Abstract:
The invention provides an image processing apparatus for embedding visible specified information (electronic watermark information etc.) in an image in a manner not easily removable. For this purpose first embedding means embeds first specified information (publicly open) in the digital image entered by input means. Second embedding means embeds second specified information (disclosed only to specified user of equipment) in the digital image in which the first specified information is embedded.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image processing method for illegal use of a digital image by embedding therein certain information such as electronic watermark information, an image processing apparatus and an image processing system such as a video camera utilizing such image processing method, and a computer readable memory medium storing process steps for executing such image processing method. 
     2. Related Background Art 
     The recording and reproduction of an image has conventionally be achieved by an analog video tape recorder (VTR) utilizing a recording medium on which the image signal is recorded in analog format (hereinafter called analog medium). 
     However, the image recorded on an analog medium is deteriorated in quality as the copying is repeated. 
     It has therefore become common, in recent years, to execute the image recording and reproduction with a VTR of digital type utilizing a recording medium on which the image is recorded in digital format (hereinafter called digital medium). 
     The image recorded on a digital medium has features of being not deteriorated in quality even after repeated copying, being easily handled on a computer and being easily transmitted through a communication line, but may cause illegal use of copyright because the unlawful copying or use can be easily achieved. 
     For preventing such illegal copying or use, there is known a method of embedding electronic watermark information into the image. 
     Such electronic watermark embedding method employs the digital ID information indicating for example the copyright owner of the image, the publication source of the image, the management number of the image, the distribution channel of the image etc. as the electronic watermark information, and mixes such electronic watermark information in the image in such a manner that such information is invisible to the user observing the image and that the source or channel of distribution of the illegally used image can be confirmed afterwards. In such information mixing, it is important that the electronic watermark information alone cannot be extracted from the image in which the electronic watermark information is embedded. 
     In such electronic watermark embedding method, the general user cannot see the content of the electronic watermark information, because such method is so constructed that the user cannot see whether the electronic watermark information is present in the image or the content of the electronic watermark information itself. 
     In certain cases, however, it is unnecessary to conceal all the content of the electronic watermark information and a part of the content may or should be made open to the general user. 
     In such case, the electronic watermark information has been disclosed to the user by embedding the watermark information visible to the user in the image whereby the user is rendered possible to display such information. 
     Such method has however been associated a drawback that such visible electronic watermark information can be removed relatively easily from the image in which such watermark information is embedded. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to solve the above-described drawbacks individually or entirely. 
     Another object of the present invention is to provide an image processing method capable of embedding specified visible information in an image in a not easily removable manner, an image processing apparatus and an image processing system utilizing such image processing method, and a computer readable memory medium storing the process steps for realizing such image processing method. 
     The above-mentioned objects can be attained, according to a first invention, by an image processing method for embedding specified information in a digital image, comprising a first embedding step of embedding first specified information in the digital image, and a second embedding step of embedding second specified information in the digital image in which the first specified information is embedded by the first embedding step. 
     Still another object of the present invention is to obtain respectively different embedding levels for plural embedded information. 
     Still another object of the present invention is to provide a novel information embedding method, an apparatus and a medium therefor. 
    
    
     Still other objects of the present invention, and the features thereof, will become fully apparent from the following description of embodiments, which is to be taken in conjunction with the attached drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the configuration of a video camera constituting a first embodiment of the present invention; 
     FIG. 2 is a block diagram showing the configuration of an image compression circuit of the above-mentioned video camera; 
     FIG. 3 is a block diagram showing the configuration of an apparatus for reproducing the compressed image data recorded on a recording medium by the above-mentioned video camera; 
     FIG. 4 is a view showing an image displayed on a monitor on the above-mentioned reproducing apparatus; 
     FIG. 5 is a block diagram showing the configuration of a video camera constituting a second embodiment of the present invention; 
     FIG. 6 is a block diagram showing the configuration of an image compression circuit in the above-mentioned video camera; and 
     FIG. 7 is a block diagram showing the configuration of an apparatus for reproducing the compressed image data recorded on a recording medium by the above-mentioned video camera. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now the present invention will be clarified in detail by preferred embodiments thereof, with reference to the attached drawings. 
