Device for optically scanning a record carrier

• US 6,415,040 B1
• Filed: 05/20/1998
• Issued: 07/02/2002
• Est. Priority Date: 05/29/1997
• Status: Expired due to Fees

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Vriens, Christianus W. F., Linnartz, Johan P. M. G., Van Dijk, Marten E., Kalker, Antonius A. C. M., Maes, Maurice J. J. J-B., Rongen, Peter M. J., Depovere, Geert F. G.
• Primary Examiner(s): Mancuso, Joseph
• Assistant Examiner(s): Miller, Martin E
• Application Number:
  US09/082,446
• Time in Patent Office: 1,504 Days
• Field of Search: 382/100, 382/232, 380/54, 380/210, 380/252, 380/287, 713/176
• US Class Current: 382/100
• CPC Class Codes: G06T 1/0078 using multiple thresholds
• CPC Class Codes: G06T 2201/0065 Extraction of an embedded watermark; Reliable detection
• CPC Class Codes: H04N 1/32149 Methods relating to embedding, encoding, decoding, detection or retrieval operations
• CPC Class Codes: H04N 1/32203 Spatial or amplitude domain methods H04N1/32309 takes precedence
• CPC Class Codes: H04N 1/32208 involving changing the magnitude of selected pixels, e.g. overlay of information or super-imposition H04N1/32219, H04N1/32224 take precedence
• CPC Class Codes: H04N 2201/3233 of authentication information, e.g. digital signature, watermark
• CPC Class Codes: H04N 2201/327 which are undetectable to the naked eye, e.g. embedded codes
• CPC Class Codes: H04N 5/913 for scrambling ; for copy protection

Abstract

A watermark detector is disclosed to judge whether multimedia content can be copied or not. The watermark detector examines the multimedia content and outputs a signal indicating whether a watermark is present or not. A decision variable indicating to which extent the watermark is present is determined, for example, the amount of correlation between the input signal and a reference copy of the watermark to be detected. The watermark is detected if the decision variable exceeds a predetermined threshold (y₂). The detector also generates a random output signal for a predetermined range of decision values between the threshold (y₂) and a further threshold (y₁).

Claims

1. A method of detecting a watermark embedded in an information signal, comprising the steps of:

determining a decision variable indicating to which extent the watermark is present in the signal; and

generating an output signal indicating detection of the watermark if the decision variable exceeds a predetermined threshold (y₂); and

randomly generating the output signal for decision values below the threshold (y₂).

2. The method as claimed in claim 1, further comprising the step of randomly generating the output signal for a range of decision values between the threshold (y₂) and a further predetermined threshold (y₁).

3. The method as claimed in claim 1, wherein the random output signal is generated with an increasing probability as the decision variable becomes closer to the predetermined threshold (y₂).

4. The method as claimed in claim 3, wherein the probability is a linear function of the decision variable within the range between the threshold (y₂) and the further threshold (y₁).

5. The method as claimed in claim 3, wherein the probability is a raised cosine function of the decision variable within the range between the threshold (y₂) and the further threshold (y₁).

6. The method as claimed in claim 1, wherein the step of randomly generating the output signal includes generating the same output signal whenever the same information signal is received.

13. The method of claim 1, in which:

the output signal is randomly generated for a range of decision values between the threshold (y₂) and a further predetermined threshold (y₁);

the random output signal is generated with an increasing probability as the decision variable becomes closer to the predetermined threshold (y₂);

the probability is a linear function of the decision variable within the range between the threshold (y₂) and the further threshold (y₁);

the probability is a raised cosine function of the decision variable within the range between the threshold (y₂) and the further threshold (y₁); and

the step of randomly generating the output signal includes generating the same output signal whenever the same information signal is received.

7. An arrangement for detecting a watermark embedded in an information signal, comprising:

means for determining a decision variable indicating to which extent the watermark is present in the signal; and

means for generating an output signal indicating detection of the watermark if the decision variable exceeds a predetermined threshold (y₂);

means for randomly generating the output signal for decision values below the threshold (y₂).

8. The arrangement as claimed in claim 7, in which the arrangement further comprises means for randomly generating the output signal for a range of decision values between the threshold (y₂) and a further predetermined threshold (y₁).

9. The arrangement as claimed in claim 7, further comprising means for generating the random output signal with an increasing probability as the decision variable becomes closer to the predetermined threshold (y₂).

10. The arrangement as claimed claim 9, wherein the means for randomly generating the output signal includes a random number generator with a seed input, and means for deriving the seed input from the information signal in accordance with a predetermined function.

11. The arrangement as claimed in claim 9, wherein the means for determining the decision variable constitute the means for deriving the seed input.

14. The arrangement of claim 7, in which:

the arrangement further comprises means for randomly generating the output signal for a range of decision values between the threshold (y₂) and a further predetermined threshold (y₁);

means for generating the random output signal with an increasing probability as the decision variable becomes closer to the predetermined threshold (y₂);

the means for randomly generating the output signal includes a random number generator with a seed input, and means for deriving the seed input from the information signal in accordance with a predetermined function; and

the means for determining the decision variable constitute the means for deriving the seed input.

12. A multimedia playing and/or recording apparatus comprising:

means for reading an information signal from and/or writing an information signal to multimedia material storage;

means for determining a decision variable indicating to which extent the watermark is present in the signal; and

means for generating an output signal indicating detection of the watermark if the decision variable exceeds a predetermined threshold;

means for randomly generating the output signal for decision values below the threshold (y₂).