US Patent 9635378 Sparse modulation for robust signaling and synchronization

Sparse signal modulation schemes encode a data channel on a host image in a manner that is robust, flexible to achieve perceptual quality constraints, and provides improved data capacity. The host image is printed by any of a variety of means to apply the image, with sparse signal, to an object. After image capture of the object, a decoder processes the captured image to detect and extract data modulated into the sparse signal. The sparse signal may incorporate implicit or explicit synchronization components, which are either formed from the data signal or are complementary to it.