| 摘要 |
PROBLEM TO BE SOLVED: To provide a processing method for hidden information having high concealability by adding a signal indicating the hidden information in the stage when the first processing of a plurality of fractional transform processing ends and the last processing is not yet completed. SOLUTION: An input section 2 inputs the signal of a real domain indicating an image which is original information to an FRFT section 4 which executes two-dimensional FRFT of the input signal with a degree (a). A signal indicating a watermark information from a watermark input section 8 is added to this output signal by an addition section 6. The added output signal is subjected to two-dimensional FRFT with a degree (b) by an FRFT section 10 and is outputted through an output section 12. The watermark information is hidden in mid-way of Fourier transform and, therefore, the disclosure thereof by ordinary Fourier transform or inverse Fourier transform does not occur and the concealability is high. Even if a third person attempts to view the watermark information by FRFT or iFRFT, the level of the signal indicating the watermark information is adequately selected, by which the watermark information may be invisible with a slight difference in the degree of iFRFT.
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