A module-based LSB substitution method with lossless secret data compression

All the various data hiding methods can be simply divided into two types: (1) the extracted important data are lossy, (2) the extracted important data are lossless. The proposed method belongs to the second type. In this paper, a module-based substitution method with lossless secret data compression function is used for concealing smoother area of secret image by modifying fewer pixels in the generated stego-image. Compared with the previous data hiding methods that extract lossless data, the generated stego-image by the proposed method is always with better quality, unless the hidden image is with very strong randomness.     

Flip visual cryptography (FVC) with perfect security,conditionally-optimal contrast,and no expansion

This paper proposes a flip visual cryptography (FVC) scheme with perfect security, conditionally optimal contrast, and no expansion of size. The proposed FVC scheme encodes two secret images into two dual-purpose transparencies. Stacking the two transparencies can reveal one secret image. Flipping one of the two transparencies and then stacking with the other transparency can reveal the second secret image. The proposed scheme is proved to have conditionally optimal contrast: its contrast is optimal if the double-secrets non-expanded FVC scheme is required to have perfect security. The perfect security is also proved.     

Optimal (2, n) and (2, infinity) visual secret sharing by generalized random grids

Based on generalized random grids, this paper proposes two visual cryptography methods denoted as (2, n) GRG and (2, infinity) GRG. The (2, n) GRG is suitable for the pre-decided number of shares, and the (2, infinity) method is suitable for the adjustable number of shares. The proposed (2, n) GRG achieves better contrast on the stacking result, and the proposed (2, infinity) GRG enables extending the number of shares anytime. Based on the definition of contrast in Shyu’s work in 2007, we also demonstrate that the stacking result of (2, n) GRG is close to the theoretical bound of the contrast, and the stacking result of (2, infinity) GRG achieves the theoretical bound of the contrast.     

Fault-tolerant and progressive transmission of images

A fault-tolerant progressive image transmission method is proposed. The advantages include the following: (1) Unlike most progressive methods, the image is divided into n parts with equal importance to avoid worrying about which part is lost or transmitted first. (2) If the image is a secret image, then the transmission can use n distinct channels (one shared result per channel), and intercepting up to r₁-1 channels by the enemy (r₁r_kn are all pre-set constants) will not reveal any secret. Meanwhile, the disconnection up to n-r_k channels will not affect the lossless recovery of the secret image.