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Random colors

These functions sample colors from palette's distributions: "uniform inside the space" as palette defines it for each space (sRGB components over 0..1, Lab a/b over -128..127, hue around the full circle, saturation/lightness weighted by the shape of the space's solid, and so on).

Every sampling function takes a seed. The same space and seed always produce the same colors, so results are reproducible across queries and machines, and safe inside EXPLAIN.

plt_random_color(space, seed)​

Signature: plt_random_color(space VARCHAR, seed BIGINT) -> plt_color

One color in the given space.

SELECT plt_random_color('oklch', 42) AS color,
       plt_to_hex(plt_random_color('oklch', 42)) AS as_hex;

The seed is the whole state: change it to get a different color, keep it to get the same one.

SELECT seed, plt_to_hex(plt_random_color('srgb', seed)) AS color
FROM range(1, 6) t(seed);

plt_random_colors(space, count, seed)​

Signature: plt_random_colors(space VARCHAR, count BIGINT, seed BIGINT) -> plt_color[]

A list of count colors drawn from one seeded sequence. Consecutive draws differ from plt_random_color with the same seed, but the sequence itself is fixed for a given (space, count, seed).

SELECT list_transform(plt_random_colors('srgb', 5, 42), lambda x: plt_to_hex(x)) AS colors,
       length(plt_random_colors('srgb', 5, 42)) AS count;

A count of zero gives an empty list; a negative count is an error:

SELECT length(plt_random_colors('lab', 0, 7)) AS empty;
 
SELECT plt_random_colors('srgb', -1, 42);

This is handy for building test data or a random categorical palette:

SELECT i, plt_to_hex(colors[i]) AS color
FROM (SELECT plt_random_colors('srgb', 6, 2026) AS colors) t,
     range(1, 7) r(i);

plt_random_spaces()​

Signature: plt_random_spaces() -> VARCHAR[]

The 34 spaces that have a random distribution: the 15 RGB spaces (gamma and linear variants), hsl, hsv, hwb, lab, lch, luv, lchuv, xyz, xyz_d50, yxy, luma, luma_linear, luma_gamma, oklab, oklch, cam16_ucs_jab, cam16_ucs_jmh, lms and lms_von_kries.

SELECT list_count(plt_random_spaces()) AS count,
       plt_random_spaces() AS spaces;

Spaces absent from this list — hsluv, okhsl, okhsv, okhwb, the partial CAM16 spaces (cam16_jch, cam16_jmh, cam16_jsh, cam16_qch, cam16_qmh, cam16_qsh) — have no palette distribution and cannot be sampled:

SELECT plt_random_color('hsluv', 42);
 
SELECT plt_random_color('oklchh', 42);

Sample in a space that is listed and convert afterwards if you need another one:

SELECT plt_convert(plt_random_color('oklch', 7), 'lch') AS as_lch;

Errors​

  • An unknown space name, or one without a random distribution, is a query error naming the function and listing the supported spaces.
  • A negative count is a query error.
  • NULL in any argument returns NULL.