Blind Digital Watermarking Technique Based on Fresnel Hologram and Discrete Cosine Transform
Liu Jian-lanb · ACTA PHOTONICA SINICA · 2007
The blind digital watermarking algorithm with positive real values is proposed based on optical Fresnel hologram,phase encryption mask (PEM) and DCT (Discrete-Cosine-Transform).The PEM is the sum of the phase angles of the E-fields which are the Fresnel diffraction transform of serial point lights with the different coordinates.The Fresnel hologram of original watermark image is obtained by a reference light through the PEM,and watermarking information are embedded into DCT of original host image.Meanwhile the original pixel value,which has been embedded watermark information,is replaced by the average value of its adjacent pixels,and the watermarked target image is regained after inverse DCT.The original watermark image can also be retrieved from the target image after the above inverse processing.Numerical experiments show that the algorithm is robust to the attacks of the JPEG lossy compressing,cropping,superposing noise and resampling from the screen copy.Because the watermark can be retrieved from the target image without the original host image,the watermark can be embedded in the host image flexibly,and the multi-keys (light wavelength,diffraction distance,a serial point light positions) can be designed in the large degrees of freedom,the algorithm has high security and practical value.