A general two-dimensional coding means is presented that allows recovery of data with only a cropped portion of the code, and without knowledge of the carrier image. A description of both an encoding and recovery system is provided, along with an illustrative example. Our solution involves repeating a payload with a fixed number of bits assigning one bit to every symbol in the image, whether that symbol is data carrying or non-data carrying, with the goal of guaranteeing recovery of all the bits in the payload. The system uses row-to-row offset itself to communicate the value of the phase of the circular payload. The recovery system is given the number bits in the payload, evaluates each candidate shift and ranks its confidence based on the variance of the payload bits. Symbols determined to be unsuitable for recovery are labeled “abstentions” and not included in the decoding process; special consideration is given to the checkerboard subsampling that can occur in the case when halftone cells are used as the data-carrying symbols. This particular application is examined via tests to quantify the likelihood of unrecoverable bits and bit redundancy as a function of phase and crop window size.
Robert Ulichney, Matthew Gaubatz, Steven Simske, "Circular Coding for Data Embedding" in Proc. IS&T Int'l Conf. on Digital Printing Technologies and Digital Fabrication (NIP29), 2013, pp 142 - 147, https://doi.org/10.2352/ISSN.2169-4451.2013.29.1.art00038_1