A Robust Hybrid Image Watermarking Scheme Based on IWT-DCT-SVD using Entropy and Edge Entropy

The rapid expansion of digital multimedia distribution has increased the demand for dependable copyright protection and content authentication. Digital image watermarking has emerged as a principal solution, yet the fundamental challenge remains in balancing imperceptibility and robustness against various signal processing and geometric attacks. This paper proposes a novel hybrid watermarking scheme that combines the Integer Wavelet Transform (IWT), the Discrete Cosine Transform (DCT), and Singular Value Decomposition (SVD), while entropy and edge entropy decide where the watermark is embedded. The use of IWT overcomes the floating-point precision loss inherent in conventional Discrete Wavelet Transform (DWT), ensuring perfect reconstruction and higher accuracy in watermark extraction. DCT is employed to leverage energy compaction in mid frequency bands, while SVD provides exceptional stability against geometric distortions due to the inherent invariance of singular values. The critical innovation lies in the integration of entropy and edge entropy metrics to dynamically identify highly textured image blocks with maximum natural masking capacity. Unlike conventional HVS or variance-based methods that often mischaracterize directional edges, the proposed dual-entropy model precisely quantifies both luminance obliviousness and structural sensitivity, enabling the embedding of stronger watermarks without compromising perceptual quality. Extensive experiments on eight standard 512×512 benchmark images demonstrate consistently high imperceptibility, with an arithmetic average PSNR of 40.46 dB, SSIM of 0.9965, and FSIM of 0.9995. Robustness evaluations under fourteen categories of signal processing and geometric attacks yield Normalized Correlation (NC) values predominantly above 0.99, outperforming four recent state-of-the-art methods in eleven of twenty attack scenarios. The identified limitations include reduced robustness against large-angle rotation attacks, an inherent SVD challenge. The proposed framework demonstrates significant potential for secure, imperceptible digital image watermarking.