Digital watermark embedding apparatus, digital watermark embedding method, and digital watermark detection apparatus

A digital watermark embedding method comprising:

• acquiring video data and digital watermark information;
• for each symbol contained in the digital watermark information, setting a time segment including a plurality of images contained in the video data;
• causing the area of a watermark pattern formed by a plurality of pixels having a prescribed value, and superimposed on each image contained in the video data, to vary the area of the watermark pattern in periodic fashion over time in the time segment according to the value of the symbol contained in the digital watermark information;
• and
• embedding the digital watermark information into the video data by correcting, using the prescribed value, the value of each pixel contained in a region where each image in the video data and the watermark pattern corresponding to the each image overlap each other.

A non-transitory computer readable recording medium having a digital watermark embedding computer program recorded thereon for causing a computer to execute the process of embedding digital watermark information into video data, and wherein the program causes the computer to carry out:

• for each symbol contained in the digital watermark information, setting a time segment including a plurality of images contained in the video data;
• causing the area of a watermark pattern formed by a plurality of pixels having a prescribed value, and superimposed on each image contained in the video data, to vary the area of the watermark pattern in periodic fashion over time in the time segment according to the value of the symbol contained in the digital watermark information;
• and
• embedding the digital watermark information into the video data by correcting, using the prescribed value, the value of each pixel contained in a region where each image in the video data and the watermark pattern corresponding to the each image overlap each other.

A digital watermark detection apparatus comprising:

• an interface circuit which acquires video data in which digital watermark information is embedded;
• and
• a processor which detects the digital watermark information embedded in the video data, wherein
• the processor is adapted to calculate, for each image contained in the video data, an average pixel value for the entire image or for a reference region that contains a watermark pattern whose area varies in periodic fashion over time with a phase or period that matches the value of a symbol contained in the digital watermark information,
• calculate a spectrum depicting how the average pixel value varies over time, by frequency-transforming a set including the average pixel value for each image contained in a time segment corresponding to one the symbol and arranged in time series order, and
• obtain the value of the symbol by extracting from the spectrum a frequency component corresponding to the periodic variation of the area of the watermark pattern and by calculating from the frequency component the phase or period of the periodic variation of the area of the watermark pattern.

A digital watermark detection method comprising:

• acquiring video data in which digital watermark information is embedded;
• for each image contained in the video data, calculating an average pixel value for the entire image or for a reference region that contains a watermark pattern whose area varies in periodic fashion over time with a phase or period that matches the value of a symbol contained in the digital watermark information;
• calculating a spectrum depicting how the average pixel value varies over time, by frequency-transforming a set including the average pixel value for each image contained in a time segment corresponding to one the symbol and arranged in time series order;
• and
• obtaining the value of the symbol by extracting from the spectrum a frequency component corresponding to the periodic variation of the area of the watermark pattern and by calculating from the frequency component the phase or period of the periodic variation of the area of the watermark pattern, and thereby detecting the digital watermark information embedded in the video data.

A non-transitory computer readable recording medium having a digital watermark detection computer program recorded thereon for causing a computer to execute the process of detecting digital watermark information embedded in video data, wherein the program causes the computer to carry out:

• for each image contained in the video data, calculating an average pixel value for the entire image or for a reference region that contains a watermark pattern whose area varies in periodic fashion over time with a phase or period that matches the value of a symbol contained in the digital watermark information;
• calculating a spectrum depicting how the average pixel value varies over time, by frequency-transforming a set including the average pixel value for each image contained in a time segment corresponding to one the symbol and arranged in time series order;
• and
• obtaining the value of the symbol by extracting from the spectrum a frequency component corresponding to the periodic variation of the area of the watermark pattern and by calculating from the frequency component the phase or period of the periodic variation of the area of the watermark pattern, and thereby detecting the digital watermark information embedded in the video data.