For this purpose, we designed a barcode for the “+” character
in Code 39 where the bars of the code were yellow using the
CMYK color mode (by setting the values of C, M, and K to 0%),
while the Y intensity was varied from 20% to 100%, in both
the printed and detection areas (Fig. 3b). The barcode was
then printed on white paper using an inkjet printer. The scanning
results of the barcode when the bars of the printed and
detection area have different yellow intensities (as shown in
Fig. 3b) have four possibilities (“+”, “−”, “+/−”, and “×”). The
“+” and “−” results indicate that the QuickMark barcode app
was able to read these characters.24 When the yellow intensity
of the detection region is low (60%)