   computing a representative motion for a frame based on motion data in the compressed data stream; and spatially adjusting a digital watermark to be embedded in the frame by the representative motion of the frame; wherein the representative motion is derived from motion in a frame, and the motion used to derive the representative motion is weighted based on the watermark energy.   
     
     
         10 . The method of  claim 9  wherein the motion data comprises motion vectors. 
     
     
         11 . The method of  claim 9  wherein spatially adjusting comprises shifting the digital watermark. 
     
     
         12 . The method of  claim 9  wherein the representative motion comprises a dominant motion derived from motion vector statistics. 
     
     
         13 . The method of  claim 9  wherein the spatially adjusted watermark is embedded into video frames so that the watermark is robust to spatial adjustment and is detectable in frames of the video despite spatial adjustment of the video. 
     
     
         14 . The method of  claim 9  wherein the representative motion is derived from motion of blocks in a frame, and the motion of the blocks used to derive the representative motion is weighted based on the watermark energy to be carried in the blocks such that blocks carrying more watermark signal are weighted more heavily. 
     
     
         15 . A computer readable storage medium on which is stored instructions, which when executed by a computer, perform the method of  claim 9 . 
     
     
         16 . A device for placing a watermark in a compressed video data stream comprised of frames of time varying data, where the data stream includes frames compressed using motion estimation, the device comprising:
 memory;   a programmable computer in communication with the memory, the programmable computer for extracting motion vectors for a frame in the compressed video data stream, for computing a representative motion for at least one part of the frame based on the motion vectors in the compressed data stream, and for spatially adjusting a digital watermark by the representative motion before embedding the adjusted watermark in the part of the frame; wherein the motion vectors are weighted according to an amount of watermark energy to be embedded in blocks of the video frame corresponding to the motion vectors.   
     
     
         17 . The device of  claim 16  wherein the representative motion is derived from a statistical distribution of motion vectors for the frame. 
     
     
         18 . The device of  claim 17  where a single, dominant motion is computed for the part of the frame where the spatially adjusted watermark is to be embedded. 
     
     
         19 . The device of  claim 16  wherein the motion vectors are weighted according to an amount of watermark energy to be embedded in blocks of the video frame corresponding to the motion vectors.