Significant difference-based watermarking in multitoned images

Digital multitoning is an advanced form of halftoning-based printing technique which renders multiple tones at each pixel of an image. This superior scheme delivers an improved print quality in terms of smooth texture, homogeneity and the suppression of artefacts. This Letter examines the potential scope of multitoning as an effective strategy to embed a binary watermark within a multitoned image. The proposed method uses the significant difference among the highpass wavelet coefficients achieved by discrete wavelet transform for watermark embedding. Furthermore, an improvised ordered dithering technique using adaptive threshold quantisation is also incorporated, which not only makes the proposed method time-efficient but also offers uniformity to the final image. The proposed watermarking technique is imperceptible and yields watermarked images with high peak signal-to-noise ratio value. Experimental simulations demonstrate that the proposed watermarking method is superior to the state-of-the-art methods in the context of both objective and subjective assessments.