Researchers at Purdue University are reportedly close to perfecting a technique that will make it practical to use ‘digital watermarking’ for video sent over the Internet, providing a reliable way to protect copyrights and to verify a video’s authenticity.
Digital watermarking, or steganography, is a procedure in which hidden patterns are embedded into an image or document on the Internet. The patterns can then be used to verify the image as authentic, protecting intellectual property rights for people who create digital media.
However, watermarking is especially difficult to use for Internet video. As video is transmitted over the ‘noisy,’ traffic-congested Internet, a number of frames never make it to the receiving end. The frames, including those that may contain digital watermarks, are lost, said Edward Delp, a professor of electrical and computer engineering at Purdue.
The Purdue research concerns a technique that ‘resynchronises’ video at the receiving end of the transmission, preventing the frames from being lost.
Because digital video will become more common over the next five years, techniques will be needed soon to maintain the quality of video as it is transmitted over the Web.
‘The network is overloaded, and you get dropouts, or missing data,’ Delp said. ‘You can get enough errors to make the video almost unwatchable.’
Standard ‘error correction’ techniques used to recover lost data in e-mail transmissions do not work for video and audio transmissions.
The researchers have created a computer algorithm – a series of steps that enable a computer to complete a task – that may solve the problem.
‘We have developed a mechanism under which, at the receiving end, you will be able to correct the errors that occurred in the Internet transmission and be able to recover the hidden messages in video,’ Delp said.
Video relies on critical split-second timing for individual frames that follow one another. The precise, rapid firing of 30 frames per second creates the illusion of continuous movement. As video is transmitted over the Internet, however, it is difficult to maintain this delicate timing.
The new technique resynchronises the transmission at the receiving end, fixing errors that throw off the timing and result in lost information.
The very nature of video makes watermarking difficult.
‘You are presented with 30 frames per second, and your eye integrates those to make it look like continuous motion,’ Delp said. ‘But your eye is real susceptible to any subtle changes in the images from one frame to the next.
‘If you don’t properly put the watermark into the video, you can see the watermarked image, which is not supposed to be visible.’
To properly embed watermarks into video, the Purdue researchers use a computer program that mimics how people see video.
‘We exploit a human visual system model that tells us what you can see and what you can’t see when its moving,’ Delp said.
The technique might be used to improve the quality of Internet video. ‘But the research is not focused in this direction yet,’ remarked Delp.