Robustness is one of the important requirements of digital watermarking.To improve robustness
CDMA (Code Division Multiple Access) technologies have been introduced into digital watermarking.However
most existing CDMA-based watermarking parameters are usually determined via experience.With the side-information embedding scheme
we have analyzed the relationship between PSNR
embedding strength
orthogonal codes length
and number of users
in the case of CDMA additive embedding.The expression for estimating the embedding strength is derived in terms of PSNR.Experimental results show the estimating is effective.Furthermore
while keeping the PSNR constant
the relationship between spread code length and watermark bit error rate is analyzed.As a conclusion
when keeping the length of watermark bits and PSNR constant
the choice of orthogonal spreading code does not influence watermark bit error rate.The conclusion can be used to guide the actual watermarking system to choose the correct embedding parameters.