Digital watermark embedding apparatus, digital watermark detecting apparatus, digital watermark embedding method, digital watermark detecting method and computer program product

Abstract

A digital watermark embedding apparatus for embedding watermark information into a digital content, obtains a predetermined topological invariant corresponding to the watermark information to be embedded into the digital content, and sets the predetermined topological invariant to the digital content by modifying the digital content into which the watermark information is to be embedded.

What is claimed is:  
     
         1 . A digital watermark embedding apparatus for embedding watermark information into a digital content, comprising: 
 a unit configured to obtain a predetermined topological invariant corresponding to the watermark information to be embedded into the digital content; and    a setting unit configured to set the predetermined topological invariant to the digital content by modifying said digital content into which said watermark information is to be embedded.    
     
     
         2 . The digital watermark embedding apparatus according to  claim 1 , wherein 
 said setting unit changes a predetermined part of a bit string corresponding to a spatial or time-basis position of the digital content to a target value determined by the position of the bit string and the predetermined topological invariant or a target value restorable value.    
     
     
         3 . The digital watermark embedding apparatus according to  claim 1 , wherein 
 said setting unit sets a value, allowing a representative value representing a divided region which is obtained by dividing the digital content in a spatial manner or a time-basis manner and obtained from a predetermined part of one or a plurality of bit strings corresponding to a spatial or time-basis position of the divided region to become a target value determined by the spatial or time-basis position of the divided region and the predetermined topological invariant or a target value restorable value, to the predetermined part of the one or the plurality of bit strings.    
     
     
         4 . The digital watermark embedding apparatus according to  claim 3 , wherein 
 the bit string corresponding to the plurality of positions configures a content of one divided region, and the representative value is an average value of values of the predetermined parts of the plurality of bit strings.    
     
     
         5 . The digital watermark embedding apparatus according to  claim 2 , wherein 
 said setting unit generates a mapping to a target topological space defined by the predetermined part of said bit string from a base topological space defined by the spatial or time-basis position, and obtains the target value corresponding to the position based on a function for applying the predetermined topological invariant.    
     
     
         6 . The digital watermark embedding apparatus according to  claim 5 , wherein 
 the function has the predetermined topological invariant as a parameter.    
     
     
         7 . The digital watermark embedding apparatus according to  claim 5 , wherein 
 the setting unit evaluates an influence on the digital content if the predetermined topological invariant is set to the digital content using a plurality of different functions, and utilizes a function evaluated to minimize the influence on the digital content as the function for applying the predetermined topological invariant.    
     
     
         8 . The digital watermark embedding apparatus according to  claim 2 , wherein 
 the target value restorable value is a value obtained by scaling the target value; and    the setting unit selects a scale power for scaling the target value so as to decrease the influence on the digital content for the target value corresponding to the position.    
     
     
         9 . The digital watermark embedding apparatus according to  claim 1 , wherein 
 the digital content into which same watermark information is to be embedded is a content dividable into a plurality sub-contents, and a same topological invariant corresponding to the watermark information is set to the plurality of sub-contents.    
     
     
         10 . The digital watermark embedding apparatus according to  claim 1 , wherein 
 the content into which a same watermark information is to be embedded is a content dividable into a plurality sub-contents, and a value according to a pseudo-random number generated based on the watermark information is set, as the topological invariant, to the plurality of sub-contents.    
     
     
         11 . The digital watermark embedding apparatus according to  claim 1 , wherein 
 the content is image data of a still image or moving image frames; and    the part is a pixel value vector of the image data.    
     
     
         12 . The digital watermark embedding apparatus according to  claim 1 , wherein 
 the content is moving image data; and    the part is a pixel value vector of the moving image data.    
     
     
         13 . The digital watermark embedding apparatus according to  claim 1 , wherein 
 the content is voice data; and    the part is an amplitude value vector of the voice data.    
     
     
         14 . The digital watermark embedding apparatus according to  claim 1 , wherein 
 the predetermined topological invariant is a homotopy invariant.    
     
     
         15 . A digital watermark detecting apparatus for detecting watermark information from a digital content, comprising: 
 a detector configured to detect a predetermined topological invariant set to the digital content based on a content into which the watermark information is embedded; and    an output unit configured to output watermark information corresponding to the detected predetermined topological invariant.    
     
     
         16 . The digital watermark detecting apparatus according to  claim 15 , wherein 
 said detector obtains a representative value representing a divided region obtained by dividing the content in a spatial manner or a time-basis manner based on a value read from a predetermined part of one or a plurality of bit strings corresponding to a spatial or time-basis position of the divided region, and obtains the predetermined topological invariant based on the representative value representing the divided region.    
     
     
         17 . The digital watermark detecting apparatus according to  claim 16 , wherein 
 a plurality of positions are provided, a content of one divided region is constituted by the bit string corresponding to the plurality of positions, and the representative value is an average value of values of the predetermined part of the plurality of bit strings.    
     
     
         18 . The digital watermark detecting apparatus according to  claim 16 , wherein 
 said detector obtains a target value standardizing the representative value of the divided region, and performs a predetermined summing arithmetic operation for the target value and a difference in target values, thereby obtaining the predetermined topological invariant.    
     
     
         19 . The digital watermark detecting apparatus according to  claim 15 , wherein 
 the content into which a same watermark information is to be embedded is a content dividable into a plurality of sub-contents, topological invariants are detected from the plurality of sub-contents, respectively, and the watermark information is obtained based on the obtained topological invariants.    
     
     
         20 . The digital watermark detecting apparatus according to  claim 15 , wherein 
 the content is image data of a still image or moving image frames; and    the part is a pixel value vector of the image data.    
     
     
         21 . The digital watermark detecting apparatus according to  claim 15 , wherein 
 the content is moving image data; and    the part is a pixel value vector of the moving image data.    
     
     
         22 . The digital watermark detecting apparatus according to  claim 15 , wherein 
 the content is voice data; and    the part is an amplitude value vector of the voice data.    
     
     
         23 . The digital watermark detecting apparatus according to  claim 15 , wherein 
 the predetermined topological invariant is a homotopy invariant.    
     
     
         24 . A digital watermark embedding method for embedding watermark information into a digital content, comprising: 
 obtaining a predetermined topological invariant corresponding to the watermark information to be embedded into the digital content; and    setting the predetermined topological invariant to the digital content by modifying said digital content into which said watermark information is to be embedded.    
     
     
         25 . A digital watermark detecting method for detecting watermark information from a digital content, comprising: 
 detecting a predetermined topological invariant set to the digital content based a content into which the watermark information is embedded; and    outputting watermark information corresponding to the detected predetermined topological invariant.    
     
     
         26 . An article of manufacture comprising a computer usable medium having computer readable program code means embodied therein, the computer readable program code means comprising: 
 computer readable program code means for causing a computer to obtain a predetermined topological invariant corresponding to the watermark information to be embedded into the digital content; and    computer readable program code means for causing a computer to set the predetermined topological invariant to the digital content by modifying said digital content into which said watermark information is to be embedded.    
     
     
         27 . An article of manufacture comprising a computer usable medium having computer readable program code means embodied therein, the computer readable program code means comprising: 
 computer readable program code means for causing a computer to detect a predetermined topological invariant set to the digital content based on a content into which the watermark information is embedded; and    computer readable program code means for causing a computer to output watermark information corresponding to the detected predetermined topological invariant.