Technology for constructing a symbol template for use by a 1D barcode decoder. One method includes obtaining a first symbol pattern representing a first symbol, the first symbol pattern comprising a plurality of elements, with each element corresponding to a 1D barcode space or bar, in which the first symbol represents one unique 1D bar (b) and space (s) pattern corresponding to a symbol or digit: 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9; obtaining prefix elements, the prefix elements comprising a subset of second symbol elements from a second symbol pattern which precedes the first symbol from within a scanline of image data, the subset being less than a total number of elements within the second symbol elements; extending the first symbol pattern with the prefix elements to yield an overlapping symbol template for use in correlation-based barcode decoding. Other technology provided as well.