DCT交换中频系数嵌入水印\Arnold.m .......................\ArnoldPeriod.m .......................\embed.m .......................\embedded.bmp .......................\extract.m .......................\extracted.bmp .......................\lena.bmp .......................\nc.m .......................\psnr.m .......................\water.bmp DCT交换中频系数嵌入水印