A reversible watermarking scheme for two-dimensional CAD engineering graphics based on improved difference expansion

Difference expansion is widely used in reversible watermarking for raster images, but it cannot be applied to data with low correlation, due to its large distortion. In this paper, an improvement is made to difference expansion technology to make it suitable for two-dimensional (2D) computer-aided design (CAD) engineering graphics. Based on improved difference expansion (IDE), a reversible watermarking scheme for 2D CAD engineering graphics is proposed. First, all vertices of the 2D CAD engineering graphics are extracted, and then the relative coordinates of these vertices are calculated. Finally, the encrypted watermark is embedded into the scale factor of the relative coordinates by using IDE technology. Experimental results show that the proposed scheme has a large capacity, good imperceptibility, and is robust against operations such as transformation, rotation, and equal scaling.

► An improvement has been made to the existing techniques for data with low correlation.
► The improved technique does not need a location map, which expands the capacity.
► A watermark is embedded into the ratio data, which improves the robustness.
► The scheme has good performances in reversibility, imperceptibility, and capacity.