Grok

Grok is an open-source JPEG 2000 codec licensed under AGPL v3.

Performance

Grok is integrated into GDAL. Benchmark results (16 threads, GDAL release build, Fedora 42):

Features

• High Throughput JPEG 2000 (HTJ2K) support
• Random-access sub-image decoding (TLM + PLT markers)
• Multi-level tile cache with LRU eviction and compressed chunk caching
• S3 / cloud storage with network fetch caching and disk spillover
• ICC color profiles, XML/IPTC/XMP/EXIF metadata
• Monochrome, sRGB, palette, YCC, extended YCC, CIELab, CMYK
• 1–16 bit precision
• Compression accepts GRK_INT_32 and GRK_INT_16 input. GRK_INT_16 supports signed precision up to 16 bits and unsigned precision up to 15 bits. Use grk_compress_get_recommended_data_type() to detect the direct 16-bit compression path.
• JPEG/PNG/BMP/TIFF/RAW/PNM/PAM I/O
• Linux (x86-64/AArch64), Windows, macOS, WebAssembly

For direct API compression, call grk_compress_get_recommended_data_type() after configuring compression and plugin state, then use its result when allocating component data. It returns GRK_INT_16 only when compression retains a 16-bit tile buffer.

For standard MCT, query all three components and use GRK_INT_32 for all three if any query returns it. GRK_INT_32 remains valid when the function recommends GRK_INT_16.

Multi-tile callers may still choose accepted GRK_INT_16 input outside the direct path to reduce source-buffer memory, at the cost of widening each tile.

Transcoding (grk_transcode)

grk_transcode rewrites JP2/J2K files at the packet level — no full decompression required. Supported operations:

• Insert TLM (Tile-part Length) and PLT (Packet Length) markers for random access
• Inject SOP / EPH markers
• Truncate quality layers (--max-layers)
• Strip resolution levels (--max-res)
• Reorder packet progression (LRCP, RLCP, RPCL, PCRL, CPRL)

Example — add TLM + PLT markers to an existing file:

grk_transcode -i input.jp2 -o output.jp2 -X -L

Testing

• 2,000+ unit tests
• Continuous fuzzing via OSS-Fuzz

Language Bindings

• Python, C#, Java (SWIG)
• Rust (bindgen)

Links

• Installation
• Testing
• Tile Cache Architecture
• S3 / Cloud Storage
• Language Bindings
• Wiki & Docs
• GitHub

Quick Build

git clone --recursive https://github.com/GrokImageCompression/grok.git
cd grok
cmake -B build
cmake --build build --parallel

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