Volume marking with low-frequency

1. A method for processing data for insertion of watermark data, the method comprising the steps of:

(a) dividing an image sequence into a plurality of regions;

(b) subdividing one of said regions into a plurality of sub-regions such that luminance in a selected sub-region is approximately equal to luminance in another sub-region, wherein the one of said regions is subdivided by selecting a plane within a volume where luminance on one side of the plane is approximately equal to luminance on a second side of the plane; and

(c) selecting a location within said selected sub-region that is suitable for inserting a luminance amplitude different from the original luminance amplitude at that location;

wherein a plane is found using a method comprising the steps of:

(i) finding luminance of a first volume containing the first frame of a region and finding luminance of a second volume containing the last frame of a region;

(ii) comparing luminance of said first volume to luminance of said second volume and finding a higher luminance volume and a lower luminance volume;

(iii) increasing said lower luminance volume by including the next frame adjacent to said lower luminance volume and finding luminance of this new volume;

(iv) comparing luminance of the new volume to luminance of said higher luminance volume to find a new higher luminance volume and a new lower luminance volume;

(v) repeating steps (iii) and (iv) using the new higher luminance and new lower luminance volumes until all frames in the region have been included in either the higher luminance volume or the lower luminance volume whereby a plane separating the two volumes is located in a single frame;

(vi) adjusting the angle of the plane separating the two volumes, relative to one or more of the axes, to optimize luminance in both sub-regions to be practically equal.

2. The method according to claim 1 , wherein a luminance amplitude representative of watermark data is inserted at a selected location.

3. The method according to claim 1 , wherein a plurality of locations suitable for inserting luminance amplitudes are selected and one or more of a plurality of luminance amplitudes representative of watermark data are inserted.

4. The method according to claim 1 , wherein luminance is subsampled to a lower resolution before selecting a plane.

5. The method according to claim 4 , wherein a plane is selected by performing a search to minimize the differences between luminance values on opposite sides of the plane.

6. The method according to claim 4 , wherein a plurality of test planes are located and a gradient descent algorithm is used to select a plane.

7. The method according to claim 4 or claim 5 or claim 6 , wherein the selected plane is used in full resolution regions or sub-regions.