Defining the whitelist of characters

Limiting a subset of characters instead of using the full list for a selected language can greatly improve recognition accuracy, increase speed, and reduce resource consumption. A list of characters can be automatically identified from an image using the built-in Aspose.OCR mechanisms.

You can define a list of characters Aspose.OCR engine will look for by specifying them as a case-sensitive string in alphabet property of recognition settings. Characters that do not match the provided list are ignored.

// Provide the image
string file = "source.png";
AsposeOCRInput source;
source.url = file.c_str();
std::vector<AsposeOCRInput> content = { source };
// Set recognition language
RecognitionSettings settings;
settings.alphabet = L"AÁBCDEÉFG12345";
// Extract text from the image
auto result = asposeocr_recognize(content.data(), content.size(), settings);
// Output the recognized text
wchar_t* buffer = asposeocr_serialize_result(result, buffer_size, export_format::text);
std::wcout << std::wstring(buffer) << std::endl;
// Release the resources
asposeocr_free_result(result);

Alternatively, you can specify the preset in allowed_characters property of recognition settings:

Preset	Allowed characters
characters_allowed_type::ALL	All characters.
characters_allowed_type::LATIN_ALPHABET	Only recognize Latin / English text (A to Z and a to z), without accented characters.
characters_allowed_type::DIGITS	Recognize only binary, octal, decimal, or hexadecimal numbers (0-9 and A to F).

// Provide the image
string file = "source.png";
AsposeOCRInput source;
source.url = file.c_str();
std::vector<AsposeOCRInput> content = { source };
// Set recognition language
RecognitionSettings settings;
settings.allowed_characters = characters_allowed_type::DIGITS;
// Extract text from the image
auto result = asposeocr_recognize(content.data(), content.size(), settings);
// Output the recognized text
wchar_t* buffer = asposeocr_serialize_result(result, buffer_size, export_format::text);
std::wcout << std::wstring(buffer) << std::endl;
// Release the resources
asposeocr_free_result(result);