Amendment 3 to ITU-T T.801 | ISO/IEC 15444-2 addresses multiple minor changes that enrich the syntax of the JPX file format and, to a minor degree, also that of the codestream.
A revised syntax for ROI boxes allows identifying rectangular regions of interest whose edges are not aligned to the image boundaries in a way that is backwards compatible to the previous ROI box.
Volume data encoded by means of multi-component transformation defined in this Recommendation | International Standard required extensive use of channel definition and compositing layer boxes to identify the components that encode the information of the volume slices; this information may easily grow several kilobytes large, even though its content is largely redundant. This enhancement introduces an alternative, compact form of the two box types that enables a more efficient annotation of channels in this and other applications.
While typically digital images are considered to contain only integer sample values, high-dynamic range imaging or compression of sensory data makes it necessary to also consider floating point sample values. A new sample definition box now allows indicating both integer and floating point channel data in a very flexible way that includes inter alia IEEE floating point formats. Colourspace definitions have been slightly revised to also define colourspace conversions for non-integer data, and a moderate extension of one of the codestream markers allows efficient entropy-coding of such data by the existing integer mechanism.
While ITU.T T.801 | ISO/IEC 15444-2 already included mechanisms for efficient rotation of images in the compressed domain, an extension of the instruction and animation subsystem of the JPX file format now allows to also annotate the orientation of images and instructs image viewers to perform an on-screen rotation of the image on rendering. This rotation mechanism is similar to that of ITU.T T.805 | ISO/IEC 15444-6 and of JPEG XR in ITU.T T.832 | ISO/IEC 29199-2.
Amendment 3 also includes two new box types that, in conjunction with the existing Association box, allow a large XML document to be embedded inside the JPEG 2000 family file to be decomposed into multiple boxes matching the XML element structure of the document. These boxes may be used to store decomposed XML content in a finished file, but they are intended to support scalable transmission of large XML embedded documents in JPIP (ITU.T T.808 | ISO/IEC 15444-9). With these new boxes, there exists a standard stream equivalent for XML content that can be used to pull and subdivide XML content into metadata bins separate from the metadata bin 1. These boxes can also be used as a way to transmit the results of performing an XPath search on XML content in such a way that the context of the resulting portion of the XML document is maintained.
As the extended file format is now powerful enough to express all syntax elements of the JPEG XR file format, a new Annex defines a mapping from the JPEG XR file format to the ISO box-based file format; this mapping is envisioned for future JPEG XR based JPIP applications that would, due to the nature of JPIP, require an ISO file structure based on boxes.
Finally, additional elements in the reader requirements list indicate all additional features included in this enhancement.