Colour image steganography method based on sparse representation

The authors address the use of sparse representation to securely hide a message within non-overlapping blocks of a given colour image in the wavelet domain. All four sub-images of the two-dimensional wavelet transform of two colour bands are used for data embedding without affecting the image perceptibility. Bit error rate of hidden data extraction is reduced to zero by introducing a novel refinement procedure in the proposed algorithm. The refinement procedure introduced solves the hidden bit extraction errors caused by the rounding process, the overflows and the nature of approximation in sparse decomposition. Capacity of the proposed method is calculated using necessary conditions for uniqueness of the sparse representations and validated by means of experimental results. The authors experimental results show that the embedded data are invisible perceptually. The average peak signal-to-noise ratio (PSNR) value of the introduced method is about 40 and 11 dB higher than the average PSNR values of the MPSteg-colour method and the wavelet domain 2-LSB embedding method, respectively. The security of the proposed method is also evaluated comparatively, using five well-known steganalysers, which confirms superior performance of the new method comparing with the MPSteg-colour method and the wavelet domain 2-LSB embedding method.