Improved watermark synchronization based on local autocorrelation function

Abstract

An autocorrelation function (ACF) to synchronize watermarks has been adopted in practical applications because of its robustness against affine transforms. However, ACFs are vulnerable to projective transform, which commonly occurs during the illegal copying of cinema footage due to the angle of the camcorder relative to the screen. The cinema footage that is captured by camcorders both is projected and has undergone digital-to-analog and analog-to-digital conversion (D-A/A-D conversion). We present a novel watermarking scheme that uses a local autocorrelation function (LACF) that can resist projective transforms as well as affine transforms. A watermark also used for synchronization is designed and additively embedded in the spatial domain. The embedded watermark is extracted in a blind way after recovering from distortions. The LACF scheme with a mathematical model is proposed to synchronize the watermark against distortions. On various video clips, experimental results show that the presented scheme is robust against projective distortions as well as D-A/A-D conversion. (C) 2009 SPIE and IS&T. [DOI: 10.1117/1.3134121]