Generating and reading optical codes with variable density to adapt for visual quality and reliability

A system comprising:

• a memory storing a 2D reference signal block comprising an array of N×N elements, each element having a value and an associated location within the N×N block, the elements in the reference signal block being multi-valued;
• a memory storing a 2D payload signal block comprising an array of M×M binary elements each having first or second values, and each having an associated location within the M×M payload signal block, where M<N;
• and
• means for producing a sparse output signal block of N×N binary elements from said reference signal block and said payload signal block, said output signal being sparse due to less than half of said N×N element binary elements having a first value, said producing includes interpolating the M×M array of first elements of the 2D payload signal to yield an N×N payload signal, said interpolating also changing the payload signal from M×M binary elements to N×N multi-valued elements.

A method of producing a bitonal 2D optical code output signal block that allows for variable spatial density of marked elements, the 2D optical code output signal comprising a 2D array of element locations, each location having a binary mark or not, wherein less than 50% of the locations have marks, the code including a reference signal component and a payload signal component, the reference signal component having a structure that enables geometric synchronization of the optical code when depicted within camera-captured imagery, the method comprising:

• taking, as inputs, (a) a 2D payload signal block and (b) a 2D reference signal block, the 2D payload signal block comprising an array of M×M binary elements each having first or second values, and each having an associated location within the M×M payload signal block, the 2D reference signal block comprising an array of N×N elements where N>M, each element having a value and an associated location within the N×N block, the elements in the reference signal block being multi-valued;
• interpolating the M×M payload signal block to yield an N×N signal block, said interpolating also changing the elements of the payload signal block from M×M binary elements to N×N multi-valued elements;
• combining the N×N reference signal block and the interpolated N×N payload signal block to yield a composite code block comprised of N×N multi-valued elements;
• sorting elements in the N×N composite code block by value, yielding a sorted list of corresponding element locations;
• and
• stepping through the list, placing marks at said corresponding locations within an N×N output signal block, until a desired spatial density of marked elements is achieved;
• wherein a variable spatial density of marked elements is achieved by selecting a smaller or larger number of locations to mark in the N×N output signal block.