A.4.4 JPEG 2000 Image Compression
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### A.4.4 JPEG 2000 Image Compression

The International Standards Organization ISO/IEC JTC1 has developed an International Standard, ISO/IS 15444-1 (JPEG 2000 Part 1), for digital compression and coding of continuous-tone still images (see Annex F for further details).

A DICOM Transfer Syntax for JPEG 2000 Image Compression shall be identified by a UID value, appropriate to the choice of JPEG 2000 coding process.

Two Transfer Syntaxes are specified for JPEG 2000 Part 1:

1. A Transfer Syntax with a UID of "1.2.840.10008.1.2.4.90 ", which specifies the use of the lossless (reversible) mode of JPEG 2000 Part 1 (ISO/IEC 15444-1) (i.e., the use of a reversible wavelet transformation and a reversible color component transformation, if applicable, and no quantization).

2. A Transfer Syntax with a UID of "1.2.840.10008.1.2.4.91", which specifies the use of either:

   1. the lossless (reversible) mode of JPEG 2000 Part 1 (ISO/IEC 15444-1) (i.e., the use of a reversible wavelet transformation and a reversible color component transformation, if applicable, and no quantization or code stream truncation), or

   2. the lossy (irreversible) mode of JPEG 2000 Part 1 (ISO/IEC 15444-1) (i.e., the use of an irreversible wavelet transformation and an irreversible color component transformation, if applicable, and optionally quantization, or the use of a reversible wavelet transformation and a reversible color component transformation, if applicable, followed by code stream truncation).

   The choice reversible versus irreversible is at the discretion of the sender (SCU or FSC/FSU).

   ### Note

   When using the irreversible wavelet transformation and an irreversible color component transformation, if applicable, even if no quantization is performed, some loss will always occur due to the finite precision of the calculation of the wavelet and multi-component transformations.

Only the features defined in JPEG 2000 Part 1 (ISO/IEC 15444-1) are permitted for these two Transfer Syntaxes. Additional features and extensions that may be defined in other parts of JPEG 2000 shall not be included in the compressed bitstream unless they can be decoded or ignored without loss of fidelity by all Part 1 compliant implementations.

If the object allows multi-frame images in the pixel data field, then for these JPEG 2000 Part 1 Transfer Syntaxes, each frame shall be encoded separately. Each fragment shall contain encoded data from a single frame.

### Note

1. That is, the processes defined in ISO/IEC 15444-1 shall be applied on a per-frame basis. The proposal for encapsulation of multiple frames in a non-DICOM manner in so-called "Motion-JPEG" or "M-JPEG" defined in 15444-3 is not used.

2. Though a fragment may not contain encoded data from more than one frame, the encoded data from one frame may span multiple fragments. See note in Section 8.2.

For all images, including all frames of a multi-frame image, the JPEG 2000 bitstream specified in ISO/IEC 15444-1 shall be used. The optional JP2 file format header shall NOT be included.

### Note

The role of the JP2 file format header is fulfilled by the non-pixel data attributes in the DICOM Data Set.

The International Standards Organization ISO/IEC JTC1 has also developed JPEG 2000 Part 2 (ISO/IEC 15444-2), which includes Extensions to the compression techniques described in Part 1 of the JPEG 200 Standard. Annex J of JPEG 2000 Part 2 describes extensions to the ICT and RCT multiple component transformations allowed in Part 1. Two types of multiple component transformations are defined in Annex J of Part 2 of JPEG 2000:

1. Array based multiple component transforms that form linear combinations of components to reduce the correlation between components. Array based transforms include prediction based transformations such as DPCM as well as more complicated transformations such as the KLT. These array based transformations can be implemented reversibly or irreversibly.

2. Wavelet based multiple component transformations using the same two wavelet filters as used in Part 1 of JPEG 2000 (5-3 reversible wavelet and 9-7 irreversible wavelet).

