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 33 submodules and binds
module’s color to the center submodule, while leaving remaining
eight submodules 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 substitution, 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.