Limits of Error Correction Coding in Video Watermarking

摘要

The paper discusses the limits of error correction coding for spread spectrum-based video watermarking. The error correction code has as input the watermark data bits and as output the values which will be scaled and used to modify the video pixels (transform coefficients). The data rate of the watermark can increase only at the expense of increasing code rate. Theoretically, the scheme is seen as a communication channel with Gaussian additive noise interference. Shannon's (ideal) spherical codes are used as the error correcting code to calculate the minimum signal to noise ratio (SNR) necessary for a coding scheme with a given block length to achieve a given error probability. This limit is different from Shannon's asymptotic limit, which is valid for infinite block lengths and zero error probability. In practice, in order to verify the Gaussian channel assumption, the error correction code is a concatenation of codes, of which the innermost is a repetition code. Several practical codes of different length and rates, such as turbo codes and BCH codes are investigated and their performance compared to that of the ideal code of the same size. The compromise block length/code rate is investigated for several marking schemes and attacks.