Using EasyBarCode

Symbologies

A symbology defines how a bar code is encoded using its bars and spaces.

In EasyBarCode, the following symbologies are enabled by default:

Code 128	Ean 8	Ean 13
GS1 128	Code 39	Code 39 Extended
Code 39 Reduced	Code 93	Code 93 Extended
GS1 DataBar Omnidirectional	GS1 DataBar Limited	GS1 DataBar Expanded
GS1 DataBar Omnidirectional Stacked	GS1 DataBar Expanded Stacked

The following symbologies are also supported:

ITF-14	Pharmacode (one track)	PDF417
Codabar	MSI	UPC A
UPC E	ADS Anker	BC412
Code 11	Code 13	Code 25 Datalogic
Code 25 Matrix	Code 25 Iata	Code 25 Industry
Code 25 Compressed	Code 25 Inverted	Code 25 Interleaved
Code 32	Code BCD Matrix	Code CIP
Code STK	IBM Delta Distance A	Plessey
Telepen	Binary Code	RSS14
RSS14 Limited	RSS14 Expanded

See also

A description of the properties and look of each symbology can be found here

To setup the symbologies to consider during the reading operation, use the following methods of the EBarCodeReader ^{.NET Python} class:

• EBarCodeReader::EnableSymbology ^{.NET Python}

• EBarCodeReader::EnableSymbologies ^{.NET Python}

• EBarCodeReader::EnableSafeSymbologies ^{.NET Python}

• EBarCodeReader::EnableDefaultSymbologies ^{.NET Python}

• EBarCodeReader::DisableAllSymbologies ^{.NET Python}

• Use EBarCodeReader::GetEnabledSymbologies ^{.NET Python} to check the enabled symbologies.

  Note

  EBarCodeReader::EnableSafeSymbologies ^{.NET Python} does not enable the EBarCodeSymbologies_PDF417 ^{.NET Python}, the EBarCodeSymbologies_CodeStk ^{.NET Python}, the EBarCodeSymbologies_BinaryCode ^{.NET Python} and the EBarCodeSymbologies_PharmacodeOneTrack ^{.NET Python} symbologies:

  • Enabling the PDF417 symbology modifies the detection process, which may be detrimental to detect other symbologies.

  • The three other symbologies are very permissive and can generate a large amount of false positives.

  You must explicitly use EBarCodeReader::EnableSymbology ^{.NET Python} to enable the PDF417, CodeStk, BinaryCode and PharmacodeOneTrack symbologies.

• Because some symbologies are similar, a given bar code can be detected as corresponding to more than one. Use EBarCode::GetSymbologies ^{.NET Python} to retrieve all compatible symbologies, in order of decreasing confidence.

• Use EBarCode::GetDecodedString ^{.NET Python} with its optional symbology parameter to retrieve the decoded string as decoded given the symbology passed as parameter. If you omit this parameter, the decoded string will be decoded using the most likely symbology.

• For the GS1-128 and GS1 DataBar Omnidirectional, Limited, Expanded, Omnidirectional Stacked and Expanded Stacked symbologies:

  • Use EBarCode::GetDecodedString ^{.NET Python} to get the machine-readable code (for example: ]C11118011215190101).

  • Use EGs1Translator::GetHumanReadableCode ^{.NET Python} to get the human-readable version (for example: (11)180112(15)190101).

• Some characters can be encoded using ECI in the EBarCodeSymbologies_PDF417 ^{.NET Python} symbology. In such cases, the returned EBarCode ^{.NET Python} contains the encoded data converted to utf-8.

Checksum and Validation

The checksum of a bar code enables the reader to validate the bar code contents, most symbologies possess one, see the list.

• By default, EasyBarCode checks the checksum validity when required by the symbology specifications.

  • The symbologies Code39 (and variants), Codabar, Code 11 and Code 25 (and variants) define but do not enforce a checksum. We call their checksum optional. By opposition, the checksums that are always present are called mandatory. When the checksum is optional, there is no way to know if the barcode contains one from the image alone and no checksum validation is performed by default.

  • For the PharmacodeOneTrack symbology, by default, no checksum is computed but additional validations are performed on the bar code vertical uniformity to rule out false positives.

• To reject bar codes if they fail mandatory or optional checksum validation or Pharmacode validation, respectively use EBarCodeReader::SetValidateMandatoryChecksum ^{.NET Python}, EBarCodeReader::SetValidateOptionalChecksum ^{.NET Python} and EBarCodeReader::SetValidatePharmacode ^{.NET Python}.

  • Set the property to true, to not return bar codes failing the corresponding validation.

  • By default, EBarCodeReader::GetValidateMandatoryChecksum ^{.NET Python} and EBarCodeReader::GetValidatePharmacode ^{.NET Python} are set to true and EBarCodeReader::GetValidateOptionalChecksum ^{.NET Python} is set to false.

• Call EBarCode::GetChecksumOK ^{.NET Python} to check the checksum status of the returned EBarCode ^{.NET Python} object.

• By default, the checksum characters are included into the string returned by EBarCode::GetDecodedString ^{.NET Python}.

  • Set the optional parameter includeChecksum to false to remove these checksum characters from the returned string,

  Note

  As mentioned above, some symbologies, such as Code39 have optional checksum characters. In those cases, determining their presence automatically is usually not possible. Thus, setting includeChecksum to false might crop parts of the decoded string.