     First Embodiment 
     The present invention is applicable for example to a video camera  100  as illustrated in FIG.  1 . 
     The video camera  100  is provided, as shown in FIG.  1 , with a lens  110  for capturing the light from an object; an image pickup element  120  for converting the light from the object, coming through the lens  110 , into an electrical image signal; a CDS/AGC circuit  130  for executing sampling-holding on the image signal from the image pickup element  120  thereby obtaining an appropriate signal level; a digital signal process circuit  140  for digitizing the image signal from the CDS/AGC circuit  130  and effecting predetermined digital signal process thereon; an image compression circuit  150  for applying a predetermined compression process on the image data from the digital signal process circuit  140 ; and a recording circuit  180  for recording the compressed image data, from the image compression circuit  150 , on a recording medium  190  such as a video tape. 
     The above-described video camera  100  is most featured by a fact that the image compression circuit  150  executes compression of the image data and embedding (superposition) of specified information (called “electronic watermark information”). 
     For this purpose, the video camera  100  is provided, in addition to the foregoing configuration, with two watermark information generating circuit  160 ,  170  for respectively generating electronic watermark information. 
     Therefore, the image compression circuit  150  is provided, as shown in FIG. 2, with a raster block conversion unit  151  receiving image data from the digital signal process circuit  140 , a DCT unit  152  receiving the outputs from the raster block conversion unit  151  and the watermark information generation circuit  160 , a quantization unit  153  receiving the outputs of the DCT (discrete cosine transformation) unit  152  and the watermark information generation circuit  170 , and a variable length encoding unit  154  receiving the output of the quantization unit  153 , wherein the output of the variable length encoding unit  154  is supplied to the recording circuit  180 . 
     In the following there will be explained the embedding process of the electronic watermark information, constituting the largest feature of the video camera  100 . 
     At first, the light from the object, coming through the lens  110 , is converted by the image pickup element  120  into an image signal which is supplied through the CDS/AGC circuit  130  to the digital signal process circuit  140  and is digitized therein. 
     The image data (original image data) obtained by the digitization are compressed in the image compression circuit  150  and recorded on the recording medium by the recording circuit  180 . In this operation, the image compression circuit  150  executes the compression process and the superposing process of the electronic watermark information in the following manner. 
     In the image compression circuit  150 , the raster block conversion unit  151  divides the image data from the digital signal process circuit  140 , namely the image data consisting of luminance data and color difference data, into blocks of a predetermined size. 
     The DCT unit  152  executes DCT (discrete cosine transformation) in the unit of a block, on the image data supplied from the raster block conversion unit  151  and divided into blocks. 
     The watermark information generation circuit  160  generates, for supply to the DCT unit  152 , electronic watermark information which can be made open to the general user (hereinafter called “electronic watermark information  1 ”) and of which extraction method is made open to the public. 
     The DCT unit  152  executes spectrum diffusion of the electronic watermark information  1  from the watermark information generation circuit  160  and superposes such information with the DCT coefficients (frequency components of the original image data) obtained in the above-mentioned DCT process. 
     More specifically, the electronic watermark information is converted with the publicized diffusion codes and is added to the corresponding frequency components among the DCT coefficients. 
     The image data, in which the electronic watermark information  1  is embedded by the above-described embedding method, are supplied to the quantization unit  153 . 
     The quantization unit  153  executes quantization on the image data supplied from the DCT unit  152 . 
     In this state, the electronic watermark information generation circuit  170  generates electronic watermark information that can be disclosed to specified users or equipment only (hereinafter called “electronic watermark information  2 ”) of which the extracting method is disclosed only to the specified users or equipment. The electronic watermark information  2  is for example information embedded in the quantizing coefficients to be used in the quantization process in the quantization unit  153 . 
     Therefore the quantization unit  153  quantizes the image-data from the DCT unit  152  while varying the quantizing coefficients little by little according to the electronic watermark information  2  from the watermark information generation circuit  170 , thereby embedding the electronic watermark information  2  into the image data. 
