Differential modulation for robust signaling and synchronization

1. A non-transitory computer readable medium on which is stored instructions, which when executed by a processor, perform the method of:

generating an auxiliary data signal comprised of variable data elements;

mapping each of the variable data elements to plural blocks within a host image signal, wherein each block comprises neighboring embedding locations within the host image signal;

for each variable data element, modulating the host image signal according to the variable data element to embed the variable data element in corresponding plural blocks, including within each of the corresponding plural blocks, modulating the host image signal by establishing differential relationships between the variable data element in non-adjacent embedding locations within each block of the plural blocks.

2. The non-transitory computer readable medium of claim 1 on which is stored instructions, which when executed by a processor, perform the method of:

mapping variable data elements in a repetitive structure that forms a template in a frequency domain transform of the host image signal.

3. The non-transitory computer readable medium of claim 1 wherein plural of the variable data elements are mapped to the same plural blocks within the host image signal, and plural variable data elements within the same block are encoded in differential relationships among interleaved embedding locations within the same block.

4. The non-transitory computer readable medium of claim 1 on which is stored instructions, which when executed by a processor, perform the method of:

mapping synchronization signal elements to plural blocks within the host image signal.

5. The non-transitory computer readable medium of claim 4 wherein embedding locations of the synchronization signal elements and the variable data elements are interleaved within the same plural blocks.

6. The non-transitory computer readable medium of claim 4 wherein differential relationships for encoding the variable data elements and synchronization signal elements are established using vectors for the variable data elements and synchronization elements that are orthogonal.

7. An apparatus for encoding auxiliary data in a host image signal, the apparatus comprising:

means for generating an auxiliary data signal comprised of variable data elements;

means for mapping each of the variable data elements to plural blocks within the host image signal, wherein each block comprises neighboring embedding locations within the host image signal;

means for modulating the host image signal according to the variable data element to embed the variable data element in corresponding plural blocks, including means for modulating the host image signal by establishing differential relationships between the variable data element in non-adjacent embedding locations within corresponding blocks where each variable data element is mapped.

8. The non-transitory computer readable medium of claim 1 , further comprising instructions, which when executed by a processor, perform a method of decoding an auxiliary data signal embedded in a host image, the method comprising:

applying geometrically distorted versions of a first extraction filter to the host image to obtain feature vectors;

obtaining geometric distortion parameters from the feature vectors;

for each of plural filtering locations within the host image, applying a second extraction filter that extracts auxiliary data signal elements from relationships between host image signal elements at embedding locations within a block of neighboring embedding locations around a filtering location, wherein the relationships are formed by differential modulation of the auxiliary data signal within the host image;

aggregating filter output across plural filtering locations for each of plural variable data signal elements within the auxiliary data signal to obtain estimates of each of the plural variable data signal elements; and

error correction decoding a variable message from the estimates.

9. The non-transitory computer readable medium of claim 8 , further comprising instructions, which when executed by a processor, perform the acts of:

transforming the host image into a frequency domain, wherein a repetitive pattern of the relationships form a template;

matching the transformed host image with a pre-determined template to obtain an estimate of rotation and scale of the auxiliary data signal within the host image.

10. The non-transitory computer readable medium of claim 9 , further comprising instructions, which when executed by a processor, perform the acts of:

with the rotation and scale to compensate for geometric distortion, applying the extraction filter to extract an approximate auxiliary data signal from the relationships;

transforming the approximate auxiliary data signal into a frequency domain; and

refining synchronization by matching the pre-determined template with the transformed approximate auxiliary data signal.

11. The non-transitory computer readable medium of claim 8 further comprising instructions, which when executed by a processor, perform the act of:

transforming the host image into a frequency domain, wherein a repetitive pattern of the relationships form a template; wherein the auxiliary data signal comprises variable data signal elements and sync signal elements that are differentially encoded within the host image according to orthogonal vectors for the variable data signal elements and the sync signal elements.

12. The non-transitory computer readable medium of claim 8 further comprising instructions, which when executed by a processor, perform the act of:

synchronizing the auxiliary data signal with nulls formed in an output of applying the second extraction filter to the host image.