QUAIL - the Quite Advanced Image Library - is a new image codec drawing on experience with QOI and QOI-Remix. After I designed QOI-R, I decided to start from scratch on a new nibble-oriented spec rather than continuing to modify QOI; QUAIL is the result of that effort. It uses the QOI harness and infrastructure (qbench/qconv) but is a largely clean-sheet encoding.
QUAIL gets solid density improvements against QOI/QOI-R with a moderate performance hit (and remains drastically higher-throughput than PNG.) Optimization will be a focus in the coming months, so throughput may improve. Additionally, I've been working to address some of what I consider to be QOI pain points - lack of support for very large images being a big one.
The spec should be considered very cold but not quite frozen. I don't expect to break compatibility, but it's not impossible. The code itself should be considered to be in a much higher state of flux than the spec.
QUAIL has been tested on Linux (Z, PPC64LE, ARM64, Itanium, x86_64) and HP-UX (Itanium.)
QOI-R remains present in the QUAIL tree, as does QOI. QOI-R work is effectively complete, with the exception that I intend to produce a spec at some point. The QOI-R format will not change.
README-QOIR.md contains the original QOI-R readme.
This is extremely sparse right now and should be considered a work in progress. Much though I hate to say it, right now the code is the spec.
8-bit channels, optional alpha depending on source PNG.
r * 3 + g * 5 + b * 7 + a * 11 - this is the same hash used by QOI.
QUAIL uses three indexes - Microindex (8 entries), Macroindex (256 entries), Last Level Index (4096 entries). These work similarly to the single-level index on QOI; the pixel value is hashed using the algorithm above to access the index. If an identical pixel is present in the index, a Retrieve From Index word is emitted for this pixel; if it is not, then the pixel is inserted into the index for future use.
As an example, if a pixel is not present in the microindex and is instead emitted as a "diff" word, it is also added to the microindex and, unless evicted by another pixel with the same hash, can be used by a later identical pixel using a Retrieve From Microindex word.