@@ 1,6 1,6 @@
# QUAIL
-QUAIL - the Quite Advanced Image Library - is a new image codec drawing on experience with QOI and QOI-Remix. After 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 - 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.
@@ 8,28 8,38 @@ The spec should be considered very cold
QUAIL has been tested on Linux (Z, PPC64LE, ARM64, Itanium, x86_64) and HP-UX (Itanium.)
+## What about QOI-R?
+
+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.
+
## QUAIL Encoding
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.
### Structures
-Pixel: 8-bit channels, optional alpha depending on source PNG.
+#### Pixel
+
+8-bit channels, optional alpha depending on source PNG.
+
+#### Hash
-Hash: r * 3 + g * 5 + b * 7 + a * 11 - this is the same hash used by QOI.
+r * 3 + g * 5 + b * 7 + a * 11 - this is the same hash used by QOI.
-Indexes: Three indexes - Microindex (8 entries), Macroindex (256 entries), Last Level Index (4096 entries). Accessed via hash of pixel, modulo size of index. Pixel encoding is hashed index. Every index miss (ie, falling through to a longer word type) results in insertion of pixel into the index.
+#### Indexes
+
+QUAIL uses three indexes - Microindex (8 entries), Macroindex (256 entries), Last Level Index (4096 entries). Accessed via hash of pixel, modulo size of index. Pixel encoding is hashed index. Every index miss (ie, falling through to a longer word type) results in insertion of pixel into the index.
### Encoding Words
-1iii - Index Into Microindex
-0010 llll - short run
-0100 iiii iiii - Index into Macroindex
-0011 llll llll - long run
-000r rrgg gbbb - Diff
-0110 gggg ggrr rbbb - Microluma; like Medium Luma with shrunken fields
-0101 0010 iiii iiii iiii - Index into pixel Last Level Index
-0111 gggg ggrr rrrb bbbb - Medium Luma, where g is difference green, r is (difference red - difference green), b is (difference blue - difference green)
-0101 1ggg gggg rrrr rrbb bbbb - Megaluma; like Medium Luma with expanded fields
-0101 0001 rrrr rrrr gggg gggg bbbb bbbb - Immediate RGB pixel
-0101 0000 rrrr rrrr gggg gggg bbbb bbbb aaaa aaaa - Immediate RGBA pixel
+- 1iii - Index Into Microindex
+- 0010 llll - short run
+- 0100 iiii iiii - Index into Macroindex
+- 0011 llll llll - long run
+- 000r rrgg gbbb - Diff
+- 0110 gggg ggrr rbbb - Microluma; like Medium Luma with shrunken fields
+- 0101 0010 iiii iiii iiii - Index into pixel Last Level Index
+- 0111 gggg ggrr rrrb bbbb - Medium Luma, where g is difference green, r is (difference red - difference green), b is (difference blue - difference green)
+- 0101 1ggg gggg rrrr rrbb bbbb - Megaluma; like Medium Luma with expanded fields
+- 0101 0001 rrrr rrrr gggg gggg bbbb bbbb - Immediate RGB pixel
+- 0101 0000 rrrr rrrr gggg gggg bbbb bbbb aaaa aaaa - Immediate RGBA pixel