A Fragile Watermarking Based on Separable Discrete Hartley Transform for Color Image Authentication (fwsdhtcia)

In this paper, a fragile watermarking based on two-dimensional Separable Discrete Hartley Transform has been proposed for color image authentication (FWSDHTCIA). Two dimensional SDHT is applied on each 2 × 2 sub-image block of the carrier image in row major order and produces four frequency components in transform domain. Due to the high sensitivity of human eye on green channel, only one authenticating message/image bit is fabricated at the second bit position of each frequency component for every 2 × 2 green sub-matrix. Unlikely, in every 2 × 2 red and blue sub-matrices, two bits from the authenticating message/image are fabricated at the second and third bit position of each frequency component as the human eye is less sensitive on red and blue channels as compared to green. After fabricating the authenticating watermark (message/image), a frequency adjustment strategy has been applied to get back the less distorted watermarked image in spatial domain. A delicate re-adjustment has been incorporated in the first frequency component of each 2 × 2 mask, to keep the quantum value positive in spatial domain without hampering the authenticating watermark bits. Two dimensional inverse SDHT (ISDHT) is applied on each 2 × 2 sub-mask as post embedding operation to produce the watermarked image. At the receiving end reverse operation is performed to extract the stream which is compared to the original stream for authentication. Experimental results conform that the proposed algorithm has improvised the payload and PSNR values over SDHTIWCIA [7] scheme which is previously proposed by us. Also, the proposed FWSDHTCIA scheme produces much better result than the Discrete Cosine Transform (DCT), Quaternion Fourier Transformation (QFT) and Spatio-Chromatic DFT (SCDFT) based techniques.