Pattern reliability evaluation: We used an open source barcode
reader, called ZBar [Brown 2007], to decode every synthetic QR
code in database. In addition to returning a boolean value indicating
the readability of the QR code, ZBar is also able to provide
module-wise response that informs whether a module is decoded
correctly. We calculate pattern reliability as a ratio of number of
successful decodes among all samples in database and properly normalize
the value. Figure 4(b) shows typical examples. Finally, we
obtain a database of 0.6 million synthetic QR codes in which the
variation of estimated pattern reliability is stabilized as shown in
Figure 4(c). To measure stability, we calculate pattern reliability
variation as norm of vector difference and use a threshold of 0:01.