Joint index coding and reversible data hiding methods for color image quantization

Abstract

In this paper, we proposed two reversible data hiding methods for color image quantization based on lossless index coding. In index coding process, the indices are classified into three types: Type-1, Type-2, and Type-3 according to the relationship between the current index and its neighbors in lossless index coding. In the first method, Type-1 indices are taken to hide secret bits. To increase the hiding capacities, not only Type-1 indices but also Type-2 indices are used to embed secret bits in the second method. The experimental results show that the proposed methods achieve high hiding capacities while keeping acceptable compression bit rates. The required bit rates of the proposed methods are less than those of the uncompressed indices. The index table of each color quantized image can be recovered without any distortion after the hidden data has been extracted. Experimental results reveal that the first method is suitable for the applications that the required embedding ratio is less than or equal to 0.5 bit/index. For applications requiring a higher embedding ratio, the second method can be used to embed the secret data. The embedding ratio of the second method can be up to 0.98 bit/index.