phone equipped with 8-megapixels camera and four popular barcode
readers.We also conducted an experiment to compare halftone
QR code with original QR code to estimate the sensitivity of readability
under various distortions. During the experiment, we showed
one QR code on a monitor per trial and user who holding the smartphone
was asked to scan the code. During the scan, he/she was allowed
to rotate the device and move it forward and backward as we
normally do, and asked to put down the device before starting the
next trial to avoid a bias scan. We define a successful scan as the
barcode reader returns a correct data string within 3 seconds