Reversible Watermarking For Multitone Images

With the rapid development of computer science and technology and the continuous improvement of human security awareness,digital watermarking technology is gradually applied to the field of multimedia information security.The digital watermarking technology of the image is mainly to embed the watermark information into the image.The hidden information is not easy to detect and does not affect the application value of the original image.It plays a good role in anti-counterfeiting traceability and copyright protection.At present,many digital watermarking algorithms have been proposed.After verification,these algorithms have been applied in many fields.In recent years,halftone technology has become very mature,and combining halftone technology with digital watermarking has become a new research hotspot.However,after reading the literature,it is found that the existing halftone reversible watermarking algorithms still have the following problems:(1)When the watermark is embedded in the halftone image,the output watermark image has obvious stripe texture and the image quality is not good;(2)In the existing algorithms,the amount of information that can be embedded is less.To solve the above problem,we propose a reversible watermarking algorithm for multitone images.Multitone technology converts continuous tones into multitone images.The image output by applying multitone technology can significantly improve the quality of output halftone images.Aiming at problem one,this thesis uses multitone technology,and proposes a multitone image reversible watermarking technology.The watermark embedding operation based on the multilevel halftone image can significantly improve the quality of the watermarked image,and cause less distortion compared to ordinary halftones;For the second problem,our embedded messages and extracted messages are operated on the basis of image blocks,so we count the embedding capacity of pixel blocks of different sizes.Considering the distortion of the image,we choose 3 by 3 pixel block to embed the messages.Not only can we improves embedding capacity,but also reduce image distortion.We proposed the multilevel halftone reversible watermarking method in this paper,it can divided into three steps:first,convert grayscale image to multitone image,then build a multi-level look-up table to embed and extract watermark messages.Finally,restore the carrier image.Experimental tests show that the image restored by this algorithm is exactly the same as the original carrier image,which can improve the embedding capacity while ensuring the image quality.