Image steganography via fully exploiting modification direction

Embedding bits by replacing pixel's least-significant bit (LSB) is a simple but great idea. Nevertheless, this method is not safe enough. Afterwards, a series of effective and safe algorithms which are based on LSB substitution method were proposed such as EMD (exploiting modification direction) and EMD-2. EMD, modifying at most one of n pixels' LSB to embed a (2n+1) -ary notational system number, achieved higher embedding efficiency than LSB method. EMD-2 modifys at most two of a group n pixels to embed a (10n-13) -ary (n > 2) notational system number, making embedding capacity improved compared with EMD. To improve embedding capacity further, we proposed a new method EMD-3 exploiting modification direction fully. EMD-3 modifys a group of n pixels by ±1 to embed a secret digit in 3ⁿ -ary notational system. The experimental results demonstrate that EMD-3 can improve embedding capacity and preserve good image quality at the same time. Besides, EMD-3 is as secure as EMD and EMD-2.