# `Color.Types`

Shared type aliases used across the `Color` library.

Pulled out into a separate module so the per-space struct modules
and the top-level `Color` module can refer to a single canonical
definition for things like alpha, illuminant, observer angle, and
rendering intent.

## Examples

    @spec lighten(Color.SRGB.t(), Color.Types.alpha()) :: Color.SRGB.t()

# `adaptation_method`

```elixir
@type adaptation_method() ::
  :bradford | :cat02 | :von_kries | :sharp | :cmccat2000 | :xyz_scaling
```

A chromatic adaptation method, used to convert between reference
whites. Bradford is the default and is what ICC v4 specifies for
D50↔D65.

# `alpha`

```elixir
@type alpha() :: float() | nil
```

An alpha (opacity) value, always a unit float in `[0.0, 1.0]`, or
`nil` to mean "not set / fully opaque". Alpha is straight
(unassociated) throughout the library.

# `illuminant`

```elixir
@type illuminant() :: :A | :B | :C | :D50 | :D55 | :D65 | :D75 | :E | :F2 | :F7 | :F11
```

A reference white. The standard CIE illuminants supported by the
library.

* `:D50` — ICC PCS, used by CSS Color 4 `lab()` and `lch()`.
* `:D65` — sRGB, Display P3, Rec. 709, Rec. 2020. The default for
  most modern computing colour science.
* `:D55`, `:D75` — alternative daylight illuminants.
* `:A` — incandescent / tungsten ~2856 K.
* `:B` — direct sunlight at noon (deprecated by CIE but still in
  legacy data).
* `:C` — average / north-sky daylight (NTSC 1953).
* `:E` — equi-energy radiator (theoretical, all wavelengths equal).
* `:F2`, `:F7`, `:F11` — fluorescent series (cool white, broadband
  daylight, narrow-band).

# `intent`

```elixir
@type intent() ::
  :relative_colorimetric | :absolute_colorimetric | :perceptual | :saturation
```

An ICC rendering intent.

* `:relative_colorimetric` (default) — chromatically adapt the
  source white to the target white. Out-of-gamut colors are
  *not* altered.
* `:absolute_colorimetric` — no chromatic adaptation. The source
  XYZ is handed to the target's `from_xyz/1` verbatim.
* `:perceptual` — chromatically adapt **and** gamut-map so the
  result is inside the target's gamut.
* `:saturation` — alias for `:perceptual` in the current
  implementation. A future release may add a true saturation
  intent.

# `observer`

```elixir
@type observer() :: 2 | 10
```

CIE standard observer angle, in degrees. `2` is the 1931
("standard") observer; `10` is the 1964 ("supplementary") observer.

# `space`

```elixir
@type space() ::
  :srgb
  | :sRGB
  | :adobe_rgb
  | :adobe
  | :rgb
  | :cmyk
  | :hsl
  | :hsv
  | :hsluv
  | :hpluv
  | :lab
  | :lch
  | :lchab
  | :luv
  | :lchuv
  | :oklab
  | :oklch
  | :xyz
  | :xyy
  | :xyY
  | :jzazbz
  | :ictcp
  | :ipt
  | :ycbcr
  | :cam16
  | :cam16_ucs
```

Short atom identifiers for colour spaces. Accepted by `Color.new/2`
and the option list of `Color.convert/3`.

# `working_space`

```elixir
@type working_space() ::
  :SRGB
  | :Adobe
  | :Apple
  | :Best
  | :Beta
  | :Bruce
  | :CIE
  | :ColorMatch
  | :Don4
  | :ECI
  | :EktaSpace
  | :NTSC
  | :PAL_SECAM
  | :ProPhoto
  | :SMPTE_C
  | :WideGamut
  | :P3_D65
  | :P3_D60
  | :Rec2020
  | :Rec709
  | :ACES
  | :ACEScg
  | :ACES_AP1
  | :Adobe_Wide
```

An RGB working space identifier (the value passed as the third
argument to `Color.convert/3` when the target is `Color.RGB`).
See `Color.RGB.WorkingSpace.rgb_working_spaces/0` for the full
list.

---

*Consult [api-reference.md](api-reference.md) for complete listing*