Reversible Watermark Using the Difference Expansion of a Generalized Integer Transform

TLDR

The paper proposes a reversible watermarking algorithm for color images that achieves very high data‑hiding capacity. The method employs a general reversible integer transform to embed bits via difference expansion of adjacent‑pixel vectors, with overflow‑avoidance conditions, a feedback system to control payload, and recursive application across color components to maximize capacity. Simulations show that the spatial, quad‑based variant achieves the largest payload and highest signal‑to‑noise ratio compared to existing reversible watermarking algorithms.

Abstract

A reversible watermarking algorithm with very high data-hiding capacity has been developed for color images. The algorithm allows the watermarking process to be reversed, which restores the exact original image. The algorithm hides several bits in the difference expansion of vectors of adjacent pixels. The required general reversible integer transform and the necessary conditions to avoid underflow and overflow are derived for any vector of arbitrary length. Also, the potential payload size that can be embedded into a host image is discussed, and a feedback system for controlling this size is developed. In addition, to maximize the amount of data that can be hidden into an image, the embedding algorithm can be applied recursively across the color components. Simulation results using spatial triplets, spatial quads, cross-color triplets, and cross-color quads are presented and compared with the existing reversible watermarking algorithms. These results indicate that the spatial, quad-based algorithm allows for hiding the largest payload at the highest signal-to-noise ratio.