A Secret Image Sharing Scheme With High Embedding Capacity

The application of images is becoming more and more widely and the protection of images is becoming more and more important. Secret image sharing(SIS), an application of the secret sharing scheme in the image field, is an effective way to protect a secret image during its transmission and storage. It is such a technology that a secret image is transformed into multiple shares or stego images, so that the secret image can be recovered with a certain set of shares or stego images. Therefore, it is an effective method to ensure the security of the secret image during transmission or storage, especially in the fields of military, commercial, financial, etc.In the field of secret image sharing, there are some hot issues. Underflow and overflow situations are normal problems. Because when binary images and some grayscale images are used as covers, the shared secret data were camouflaged into quantized cover image data, and the value of pixels of the stego image may exceed the grayscale boundary. Thus, the secret image can not be revealed without distortion. Since the application of binary images and grayscale images are widely used, binary covers are necessary in secret image sharing. Now, some CSIS schemes that used new technologies have been proposed which can prevent the underflow and overflow situations. Pixel Mapping Matrix(PMM) embedding is such a technology that cannot cause the underflow and overflow situations. Though schemes which use Pixel Mapping Matrix(PMM) embedding can prevent the underflow and overflow situations, they have some drawbacks in computational complexity, visual quality and efficiency. Thus, the proposed scheme provides a new method which uses the PMM embedding but has better effects on computational complexity, visual quality and efficiency.Embedding capacity is another important issue in the secret image sharing field. The embedding capacity is an important index that refers to the maximum amount of secret data that can be hidden in given cover images without affecting imperceptibility. It is shown by the size of the cover image. Generally, large embedding capacity means that the cover image can share a large secret image and thus it can decrease the need for cover images when the size of the secret image is constant. Therefore, the embedding capacity is related to the size of cover images, and it is usually expressed by how much of the size of cover images. The larger the embedding capacity is, the smaller cover images are needed, which also results that less time and space are demanded during transmission and storage. It is very popular in real-time system and the band width is limited. Many schemes aim to improve the embedding capacity and until now, the highest embedding capacity in the existing scheme is(t-1)/3 of the size of the cover image. However, the embedding capacity was still limited and thus new technologies should be used to get high embedding capacity. In the proposed scheme, the differencing function, a Huffman coding and data converting are applied to compress the secret image firstly, and then the PMM embedding method with a newly designed pixel mapping matrix is used to embed secret image data into the cover image, which can improve the embedding capacity largely. The embedding capacity was(t-1)RC/2 of the size of cover images, RC is the ratio of compression with the average value of 2. It is clearly that the average value of the embedding capacity of proposed scheme is(t-1) of the size of cover images, which is larger than previous scheme.