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Barcode reading

Barcodes in the Passport Reader

Barcodes are line drawings which are designed to be recognized and read automatically. They are built from bars (lines) and spaces (gaps between lines). The thinnest line is called module, and is the basic element of a barcode. There are many barcode types. The simplest ones contain bars and spaces with two different widths. The most complex ones are the two dimensional coloured barcode images. The PR system currently recognizes 8 different barcode types: EAN, Code39, Code128, Interleaved 2 of 5, and PDF417, DataMatrix, QR Code, and Aztec Code.

Barcode types

Interleaved 2 of 5

This barcode can be used for storing numbers only. It has two different sizes for the elements, and 2 elements out of 5 are wide. The possible checksum value is up to the user level, its presence cannot be determined automatically.

Code 3 of 9

This is an alphanumerical barcode but it basically can store capital letters only. It also contains two element sizes, and 3 elements out of 9 are wide. The possible checksum value is up to the user level, its presence cannot be determined automatically. The Full ASCII Mode (characters with value of 0 to 127) can be represented by using escape sequences.

European Article Numbering

This barcode stores a 13 digit (or 8 digit in short version) number. It contains elements in at most 4 different widths. The checksum is a mandatory part of the barcode. It is used for article numbering only.

Code 128

This is a generally used alphanumeric barcode. It can store characters in 3 character sets including a compressed numeric representation and the Full ASCII Mode (characters with value of 0 to 127). It contains elements in at most 4 different widths. The checksum is a mandatory part of the barcode.

Portable Data File 417

This is a 2D (multi-row) barcode. It can store binary or alphanumeric data in byte, text or numeric mode. The text mode uses 4 character sets. A PDF417 symbol character is build from 17 modules and it contains four bars and four spaces. An element can be 1 to 6 modules wide. The barcode contains Reed-Solomon error correction coding through 2 to 512 error correction codewords.

Data Matrix

This is a 2D matrix barcode. It can store binary or alphanumeric data, and contains error correction coding.

Quick Response Code

This is a 2D matrix barcode. It can store binary or alphanumeric data, and contains Reed-Solomon error correction coding with 7 to 30 percent correction capacity.

Aztec Code

This is a 2D matrix barcode. It can store binary or alphanumeric data, and contains Reed-Solomon error correction coding with wide range of correction capacity.

Barcode basics

Barcodes can be read with the GetBarcode function. If the type of the barcode is known beforehand, the process can be sped up by specifying the type parameter. If the type parameter is not set then the barcode/recog_order property can be used to control and speed up the process.

Basically barcodes can be read only in horizontal direction. This behaviour can be changed with the barcode/enable_vertical property.

Advanced properties

The barcode/contrast property controls the contrast compensation level. The default value is 1.5. Changing this value affects the barcode reading accuracy.

There are some special cases when the barcode/deglinter property can be useful. It reduces the noise of the damages of the covering foil. It is developed to eliminate the light horizontal thin lines produced by the glinting of the broken foil. The deglinting process works only when the height of the noise line is significantly smaller than the size of the barcode signs.

bc-deglint1.jpg
bc-deglint2.jpg
Sample image: Deglinter effect


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