Reducing shadow size in essential secret image sharing by conjunctive hierarchical approach

Recently, Li et al. proposed a (t, s, k, n) essential secret image sharing (ESIS) scheme with different importance of shadows, which has s essential shadow images and n−s non-essential shadow images. This (t, s, k, n)-ESIS scheme can simultaneously provide the conventional threshold property (k or more shadow images are required in reconstruction) and the essential-threshold property (these involved k shadow images should include at least t essential shadow images). Generally, small shadow images have advantages in storage or transmission, and will be suitable for modern visual communication applications where features such as secure transmission and storage are required. Therefore, the size of shadow image is a critical consideration for designing ESIS-(t, s, k, n) scheme. In this paper, we propose a (t, s, k, n)-ESIS scheme to achieve the less size of total shadow images and the less size of required shadow images in reconstruction when compared with Li et al.'s (t, s, k, n)-ESIS scheme.