Apparatus and method for augmenting a video image

1. A method of augmenting a video image, comprising the steps of:

estimating an extent of an identified surface captured within the video image, the identified surface having a non-skin tone;

identifying skin pixels within a test area corresponding to the estimated extent of the identified surface within the video image;

extrapolating positions for skin pixels within the video image that are outside the test area, based upon the identified skin pixels;

setting an extent of a computer graphic to be superposed substantially on top of the identified surface within the video image, the extent being greater than the estimated extent of the identified surface;

generating a mask from a combination of identified skin pixels and extrapolated skin pixels, the mask having at least the same extent as the computer graphic; and

superposing a graphical augmentation of the video image responsive to the generated mask.

2. A method according to claim 1 , in which the test area is the same as the estimated extent of the identified surface within the video image.

3. A method according to claim 1 , in which the test area extends to within a predetermined number of pixels from the edge of the estimated extent of the identified surface within the video image.

4. A method according to claim 1 , in which the extrapolating step comprises:

identifying a region of skin pixels that intersects the edge of the test area; and

for the identified region:

identifying a first peripheral skin pixel at the edge;

tracing the periphery of the region away from the edge for a predetermined distance; and

extrapolating the trace out from the edge of the test area.

5. A method according to claim 1 , in which the extrapolating step comprises:

identifying a region of skin pixels that intersects the edge of the test area; and

for the identified region:

calculating a centreline that intersects with the edge of the test area;

calculating a region width perpendicular to the centreline; and

propagating the identified region outside the edge of the test area responsive to the direction of the centreline and the calculated region width.

6. A method according to claim 1 in which the step of generating a mask comprises:

identifying the region of extrapolated skin pixels between the edge of the test area and the edge of the extent of the computer graphic; and

generating the mask representative of the identified skin pixels and the identified extrapolated skin pixels.

7. A method according to claim 6 , in which the step of identifying the region of extrapolated skin pixels comprises:

detecting whether an extrapolated skin pixel satisfies a skin pixel colour test, and

identifying the pixel as an extrapolated skin pixel if it passes the test.

8. A non-transitory computer program product comprising computer program instructions that when performed by a processor implement a method comprising the steps of:

estimating an extent of an identified surface captured within the video image, the identified surface having a non-skin tone;

identifying skin pixels within a test area corresponding to the estimated extent of the identified surface within the video image;

extrapolating positions for skin pixels within the video image that are outside the test area, based upon the identified skin pixels;

setting an extent of a computer graphic to be superposed substantially on top of the identified surface within the video image, the extent being greater than the estimated extent of the identified surface;

generating a mask from a combination of identified skin pixels and extrapolated skin pixels, the mask having at least the same extent as the computer graphic; and

superposing the graphical augmentation of the video image responsive to the generated mask.

9. An entertainment device for augmented reality applications, comprising:

a video input configured to receive a video image;

an image processor configured to estimate an extent of an identified surface captured within the video image, the identified surface having a non-skin tone;

a skin pixel detector operable to identify skin pixels within a test area corresponding to the estimated extent of the identified surface within the video image;

a processor arranged in operation to extrapolate positions for skin pixels within the video image that are outside the test area, based upon the identified skin pixels,

the processor being configured to set an extent of a computer graphic to be superposed substantially on top of the identified surface within the video image, the extent being greater than the estimated extent of the identified surface;

a mask generator configured to generate a mask from a combination of identified skin pixels and extrapolated skin pixels, the mask having at least the same extent as the computer graphic; and

the image processor being configured to superpose the graphical augmentation of the video image responsive to the generated mask.

10. An entertainment device according to claim 9 , in which the test area is the same as the estimated extent of the identified surface within the video image.

11. An entertainment device according to claim 9 , in which the test area extends to within a predetermined number of pixels from the edge of the estimated extent of the identified surface within the video image.

12. An entertainment device according to claim 9 , in which the processor is arranged in operation to:

identify a region of skin pixels that intersects the edge of the test area; and

for the identified region:

identify a first peripheral skin pixel at the edge;

trace the periphery of the region away from the edge for a predetermined distance; and

extrapolate the trace out from the edge of the test area.

13. An entertainment device according to claim 9 , in which the processor is arranged in operation to:

identify a region of skin pixels that intersects the edge of the test area; and

for the identified region:

calculate a centreline that intersects with the edge of the test area;

calculate a region width perpendicular to the centreline; and

propagate the identified region outside the edge of the test area responsive to the direction of the centreline and the calculated region width.

14. An entertainment device according to claim 9 , in which the mask generator is arranged in operation to:

identify the region of extrapolated skin pixels between the edge of the test area and the edge of the extent of the computer graphic;

detect whether an extrapolated skin pixel in the identified region satisfies a skin pixel colour test, and

identify the pixel as an extrapolated skin pixel if it passes the test; and

generate the mask representative of the identified skin pixels and the identified extrapolated skin pixels.

15. An augmented reality system, comprising:

an entertainment device for augmented reality applications, comprising:

a video input configured to receive a video image;

an image processor configured to estimate an extent of an identified surface captured within the video image;

a skin pixel detector operable to identify skin pixels within a test area corresponding to the estimated extent of the identified surface within the video image;

a processor arranged in operation to extrapolate positions for skin pixels within the video image that are outside the test area, based upon the identified skin pixels,

the processor being configured to set an extent of a computer graphic to be superposed substantially on top of the identified surface within the video image, the extent being greater than the estimated extent of the identified surface;

a mask generator configured to generate a mask from a combination of identified skin pixels and extrapolated skin pixels, the mask having at least the same extent as the computer graphic; and

the image processor being configured to superpose the graphical augmentation of the video image responsive to the generated mask;

a video camera operably coupled to the entertainment device; and

a book comprising a fiduciary marker for the purpose of identifying a surface of the book.