Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Time-Frequency Signal Synthesis and Its Application in Multimedia Watermark Detection | Hindawi Publishing Corporation EURASIP Journal on Applied Signal Processing Volume 2006 Article ID 86712 Pages 1-14 DOI ASP 2006 86712 Time-Frequency Signal Synthesis and Its Application in Multimedia Watermark Detection Lam Le and Sridhar Krishnan Department of Electrical and Computer Engineering Ryerson University Toronto ON Canada M5B 2K3 Received 29 March 2005 Revised 28 January 2006 Accepted 5 February 2006 Recommended for Publication by Alex Kot We propose a novel approach to detect the watermark message embedded in images under the form of a linear frequency modulated chirp. Localization of several time-frequency distributions TFDs is studied for different frequency modulated signals under various noise conditions. Smoothed pseudo-Wigner-Ville distribution SPWVD is chosen and applied to detect and recover the corrupted image watermark bits at the receiver. The synthesized watermark message is compared with the referenced one at the transmitter as a detection evaluation scheme. The correlation coefficient between the synthesized and the referenced chirps reaches or above for a maximum bit error rate of 15 under intentional and nonintentional attacks. The method provides satisfactory result for detection of image watermark messages modulated as chirp signal and could be a potential tool in multimedia security applications. Copyright 2006 Hindawi Publishing Corporation. All rights reserved. 1. INTRODUCTION Chirp signals are present ubiquitously in many areas of science and engineering. Chirps are identified in natural signals such as animal sounds birds frogs whales and bats whistling sound as well as in man-made systems such as in radar sonar telecommunications physics and acoustics. For example in radar applications chirp signals are used to analyze the trajectories of moving objects. Due to its inherent ability to reject interference linear frequency modulated signals or chirp signals are also used widely in spread spectrum communication. Chirps
