Content encoded luminosity modulation

1. A content encoder for encoding content into a source image for display on a display device, the content encoder comprising: inputs for receiving data representing content to be encoded into the source image; a processor arranged to encode the content into a sequence of display frames each including the source image, the content encoded as a time varying two-dimensional pattern of luminosity modulations of portions of the source image to form a sequence of encoded images of the source image; outputs arranged to output the sequence of encoded images to the display device.

2. A content encoder as claimed in claim 1 , wherein the time varying two-dimensional pattern of luminosity modulations comprises a pattern of increased and decreased brightness of pixels of the source image.

3. A content encoder as claimed in claim 1 , wherein each display frame in the sequence of display frames comprises a copy of the source image encoded with the content.

4. A content encoder as claimed in claim 1 , wherein the two dimensional pattern of luminosity modulations encoded by the processor into the source image varies between image frames.

5. A content encoder as claimed in claim 1 , wherein the two dimensional pattern is a grid of cells and the content is encoded into the source image by raising or lowering the luminosity of pixels within a given cell of the grid.

6. A content encoder as claimed in claim 5 , wherein each cell in the grid is arranged to encode one bit of content related data.

7. A content encoder as claimed in claim 1 , wherein the processor is arranged to scale the luminosity of the source image prior to encoding the content into the source image.

8. A content encoder as claimed claim 1 , wherein the processor is arranged to modulate the luminosity of the source image by a first amount in order to encode the content into the source image and wherein the processor is arranged to modulate the luminosity of the source image by a further amount in order to insert an orientation flag into the encoded image.

9. A content encoder as claimed in claim 8 , wherein the processor is arranged to insert the orientation flag within a predefined portion of the encoded image.

10. A content encoder as claimed in claim 1 , wherein the two dimensional pattern is a grid of cells and the processor is arranged to attenuate the luminosity modulation applied to any given cell towards the edges of the cell.

11. A content encoder as claimed in claim 1 , wherein the processor is arranged to invert or mirror the content encoded to a subset of the display frames within the sequence of display frames.

12. A content decoder for decoding content encoded into a sequence of display frames, each display frame comprising an encoded image of a source image, and each encoded image comprising a two dimensional pattern of luminosity modulations of portions of the source image to encode the content into the source image, the content decoder comprising: inputs for receiving the sequence of display frames; a processor arranged to (i) process the sequence of display frames to determine the two dimensional pattern of luminosity modulations; (ii) sample the two dimensional pattern of luminosity modulations of portions of the source image to determine the encoded content within each display frame, and (iii) decode the encoded content to determine the content; outputs to output the content.

13. A content decoder as claimed in claim 12 , wherein the processor is arranged to analyse a number of display frames in the received sequence of display frames and determine a mean value for the luminosity of each pixel in the display frame in order to determine the source image.

14. A content decoder as claimed in claim 12 , wherein the inputs are arranged to receive an unmodulated version of the source image.

15. A content decoder as claimed in claim 12 , wherein the two dimensional pattern of luminosity modulations comprises a pattern of increased and decreased brightness of pixels of the source image.

16. A content decoder as claimed in claim 12 , wherein the processor is arranged to analyse the sequence of display frames in order to locate the pattern of luminosity modulations within the display frame and the processor is arranged to crop the pattern from the display frame or warp the pattern to a fixed two dimensional shape.

17. A content decoder as claimed in claim 12 , wherein the processor is arranged to rotate each display frame in the sequence of display frames to a predetermined orientation based on an orientation flag inserted into the encoded image by further modulation of the luminosity of the source image.

18. A content decoder as claimed in claim 12 , wherein the pattern of luminosity modulations is in the form of a grid of cells and the processor is arranged to determine the resolution of the grid in the sequence of display frames.

19. A content decoder as claimed in claim 18 , wherein the processor is arranged to analyse each grid cell in order to determine content encoded within the grid and the processor is arranged to analyse the content decoded from a current display frame and to compare it to content decoded from the previous display frame in the sequence, the current display frame being discarded if it is substantially similar to the previous display frame.

20. A method of encoding content into a source image for display on a display device, the method comprising: receiving data representing content to be encoded into the source image; encoding the content into a sequence of display frames each including the source image to form a sequence of encoded images of the source image, the content being encoded as a time varying two-dimensional pattern of luminosity modulations of portions of the source image; outputting the sequence of encoded images to the display device.