Encoding apparatus and method

• US 20060110005A1
• Filed: 10/28/2005
• Published: 05/25/2006
• Est. Priority Date: 11/01/2004
• Status: Active Grant

• Current Assignee: Sony United Kingdom Limited (Sony Group Corp.)
• Original Assignee: Sony United Kingdom Limited (Sony Group Corp.)
• Inventors: Tapson, Daniel Warren
• Granted Patent: US 7,792,322 B2
• Time in Patent Office: Days
• US Class Current: 382/100
• CPC Class Codes: G06T 1/0028 Adaptive watermarking, e.g. Human Visual System [HVS]-based watermarking
• CPC Class Codes: G06T 2201/0052 Embedding of the watermark in the frequency domain
• CPC Class Codes: G06T 2201/0202 whereby the quality of watermarked images is measured; Measuring quality or performance of watermarking methods; Balancing between quality and robustness

Abstract

An encoding data processing apparatus is arranged to generate a marked copy of an image by introducing a code word into a copy of the image. The apparatus comprises a code word generator operable to generate the code word having a plurality of code word coefficients. The encoding apparatus includes an image perception analyser and a strength adapter. The image perception analyser is operable to receive the image and to generate weighting factors for scaling the code word coefficients with respect to parts of the image with which the code word coefficients are to be combined. The strength adapter is operable to combine the weighting factors with the code word coefficients, and a combiner is operable to combine the weighted code word with the image. The image perception analyser includes a contrast masking engine, a smoothness compensation engine and a compensation combiner. The contrast masking engine is operable to determine for each of a plurality of parts of the image a relative measure of contrast and to calculate for each part at least one weighting factor in accordance with the relative contrast measure. The weighting factor has an effect of reducing the code word coefficients for image parts having lower relative contrast measures. The smoothness compensation engine is operable to determine for each image part a smoothness factor, and to generate compensation factors in accordance with the smoothness factors, which when combined with the corresponding weighting factors have an effect of reducing the strength of the code word coefficients for higher smoothness factors. The compensation combiner is operable to combine the compensation factors with the weighting factor to provide compensated weighting factors for adapting the strength of the watermark code word. The encoding data processing apparatus is provided with an advantage in that a likelihood of an effect of a code word being perceivable when the code word is combined with an image is reduced.

Claims

1. An encoding data processing apparatus for generating a marked copy of an image by introducing a code word into a copy of the image, the apparatus comprising

a code word generator operable to generate the code word having a plurality of code word coefficients,

an image perception analyser operable to receive the image and to generate weighting factors for scaling the code word coefficients with respect to parts of the image with which the code word coefficients are to be combined,

a strength adapter operable to combine the weighting factors with the code word coefficients, and

a combiner operable to combine the weighted code word coefficients with the image, wherein

the image perception analyser includes a contrast masking engine, a smoothness compensation engine and a compensation combiner,

the contrast masking engine being operable

to determine for each of a plurality of parts of the image a relative measure of contrast,

to calculate for each part, a weighting factor in accordance with the relative contrast measure, the weighting factor having an effect of reducing the code word coefficients for image parts having a lower relative contrast measure, and the smoothness compensation engine is operable

to determine for each image part a smoothness factor, and

to generate compensation factors in accordance with the smoothness factors, which when combined with the corresponding weighting factors have an effect of reducing the strength of the code word coefficients for higher smoothness factors, and

the compensation combiner is operable to combine the compensation factors with the weighting factor to provide compensated weighting factors for adapting the strength of the code word.

2. An encoding data processing apparatus as claimed in claim 1, wherein the contrast masking engine includes

a transform processor operable to perform a discrete cosine transform on the image parts,

a contrast calculator operable to calculate the relative contrast measure for each of the image parts from a comparison of each Alternating Current coefficient with a Direct Current coefficient of each of a plurality of Discrete Cosine Transform coefficients provided by the Discrete Cosine Transform of the image, and

a masking function operable

to determine the weighting factor value in accordance with the comparison of the Alternating Current coefficients to the Direct Current coefficients.

3. An encoding data processing apparatus as claimed in claim 2, wherein the masking function is operable for each code word coefficient

to determine a maximum allowable relative contrast measure which the code word coefficient would produce in the image by comparing the relative contrast measure of the image part with a predetermined perceptibility relationship between the relative contrast measure of the image and the relative contrast measure which would be produced by the code word coefficients, and

to calculate the weighting factor value by scaling the determined maximum allowable contrast of the code word coefficient and the Direct Current Discrete Cosine Transform coefficient value of the code word coefficient in the Discrete Cosine Transform domain.

