Add HTJ2K Compressor

[palemieux]

WIP DO NOT MERGE

This patch fulfills my action item from the September 19 TSC meeting.

Introduction

This patch proposes to add support for High-Throughput JPEG 2000 (HTJ2K) compression to OpenEXR -- HTJ2K is JPEG 2000 with the HT block coder standardized in Rec. ITU-T T.814 | ISO/IEC 15444-15. As detailed at Evaluating HTJ2K as a compressor option for OpenEXR, HTJ2K demonstrates significant improvements in both speed and file size over other OpenEXR compressors. Furthermore, HTJ2K is a worldwide standard that benefits from a diversity of implementations, builds on JPEG 2000, which is in broad use in studio workflows, is appropriate for long-term preservation, has both lossy and lossless modes and supports integer and floating point samples. Finally, the unique features of HTJ2K could be powerful additions to high-performance OpenEXR workflows where the full image may not always be viewed at its full resolution.

The patch currently defines four compressors:

• HT: Lossless coding using HTJ2K. Each chunk is the full image frame and the open-source OpenJPH library is used.
• HT256: Lossless coding using HTJ2K. Each chunk is 256 lines and the open-source OpenJPH library is used.
• HTK: Lossless coding using HTJ2K. Each chunk is the full image frame and the commercial KDU library is used.
• HTK256: Lossless coding using HTJ2K. Each chunk is 256 lines and the commercial KDU library is used.

Questions

• can a compressor store configuration information once in a file, so that the same information is available for each chunk to both the compressor and decompressor?

Notes

• HT and HTK Compressors are identical and use the open-source OpenJPH library is the Kakadu SDK is not found
• Ultimately there will be a single lossless HTJ2K Compressor. The HT and HTK Compressors are currently offered to ensure interop, and facilitate comparisons, between OSS and commercial options.
• The full-frame and 256-line chunk options are currently offered to evaluate the impact of sub-frame chunking on coding efficiency performance.

Todo

• add support for 32-bit samples to OpenJPH
• explore adding a progressive decoding API to OpenEXR
• explore tradeoff of chunk-size (currently set to 256) on compression efficiency, single-threaded/multi-threaded throughput and partial decoding (low-resolution and/or region of interest)
  • can chunking can be replaced with full-frame coding and J2K accessibility features? This is more important in lossy coding to avoid edge effects.
  • select a chunk size, i.e., is 256-line a reasonable value?
  • can J2K tiles be used instead of independent codestreams to remove JPEG 2000 codestream header overhead?

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