Digital watermarking: Spreading code versus channel coding

The effect of error correcting codes (ECC) on an oblivious CDMA based watermarking scheme is studied in this paper. Obviously, ECC is employed to increase the robustness of watermarking algorithms, but in order to accomodate the additional bits of the ECC, the strength of watermark signal has to be reduced to keep the PSNR value constant. Therefore, introducing ECC and decreasing the strength of the watermark signal contradict each other concerning robustness. In this paper it is studied whether it is feasible to apply computationally complex ECC at the cost of watermark strength for CDMA based watermarking schemes. Furthermore, a new technique called "by parts interleaving" is introduced in this paper. Spreaded watermark bits are in parts interleaved in different regions of the image to make the algorithm robust against cropping.