说明：  nsf5隐写算法，DCT的升级版，MATLAB实现，可以抵抗一般的DCT隐写分析
(The algorithm nsF5 evolved from the F5 algorithm originally proposed by Andreas Westfeld in 2001. F5 decreases the absolute value of DCT coefficients and incorporates matrix embedding - a coding scheme that decreases the number of changes and consequently increases the steganographic security. F5 embeds only into nonzero AC DCT coefficients; if a coefficient becomes zero after embedding (the so called shrinkage), the same bit is reembedded at the next coefficient. Shrinkage substantially decreases the embedding efficiency as the values +1 and -1 are the most frequent nonzero DCT coefficients in natural images.)