     The image data, in which the electronic watermark information  2  is embedded by the quantization process with variation of the quantizing coefficients, are subjected to variable length encoding in the variable length encoding unit  154  and are supplied, as compressed image data, to the recording circuit  180 . 
     Consequently the compressed image data, recorded on the recording medium  190  by the recording circuit  180 , contain the electronic watermark information  1  and the electronic watermark information  2  embedded therein. 
     The compressed image data recorded on the above-mentioned recording medium  190  can be reproduced by a reproducing apparatus  200  as shown in FIG.  3 . 
     The reproducing apparatus  200  is provided, as shown in FIG. 3, with an image expansion circuit  210  for expanding the compressed image data recorded on the recording medium  190  thereby restoring the image data prior to compression, an NTSC encoder  220  for generating the signal of a predetermined television format (NTSC format) based on the image data from the image expansion circuit  210 , and a monitor  230  for executing image display according to the NTSC signal from the NTSC encoder  220 . 
     In case the reproducing apparatus  200  is usable by the unspecified general user, the image expansion circuit  210  expands the compressed image data by an inverse DCT process and an inverse quantization and extracts the electronic watermark information  1  embedded in the above-mentioned compressed image data, utilizing the publicized extraction method for the electronic watermark information  1 , namely a method inverse to the aforementioned embedding method utilizing the publicized diffusion codes. 
     The NTSC encoder  220  of the present embodiment generates the NTSC signal by expanding the image data before compression obtained by the image expansion circuit  210  and simply adding the extracted electronic watermark information  1 . 
     The monitor  230  executes image display of the NTSC signal from the NTSC encoder  220 . As an example, if the electronic watermark information  1  is character information “sample”, there is displayed, as shown in FIG. 4, the original image superposed with the information “sample”. 
     As the extraction method for the electronic watermark information  2  is not made public to the general user, the reproducing apparatus  200  usable by the general user can extract the electronic watermark information  1  from the compressed image data recorded on the recording medium, but cannot extract the electronic watermark information  2 . Also it is not possible to delete the electronic watermark information  2 . 
     In case the reproducing apparatus  200  is to be used by the specified user, the image expansion circuit  210  also executes extraction of the electronic watermark information  2 , utilizing the extraction method therefor publicized to the specified users only. Thus the NTSC encoder  220  mixes the image data, the electronic watermark information  1  and the electronic watermark information  2  whereby the monitor  230  displays the original image with the electronic watermark information  1  and the electronic watermark information  2  superposed thereon. 
     In the present embodiment, as explained in the foregoing, the compressed image data are subjected to the superposition of the electronic watermark information  1 , of which extraction method is made public to the general user, and then subjected to the superposition of the electronic watermark information  2  of which extraction method is made open only to the specified user. The electronic watermark information  1  is superposed with the compressed image data by the superposing method publicized to the general user, and the electronic watermark information  2  is superposed with the compressed image data, already superposed with the electronic watermark information  1 , by the superposing method publicized only to the specified user. 
     Such configuration allows the general user to see the content of the electronic watermark information  1  but not the content of the electronic watermark information  2 . Also, the electronic watermark information  1  and  2  has to be removed together in order to completely eliminate the electronic watermark information from the image, so that it is very difficult for the general user to eliminate such electronic watermark information. 
     Second Embodiment 
     The present invention is applicable for example to a video camera  300  shown in FIG.  5 . 
     The video camera  300  is similar in configuration to the above-described video camera  100  shown in FIG. 1, but the superposition of the electronic watermark information  1  and  2  is executed, in the video camera  100 , by the DCT unit  152  and the quantization unit  153  of the image compression circuit  310  while the superposition is executed, in the video camera  300 , by a watermark superposition unit of the image compression circuit  310 . 
     In the video camera  300  shown in FIG. 5, components same as those in the video camera  100  shown in FIG. 1 are represented by same numbers and will not be explained further. 
