Function reference overview

Loading duckfn_palette registers 160 names / 169 signatures, all under the plt_ prefix. They are ordinary DuckDB scalar functions: use them in a projection, a WHERE clause, a GROUP BY, a LATERAL join or a list lambda, exactly like a built-in function.

The value they operate on

A color is a single STRUCT, so it can live in a column, be compared, grouped and passed to any other function:

STRUCT(space VARCHAR, c1 DOUBLE, c2 DOUBLE, c3 DOUBLE, alpha DOUBLE)

space is one of the 44 names in plt_color_spaces(); c1..c3 are that space's components in palette's Color::new order; alpha is 0 (transparent) to 1 (opaque) and is carried through conversions untouched.

SELECT plt_color_spaces() AS spaces;

Three rules that apply everywhere

• NULL in, NULL out. A NULL in any argument makes the whole call NULL, including a NULL inside a LIST. Results palette cannot define (an unknown name, a difference with no value) are NULL too — never NaN and never 0.
• A bad argument fails the statement. Unknown space, mode, metric, white point or format names, a wrong list length and an out-of-range index raise an error whose message starts with the function name, e.g. plt_convert: unknown color space 'nope'.
• Names are normalized. Space, mode, metric, white-point and format names are case-insensitive, and hyphens and spaces count as underscores: 'OKLCH', 'ok-lch' and ' ok lch ' all work.

SELECT plt_to_hex(plt_convert(plt_srgb(1, 0.5, 0), 'OK-LCH')) AS normalized;

Where each family lives

Page	What it covers
Colors and spaces	The color value, its accessors, alpha, and one constructor per space (44)
Conversion and clamping	plt_convert, plt_convert_clamped, plt_clamp, plt_is_within_bounds, plt_equals
Manipulation	Mixing, lightening, darkening, brightening, greyscale, tint and shade, saturation, hue and premultiplied alpha
Blending and compositing	11 blend modes, 6 Porter-Duff operators, custom OpenGL factors
Color difference and contrast	7 difference metrics, WCAG 2.1 luminance, ratio and criteria, most-readable picking, YIQ brightness
Color schemes	Complementary, split-complementary, analogous, triadic, tetradic, monochromatic
Strings, hex and named colors	Hex (including fixed-width), full CSS Color Level 4, extra output formats, the 148 SVG/CSS3 names, nearest name
8-bit packing	Pack and unpack ARGB/RGBA/ABGR/BGRA integers
White points, adaptation and encoding	White points, adaptation matrices, transfer functions, primaries, matrices
CAM16 with custom viewing conditions	Full CAM16 attributes and the eight CAM16 spaces under your own conditions
colorous palettes	d3-style gradients and categorical palettes
Random colors	Reproducible sampling from palette's distributions

Finding a function at runtime

SELECT function_name, parameters, return_type, description
FROM duckdb_functions()
WHERE function_name LIKE 'plt_%'
ORDER BY function_name;

Two habits that avoid most surprises

Convert before an operation that needs a particular kind of component. plt_saturate needs a hue-based space, plt_blend an RGB-like one, and the scheme functions a color that carries a hue. The error message says which function failed and suggests converting first:

SELECT plt_saturate(plt_srgb(1, 0, 0), 0.2);

Work in a perceptually uniform space when mixing or comparing. oklab / oklch mix and compare far more evenly than srgb; convert in, do the work, convert back:

SELECT plt_to_hex(plt_mix(plt_convert(plt_srgb(1, 0, 0), 'oklab'),
                          plt_convert(plt_srgb(0, 0, 1), 'oklab'),
                          0.5)) AS purple;