- Compression and decompression speed is 500MB/sec for byte data and close to 4GB/sec for 64 bit data
- Better compression than PNG in most cases
- No external dependencies
- Any integer type, from 8 to 64bit per value, signed and unsigned
- No significant memory footprint during encoding or decoding
- Very low complexity
The library, located in QB3lib provides the core QB3 algorithm implementation with a C API. Implemented in C++, can be built on most platforms using cmake. It requires a little endian, two's complement architecture with 8, 16, 32 and 64 bit integers, which includes the common AMD64 and ARM64 platforms. Only 64bit builds should be used since this implementation uses 64 bit integers heavily.
The included cqb3 utility conversion program converts PNG or JPEG images to QB3, for 8 and 16 bit images. It can also decode QB3 to PNG. The source code serves as an example of using the library. This optional utility does have an external library dependency to read and write JPEG and PNG images.
Another option is to build GDAL with QB3 in MRF enabled, and then using gdal_translate to and from many other types of rasters.
QB3.h contains the public C API interface. The workflow is to create opaque encoder or decoder control structures, set or query options and encode or decode the raster data. There are a couple of QB3 encoder modes. The default one is the fastest. The other modes extend the encoding method, which results in slighlty better compression at the expense of encoding speed. For 8bit natural images the compression ratio gain from using the extended methods are usually very small. If a better compression ratio is needed, a good option is to combine the raster specific QB3 default output with a second pass generic lossless compressions such as ZSTD or DEFLATE at a very low effort setting. This second pass is especially useful for synthetic images that include repeated identical sequences.
The low level QB3 algorithm is implemented in the qb3decode.h and qb3encode.h as C++ templates. While the core implementation is C++, it does not make use of any advanced features other than templates, conversion to C is very easy. The higher level C API located in qb3encode.cpp and qb3decode.cpp, it adds a file format that in addition to the QB3 raw stream includes sufficient metadata to allow decoding.
- Bug fix, decoding of best mode could fail for 32 and 64 bit integers, due to overflow of an internal accumulator used to decode index groups.
- Removed encoding dependency on STL::sort by including an implementation of bubble sort. Since the sorted vector had at most 8 values, the use of STL sort was overkill and increased size of the library code without a noticeable performance benefit. A side benefit is that porting to C is now easier.
- Speed optimizations, both compression and decompression
- More than 400MB/sec for byte data using the default mode
- New QB3M_FTL mode, 25% faster than QB3M_DEFAULT with a tiny compression loss
- 500MB/sec for byte data
- Test availability by checking that QB3_HAS_FTL is defined
- WASM test
- Better scan ordering, second order Hilbert curve is the default
- 5% better compression with no speed penalty
- Legacy scan order (Morton) is optional
- Minor performance improvements and bug fixes
- Simplified code, removal of lookup tables for non-byte data
- Stride decoding to non-contiguous line buffers
- Build system changes
- Removed MSVC project
- CMake is the only build system
- Default build target is the library, eliminating external dependencies
- Conversion utility is optional
- Initial release
- C API
- All integer types
