In this paper a digital invisible image watermarking technique is proposed based on the numerical simulation of\udoptical Double Random Phase Encoding (DRPE). This technique utilizes the capability of the DRPE to spread\udthe energy of the input information in both the space and the spatial frequency domains using two diffusers. The\udwatermark is in the form of a digital barcode image which is numerically encrypted using a simulation of the\udoptical DRPE process. This produces a random complex image, which is then processed to form a real valued\udrandom image with a low number of quantization levels. This signal is added to the host image. Extraction of\udthe barcode, involves applying an inverse DRPE process to the watermarked image followed by a low pass filter.\udThe results presented indicate the feasibility and robustness of the proposed method and it is demonstrated that\udeven when using very few quantization levels, i.e. 2-levels, the watermark can still be extracted with very small\uderrors.
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