Indexed on: 26 Nov '15Published on: 26 Nov '15Published in: Multimedia Tools and Applications
There have been discussed several data hiding techniques which can hide the secret data in an image. However, after extracting the secret data some of the image information gets lost. It is an important issue to have a data hiding scheme which can extract the secret data as well as can restore the original image without any loss of information. Such types of schemes are called reversible data hiding schemes which are commonly used in sensitive military, legal, and medical applications. The existing reversible data hiding schemes either provide good hiding capacity but inferior stego-image quality or good stego-image quality but poor hiding capacity because the stego-image quality and the hiding capacity are diametrically related parameters. In this paper, we propose a novel high capacity reversible data hiding scheme which has high data hiding capacity while maintaining good quality stego-image. In this scheme, we first cryptographically encode the secret data using a private key so that even if an attacker is able to extract the embedded secret data, he cannot get the original secret message unless he has the private key. Our scheme hides the secret data in two phases. In first phase, it uniformly divides the pixel intensity levels i.e., 0-255, into odd sized segments. Then the image is scanned in zigzag order to identify the concealable pixels, which have the same value as the middle elements of a segment. Some of the secret data is hidden into these identified pixels. In second phase, the intensity levels are again divided in reverse order, i.e., 255 to 0, into odd sized segments of uniform length like as in the first phase. The resultant image is again scanned in zigzag order and concealable pixels are identified. The remaining secret data is embedded into the concealable pixels. To ensure reversibility of our algorithm, a location map is maintained for each phase. The location maps are compressed using JBIG1 scheme and are transmitted through a secure channel along with other auxiliary information that contains private key and segment size. Experimentally our scheme achieves very high capacity without deteriorating the image quality. It is because we select the exact middle pixels of the segments to hide the secret data, which ensures that the pixel value does not get altered unevenly while embedding the secret data. It further helps in increasing the hiding capacity. Moreover, it is very simple as it does not require much computation for embedding the secret data.