Methods and apparatus for embedding watermarks
View Patent ↗Methods and apparatus for embedding a watermark are disclosed. An example method disclosed herein to embed a watermark in a compressed data stream comprises obtaining a set of transform coefficients included in the compressed data stream, the set of transform coefficients having a respective first set of mantissa codes and a respective set of exponents, the first set of mantissa codes associated with a respective set of mantissa step sizes, identifying a first transform coefficient from the set of transform coefficients having a smallest magnitude among the set of transform coefficients, determining a second set of mantissa codes based on the first transform coefficient and the set of step sizes, and replacing the first set of mantissa codes included in the compressed data stream with the second set of mantissa codes to embed the watermark without uncompressing the compressed data stream.
1. A method to embed a watermark in a compressed data stream, the method comprising:
obtaining a set of transform coefficients from the compressed data stream, the set of transform coefficients comprising a first set of mantissa codes and a first set of exponents, respective ones of the first set of mantissa codes being represented by a first number of bits;
determining a second set of mantissa codes based on the first set of mantissa codes and the watermark, respective ones of the second set of mantissa codes being represented by the same first number of bits as the respective ones of the first set of mantissa codes; and
replacing the first set of mantissa codes in the compressed data stream with the second set of mantissa codes to embed the watermark in the compressed data stream without uncompressing the compressed data stream.
2. A method as defined in claim 1 , wherein the first set of exponents is unchanged in the compressed data stream after the watermark is embedded.
3. A method as defined in claim 1 , wherein determining the second set of mantissa codes comprises:
modifying a first mantissa code from the first set of mantissa codes based on the watermark to determine a second mantissa code;
quantizing the second mantissa code based on the first number of bits to determine a third mantissa code; and
including the third mantissa code in the second set of mantissa codes.
4. A method as defined in claim 3 , wherein quantizing the second mantissa code based on the first number of bits to determine the third mantissa code comprises setting a value of the third mantissa code to a largest value represented by the first number of bits in response to determining that a value of the second mantissa code is greater than the largest value represented by the first number of bits.
5. A method as defined in claim 3 , wherein quantizing the second mantissa code based on the first number of bits to determine the third mantissa code comprises setting a value of the third mantissa code to a smallest value represented by the first number of bits in response to determining that a value of the second mantissa code is less than the smallest value represented by the first number of bits.
6. A method as defined in claim 1 , further comprising determining the first number of bits from information included in the compressed data stream.
7. A computer readable storage device or storage disc comprising computer readable instructions which, when executed, cause a computer to at least:
obtain a set of transform coefficients from a compressed data stream, the set of transform coefficients comprising a first set of mantissa codes and a first set of exponents, respective ones of the first set of mantissa codes being represented by a first number of bits;
determine a second set of mantissa codes based on the first set of mantissa codes and a watermark, respective ones of the second set of mantissa codes being represented by the same first number of bits as the respective ones of the first set of mantissa codes; and
replace the first set of mantissa codes in the compressed data stream with the second set of mantissa codes to embed the watermark in the compressed data stream without uncompressing the compressed data stream.
8. A storage device or storage disc as defined in claim 7 , wherein the first set of exponents is unchanged in the compressed data stream after the watermark is embedded.
9. A storage device or storage disc as defined in claim 7 , wherein to determine the second set of mantissa codes, the instructions, when executed, further cause the computer to:
modify a first mantissa code from the first set of mantissa codes based on the watermark to determine a second mantissa code;
quantize the second mantissa code based on the first number of bits to determine a third mantissa code; and
include the third mantissa code in the second set of mantissa codes.
10. A storage device or storage disc as defined in claim 9 , wherein to quantize the second mantissa code based on the first number of bits to determine the third mantissa code , the instructions, when executed, further cause the computer to set a value of the third mantissa code to a largest value represented by the first number of bits in response to determining that a value of the second mantissa code is greater than the largest value represented by the first number of bits.
11. A storage device or storage disc as defined in claim 9 , wherein to quantize the second mantissa code based on the first number of bits to determine the third mantissa code , the instructions, when executed, further cause the computer to set a value of the third mantissa code to a smallest value represented by the first number of bits in response to determining that a value of the second mantissa code is less than the smallest value represented by the first number of bits.
12. A storage device or storage disc as defined in claim 7 , wherein the instructions, when executed, further cause the computer to determine the first number of bits from information included in the compressed data stream.
13. A watermark embedding device comprising:
an unpacking unit to obtain a set of transform coefficients from a compressed data stream, the set of transform coefficients comprising a first set of mantissa codes and a first set of exponents, respective ones of the first set of mantissa codes being represented by a first number of bits; and
a modification unit to:
determine a second set of mantissa codes based on the first set of mantissa codes and a watermark, respective ones of the second set of mantissa codes being represented by the same first number of bits as the respective ones of the first set of mantissa codes; and
replace the first set of mantissa codes in the compressed data stream with the second set of mantissa codes to embed the watermark in the compressed data stream without uncompressing the compressed data stream.
14. A watermark embedding device as defined in claim 13 , wherein the first set of exponents is unchanged in the compressed data stream after the watermark is embedded.
15. A watermark embedding device as defined in claim 13 , wherein to determine the second set of mantissa codes, the modification unit is to:
modify a first mantissa code from the first set of mantissa codes based on the watermark to determine a second mantissa code;
quantize the second mantissa code based on the first number of bits to determine a third mantissa code; and
include the third mantissa code in the second set of mantissa codes.
16. A watermark embedding device as defined in claim 15 , wherein to quantize the second mantissa code based on the first number of bits to determine the third mantissa code , the modification unit is to set a value of the third mantissa code to a largest value represented by the first number of bits in response to determining that a value of the second mantissa code is greater than the largest value represented by the first number of bits.
17. A watermark embedding device as defined in claim 15 , wherein to quantize the second mantissa code based on the first number of bits to determine the third mantissa code , the modification unit is to set a value of the third mantissa code to a smallest value represented by the first number of bits in response to determining that a value of the second mantissa code is less than the smallest value represented by the first number of bits.
18. A watermark embedding device as defined in claim 13 , wherein the unpacking unit is further to determine the first number of bits from information included in the compressed data stream.