Expansion Embedding Techniques for Reversible Watermarking

TLDR

Reversible watermarking embeds information without loss of the host signal, and Tian’s difference‑expansion method offers high capacity but suffers distortion at low capacities and lacks capacity control due to the required location map. The authors propose histogram shifting to replace the location map and a prediction‑error expansion technique to better exploit pixel‑neighborhood correlation. Histogram shifting and prediction‑error expansion together form an effective reversible data‑embedding method that replaces the location map and leverages local pixel correlation. Experimental results on standard test images show that the new method halves distortion at low capacities, doubles maximum embedding capacity versus difference expansion, and yields significantly higher image quality at moderate capacities.

Abstract

Reversible watermarking enables the embedding of useful information in a host signal without any loss of host information. Tian's difference-expansion technique is a high-capacity, reversible method for data embedding. However, the method suffers from undesirable distortion at low embedding capacities and lack of capacity control due to the need for embedding a location map. We propose a histogram shifting technique as an alternative to embedding the location map. The proposed technique improves the distortion performance at low embedding capacities and mitigates the capacity control problem. We also propose a reversible data-embedding technique called prediction-error expansion. This new technique better exploits the correlation inherent in the neighborhood of a pixel than the difference-expansion scheme. Prediction-error expansion and histogram shifting combine to form an effective method for data embedding. The experimental results for many standard test images show that prediction-error expansion doubles the maximum embedding capacity when compared to difference expansion. There is also a significant improvement in the quality of the watermarked image, especially at moderate embedding capacities.