find_bar_code — Detect and read bar code symbols in an image.
The operator find_bar_code finds and reads bar code symbols in a given image (Image) and returns the decoded data. In one image an arbitrary number of bar codes of a single type can be read. The type of the desired bar code symbology is given by CodeType. The decoded strings are returned in DecodedDataStrings and the corresponding bar code regions in SymbolRegions. For a total of n successfully read bar codes, the indices from 0 to (n-1) can be used as candidate handle in the operators get_bar_code_object and get_bar_code_result in order to retrieve the desired data of one specific bar code result.
Bar codes are expected to appear dark on a light background. To read light bar codes on a dark background, invert the input image using the operator invert_image beforehand.
Before calling find_bar_code a bar code model must be created by calling create_bar_code_model. This operator returns a bar code model BarCodeHandle, which is input to find_bar_code.
The output value DecodedDataStrings contains the decoded string of the symbol for each bar code result. The contents of the strings are conform to the appropriate standard of the symbology. Typically, DecodedDataStrings contains only data characters. For bar codes with a mandatory check character the check character is not included in the string. For bar codes with an optional check character, like for example Code 39, Codabar, 2/5 Industrial or 2/5 Interleaved, the result depends on the value of the 'check_char' parameter, which can be set in create_bar_code_model, set_bar_code_param or set_bar_code_param_specific: The default setting of 'absent' assumes that no check character is present. In this case, no check is performed and all characters are returned as data. When set to 'present', a check character is expected and used to verify the correctness of the bar code. The bar code is graded as unreadable if the check sum does not match. Accordingly, the symbol region and the decoded string do not appear in the list of resulting strings (DecodedDataStrings) and in the list of resulting regions (SymbolRegions). The check character itself is stripped from the data. If this stripping is undesired, the mode 'preserved' allows to verify the bar code while still keeping the check character in the data.
The underlying decoded reference data, including start/stop and check characters, can be queried by using the get_bar_code_result operator with the option 'decoded_reference'.
Following bar code symbologies are supported:
|2/5 Interleaved||EAN-8 Add-On 2||GS1 DataBar Omnidir|
|Codabar||EAN-8 Add-On 5||GS1 DataBar Truncated|
|Code 39||EAN-13||GS1 DataBar Stacked|
|Code 32 (converted from Code 39)||EAN-13 Add-On 2||GS1 DataBar Stacked Omnidir|
|Code 93||EAN-13 Add-On 5||GS1 DataBar Limited|
|Code 128||UPC-A||GS1 DataBar Expanded|
|MSI||UPC-A Add-On 2||GS1 DataBar Expanded Stacked|
|PharmaCode||UPC-A Add-On 5|
|UPC-E Add-On 2|
|UPC-E Add-On 5|
Note that the PharmaCode can be read in forward and backward direction, both yielding a valid result. Therefore, both strings are returned and concatenated into a single string in DecodedDataStrings by a separating comma.
Note that the GS1 DataBar bar codes may contain an additional composite code component. To find and decode this component, set the parameter 'composite_code' to 'CC-A/B' using the operator set_bar_code_param.
Note that also a barcode of type 'Code 32' can be read by using find_bar_code with CodeType set to 'Code 39' in combination with the external procedure convert_decoded_string_code39_to_code32.
Autodiscrimination describes the simultaneous decoding of multiple bar code types in one call of find_bar_code. For this purpose a tuple of bar code types is specified for the parameter CodeType. Using the generic value 'auto' all known bar code types are decoded - except 'PharmaCode' and 'MSI' because these codes don't have enough features to be reliably separated from other bar code types. The tuple can also contain bar code types with the tilde prefix (~) which won't be decoded. For example
['auto', '~EAN-8', '~EAN-8 Add-On 2', '~EAN-8 Add-On 5']describes all bar code types without 'PharmaCode', 'MSI' and all kinds of 'EAN-8'. Please note that each additionally allowed bar code type increases the run-time of the operator. Using too many bar code types the reliability of the decoding could decrease because not all bar code types can be discriminated reliably. To improve autodiscrimination compatibility bar codes with a check character or check sum should be used.
The bar code reader tries to decode the bar code types in the following order:
GS1 DataBar Omnidirectional, GS1 DataBar Truncated, GS1 DataBar Stacked, GS1 DataBar Stacked Omnidirectional, GS1 DataBar Limited, GS1 DataBar Expanded, GS1 DataBar Expanded Stacked, GS1-128, Code 128, EAN-13 Add-On 5, EAN-13 Add-On 2, EAN-13, UPC-A Add-On 5, UPC-A Add-On 2, UPC-A, EAN-8 Add-On 5, EAN-8 Add-On 2, EAN-8, UPC-E Add-On 5, UPC-E Add-On 2, UPC-E, Code 93, Code 39, Codabar, 2/5 Interleaved, 2/5 Industrial.
Therefore you should exclude at least all definitely not occurring bar code types that are scanned before the first of the bar code types you expect to find or, better, just scan for the explicit list of bar code types you expect.
Especially for the autodiscrimination there is the operator set_bar_code_param_specific. With it some parameters of the bar code model can be set specifically for certain bar code types.
If the bar code reader is in training mode, the operator find_bar_code executes a training cycle. The training mode is described with the operator set_bar_code_param.
With the operator set_bar_code_param you can specify a timeout for find_bar_code. If find_bar_code reaches this timeout, it returns all codes decoded so far. Whether a timeout occurred or not can be queried by calling get_bar_code_result with the parameter 'timeout_occurred'.
Advice on low resolution bar code imaging systems
This advice applies to bar code applications that use low resolution images, i.e., images in which a single bar is between one and two pixels wide.
In these cases, one should optimize the bar code imaging system in order to eliminate noise and focal blur because a combination of these optical distortions lead to problems in the decodability of low resolution bar codes.
This operator modifies the state of the following input parameter:
Input image. If the image has a reduced domain, the barcode search is reduced to that domain. This usually reduces the runtime of the operator. However, if the barcode is not fully inside the domain, the barcode cannot be decoded correctly.
Regions of the successfully decoded bar code symbols.
Handle of the bar code model.
Type of the searched bar code.
Default value: 'auto'
List of values: '2/5 Industrial', '2/5 Interleaved', 'Codabar', 'Code 128', 'Code 39', 'Code 93', 'EAN-13 Add-On 2', 'EAN-13 Add-On 5', 'EAN-13', 'EAN-8 Add-On 2', 'EAN-8 Add-On 5', 'EAN-8', 'GS1 DataBar Expanded Stacked', 'GS1 DataBar Expanded', 'GS1 DataBar Limited', 'GS1 DataBar Omnidir', 'GS1 DataBar Stacked Omnidir', 'GS1 DataBar Stacked', 'GS1 DataBar Truncated', 'GS1-128', 'MSI', 'PharmaCode', 'UPC-A Add-On 2', 'UPC-A Add-On 5', 'UPC-A', 'UPC-E Add-On 2', 'UPC-E Add-On 5', 'UPC-E', 'auto'
Data strings of all successfully decoded bar codes.
The operator find_bar_code returns the value 2 (H_MSG_TRUE) if the given parameters are correct. Otherwise, an exception will be raised.
get_bar_code_result, get_bar_code_object, clear_bar_code_model