Digital Watermarking Algorithm For Two-dimensional CAD Grapics

With the rapid development of information technology and industrial automation, thecomputer-aided design and manufacturing (CAD/CAM) technology has been widely used inthe machinery industry, construction industry, garment industry, electrical and electronicfields. It has generated a huge of economic and social benefits and also had a good applicationprospect. As a mainstream digital product in CAD/CAM technology, many problems incopyright protection, content authentication of the CAD engineering drawings are becomingmore and more outstanding. In order to protect the copyright of engineering drawings, CADengineering graphics watermarking algorithm emerges as the times require, and is growingattention and concern of people。This paper, firstly, introduces the meaning and purpose of the two-dimensional (2-D)CAD engineering graphics watermarking algorithm. Then, from the spatial domain andfrequency domain perspectives, this paper respectively analyzes the latest research progress ofthe2-D CAD engineering graphics watermarking algorithm. Based on the characteristics of2-D CAD graphic watermarking algorithm, this paper further explores the feasibility andapplicability of the2-D CAD engineering graphics digital watermarking algorithm.On this basis, a two-dimensional CAD graphics watermarking algorithm based onanonymous block is proposed. At first, an anonymous block in graphics is created, then agroup of points will be added in the anonymous block, meanwhile, the watermark is hid intothe point coordinates. Next, all the lines is extracted from the2-D CAD engineering graphics.In order to getting the same watermark of anonymous block, lines are divided and sorted bythe length of lines, and marked as0,1. To improve the security of the algorithm, Arnoldtransform is used before embedding watermark. While the watermark is extracted by secretkeys from anonymous block, the algorithm realizes blind extraction in the extract process ofwatermark signal. The experimental results show that the algorithm can resist the attacks oftranslation, rotation, adding or deleting the objects, with a strong robustness. As anonymousblocks and the differences of the lines, the proposed algorithm increases the amount ofembedded watermark information, overcomes the shortcomings of algorithm’s carrier formsimplification and achieves multiple watermarks. At the same time, this algorithm canguarantee the shapes and precision of watermarked graphic, so that it can keep identical withthe original graphic.In addition, on the basis of the existing algorithm, another watermarking algorithm oftwo-dimensional CAD engineering graphic based on morphological Haar wavelet (MHW)watermarking is also proposed in this paper. Firstly, the line entities are replaced as multi-segments lines in the graphic; then, by transforming vertexes, a uniform transformationunit with affine transformation invariance as the embedding carrier can be gained; next, thevertex coordinate of the transformation unit is decomposed by two levels morphological Haarwavelet transform and the watermark is embedded into the MHW approximate coefficient ofthe unit. Meanwhile, in order to improve the security of the watermark, the watermark isencrypted with Logistics chaotic sequences before embedding. Experimental results show that:this algorithm is robust and invisible, while against affine transform with vertextransformation.