Digital-watermark embedding method and device and storage medium for storing the method

Abstract

An object of the present invention is to efficiently embed digital-watermark information in a document image by adjusting robustness and quality of the image. In order to achieve the object, watermark information and image information are input, a first parameter determining embedding strength and a second parameter determining image quality are set, and the digital-watermark information is embedded in the image based on the first and second parameters. When the entire information cannot be embedded, the first or second parameter is adjusted so as to embed a larger amount of digital-watermark information in the image.

What is claimed is:  
     
         1 . A digital-watermark embedding method comprising: 
 a generating step of generating digital-watermark information;    an input step of inputting an image;    a setting step of setting a first parameter determining robustness to attack on the digital-watermark information embedded in the image and a second parameter determining quality of the image in which the digital-watermark information is embedded;    an embedding step of embedding the digital-watermark information in the input image by using the first and second parameters;    a determination step of determining whether or not the entire digital-watermark information can be embedded in the image;    an update step of updating one of the parameters so as to embed a larger amount of digital-watermark information in the image when it is determined that the entire digital-watermark information cannot be embedded in the determination step, the update step being performed as a first stage; and    an embedding step of embedding the digital-watermark information in the input image again by using the updated parameter,    wherein the determination step is performed for each of the embedding steps.    
     
     
         2 . A method according to  claim 1 , further comprising: 
 an update step of updating the second parameter so as to degrade the image quality when it is determined that the entire digital-watermark information cannot be embedded in the determination step, the update step being performed as a first stage; and    an embedding step of embedding the digital-watermark information in the input image again by using the first parameter and the updated second parameter.    
     
     
         3 . A method according to  claim 2 , further comprising: 
 an update step of updating the first parameter so as to degrade the robustness when it is determined that the entire digital-watermark information cannot be embedded in the determination step and when the degradation of the image quality reaches a first threshold value, the update step being performed as a second stage; and    an embedding step of embedding the digital-watermark information in the input image again by using the updated first parameter and the second parameter.    
     
     
         4 . A method according to  claim 3 , further comprising: 
 an update step of updating the second parameter so as to degrade the image quality when it is determined that the entire digital-watermark information cannot be embedded in the determination step, when the degradation of the image quality reaches the first threshold value, and when the degradation of the robustness reaches a first threshold value, the update step being performed as a third stage; and    an embedding step of embedding the digital-watermark information in the input image again by using the first parameter and the updated second parameter.    
     
     
         5 . A method according to  claim 1 , further comprising: 
 an update step of updating the first parameter so as to degrade the robustness when it is determined that the entire digital-watermark information cannot be embedded in the determination step, the update step being performed as a first stage; and    an embedding step of embedding the digital-watermark information in the input image again by using the updated first parameter and the second parameter.    
     
     
         6 . A method according to  claim 5 , further comprising: 
 an update step of updating the second parameter so as to degrade the image quality when it is determined that the entire digital-watermark information cannot be embedded in the determination step and when the degradation of the robustness reaches a first threshold value, the update step being performed as a second stage; and    an embedding step of embedding the digital-watermark information in the input image again by using the first parameter and the updated second parameter.    
     
     
         7 . A method according to  claim 6 , further comprising: 
 an update step of updating the first parameter so as to degrade the robustness when it is determined that the entire digital-watermark information cannot be embedded in the determination step, when the degradation of the robustness reaches the first threshold value, and when the degradation of the image quality reaches a first threshold value, the update step being performed as a third stage; and    an embedding step of embedding the digital-watermark information in the input image again by using the updated first parameter and the second parameter.    
     
     
         8 . A method according to  claim 1 , wherein a plurality of letters are included in the image, and, in the embedding step, the digital-watermark information is embedded in the image by rotating the letters so as to change the inclination angle of the letters.  
     
     
         9 . A method according to  claim 8 , wherein the second parameter specifies the range of rotation angle of the letters.  
     
     
         10 . A method according to  claim 8 , wherein the first parameter specifies the repetition number of embedding the digital-watermark information in the image.  
     
     
         11 . A method according to  claim 8 , wherein the digital-watermark information is encoded with an error-correction code, and the first parameter specifies the error-correction ability of the encoded digital-watermark information.  
     
     
         12 . A method according to  claim 1 , wherein a plurality of letters are included in the image, and, in the embedding step, the digital-watermark information is embedded in the image by changing the positions of the letters so as to adjust spaces between the letters.  
     
     
         13 . A method according to  claim 12 , wherein the second parameter specifies the range of movement of the letters.  
     
     
         14 . A method according to  claim 12 , wherein the first parameter specifies the repetition number of embedding the digital-watermark information in the image.  
     
     
         15 . A method according to  claim 12 , wherein the digital-watermark information is encoded with an error-correction code, and the first parameter specifies the error-correction ability of the encoded digital-watermark information.  
     
     
         16 . A method according to  claim 1 , wherein the both parameters are updated so as to embed a larger amount of digital-watermark information in the image when it is determined that the entire digital-watermark information cannot be embedded in the determination step, the update step being performed as a first stage.  
     
     
         17 . A digital-watermark embedding device comprising: 
 a generator for generating digital-watermark information;    an input unit for inputting an image;    a setting unit for setting a first parameter determining robustness to attack on the digital-watermark information embedded in the image and a second parameter determining quality of the image in which the digital-watermark information is embedded;    an embedding unit for embedding the digital-watermark information in the input image by using the first and second parameters;    a determination unit for determining whether or not the entire digital-watermark information can be embedded in the image; and    an update unit for updating one of the parameters so as to embed a larger amount of digital-watermark information in the image when the determination unit determines that the entire digital-watermark information cannot be embedded, the update being performed as a first stage,    wherein the embedding unit embeds the digital-watermark information in the input image again by using the updated parameter, and    the determination unit performs determination every time embedding is performed.    
     
     
         18 . A storage medium storing a digital-watermark embedding program, the program comprising: 
 a generating step of generating digital-watermark information;    an input step of inputting an image;    a setting step of setting a first parameter determining robustness to attack on the digital-watermark information embedded in the image and a second parameter determining quality of the image in which the digital-watermark information is embedded;    an embedding step of embedding the digital-watermark information in the input image by using the first and second parameters;    a determination step of determining whether or not the entire digital-watermark information can be embedded in the image;    an update step of updating one of the parameters so as to embed a larger amount of digital-watermark information in the image when it is determined that the entire digital-watermark information cannot be embedded in the determination step, the update step being performed as a first stage; and    an embedding step of embedding the digital-watermark information in the input image again by using the updated parameter,    wherein the determination step is performed for each of the embedding steps.