handle generic group length tags

and start to look at tags that need contextual VRs

Author: jcupitt

src/dicom-data.c

@@ -216,13 +216,13 @@ void dcm_element_destroy(DcmElement *element)
 
 uint16_t dcm_element_get_group_number(const DcmElement *element)
 {
-    return (uint16_t)(element->tag >> 16);
+    return element->tag >> 16;
 }
 
 
 uint16_t dcm_element_get_element_number(const DcmElement *element)
 {
-    return (uint16_t)(element->tag);
+    return element->tag & 0xffff;
 }
 
 

src/dicom-dict.c

@@ -304,6 +304,7 @@ static const struct _DcmAttribute attribute_table[] = {
     {0X00041512, DCM_VR_TAG_UI, "ReferencedTransferSyntaxUIDInFile"},
     {0X0004151A, DCM_VR_TAG_UI, "ReferencedRelatedGeneralSOPClassUIDInFile"},
     {0X00041600, DCM_VR_TAG_UL, "NumberOfReferences"},
+    {0X00080000, DCM_VR_TAG_UL, "GenericGroupLength"},
     {0X00080001, DCM_VR_TAG_UL, "LengthToEnd"},
     {0X00080005, DCM_VR_TAG_CS, "SpecificCharacterSet"},
     {0X00080006, DCM_VR_TAG_SQ, "LanguageCodeSequence"},
@@ -5281,6 +5282,13 @@ static const struct _DcmAttribute *attribute_from_tag(uint32_t tag)
 
     dcm_init();
 
+    // tags with element number 0 are generic group length tags ... map all of
+    // these (except 0000,0000) to tag 0008,0000 (GenericGroupLength)
+    if (tag != 0 &&
+        (tag & 0xffff) == 0) {
+        tag = 0x00080000;
+    }
+
     HASH_FIND_INT(attribute_from_tag_dict, &tag, entry);
 
     return (const struct _DcmAttribute *)entry;
@@ -5313,12 +5321,11 @@ DcmVR dcm_vr_from_tag(uint32_t tag)
 {
     const struct _DcmAttribute *attribute;
 
-    if ((attribute = attribute_from_tag(tag)) &&
-        dcm_dict_str_from_vr((DcmVR) attribute->vr_tag)) {
-        return (DcmVR) attribute->vr_tag;
+    if (!(attribute = attribute_from_tag(tag))) {
+        return DCM_VR_ERROR;
     }
 
-    return DCM_VR_ERROR;
+    return (DcmVR) attribute->vr_tag;
 }
 
 

src/dicom-file.c

@@ -353,12 +353,15 @@ static DcmElement *read_element_header(DcmError **error,
 
     DcmVR vr;
     if (implicit) {
+        // this can be an ambiguious VR, eg. pixeldata is allowed in implicit
+	// mode and has to be disambiguated later from other tags
         vr = dcm_vr_from_tag(tag);
         if (vr == DCM_VR_ERROR) {
             dcm_error_set(error, DCM_ERROR_CODE_PARSE,
                           "Reading of Data Element header failed",
                           "Tag %08X not allowed in implicit mode", tag);
         }
+
         if (!read_uint32(error, filehandle, length, position)) {
             return NULL;
         }