Bar Code

List of Operators ↓

This chapter provides an introduction to bar codes and the most important terms used when finding and reading bar codes in HALCON.

Structure of linear (1D) bar codes

A bar code consists of several dark bars and bright spaces. For every bar code there is a smallest possible element, the narrowest possible bar or the narrowest possible space, which is called module. In general, the width of the bars and spaces is different, but always a multiple of the module. Several bars and spaces together form a pattern. This pattern encodes a symbol defined in a decoding table. The conventions how such a binary pattern encodes a symbol and the corresponding decoding table lead to the respective bar code type. In addition to the patterns encoding the symbols, there are also patterns with special tasks. Depending on the type there are further patterns which can or must be part of the bar code:

Structure of a composite bar code

Composite bar codes consist of the following elements:

The following figure shows a schematic representation of a composite bar code.
image/svg+xml 1 6 8 7 5 4 2 3 9 0 1 2
Schematic representation of a composite bar code by means of an example bar code of type UPC-A Composite: Linear bar code (black), 2D code (light blue), and the linking pattern (orange).

Reading of a bar code

To be able to read a bar code in an image, it must be found first. The regions in which HALCON assumes a bar code are called candidates.

In order to read a candidate, different lines are laid through the region, called scanlines. Although theoretically a single scanline would be sufficient, one tries to decode the bar code along all scanlines. This increases the chance of decoding the code correctly. In addition, several successfully decoded scanlines allow additional plausibility checks, i.e., reading several scanlines equally decreases the chance of false positives.
image/svg+xml H A L C O N
Schematic representation of different scanlines of a candidate. Certain scanlines were read successfully (green), while the reading failed for others (red).

The workflow and various examples showing how to read bar codes in HALCON can be found in the “`Solution Guide I - Basics.

List of Operators

Delete a bar code model and free the allocated memory
Create a model of a bar code reader.
Decode bar code symbols within a rectangle.
Deserialize a bar code model.
Detect and read bar code symbols in an image.
Access iconic objects that were created during the search or decoding of bar code symbols.
Get one or several parameters that describe the bar code model.
Get parameters that are used by the bar code reader when processing a specific bar code type.
Get the alphanumerical results that were accumulated during the decoding of bar code symbols.
Get the names of the parameters that can be used in set_bar_code* and get_bar_code* operators for a given bar code model
Read a bar code model from a file and create a new model.
Serialize a bar code model.
Set selected parameters of the bar code model.
Set selected parameters of the bar code model for selected bar code types
Write a bar code model to a file.