Color.YCbCr (Color v0.4.0)

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YCbCr digital-video color space with BT.601, BT.709 and BT.2020 variants.

YCbCr operates on gamma-encoded RGB (the corresponding working-space companded values), not linear RGB. The :variant field selects the luma coefficients and the matching RGB working space / transfer function:

  • :bt601 — SDTV (ITU-R BT.601). Uses sRGB primaries for the underlying RGB.

  • :bt709 — HDTV (ITU-R BT.709). Uses sRGB primaries (which match BT.709 primaries) with the BT.709 transfer function.

  • :bt2020 — UHDTV (ITU-R BT.2020). Uses BT.2020 primaries and transfer function. Non-constant luminance variant.

Channels are normalised full-range floats:

  • y ∈ [0, 1] — luma.

  • cb, cr ∈ [-0.5, 0.5] — chroma differences.

If you need the 8-bit TV-range (Y ∈ [16, 235], Cb/Cr ∈ [16, 240]) values, scale on the outside.

Summary

Types

t()

Digital video YCbCr. y is luma; cb and cr are the blue-difference and red-difference chroma channels. The :variant field selects the matrix coefficients (:bt601, :bt709, :bt2020).

Functions

from_rgb(arg, variant \\ :bt709)

Converts a gamma-encoded RGB triple to YCbCr.

from_xyz(xyz, variant \\ :bt709)

Converts a CIE XYZ color to YCbCr using the given variant.

to_rgb(y_cb_cr)

Converts a YCbCr color to its corresponding gamma-encoded RGB triple.

to_xyz(ycbcr)

Converts a YCbCr color to CIE XYZ.

Types

t()

@type t() :: %Color.YCbCr{
  alpha: Color.Types.alpha(),
  cb: float() | nil,
  cr: float() | nil,
  variant: :bt601 | :bt709 | :bt2020,
  y: float() | nil
}

Digital video YCbCr. y is luma; cb and cr are the blue-difference and red-difference chroma channels. The :variant field selects the matrix coefficients (:bt601, :bt709, :bt2020).

Functions

from_rgb(arg, variant \\ :bt709)

Converts a gamma-encoded RGB triple to YCbCr.

Arguments

  • rgb is a {r, g, b} tuple of unit floats in the variant's working space.

  • variant is :bt601, :bt709 (default) or :bt2020.

Returns

from_xyz(xyz, variant \\ :bt709)

Converts a CIE XYZ color to YCbCr using the given variant.

Arguments

  • xyz is a Color.XYZ struct (D65/2°).

  • variant is :bt601, :bt709 (default) or :bt2020.

Returns

to_rgb(y_cb_cr)

Converts a YCbCr color to its corresponding gamma-encoded RGB triple.

The result is a {r, g, b} tuple in the working space selected by the variant (sRGB for BT.601/BT.709, BT.2020 for :bt2020).

Arguments

Returns

  • A {r, g, b} tuple of unit floats.

Examples

iex> Color.YCbCr.to_rgb(%Color.YCbCr{y: 1.0, cb: 0.0, cr: 0.0})
{1.0, 1.0, 1.0}

to_xyz(ycbcr)

Converts a YCbCr color to CIE XYZ.

For BT.601 and BT.709 the underlying RGB is treated as sRGB. For BT.2020 it is linearised with the BT.2020 transfer function and converted via the BT.2020 working space.

Arguments

Returns

Examples

iex> {:ok, xyz} = Color.YCbCr.to_xyz(%Color.YCbCr{y: 1.0, cb: 0.0, cr: 0.0, variant: :bt709})
iex> {Float.round(xyz.x, 4), Float.round(xyz.y, 4), Float.round(xyz.z, 4)}
{0.9505, 1.0, 1.0888}