Method and apparatus for superimposing additional information with image signal

#The present invention pertains to superimposing additional information, such as copy control information, onto image information in an inconspicuous manner.

#With the widespread use of digitally stored material in recent years, such as on Internet databases and portable storage media as digital video discs (DVDs), copyright infringement of such material has become problematic. One method that has been commonly used to mitigate this problem is to store copy control information as additional information along with the digital content on the storage medium. The copy control information typically consists of a code containing two or more bits indicating a copy generation number of the storage medium and/or whether copying of the storage medium contents is permitted. In any event, it is desirable to prevent a potential pirate from knowing and/or altering the additional information.

#As a method for superimposing additional information with digitally stored image information, a digital watermark process has attracted attention from the point of view of difficulty of falsification of the additional information. See, for example, the February 24 issue of “Nikkei Electronics” magazine, 1997, No. 683, which describes contemporary digital watermark techniques and their advantages.

#The above and further objects, aspects and novel features of the invention will become more apparent from the following detailed description when read in connection with the accompanying drawings.

#The following detailed description, given by way of example and not intended to limit the present invention solely thereto, will best be appreciated in conjunction with the accompanying drawings, in which like reference numerals denote like elements and parts, wherein:

#FIG. 1 is a block/flow diagram of an apparatus/method for superimposing additional information with an image signal according to an embodiment of the present invention;

#Illustrative embodiments of the present invention will be now be described with reference to the accompanying drawings. Briefly, the embodiments employ a digital watermark process to obscure an additional information signal such as a copy prevention control signal. The additional information signal, e.g., a code of a few bits, is spread out in time by converting the few bits to a large number of bits using a spreading technique. The spread additional information is to be superimposed with an image signal. To render the thus spread additional information inconspicuous on a display, a masking/dithering technique is implemented in which different masking patterns are applied to respective pixel blocks on a random basis. In addition, high frequency noise is added to further diminish the perceptible effects of the spread additional information on the image.

#In the below-described embodiment, a pseudo-random noise (PN) code is generated at a sufficiently early cycle and is multiplied by an additional information signal such as a two bit copy prevention control signal. This produces a spread or “distributed” additional information signal in which the additional information is contained within a code of many bits superimposed throughout the image signal. The spread additional information signal is a very low level signal that does not exert much influence on the image signal. High frequency noise is preferably added to the spread signal to further diminish the visual effect of the additional information signal when added to the image signal. The image signal is in a baseband state (analog or digital) when the noise-added, spread additional information signal is superimposed with it.

#Thus, with the method disclosed herein, since a spread additional information signal of about the same frequency range of an image signal is superimposed within the same time period as the image signal, it is difficult for a person attempting illegal copying to remove the spread additional information signal from the image signal. On the other hand, by using a proper decoding system employing the same PN code used for the spreading technique, it is possible to detect and utilize the superimposed additional information signal by performing inverse spreading on the composite signal.