Annex J of JPEG 2000 Part 2 also describes a flexible mechanism to allow these techniques to be applied in sequence. Furthermore, it provides mechanisms that allow components to be re-ordered and grouped into component collections. Different multiple component transformation can then be applied to each component collection.

Two additional Transfer Syntaxes are specified for Part 2 JPEG 2000:

1. A Transfer Syntax with a UID of 1.2.840.10008.1.2.4.92, which specifies the use of the lossless (reversible) mode of JPEG 2000 Part 2 (ISO/IEC 15444-2) multiple component transformation extensions, as defined in Annex J of JPEG 2000 Part 2 (i.e., the use of a reversible wavelet transformation and a reversible multiple component transformation, and no quantization or code stream truncation).

2. A Transfer Syntax with a UID of 1.2.840.10008.1.2.4.93, which specifies the use of either:

   1. the lossless (reversible) mode of JPEG 2000 Part 2 (ISO/IEC 15444-2) multiple component transformation extensions, as defined in Annex J of JPEG 2000 Part 2 (i.e., the use of a reversible wavelet transformation and a reversible multiple component transformation, and no quantization), or

   2. the lossy (irreversible) mode of JPEG 2000 Part 2 (ISO/IEC 15444-2) multiple component transformation extensions, as defined in Annex J of JPEG 2000 Part 2 (i.e., the use of an irreversible wavelet transformation and an irreversible multiple component transformation, and optionally quantization, or the use of an reversible wavelet transformation and a reversible multiple component transformation, followed by code stream truncation).

Only the multiple component transformation extensions defined in Annex J of JPEG 2000 Part 2 (ISO/IEC 15444-2) are permitted for these two Transfer Syntaxes. Additional features and extensions that may be defined in other Annexes of JPEG 2000 Part 2 shall not be included in the compressed bitstream.

### Note

the arbitrary wavelet transformations, as defined in Annex H of JPEG 2000 Part 2 (ISO/IEC 15444-2) are not allowed for these two Transfer Syntaxes. The only wavelet transformations that are allowed to be used as multiple component transformations are the reversible 5-3 wavelet transformation and the irreversible 9-7 wavelet transformation, as defined in Annex F of JPEG 2000 Part 1 (ISO/IEC 15444-1).

If the object allows multi-frame images in the pixel data field, then, for these JPEG 2000 Part 2 Transfer Syntaxes, the frames in the object are first processed using the multi-component transformation. After the multiple component transformation has been applied, the transformed frames are encoded using the process described in JPEG 2000 Part 1.

Optionally, the frames can be grouped into one or more component collections. The multiple component transformations are then applied to each component collection independently. The use of component collections can be used to reduce computational complexity and to improve access to specific frames on the decoder. If component collections are used, each fragment shall contain encoded data from a single component collection.

### Note

1. The 3rd dimension transformations that are described in this Supplement are treated in Part 2 of JPEG 2000 as direct extensions to the color component transformations (RGB to YUV) that are described in Part 1 of JPEG 2000. For this reason, each image or frame in the sequence is called a "component". Although the term component is used as a generic term to identify an element of the 3rd dimension, no restriction is made or implied that the transformations in this Supplement apply only to multi-component (or multiple color channel) data. To compress a volumetric data set using this transfer syntax, each frame of the DICOM image is treated as a component of a multi-component image.

2. The progressive nature of the JPEG 2000 code stream allows for the decompression of the image before the complete image has been transferred. If a Storage SCP truncates the code stream by aborting the association, the instance has not been completely transferred and hence should not persist unless different UIDs are assigned (even though it may have been transiently used for display purposes).

3. It has been shown that the use of component collections does not significantly affect the compression efficiency (for details, see http://medical.nema.org/Dicom/minutes/WG-04/2004/2004-02-18/3D_compression_RSNA_2003_ver2.pdf).

4. Though a fragment may not contain encoded data from more than one component collection, the encoded data from one component collection may span multiple fragments.

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