After capturing a barcode image, generate at least one sample line accordingly, acquire sample data of the at least one sample line, generate a first and a second reference lines, generate an upper bound and a lower bound according to the first and the second reference lines, generate a first curve by interpolating all sample points, generate a plurality of effective sample shapes of the first curve according to the upper bound and the lower bound, identify an internal point of each effective sample shape, generate a second curve by interpolating all internal points, and digitize the barcode image to binary data by comparing sample data with the second curve.