DICOM defines defaults for Lossy JPEG Image Compression, one for 8-bit images and the other for 12-bit images. JPEG coding Process 1 (identified by Transfer Syntax UID = "1.2.840.10008.1.2.4.50") is used for 8-bit images. JPEG coding Process 4 (identified by Transfer Syntax UID = "1.2.840.10008.1.2.4.51") is used for 12-bit images. This implies that:
a) If an Application Entity issues an A-ASSOCIATE request where any offered Abstract Syntaxes is associated in one or more Presentation Context(s) with a JPEG lossy compression Transfer Syntax, at least one of the Presentation Contexts that include this Abstract Syntax, shall include the appropriate DICOM Default Lossy JPEG Compression Transfer Syntax.
Note: 1. Offering Abstract Syntax (AS1) in two Presentation Contexts with Transfer Syntaxes JPEG lossy (JL1) and (JL2) is not valid, but offering AS1-JL1, AS1-JL2 and AS1-JLD is valid because the DICOM Default JPEG Lossy Transfer Syntax (JLD) is present in at least one of the Presentation Contexts that are based on Abstract Syntax (AS1).2. The DICOM Default Transfer Syntax (uncompressed) may be offered if the sender has access to the original pixel data in an uncompressed or lossless compressed form.
b) If an Application Entity that supports one or more Lossy JPEG Transfer Syntaxes receives an A-ASSOCIATE indication corresponding to a request which follows the requirements specified in Section 10.3 a), every Presentation Context related to a given Abstract Syntax cannot be rejected in an A-ASSOCIATE response for the reason that the DICOM Default lossy JPEG Transfer Syntax is not supported.