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1 .. _implementation-notes:
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2
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3 Implementation notes
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4 ====================
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5
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6 Encodings
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7 ---------
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8
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9 DICOM supports many codepages to encode strings. DICOM instances using
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10 special characters should contain the ``SpecificCharacterSet
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11 (0008,0005)`` tag. The latter tag `specifies which codepage
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12 <http://dicom.nema.org/dicom/2013/output/chtml/part03/sect_C.12.html#sect_C.12.1.1.2>`__
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13 is used by the DICOM instance. Internally, Orthanc converts all these
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14 codepages to the `UTF-8 encoding
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15 <https://en.wikipedia.org/wiki/UTF-8>`__ (cf. the
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16 ``Orthanc::ParsedDicomFile`` class).
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73
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17
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18 In particular, :ref:`plugins <creating-plugins>` must assume that any
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19 string or JSON file coming from the Orthanc core is encoded using
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20 UTF-8. Similarly, plugins must use UTF-8 when calling services
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21 provided by the Orthanc core. The conversion to/from UTF-8 is done
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22 transparently by the plugin engine.
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23
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24 The :ref:`configuration option <configuration>` ``DefaultEncoding``
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25 plays an important role. It is used in three cases:
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26
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27 1. If receiving a DICOM instance without the ``SpecificCharacterSet
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28 (0008,0005)`` tag, Orthanc will interpret strings within this
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29 instance using this default encoding. This is important in
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30 practice, as many DICOM modalities are not properly configured with
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31 respect to encodings.
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32
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33 2. When answering a :ref:`C-Find query <dicom-find>` (including for
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34 worklists), Orthanc will use its default encoding. If one single
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35 answer uses a different encoding, it will be transcoded.
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36
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37 3. If creating a new instance (e.g. through the
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38 ``/tools/create-dicom`` URI of the :ref:`REST API <rest>`, or
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39 through the ``OrthancPluginCreateDicom()`` primitive of the plugin
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40 SDK) and if ``SpecificCharacterSet (0008,0005)`` is not provided
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41 for this instance, Orthanc will use its default encoding. Note
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42 however that if ``SpecificCharacterSet`` is set, Orthanc will
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43 transcode the incoming UTF-8 strings to the codepage specified in
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44 this tag, and not to the default encoding.
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