Re: [WM]: Watermark Detection Threshold Determination

["Jeffrey Bloom" <jbloom@sarnoff.com>]

Since you know that your watermarks are spherically symmetric and since you 
are using normalized correlation, you should look at the following paper:

M. L. Miller and J. A. Bloom, ``Computing the Probability of False 
Watermark Detection'', Proceedings of the Third International Workshop on 
Information Hiding, pp. 146-158, 1999.  (the pdf is available on my web 
page listed below)

This paper will give an exact formulation of the false positive probability 
as a function of threshold.  So, you set your threshold by first 
determining what false positive probability your application 
requires.  Plug in this false positive probability and your watermark 
dimension (N) and then simply turn the crank to find the required threshold.

- Jeffrey

At 06:45 AM 11/28/2001 +0800, Eric Sheo wrote:
>Hi everyone,
>
>I have doubts on the determination of the 'detection
>threshold'.
>
>By approaching experimentally, assuming watermark
>(org_wm) is the original gaussian sequence of
>pseudo-random real numbers of length N.
>
>Step 1. I generate 1000 gaussian sequences of
>pseudo-random real numbers of length N.
>
>Step 2. I calculate the normalized correlation (NC)
>using org_wm with respect to each generated gaussian
>sequences of pseudo-random real numbers (step1).
>
>To determine the detection threshold, do i sum all the
>normalized correlation (NC) and take the average of
>the NC and is there anything wrong with my steps? Pls
>give me your valuable advises. Thank you.
>
>Eric

---
Dr. Jeffrey A Bloom, Web and Database Systems
Sarnoff Corporation, 201 Washington Road, CN 3500, Princeton, NJ 08543-5300

Digital Watermarking,
Morgan Kaufmann Publishers, 2001
http://www.mkp.com/books_catalog/catalog.asp?ISBN=1-55860-714-5

Purchase from Amazon.com
http://www.amazon.com/exec/obidos/ASIN/1558607145/jeffrebloomsh-20

Email: jbloom@sarnoff.com
WWW: www.geocities.com/Jeffrey_Bloom
Phone: (609) 734-3287
Fax: (609) 734-2662




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