@spec contrast_ratio(rgb(), rgb()) :: float()

Calculates the WCAG 2.1 contrast ratio between two colors.

WCAG AA requires 4.5:1 for normal text, 7:1 for AAA.

@spec delta_e(rgb(), rgb()) :: float()

Calculates the Delta E 1976 distance between two colors.

This is the Euclidean distance in CIELAB space. Values < 1.0 are imperceptible.

@spec from_lab(lab()) :: rgb()

Converts CIELAB to RGB (sRGB D65).

@spec from_oklab(oklab()) :: rgb()

Converts OKLab to RGB (sRGB D65).

@spec from_oklch(oklch()) :: rgb()

Converts OKLCH to RGB (sRGB D65).

@spec from_xyz(xyz()) :: rgb()

Converts CIE XYZ to RGB (sRGB D65).

@spec from_ycbcr(ycbcr()) :: rgb()

Converts YCbCr (BT.601) to RGB.

@spec from_yuv(yuv()) :: rgb()

Converts YUV (BT.601) to RGB.

@spec kelvin_to_rgb(pos_integer()) :: rgb()

Converts temperature in Kelvin to RGB.

Based on Tanner Helland's algorithm for black-body radiation approximation.

@spec nearest_pantone(rgb()) :: {String.t(), float()} | nil

Finds the closest Pantone color for an RGB color.

Uses a curated list of popular Pantone colors and searches for the closest match using Delta E distance in CIELAB space.

Parameters

• rgb - RGB tuple {r, g, b}

Returns

• tuple {pantone_name, distance} or nil if there is no close match

Example

iex> Pote.Converters.Advanced.nearest_pantone({255, 0, 0})
{"Red 032 C", 0.0}

@spec nearest_pantone_name(rgb()) :: String.t() | nil

Finds the closest Pantone name for an RGB color. Returns only the name, or nil if there is no close match.

Example

iex> Pote.Converters.Advanced.nearest_pantone_name({255, 0, 0})
"Red 032 C"

@spec relative_luminance(rgb()) :: float()

Calculates the WCAG 2.1 relative luminance of a color.

@spec rgb_to_kelvin(rgb()) :: pos_integer() | nil

Approximates the correlated color temperature (CCT) in Kelvin from an RGB color.

Uses an iterative search over kelvin_to_rgb/1 to find the closest matching temperature.

@spec to_lab(rgb()) :: lab()

Converts RGB to CIELAB (D65 illuminant).

@spec to_oklab(rgb()) :: oklab()

Converts RGB to OKLab (Ottosson's perceptual space).

OKLab is a perceptual color space designed for smooth, uniform interpolation: midpoints stay perceptually consistent, avoiding the "muddy middle" of RGB/HSL interpolation.

@spec to_oklch(rgb()) :: oklch()

Converts RGB to OKLCH (OKLab in polar form).

Returns {l, c, h} where l is perceptual lightness (0..1), c is chroma, and h is hue in degrees (0..360).

@spec to_xyz(rgb()) :: xyz()

Converts RGB to CIE XYZ using the sRGB D65 matrix.

@spec to_ycbcr(rgb()) :: ycbcr()

Converts RGB to YCbCr (BT.601, digital video).

@spec to_yuv(rgb()) :: yuv()

Converts RGB to YUV (BT.601, PAL/NTSC broadcast).

@spec wcag_level(float(), :normal | :large) :: :aaa | :aa | :fail

Returns the WCAG 2.1 conformance level for a given contrast ratio.

Levels (for normal text):

• :aaa — 7.0+ (enhanced)
• :aa — 4.5+ (minimum)
• :fail — < 4.5

For large text (18pt+ or 14pt+ bold), the thresholds are lower:

• :aaa — 4.5+
• :aa — 3.0+
• :fail — < 3.0

Examples

iex> Pote.Converters.Advanced.wcag_level(7.5)
:aaa

iex> Pote.Converters.Advanced.wcag_level(4.5)
:aa

iex> Pote.Converters.Advanced.wcag_level(2.0)
:fail