Research On Digital Image Watermarking Based On Amplitude Modulation Screening

In recent years,the public’s awareness of copyright in digital media has been significantly improved.The watermark hiding technology based on Amplitude Modulation screening has the characteristics of low cost and easy implementation,and can be used not only for digital images,but also for printed images.However,there are two key problems with this technology.Firstly,the traditional method will appear obvious watermark contour trace after adding watermark,which breaks the original image from the visual effect.Secondly,the watermark detection method is too single,and the complete watermark information can not be clearly extracted.By studying the AM screening technology and dot characteristics,this thesis implementes the watermark hiding algorithm based on mapping elements.A dot offset watermark hiding algorithm is proposed,which effectively solves the problem of watermark contour trace.Two watermark hiding algorithms are proposed to significantly improve the recognition of watermark extraction results.The main work and contributions of this thesis are as follows:1.This thesis deeply studies the rational tangent screening algorithm based on the minimum threshold matrix,and analyzes the relevant parameters of AM screening technology;dissects the relationship between the minimum threshold matrix and the mesh unit,which provides a theoretical basis for exploring the characteristics of mapping elements;analyzes the principle of grating detection technology and demonstrates the feasibility of grating detection.2.Through the mapping relationship between the mapping unit and the original pixels,a watermark hiding algorithm based on the mapping unit is realized.The algorithm uses the traditional offset method,and the result image will appear watermark contour traces.The experimental results show that the trace is caused by the dislocation or overlap of watermark boundary nodes.Taking the dot as the basic offset unit,this thesis proposes a dot offset watermark hiding algorithm and a watermark boundary dot trace optimization algorithm,which avoids the distortion of dot structure.3.Based on dot threshold and dot arrangement rules,a variety of minimum threshold matrices of detection grating are designed,and grating images can be generated by AM screening algorithm.A cross grating detection method is proposed,which can directly display the watermark information hidden in two different channels while simplifying the operation.4.In order to get complete watermark information and expand the watermark extraction method,a watermark extraction algorithm based on mapping element threshold hash table is proposed.According to the principle that the coordinates of the dot center are unchanged,a dot matching watermark extraction algorithm is proposed.Compared with traditional grating detection,the watermark extraction result is more recognizable.5.The evaluation criteria of watermark hiding effect and watermark extraction effect are determined.Through experiments,we study the effects of watermark hiding channel,dot area ratio and watermark embedding rate on the hiding effect.In the experiment,the actual effects of two hiding algorithms and two extraction algorithms are compared.The experimental results show that the proposed dot offset watermark hiding algorithm has better hiding effect and solves the problem of obvious watermark boundary trace;among the two proposed watermark extraction algorithms,the extraction accuracy of the watermark extraction algorithm based on the mapping element threshold hash table can reach 99.83%,and the dot matching watermark extraction algorithm has faster execution speed on the premise of 98.65% extraction accuracy.These two extraction algorithms can be applied to different usage scenarios according to actual demands.