The IOD (Information Object Definition) and SOP (Service-Object Pair) Class specifications are defined in DICOM standard section PS3.3.

In general, the SOP Class defines what kind of medical information (not Pixel Data) is being stored in the Data Set (metadata tree). So, it defines the set of mandatory DICOM Tags that must be present in the metadata to claim that the file contains some particular SOP Class. This set of Tags defines the Information Object Definition (IOD).

ImageGear always loads the entire metadata tree of the DICOM file without taking into account what kind of SOP Class is actually defined. Any DICOM image can contain either Image Module (that is Pixel Data), or Waveform Sequence (that is Waveform Data), or it can represent a Structured Report (SR), which does not have any pixel or waveform displayable data – it contains only metadata with patient-specific information. All of these are supported by ImageGear.

For more details, see the Waveform Image Support and DICOM Metadata Support sections.

The Pixel Data's compression is determined by the corresponding Transfer Syntax (TransferSyntaxUID (0002,0010) Tag) and does not depend on the SOP class value. See the ImGearDICOMTransferSyntaxes Enumeration section for more details.

ImageGear is able to open a DICOM file with any SOP class as soon as the file's Transfer Syntax is supported. The corresponding SOP class value of the file can be obtained from metadata by looking up the MediaStorageSOPClassUID (0002,0002) Tag.