Implementation notes¶

Encodings¶

DICOM supports many codepages to encode strings. DICOM instances using special characters should contain the SpecificCharacterSet (0008,0005) tag. The latter tag specifies which codepage is used by the DICOM instance. Internally, Orthanc converts all these codepages to the UTF-8 encoding (cf. the Orthanc::ParsedDicomFile class).

In particular, plugins must assume that any string or JSON file coming from the Orthanc core is encoded using UTF-8. Similarly, plugins must use UTF-8 when calling services provided by the Orthanc core. The conversion to/from UTF-8 is done transparently by the plugin engine.

The configuration option DefaultEncoding plays an important role. It is used in three cases:

1. If receiving a DICOM instance without the SpecificCharacterSet (0008,0005) tag, Orthanc will interpret strings within this instance using this default encoding. This is important in practice, as many DICOM modalities are not properly configured with respect to encodings.
2. When answering a C-Find query (including for worklists), Orthanc will use its default encoding. If one single answer uses a different encoding, it will be transcoded.
3. If creating a new instance (e.g. through the /tools/create-dicom URI of the REST API, or through the OrthancPluginCreateDicom() primitive of the plugin SDK) and if SpecificCharacterSet (0008,0005) is not provided for this instance, Orthanc will use its default encoding. Note however that if SpecificCharacterSet is set, Orthanc will transcode the incoming UTF-8 strings to the codepage specified in this tag, and not to the default encoding.