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 hasbeen proposed for color image authentication (FWSDHTCIA). Two dimensional SDHT is applied on each2 × 2 sub-image block of the carrier image in row major order and produces four frequency components intransform domain. Due to the high sensitivity of human eye on green channel, only one authenticatingmessage/image bit is fabricated at the second bit position of each frequency component for every 2 × 2green sub-matrix. Unlikely, in every 2 × 2 red and blue sub-matrices, two bits from the authenticatingmessage/image are fabricated at the second and third bit position of each frequency component as thehuman eye is less sensitive on red and blue channels as compared to green. After fabricating theauthenticating watermark (message/image), a frequency adjustment strategy has been applied to get backthe less distorted watermarked image in spatial domain. A delicate re-adjustment has been incorporated inthe first frequency component of each 2 × 2 mask, to keep the quantum value positive in spatial domainwithout hampering the authenticating watermark bits. Two dimensional inverse SDHT (ISDHT) is appliedon each 2 × 2 sub-mask as post embedding operation to produce the watermarked image. At the receivingend reverse operation is performed to extract the stream which is compared to the original stream forauthentication. Experimental results conform that the proposed algorithm has improvised the payload andPSNR values over SDHTIWCIA [7] scheme which is previously proposed by us. Also, the proposedFWSDHTCIA scheme produces much better result than the Discrete Cosine Transform (DCT), QuaternionFourier Transformation (QFT) and Spatio-Chromatic DFT (SCDFT) based techniques.