See also

Refer to the following code snippet as an example: Reading a Bar Code Following a Given Symbology

Grading Bar Codes

To compute the print quality indicators as defined by the ISO 15416 standard:

1. Set the EBarCodeReader::SetComputeGrading ^{.NET Python} to true.

2. The print quality of the bar codes is computed during the EBarCodeReader::Read ^{.NET Python} operation.

3. Retrieve the grades with the accessor EBarCode::GetGradingParameters ^{.NET Python} of the class EBarCode ^{.NET Python}.

   This will retrieve an EBarCodeGradingParameters ^{.NET Python} object.

4. Retrieve the numeric grades (0 to 40) directly from the object.

5. Use the method EBarCodeGradingParameters::ConvertToAlphabeticGrade ^{.NET Python} to convert the numeric grades to alphabetic grades (F to A).

Note

At the moment, grading is only supported for the Ean 13, Code 128 and GS1 128 symbologies. Don’t hesitate to contact the support if you need grading of other symbologies.

See also

• Refer to the following code snippet as an example: Grading a Bar Code.

• For more information on code grading, see Code Grading.

Advanced Features

Contents of the EBarCode Object

When a bar code is read from an image, the EBarCode ^{.NET Python} object contains the following information:

• The decoded string ^{.NET Python} of the bar code.

• The position ^{.NET Python} of the bar code.

• One or several symbologies ^{.NET Python} compatible with the bar code.

• Whether the checksum of the barcode is ok ^{.NET Python}.

• Whether the pattern ^{.NET Python}, advanced decoding ^{.NET Python} or printing error ^{.NET Python} error correction was used.

• The grading parameters ^{.NET Python} of the bar code.

• Draw methods for the decoded string ^{.NET Python} and position ^{.NET Python} of the bar code.

Reading using an ERegion

• Use EBarCodeReader::Read ^{.NET Python}, using an overload taking an ERegion ^{.NET Python} to restrict the domain on which the EBarCodeReader ^{.NET Python} detects and reads the bar codes .

Reading a bar code (green) with an ERegion (blue).

Reading using a Grid

If the codes in the images are arranged in a regular grid-like fashion:

• Use the dedicated EBarCodeReader::Read ^{.NET Python} overloads that take an EGrid ^{.NET Python} object to improve the reliability and the speed of the reading.

• Use the methods EGrid::SetEnableCell ^{.NET Python}, EGrid::SetEnableRow ^{.NET Python}, EGrid::SetEnableColumn ^{.NET Python} or EGrid::SetEnableAll ^{.NET Python} to disable the processing of cells that you know do not contain any code.

• Use the method EBarCodeGrid::GetResults ^{.NET Python} of the returned EGrid ^{.NET Python} object to retrieve the codes read in each cell of the defined grid.

See also

For an example, see Reading a Grid of Bar Codes

Reading of 4 bar codes arranged in a grid.

Using a Timeout

If you have a defined time constraint:

• Use EBarCodeReader::SetTimeOut ^{.NET Python} to define a timeout for the EBarCodeReader ^{.NET Python} object. This timeout limits the amount of time available to the EBarCodeReader::Read ^{.NET Python} method and forces it to return early if needed.

Specifying the Orientation of your Codes

For most symbologies, a pattern identifies whether the codes must be read from left to right or right to left.

This is however not the case for the Code STK, Binary Code and Pharmacode symbologies.

For these symbologies, you must know whether to decode the bar code from left to right or from right to left. Use the method EBarCodeReader::SetReadingOrientation ^{.NET Python} to specify it.

Learning from provided Images to Improve the Detection Performances

• The learning automatically tunes the scales at which you try to find a bar code to best fit the set of images you gave it. The scales are modified to read the maximum number of codes depending on the parameters of the learn method.

• EBarCodeReader::Learn ^{.NET Python} has two Boolean parameters:

  • keepDefaultScales indicates that the scales used by default should not be disabled by the learning (true by default).

  • addAllScales indicates that all the scales that allow to detect one code should be enabled (true by default).

• Tips:

  • If you perform a learning on a few problematic images, set both parameters to true.

  • If you perform a learning on a representative set of problematic images, set keepDefaultScales to true and addAllScales to false.

  • If you perform a learning on a representative set of all the images you want to read, set both parameters to false.

  • The only benefit to set either of these parameters to false is the reading speed. In most cases, the impact should not be important, so you can leave them to true. When less than maxNumCodes are read in an image, the reader tries to find a code in all the scales enabled, which takes time. In that case, setting these parameters to false may have an important impact on the speed.

See also

For an example, see Learning a Bar Code

Correcting Errors

• EasyBarCode implements three methods to read more difficult codes. In rare cases, these can cause false positives and so you can disable them.

  • EBarCodeReader::SetEnablePatternCorrection ^{.NET Python}: Most bar codes symbologies (Code128, Ean13,…) group consecutive strips into patterns. The algorithm then decodes the bar code one pattern at a time, and, when the current pattern does not match one of the patterns of the symbology, it tries to match the closest pattern (under some constraints).

  • EBarCodeReader::SetEnableAdvancedDecoding ^{.NET Python}: Specifically for Ean13, Code128 and GS1-128, an advanced algorithm determines the most likely pattern sequence that enforces the checksum.

  • EBarCodeReader::SetEnablePrintingErrorCorrection ^{.NET Python}: Some printing defects can occur in bar codes (like a bar being one module wide instead of two). Some error correction is enabled for these cases specifically and, as this method is more likely to generate false positives than the other ones, it is disabled by default.

• Once a bar code is returned, use the methods EBarCode::GetPatternCorrectionUsed ^{.NET Python}, EBarCode::GetAdvancedDecodingUsed ^{.NET Python} and EBarCode::GetPrintingErrorCorrectionUsed ^{.NET Python} to check if each of these algorithms was used to detect the bar code.