Watermarking of sprites in MPEG-4

The rapid proliferation of Multimedia content and the increasing number of transactions through the internet has placed high importance to data/,media security. Digital watermarking, a process of embedding secondary digital data in the primary digital medium, is one of the common methods used for copyright protection. In this paper, we propose a technique for robust and invisible watermarking of sprite in MPEG-4. Sprite coding is a new scheme proposed in the MPEG-4 standard for encoding the background in a scene which have less or no local motion. There are three steps involved in the generation of sprites - Initialization, Updating and Blending. The sprite is initialized for the very first Video Object Plane(VOP) of the video object sequence by just placing the VOP at a pre-specified location within the sprite. The sprite is then updated for each of the subsequent VOPs of the video object sequence by estimating the motion of the VOP with respect to the sprite. The VOP is then warped by the estimated motion parameters. The warped VOP and the sprite are then blended together. The blending factor may be different for different pixels on the sprite and this is a function of the number of times this pixel has been blended in the past. The details of the proposed watermarking technique are as follows. The contents of the sprite are first classified as strong texture, smooth and edge regions. The pixels in the sprite are then re-classified depending on the number of time search pixel has been blended. A pseudo noise sequence is generated and this sequence is modulated with the image using the basic sequence amplified according to an apriori classification and pixel blending weights. Abstraction of the watermark is done by demodulating the sprite with the same pseudo-noise sequence. Provisions for extracting the watermark from the individual frames have also been provided. The principal advantage of this watermarking technique is that the watermark bits are modulated onto the sprite depending on the merit of each pixel. Preliminary investigations have shown that the proposed scheme has the potential for superior watermarking performance. Details of the technique along with results will be discussed in detail in the final paper.