Bar codes

Linear barcodes

• Discrete vs. continuous. In discrete bar codes, there is a non-coding gap between symbols, usually a minimum-width space, so symbols consist of k bars and k−1 spaces. In continuous bar codes, all element widths are significant.
• Two-width vs. multi-width. Simple bar codes have only two choices for each element, usually "narrow" and "wide" widths for each bar or space, with the wide elements being between 2 to 3 times the width of the narrow. Alternatively, some post office codes use the height of a bar, or its absence, to distinguish two types. More complex encodings use multiple element widths, usually 1, 2, 3, or 4 times a basic "module" width.