Study On Digital Watermarking-based Channel Quality Assessment Technique For JPEG Image Transmission

With the rapid development of the computer and the multimedia, more researchers put their efforts into the study of digital watermarking, thus the digital watermarking get great development, and its application becomes more and more widely at the same time, it no longer be confined to the original use——copyright protection. This technology more and more widely affects our daily life.Considering the JPEG standard is designed for the low bit error rate channels, it is difficult to transmit under the high ones. Based on the analysis of the influence of the restart markers defined in the JPEG standard to the quality of decoded images, the restart capability of JPEG images is enabled in this paper, the eight unique restart markers are inserted into the JPEG compressed image bitstream, which can solve the problem of error decoding and synchronization distortion, through the experiment we demonstrate its effectiveness.Based on the published pappers, which using digital watermarking to assessment the qulity of communication channels are as videos for cover, and considering the generalization of image communications, a novel method is proposed in this papper to assess the quality of channel based digital watermarking which the JPEG image communication. Based on the block discrete cosine transform used in JPEG format, a watermarking algorithm is designed, the watermark is embedded into each block by modifying the parity of the number of the non-zero AC coefficients according to the message bit. And then analyze the influence of the watermark to the image quality and the length of compressed image bitstream. The watermarked data are coded and then transmitted over a noisy channel that is simulated by transmission errors, at the receiving side, according to the errors while decoding the image and the comparison between the extracted watermark and the original watermark, we can effectively assess the quality of the communication channel by using the index factor Q defined in this papper. While using digital watermark to assess the quality of channel, the watermark data does not affect the quality of the carrier images, at the same time, it dosen't add extra communication bits for the introduced watermark data, this method belongs to a kind of an no parameters objective evaluation method. Experimental results illustrate that the index factor Q in this papper can present the quality of the communication channels exactly. The value of Q increases as channel bit error rate, and it does not be affected by the size the content and the texture characteristics of images in the test. Experimental results also indicate that the proposed scheme can be used to assess the quality of channel which signal image transmission, and provide a reference of payment for the operators and users.