Watermark information embedding device, watermark information processing system, watermark information embedding method, and program

A watermark information processing system, comprising:

• a watermark information embedding device and a watermark information extraction device, wherein
• the watermark information embedding device comprises:
• a color component separator for separating an original image of a two-dimensional code into color components;
• a first wavelet transformer for performing, for each of the color components separated by the color component separator, a wavelet transform on the original image of the two-dimensional code to decompose this image into various frequency components;
• a watermark information embedder for embedding watermark information, as a high-frequency component in an oblique direction, in a high-frequency component in the oblique direction of the each of the color components out of the various frequency components decomposed by the first wavelet transformer with an embedding strength weighted in accordance with a usage frequency of the each of the color components in the original image of the two-dimensional code;
• an inverse wavelet transformer recomposing the two-dimensional code containing watermark information by performing an inverse wavelet transform on frequency components other than the high-frequency component in the oblique direction, out of the various frequency components decomposed by the first wavelet transformer, and the high-frequency component in the oblique direction in which the watermark information is embedded by the watermark information embedder;
• and
• a color component integrator for integrating the two-dimensional code containing watermark information for the each of the color components recomposed by the inverse wavelet transformer, and
• the watermark information extraction device comprises:
• a two-dimensional code capturer for capturing an input image of the two-dimensional code containing watermark information recomposed by the inverse wavelet transformer;
• a second wavelet transformer for performing a wavelet transform on the input image of the two-dimensional code containing watermark information captured by the two-dimensional code capturer and producing high-frequency components;
• and
• a watermark information extractor for extracting watermark information from a high-frequency component in an oblique direction out of the high-frequency components produced by the second wavelet transformer.

A watermark information embedding method, comprising:

• a color component separation step for separating an original image of a two-dimensional code into color components;
• a first wavelet transform step for performing, for each of the color components separated by the color component separation step, a wavelet transform on the original image of the two-dimensional code to decompose this image into various frequency components;
• a watermark information embedding step for embedding watermark information, as a high-frequency component in an oblique direction, in a high-frequency component in the oblique direction of the each of the color components out of the various frequency components decomposed by the first wavelet transform step with an embedding strength weighted in accordance with a usage frequency of the each of the color components in the original image of the two-dimensional code;
• an inverse wavelet transform step for recomposing the two-dimensional code containing watermark information by performing an inverse wavelet transform on frequency components other than the high-frequency component in the oblique direction, out of the various frequency components decomposed by the first wavelet transform step, and the high-frequency component in the oblique direction in which the watermark information is embedded by the watermark information embedding step;
• and
• a color component integration step for integrating the two-dimensional code containing watermark information for the each of the color components recomposed by the inverse wavelet transform step.

A non-transitory computer-readable recording medium storing a program for causing a computer to execute a procedure comprising:

• a color component separation procedure for separating an original image of a two-dimensional code into color components;
• a first wavelet transform procedure for performing, for each of the color components separated by the color component separation procedure, a wavelet transform on the original image of the two-dimensional code to decompose this image into various frequency components;
• a watermark information embedding procedure for embedding watermark information, as a high-frequency component in an oblique direction, in a high-frequency component in the oblique direction of the each of the color components out of the various frequency components decomposed by the first wavelet transform procedure with an embedding strength weighted in accordance with a usage frequency of the each of the color components in the original image of the two-dimensional code;
• an inverse wavelet transform procedure for recomposing the two-dimensional code containing watermark information by performing an inverse wavelet transform on frequency components other than the high-frequency component in the oblique direction, out of the various frequency components decomposed by the first wavelet transform procedure, and the high-frequency component in the oblique direction in which the watermark information is embedded by the watermark information embedding procedure;
• and
• a color component integration procedure for integrating the two-dimensional code containing watermark information for the each of the color components recomposed by the inverse wavelet transform procedure.