目的 为提高隐写方案的安全性，提出一种基于DCT（discrete cosine transform）块标准差的JPEG图像自适应隐写算法。方法 DCT块标准差可以反映图像各区域的复杂情况，为此根据取整失真、量化步长以及标准差设计了失真函数，然后结合STC（syndrome-trellis code）编码设计了隐写算法。结果 引入DCT块标准差可使失真函数定义更合理，因此图像经隐写后总体失真减小，安全性能得到提高。结论 实验结果表明，本文算法与其他同类算法相比具有更强的抵抗隐写检测能力，在质量因子为75时安全容量可达到0.35（嵌入总量和非零AC（交流）DCT系数个数之比）。

Objective In order to improve the security of a steganography system,an adaptive steganographic algorithm for JPEG images based on the block standard deviation of the DCT(discrete cosine transform)coefficients is proposed. Method Block standard deviation of the DCT coefficients can reflect the complexity of image regions. Therefore, a distortion function is designed according to rounding distortion,quantization step,and standard deviation. Then,the STC(Syndrome-Trellis Code)is combined with the distortion function to propose the steganographic algorithm. Result Distortion function can be more rational when block standard deviation of DCT coefficients is used in design. In this way, the total distortion of the image is reduced after embedding and the security is improved. Conclusion Experiments show that the proposed algorithm possesses a better undetectability. The security embedding rate can be about 0.35 when the quality factor is 75.