Development of and improved reversible image watermarking scheme

Abstract

Visual content tends to engage readers’ attention, helps in better understanding of material and cling to their memories for a longer period of time. In todays world, smart phones, digital mobiles, camera phones and other forms of image capturing devices are widely used, these images are shared and sent worldwide. This increases the need of protection of copyrights of the images to lessen forgery, tempering and illegal copies of original image. In order to protect ownership information, watermarking technique comes into action. In this technique, secret bits are inserted in an image corresponding to ownership information. The insertion of secret bits can be visible or invisible, however invisible watermarks add more protection because they are often ignored by copier or modifier. Watermarking whether visible or invisible, tends to degrade the visual quality of original image. Various watermarking techniques are being developed in recent times to protect ownership information of images with main focus on less degradation of visual quality. This thesis proposes a novel technique for image watermarking comprising of real time image segmentation, adaptive image interpolation and additive prediction error expansion. The cover image is interpolated using adaptive image interpolation that mainly focuses on detection of edges in an image for minimizing the artifacts imposed by interpolation process. The cover image is also segmented at real time by using k-means clustering approach. The segmentation technique groups pixels of similar nature in a segment. The overall nature of each segment is determined. Nature of a segment can be smooth or sharp. After categorizing nature of each segment, the embedding capacity of each segment is defined. Segments with sharp edges tend to embed more bits as compared to smooth segments, thus embedding capacity is set accordingly. Additive prediction error expansion is utilized to hide invisible watermark inside the cover image. The proposed watermarking technique finds its application in protecting ownership, origin authenticity, copyrights information and temper proofing sensitive military, satellite and medical images. The proposed watermarking technique not only embeds data but also extracts data accurately. The extensive experiments performed show that proposed scheme out performs other recent schemes in terms of higher speed, embedding capacity and better visual quality calculated by Peak Signal to Noise Ratio (PSNR).