A Query.Farm VGI worker for DuckDB.
vgi-color · a Query.Farm VGI worker
A VGI worker that brings color science — color-space conversions, CIEDE2000 color difference (ΔE), and WCAG contrast — to DuckDB over Apache Arrow.
LOAD vgi;
ATTACH 'color' (TYPE vgi, LOCATION './target/release/color-worker');
SET search_path = 'color.main';
SELECT to_hex(255, 0, 0); -- '#ff0000'
SELECT (from_hex('#ff0000')).*; -- (r := 255, g := 0, b := 0)
SELECT (rgb_to_hsl(255, 0, 0)).*; -- (h := 0, s := 1, l := 0.5)
SELECT (rgb_to_lab(255, 0, 0)).*; -- (l := 53.24, a := 80.09, b := 67.20)
SELECT ROUND(delta_e('#ff0000', '#ff4500'), 2); -- CIEDE2000 ΔE
SELECT ROUND(contrast_ratio('#000000','#ffffff'), 1); -- 21.0
SELECT wcag_level('#000000', '#ffffff'); -- 'AAA'
SELECT is_dark('#222222'); -- true
SELECT nearest_color_name('#ff0000'); -- 'red'
SELECT * FROM named_colors(); -- CSS named-color tableThe worker implements every transform directly from the standard formulas —
no third-party color crate — so it carries no extra dependency and no MSRV risk
(it builds on the workspace rust-version = 1.86). The pure engine lives in
crates/color-worker/src/color.rs; the scalar/ and table/ modules are thin
Arrow adapters over it.
| Transform | Standard |
|---|---|
| sRGB ⇄ linear | IEC 61966-2-1 piecewise companding (0.04045/12.92, 2.4 gamma, 0.055 offset) |
| Relative luminance | WCAG 2.x: 0.2126 R + 0.7152 G + 0.0722 B over linearized channels |
| Contrast ratio | WCAG 2.x: (L_light + 0.05) / (L_dark + 0.05), 1.0 … 21.0 |
| HSL ⇄ RGB | Standard hue-sector conversion (h degrees, s/l in 0..1) |
| CIELAB | linear-sRGB → CIE XYZ (sRGB/D65 matrix) → L*a*b* with the D65 white |
| CIEDE2000 (ΔE₀₀) | Sharma, Wu & Dalal (2005) reference implementation |
The CSS Color Module Level 4 named-color table (147 names) backs
nearest_color_name (closest name by ΔE₀₀) and the named_colors() table.
A
palette-crate-based implementation was considered; implementing the formulas directly was chosen for zero added dependencies and full MSRV control.paletteis BSD/MIT/Apache; this worker uses none of it.
Scalars (positional-only):
| Function | Signature | Notes |
|---|---|---|
to_hex |
to_hex(r INT, g INT, b INT) -> VARCHAR |
'#rrggbb'; channels clamped to 0-255 |
from_hex |
from_hex(hex VARCHAR) -> STRUCT(r INT, g INT, b INT) |
Accepts #rgb/#rrggbb/#rrggbbaa; NULL if invalid |
rgb_to_hsl |
rgb_to_hsl(r, g, b) -> STRUCT(h DOUBLE, s DOUBLE, l DOUBLE) |
h in [0,360), s/l in [0,1] |
hsl_to_rgb |
hsl_to_rgb(h, s, l) -> STRUCT(r INT, g INT, b INT) |
h degrees, s/l clamped to 0..1 |
rgb_to_lab |
rgb_to_lab(r, g, b) -> STRUCT(l DOUBLE, a DOUBLE, b DOUBLE) |
CIELAB, D65 |
delta_e |
delta_e(hex_a, hex_b) -> DOUBLE |
CIEDE2000 ΔE₀₀ |
luminance |
luminance(hex) -> DOUBLE |
WCAG relative luminance, 0..1 |
contrast_ratio |
contrast_ratio(hex_a, hex_b) -> DOUBLE |
WCAG, 1..21 |
wcag_level |
wcag_level(hex_fg, hex_bg) -> VARCHAR |
'AAA'/'AA'/'AA Large'/'fail' (normal text) |
is_dark |
is_dark(hex) -> BOOLEAN |
luminance < 0.5 |
nearest_color_name |
nearest_color_name(hex) -> VARCHAR |
Closest CSS named color by ΔE |
color_version |
color_version() -> VARCHAR |
Worker version |
Table function:
| Function | Columns |
|---|---|
named_colors() |
name VARCHAR, hex VARCHAR |
NULL input → NULL output. Invalid hex strings and out-of-range RGB channels are
treated as data (invalid hex → NULL; channels clamped to 0..=255). The worker
never panics.
make test # cargo unit/integration tests + SQL E2E
make test-unit # cargo test --workspace
make test-sql # build release worker + DuckDB sqllogictest suite (haybarn-unittest)
make lint # clippy (deny warnings) + rustfmt --check
make fmt # rustfmt the workspaceThe SQL E2E suite uses haybarn-unittest
(uv tool install haybarn-unittest).
MIT — see LICENSE.
Written by Query.Farm.
Copyright 2026 Query Farm LLC - https://query.farm