4. An encoding data processing apparatus as claimed in claim 1, wherein the smoothness compensation engine includes

a neighbour contrast function operable to determine a smoothness factor for each part of the image in accordance with a relative change between pixel values of the image part, and

a smoothness masking function operable to determine the compensation value with respect to the smoothness factor, to the effect that the compensation factors reduce the weighting factors for higher smoothness factor values.

5. An encoding data processing apparatus as claimed in claim 4, wherein the smoothness masking function determines the compensation factors in accordance with a predetermined relationship established with respect to the human eye'"'"'s sensitivity to visual changes within the image part.

6. An encoding data processing apparatus as claimed in claim 1, wherein the image perception analyser includes

a temporal masking engine operable to generate compensation values which when combined with the weighting factor values by the compensation combiner has an effect of increasing code word coefficients when the images change with respect to time.

7. An encoding data processing apparatus as claimed in claim 6, wherein the change of the images includes scene changes in video material represented by the images.

8. An encoding data processing apparatus as claimed in claim 1, wherein the image perception analyser includes

a perceptual weighting function operable to generate compensation factors with respect to the image parts, which when combined with the weighting factors have an effect of reducing the code word coefficients for image parts in which changes are more noticeable to the human eye than other image parts.

9. An encoding data processing apparatus as claimed in claim 1, wherein the image parts are formed by dividing each image into blocks of pixels having an equal number of pixels.

10. A cinema projector including an encoding data processing apparatus according to claim 1, wherein the encoding data processing apparatus is operable to receive image signals, and to introduce code words into the image signals before reproduction.

11. A media terminal including an encoding data processing apparatus according to claim 1, wherein the encoding data processing apparatus is operable to receive image signals, and to introduce code words into the image signals.

12. A method of generating a marked copy of an image by introducing a code word into a copy of the image, the method comprising

generating the code word having a plurality of code word coefficients,

generating weighting factors for scaling the code word coefficients with respect to a part of the image with which the code word coefficients are to be combined,

combining the weighting factors with the code word coefficients, and

combining the weighted code word with the image, wherein the generating the weighting factors comprises

determining for each of a plurality of parts of the image a relative measure of contrast,

calculating for each part a weighting factor in proportion with the relative contrast measure, the weighting factor having an effect of reducing the code word coefficients for image parts having relatively low contrast,

determining for each image part a smoothness factor, and

generating compensation factors in accordance with the smoothness factors, which compensation factors when combined with the corresponding weighting factors have an effect of reducing the strength of the code word coefficients for higher smoothness factors, and

combining the compensation factors with the weighting factor to provide compensated weighting factors for adapting the strength of the watermark code word.

13. A method as claimed in claim 12, wherein the calculating the weighting factor comprises

performing a Discrete Cosine Transform on the image parts,

calculating the relative contrast measure for each of the image parts from a comparison of each Alternating Current coefficient with a Direct Current coefficient of each of a plurality of Discrete Cosine Transform coefficients provided by the Discrete Cosine Transform,

determining a maximum allowable relative contrast measure which the code word coefficient would produce in the image by comparing the relative contrast measure of the image part with a predetermined perceptibility relationship between the relative contrast measure of the image and the relative contrast measure which would be produced by the code word coefficients, and

calculating the weighting factor value by scaling the determined maximum allowable contrast of the code word coefficient and the Direct Current Discrete Cosine Transform coefficient value of the code word coefficient in the Discrete Cosine Transform domain.

14. A method as claimed in claim 12, wherein the determining the smoothness compensation factors includes

determining a smoothness factor for each part of the image in accordance with a relative change between pixel values of the image part, and

determining the compensation factor value with respect to the smoothness factor, to the effect that the compensation factors reduce the weighting factors for higher smoothness factor values.

15. Computer software having program code, which when loaded onto a data processor, causes the data processor to perform the method according to claim 12.

16. A data bearing medium bearing computer program code, which when loaded onto a data processor performs the method according to claim 12.

17. A data bearing medium according to claim 16, wherein the medium is a storage medium.

18. A data bearing medium bearing data representing a marked image encoded by the encoding method according to claim 12.