     More specifically, the image compression circuit  310  is provided, as shown in FIG. 6, with a compression process unit  311  for compressing the image data from the digital signal process circuit  140  to obtain compressed image data, and a watermark superposing unit  312  for superposing the electronic watermark information  1  and  2  in the compressed image data from the compression process unit  311 , whereby the output of the watermark superposing unit  312  is supplied to the recording circuit  180 . 
     The watermark superposing unit  312  is provided with an encryption unit  312   b  for encrypting the electronic watermark information  1  from the watermark information generation circuit  160  utilizing an encryption key  1 , an encryption unit  312   c  for encrypting the electronic watermark information  2  from the watermark information generation circuit  170  utilizing an encryption key  2 , and a superposition unit  312   a  for superposing, with the compressed image data from the compression process unit  311 , the encrypted data obtained in the encrypting units  312   b ,  312   c  and the encryption key  1 . 
     The encryption key  1  is made public to the general users, while the encryption key  2  is made open only to the specified users. 
     At first the compression process unit  311  obtains the compressed image data by executing, on the image data from the digital signal process circuit  140 , the above-described processes such as the raster block conversion, DCT process, quantization and variable length encoding. 
     The obtained compressed image data are supplied to the superposition process unit  312   a.    
     The encrypting unit  312   b  encrypts the electronic watermark information  1  from the watermark information generation circuit  160 , utilizing the encryption key  1 , and the resulting encrypted data  1  are supplied to the superposition process unit  312   a.    
     Also the encrypting unit  312   c  encrypts the electronic watermark information  2  from the watermark information generation circuit  170 , utilizing the encryption key  2 , and the resulting encrypted data  2  are supplied to the superposition process unit  312   a.    
     The superposition process unit  312   a  superposes the encrypted data  1  from the encryption unit  312   b , the encrypted data  2  from the encryption unit  312   c  and the encryption key  1  employed in the encryption unit  312   c  with the compressed image data obtained in the compression process unit  311 , and sends the obtained data to the recording circuit  180 . Such superposition process unit can employ various superposing methods, for example multiplexing or embedding divided codes. 
     Consequently the recording medium  190  records, by the recording circuit  180 , the compressed image data in which the encrypted data  1 , the encrypted data  2  and the encryption key  1  are superposed. 
     The compressed image data thus recorded on the recording medium  190  are reproduced by a reproducing apparatus  400  as shown in FIG.  7 . 
     In the reproducing apparatus  400  shown in FIG. 7, components same as those in the reproducing apparatus  1 .  200  shown in FIG. 3 are represented by same numbers and will not be explained further. 
     In case the reproducing apparatus  400  is usable by the unspecified general users, an image expansion circuit  410  expands the compressed image data, recorded on the recording medium  190 , by inverse DCT process and inverse quantization, and restores the electronic watermark information  1  contained in the compressed image data, utilizing the encryption key  1  contained therewith. 
     The NTSC encoder  220  mixes the image data prior to compression, obtained in the image expansion circuit  210 , and the electronic watermark information  1  restored with the encryption key  1 , thereby generating an NTSC signal. 
     The monitor  230  executes image display of the NTSC signal from the NTSC encoder  220 . Thus the monitor  230  displays the original image on which the electronic watermark information  1  is superposed. 
     Since the encryption key  2  for restoring the electronic watermark information  2  is not disclosed to the general users, the reproducing apparatus  400  usable by the general user can extract the electronic watermark information  1  only from the compressed image data recorded on the recording medium  190  but cannot extract the electronic watermark information  2 . Also it is not possible to delete the electronic watermark information  2 . 
     In case the reproducing apparatus  400  is to be used by the specified users only, the image expansion circuit  410  also restores the electronic watermark information  2 , utilizing the encryption key  2  disclosed to the specified users only. Thus the NTSC encoder  220  mixes the image data with the electronic watermark information  1  and  2 , whereby displayed is the original image superposed with the electronic watermark information  1  and  2 . 
