High capacity image steganographic model - Vision, Image and Signal Processing, IEE Proceedings-

Steganography is an ancient art o r conveying messages in a secret way thal only Ihe receiver knows the existence of a message. So a fundamental requirement for a steganographic method is imperceptibility; this means that the embedded messages should not bc discernible to the human eye. There are two other requirements, one is to maximise the embedding capacity, and the other is security. Thc least-significant bit (LSB) inscrtion mcthod is Ihc most common and easiest method for embedding messages in an image. However, how lo decide on the maximal embedding capacity for each pixel is still an open issne. An image steganographic model is proposcd that is bascd on variable-six LSB insertion to maximise thc cmbcdding capacity while maintaining image fidelily. For each pixel o r a grey-scale image, at least Cour bits cau be used for mcssagc cmbedding. Thrcc components arc provided to achicvc thc goal. First, according to contrast and luminance characteristics, the capacity evaluation is provided to estimate the maximum embedding capacity of each pixel. Tlicn thc minimuin-error rcplaccmcnt method is adapted to find a grey scale as close to thc original one as possible. Finally, the improved greyscale compensation, which takcs advantagc of thc pcculiaritics of human visual system, is used to eliminate the false contouring effect. Two methods, pixelwise and bitwisc, are provided to deal with the security issue when using the proposed model. Experimental results show effectiveness and efficiency of thc proposcd modcl.