Controllable transparency image sharing scheme for grayscale and color images with unexpanded size

Aimed at transparency controlling to secret image, we propose an image sharing scheme to encrypt secret image among two or more sharing images. The overall effects of the proposed method are the achievements of controllable transparency of secret image and unexpanded size of sharing images. The controllable transparency image sharing scheme is realized based on the principle of penetrability. While light passes through a medium, medium declines illumination of light. We treat pixel as medium and adjust pixels´ value of multiple sharing images, so that transparency of decrypted-secret image is controllable. The experiment results will demonstrate that our scheme can be applied to grayscale and color images for visual cryptography. Furthermore, similarity between sharing image and secret image is low by using the proposed scheme.