Methods for encoding data in an analog video signal such that it survives resolution conversion
View Patent ↗VEIL modulation is a method of “subliminal” encoding of data in a video image that is similar to a watermark. The encoding consists of alternately proportionately raised and lowered luminance on selected horizontal scan lines. The encoding can be detected using a notch filter centered at half the line frequency. The encoding is lost, however, if the resolution of the video signal is changed downward. The invention preserves the encoding by coding alternate groups of lines, not alternate lines. This allows detection with a notch filter even after a reduction in resolution.
1. A method for subliminally encoding data in the image portion of a video signal, wherein the resolution of the image is decreased by a factor of N comprising:
selecting a plurality of 2N consecutive lines in a frame of the video signal;
increasing the luminances of N consecutive lines by an amount that is not visually perceptible; and
decreasing the luminances of the next N consecutive lines.
2. A method for subliminally encoding data in accordance with claim 1 wherein when the luminance of each line is increased or decreased uniformly.
3. A method for subliminally encoding data in the image portion of a video signal in accordance with claim 2 wherein the luminances of said N lines is varied according to a sinusoidal function.
4. A method for subliminally encoding data in the image portion of a video signal in accordance with claim 2 wherein the luminances of said N lines is changed according to a sawtooth function.
5. A method for subliminally encoding data in the image portion of a video signal in accordance with claim 2 wherein the luminance is increased a constant amount for N/2 lines and decreased by the same constant amount for N/2 lines.
6. A method for subliminally encoding data in the image portion of a video signal in accordance with claim 2 wherein for each of said N lines for which the luminance is increased by a certain amount there is a corresponding line for which the luminance is decreased by the same amount.
7. A method for encoding data in the image portion of a video signal comprising:
modifying a group of adjacent lines of a frame by increasing and decreasing the luminances of said group lines in a frame following a prescribed pattern that does not affect the image perceived by the human eye, the luminances of the lines being increased and decreased by amounts selected to render said increases and decreases substantially invisible to a human eye, wherein in said prescribed pattern wherein substantially all of the lines are adjacent other lines whose luminances are changed in the same direction;
transmitting said video signal with said modified lines;
downrezing said video signal; and
extracting said data from said modified lines, wherein said data survives said downrezing.
8. A method for encoding data in the image portion of a video signal in accordance with claim 7 wherein when the luminance of a line is increased or decreased uniformly.
9. A method for encoding data in the image portion of a video signal in accordance with claim 7 wherein the luminances of said lines are changed according to a sinusoidal function.
10. A method for encoding data in the image portion of a video signal in accordance with claim 7 wherein the luminances of said lines are changed according to a sawtooth function.
11. A method for encoding data in the image portion of a video signal in accordance with claim 7 wherein the luminance is increased a constant amount for half the lines and decreased by the same constant amount for the other half of the lines of said group.
12. A method for encoding data in the image portion of a video signal in accordance with claim 7 wherein for each of said lines for which the luminance is increased by a certain amount there is a corresponding line for which the luminance is decreased by the same amount.
13. A method for subliminally encoding data in the image portion of a video signal comprising selecting 2N consecutive lines in a frame increasing the luminances of a group of consecutive N lines from said 2N consecutive lines and decreasing the luminance of the next group of consecutive N lines, said increasing and decreasing of said luminance being performed in a prescribed pattern selected to eliminate any effects on the image perceived by the human eye.
14. A method for encoding data in the image portion of a video signal in accordance with claim 13 wherein when the luminance of a line is increased or decreased, the entire line is changed uniformly.
15. A method for encoding data in the image portion of a video signal in accordance with claim 13 wherein the luminances of said lines are changed according to a sinusoidal function.
16. A method for encoding data in the image portion of a video signal in accordance with claim 13 wherein the luminances of said lines are changed according to a sawtooth function.
17. A method for encoding data in the image portion of a video signal in accordance with claim 13 wherein the luminance is increased a constant amount for half the lines and decreased by the same constant amount for the other half of the lines.
18. A method for encoding data in the image portion of a video signal in accordance with claim 13 wherein for each of said lines for which the luminance is increased by a certain amount there is a corresponding line for which the luminance is decreased by the same amount.
19. A method of encoding data in the image portion of the video signal wherein said video signal is downrezed by a factor N further comprising:
selecting a group of 2N successive lines from a frame of the video signal;
raising the amplitude of N successive lines of said group by an amount small enough so that the change in the video signal is substantially imperceptible;
lowering the amplitude of the remaining N successive lines of said group by the same amount; and
decoding said data, wherein the decoded data is unaffected by said downrezing.