A Novel Ideal Contrast Visual Secret Sharing Scheme with Reversing

In visual secret sharing (VSS) schemes, a secret image can be visually revealed from overlapping shadow images without additional computations. However, the contrast of reconstructed image is much lost. Employing reversing operation to reverse black and white pixels as well as increasing encoding runs is an effective way to improve the contrast. A novel VSS scheme with reversing is presented in this paper. It achieves really ideal contrast within only / m h ⎡ ⎤ ⎢ ⎥ encoding runs (where m and h are the number of the total columns and the number of the wholewhite columns in the basis matrix to encode white pixels, respectively) and no pixel expansion occurs. It encodes the secret image block by block. A block consists of m pixels, which means that m pixels together join into each encoding step. It is suitable for all access structures and can be applied to encrypt black-white, gray-scale and chromatic images. The experimental results, analyses and comparisons show that the proposed scheme is optimal among those schemes with reversing in encoding runs, pixel expansion, complexity, system capacity and encoding efficiency.