Research On Image Digital Watermarking Algorithm Based On DCT Domain And Quantization

With the rapid development of computer and network technology, information security and copyright protection of the digital media have become an urgent problem. As an important means to protect the digital media effectively, the digital watermarking technique has become a hot research topic.This thesis focuses on images. Firstly research backgrounds, basic characteristics, classifications and applications of digital watermarking are introduced. The paper formulates the basic principles and representative algorithms, and the attack of the image digital watermarking is discussed in detail. Then, based on the existing watermarking algorithm, with the chaotic theory and discrete cosine transform, and two new algorithms based on DCT and quantization are proposed. Finally, the good performance of the two algorithms is verified by some common image processing and attack experiments.1. An image-watermarking algorithm based on uniformity quantization . This algorithm uses the Arnold mapping sequences to scramble and encrypt the binary image watermark. Then DCT is performed on the original image, and then the DC ponderances are used as the watermarking imbedding domain. Uniformity quantization and dithered modulation are adopted in this arithmetic. The experimental result shows, in contrast with common middle frequency embedding algorithms, this paper proposed algorithm can get well transparency, and at the same time, facing kinds of common image attack, especially the JPEG loss compression attack, it shows strong robustness.2. Adaptive quantization watermark is introduced to enhance the robustness to multiplication noises according to the characteristics of Human Visual System. Since the quantization step changes synchronously with the multiplication noises, this algorithm is robust to multiplication noises in principle. Experiment results prove that adaptive quantization watermark is superior to its uniform quantization counterpart.This thesis proposed two image digital watermarks algorithm based on quantization is simple and convenient to implement, and therefore has well practicality in the image digital production copyright protection area.