+ * \brief writes on disc according to the requested format
+ * \ (ACR-NEMA, DICOM, RAW) the image
+ * \ warning does NOT add the missing elements in the header :
+ * \ it's up to the user doing it !
+ * \ (function CheckHeaderCoherence to be written)
+ * @param type type of the File to be written
+ * (ACR-NEMA, DICOM, RAW)
+ * @param _fp already open file pointer