     In the present embodiment, as explained in the foregoing, means for superposing the electronic watermark information  1  and  2  with the compressed image data is constructed as one of the watermark superposing units  312 . Consequently there can be obtained a cost reduction in the apparatus, in addition to the effect of the foregoing first embodiment. 
     In the foregoing embodiments, the compression of the image data is achieved by DCT process, but such method is not restrictive and there may be employed other methods such as wavelet transformation or other orthogonal transformations. 
     Also the apparatus of the foregoing embodiments may be provided with transmission means for transmitting the digital image signal in which specified information is embedded, thereby embedding various information in such transmitted image information. 
     The objects of the present invention can naturally be attained also in a case where a memory medium storing the program codes of a software for realizing the functions of the host equipment and the terminals in the aforementioned embodiments is supplied to a system or an apparatus and a computer (CPU or MPU) in the above-mentioned system or apparatus reads and executes the program codes stored in the memory medium. 
     In such case the program codes themselves read from the memory medium realize the functions of the aforementioned embodiments, and the memory medium storing such program codes constitute the present invention. 
     The memory medium storing such program codes can be, for example, a ROM, a floppy disk, a hard disk, an optical disk, a magnetooptical disk, a CD-ROM, a CD-R, a magnetic tape, a non-volatile memory card. 
     The present invention also includes, not only the case where the functions of the aforementioned embodiments are realized by the execution of the read program codes by the computer, a case where an operating system or the like functioning on the computer executes all the process or a part thereof according to the instructions of the program codes, thereby realizing the functions of the aforementioned embodiments. 
     The present invention further includes a case wherein the program codes read from the memory medium are once stored in a memory provided in a function expansion board inserted in the computer or a function expansion unit connected to the computer, and a CPU or the like provided in the function expansion board or the function expansion unit executes all the process or a part thereof according to the instructions of such program codes, thereby realizing the functions of the aforementioned embodiments. 
     As explained in the foregoing, the embodiments are so constructed as to embed first specified information in the digital image in not easily visible manner and to further embed second specified information. 
     It thus becomes very difficult to eliminate the specified information from the digital image, since not only the first specified information but also the second specified information have to be eliminated in order to completely remove the specified information (such as electronic watermark information) from the digital image. 
     It is thus rendered possible to realize embedding of the specified information of an increased strength. It is also possible to publicize only a part of the specified information attached to the digital image. 
     More specifically, the original digital image is subjected to an orthogonal transformation such as DCT process, and the transformation coefficients (frequency components) thus obtained are subjected to the embedding (superposition) of the first electronic watermark information (first specified information) by spectrum diffusion. Such embedding may be achieved by a publicly known method. In the quantization, after the orthogonal transformation, of the digital image in which the first electronic watermark information is thus embedded, the quantization coefficient employed in such quantization process is varied little by little according to the second electronic watermark information (second specified information) thereby embedding such second electronic watermark information. This embedding method is assumed to be disclosed only to the specified users or equipment. 
     Therefore, as the general users or equipment can only publicly know the embedding method of the first electronic watermark information, or the extraction method thereof, such general users or equipment can only extract the first electronic watermark information and can only see the content thereof. On the other hand, as the specified users or equipment can know the extraction method of the first and second electronic watermark information, such specified users or equipment can extract both electronic watermark information and can see the contents thereof. 
     There may also be adopted a configuration adapted, after the compression of the digital image, to embed first specified information (encrypted data) encrypted with a publicly open key (first encryption key) and second specified information (encrypted data) encrypted with a key made open only to the specified users or equipment (second encryption key) into the compressed digital image. 
     In such configuration, since the first encryption key alone is made public to the general users or equipment, such general user can only restore the first specified information and see the content thereof. On the other hand, since the first and second encryption keys are both made known to the specified users or equipment, such specified users can extract both the first and second specified information and see the contents thereof. Also this configuration can reduce the cost of the apparatus or the system, as there is required only one means for embedding the specified information. 
     The present invention is subject to various modifications within the scope and spirit of the appended claims. In particular, the information embedding method and the encrypting method are not limited to those described in the foregoing embodiments but can be replaced by various methods such as methods suitable for data compression.