JPEG 2000 codestreams and JP2 containers

JPEG 2000 refers to both an image compression standard and its codestream format. A raw JPEG 2000 codestream begins with the FF 4F Start of Codestream (SOC) marker. The FF 51 Start of Image and Size (SIZ) marker normally follows it. Depending on the encoder settings, the codestream can use the reversible 5/3 wavelet transform for lossless compression or the irreversible 9/7 wavelet transform for lossy compression.

JP2 is a container format around a JPEG 2000 codestream. A JP2 file begins with a JP2 signature box and consists of boxes such as ftyp, jp2h, and jp2c. The payload of the jp2c box must be a JPEG 2000 codestream; it is not an arbitrary-data box. The other boxes describe the image and container but do not redefine the compression format.

DICOM encapsulation

DICOM JPEG 2000 transfer syntaxes encapsulate the raw JPEG 2000 codestream in Pixel Data, not the complete JP2 container. Container-aware processing must extract the payload of the jp2c box before encapsulation when the source is a JP2 file. The selected lossless or lossy transfer syntax and compression attributes must describe the codestream’s actual compression.

Detect the format from its byte structure rather than its filename extension:

• A raw codestream starts with the FF 4F SOC marker.

• A JP2 container starts with the 12-byte signature 00 00 00 0C 6A 50 20 20 0D 0A 87 0A.