# `Color.ICtCp`

ICtCp color space (ITU-R BT.2100).

ICtCp is the HDR/WCG color space used by Dolby Vision, HDR10+ and
Rec. 2100. It operates on Rec. 2020 primaries with either the PQ
(default) or HLG transfer function. Use PQ for cinema/OTT, HLG for
broadcast.

The `:transfer` field selects the transfer function — `:pq`
(default) or `:hlg`.

PQ is an absolute transfer function: input `1.0` corresponds to
10,000 cd/m². Since our `Color.XYZ` uses `Y = 1.0` for the reference
white, we scale by a `:reference_luminance` option (default
`100` cd/m², matching SDR diffuse white) before encoding and
divide on the way back.

# `t`

```elixir
@type t() :: %Color.ICtCp{
  alpha: Color.Types.alpha(),
  cp: float() | nil,
  ct: float() | nil,
  i: float() | nil,
  transfer: :pq | :hlg
}
```

An ITP (ICtCp) colour for HDR signals (Rec. 2100). `i` is intensity,
`ct` and `cp` are the tritan / protan chroma channels. The
`:transfer` field selects PQ (`:pq`, the default) or HLG (`:hlg`).

# `from_xyz`

Converts CIE `XYZ` (D65) to ICtCp using the PQ transfer function.

### Arguments

* `xyz` is a `Color.XYZ` struct.

### Returns

* A `Color.ICtCp` struct with `transfer: :pq`.

### Examples

    iex> {:ok, ictcp} = Color.ICtCp.from_xyz(%Color.XYZ{x: 0.95047, y: 1.0, z: 1.08883, illuminant: :D65, observer_angle: 2})
    iex> Float.round(ictcp.i, 3)
    0.508

# `to_xyz`

Converts ICtCp to CIE `XYZ` (D65).

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