A key component in generating halft

A key component in generating halftone QR code is a representation model that minimally binds to the original module, and yet
is flexible to adapt target halftone image. To this end, we propose a
model that subdivides each module into 3× 3 sub modules and binds
module’s color to the center sub module, while leaving remaining
eight sub modules free to independently change their appearance.
By rendering a subdivided module as a binary image of 3 × 3 pixels, we obtain a set of 512 binary patterns (or simply patterns hereafter), which is used to characterize the appearance of modules.

For each pattern, we introduce a novel term pattern reliability, which is modeled as a probability that a module’s readability is not compromised by a pattern sub stitution, and is evaluated through a large database of synthetic QR codes.

Note that in absence of any analytic function quantifying readability of QR code under variations, pattern reliability characterizes the preference among patterns towards controllable levels of readability.