To enlarge the capacity of the hidden secret information and to provide an imperceptible stego-image for human vision, a novel steganographic approach using tri-way pixel-value differencing (TPVD) is proposed in this paper. To upgrade the hiding capacity of original PVD method referring to only one direction, three different directional edges are considered and effectively adopted to design the scheme of tri-way pixel-value differencing. In addition, to reduce the quality distortion of stego-image brought from setting larger embedding capacity, an optimal approach of selecting the reference point and adaptive rules are presented. Theoretical estimation and experimental results demonstrate that the proposed scheme can provide superior embedding capacity and give secrecy protection from dual statistical stego-analysis. Besides, the embedded confidential information can be extracted from stego-images without the assistance of original images.
Among various image fusion methods, intensity-huesaturation ͑IHS͒ and Brovey transforms ͑BT͒ can quickly merge huge amounts of IKONOS/QuickBird imagery. However, spectral degradation often appears in the fused images. Moreover, IHS and BT suffer from individual color distortion on saturation compression and saturation stretching, respectively. To balance these two saturation changes during the fusion process, an adjustable IHS-BT approach with spectral adjustment is proposed. Furthermore, to solve the typical bright target recovery ͑BTR͒ problems, a simple procedure of dynamic range adjustment ͑DRA͒ is also presented. By adopting different DRA techniques, the proposed IHS-BT method is divided into two different fusion approaches: the model of preserving spectral information and the model of enhancing spatial details. Experimental results demonstrate that the proposed combined approaches can achieve significant improvement over other current approaches.
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