Rgb

class Rgb : ColorSpace
kotlin.Any
   ↳ androidx.ui.graphics.colorspace.ColorSpace
   ↳ androidx.ui.graphics.colorspace.Rgb

An RGB color space is an additive color space using the RGB color model (a color is therefore represented by a tuple of 3 numbers).

A specific RGB color space is defined by the following properties:

  • Three chromaticities of the red, green and blue primaries, which define the gamut of the color space.
  • A white point chromaticity that defines the stimulus to which color space values are normalized (also just called "white").
  • An opto-electronic transfer function, also called opto-electronic conversion function or often, and approximately, gamma function.
  • An electro-optical transfer function, also called electo-optical conversion function or often, and approximately, gamma function.
  • A range of valid RGB values (most commonly [0..1]).

The most commonly used RGB color space is sRGB.

Primaries and white point chromaticities

In this implementation, the chromaticity of the primaries and the white point of an RGB color space is defined in the CIE xyY color space. This color space separates the chromaticity of a color, the x and y components, and its luminance, the Y component. Since the primaries and the white point have full brightness, the Y component is assumed to be 1 and only the x and y components are needed to encode them.

For convenience, this implementation also allows to define the primaries and white point in the CIE XYZ space. The tristimulus XYZ values are internally converted to xyY.

sRGB primaries and white point

Transfer functions

A transfer function is a color component conversion function, defined as a single variable, monotonic mathematical function. It is applied to each individual component of a color. They are used to perform the mapping between linear tristimulus values and non-linear electronic signal value.

The opto-electronic transfer function (OETF or OECF) encodes tristimulus values in a scene to a non-linear electronic signal value. An OETF is often expressed as a power function with an exponent between 0.38 and 0.55 (the reciprocal of 1.8 to 2.6).

The electro-optical transfer function (EOTF or EOCF) decodes a non-linear electronic signal value to a tristimulus value at the display. An EOTF is often expressed as a power function with an exponent between 1.8 and 2.6.

Transfer functions are used as a compression scheme. For instance, linear sRGB values would normally require 11 to 12 bits of precision to store all values that can be perceived by the human eye. When encoding sRGB values using the appropriate OETF (see sRGB for an exact mathematical description of that OETF), the values can be compressed to only 8 bits precision.

When manipulating RGB values, particularly sRGB values, it is safe to assume that these values have been encoded with the appropriate OETF (unless noted otherwise). Encoded values are often said to be in "gamma space". They are therefore defined in a non-linear space. This in turns means that any linear operation applied to these values is going to yield mathematically incorrect results (any linear interpolation such as gradient generation for instance, most image processing functions such as blurs, etc.).

To properly process encoded RGB values you must first apply the EOTF to decode the value into linear space. After processing, the RGB value must be encoded back to non-linear ("gamma") space. Here is a formal description of the process, where f is the processing function to apply:

See RGB equation

If the transfer functions of the color space can be expressed as an ICC parametric curve as defined in ICC.1:2004-10, the numeric parameters can be retrieved from transferParameters. This can be useful to match color spaces for instance.

Some RGB color spaces, such as ColorSpaces.Aces and scRGB, are said to be linear because their transfer functions are the identity function: f(x) = x. If the source and/or destination are known to be linear, it is not necessary to invoke the transfer functions.

Range

Most RGB color spaces allow RGB values in the range [0..1]. There are however a few RGB color spaces that allow much larger ranges. For instance, scRGB is used to manipulate the range [-0.5..7.5] while ACES can be used throughout the range [-65504, 65504].

Extended sRGB and its large range

Converting between RGB color spaces

Conversion between two color spaces is achieved by using an intermediate color space called the profile connection space (PCS). The PCS used by this implementation is CIE XYZ. The conversion operation is defined as such:

See RGB equation

Where Tsrc is the RGB to XYZ transform of the source color space and Tdst^-1 the XYZ to RGB transform of the destination color space.

Many RGB color spaces commonly used with electronic devices use the standard illuminant D65. Care must be take however when converting between two RGB color spaces if their white points do not match. This can be achieved by either calling adapt to adapt one or both color spaces to a single common white point. This can be achieved automatically by calling ColorSpace.connect, which also handles non-RGB color spaces.

To learn more about the white point adaptation process, refer to the documentation of Adaptation.

Summary

Public constructors

<init>(name: String, toXYZ: FloatArray, oetf: (Double) -> Double, eotf: (Double) -> Double)

Creates a new RGB color space using a 3x3 column-major transform matrix.

<init>(name: String, primaries: FloatArray, whitePoint: WhitePoint, oetf: (Double) -> Double, eotf: (Double) -> Double, min: Float, max: Float)

Creates a new RGB color space using a specified set of primaries and a specified white point.

<init>(name: String, toXYZ: FloatArray, function: TransferParameters)

Creates a new RGB color space using a 3x3 column-major transform matrix.

<init>(name: String, primaries: FloatArray, whitePoint: WhitePoint, function: TransferParameters)

Creates a new RGB color space using a specified set of primaries and a specified white point.

<init>(name: String, toXYZ: FloatArray, gamma: Double)

Creates a new RGB color space using a 3x3 column-major transform matrix.

<init>(name: String, primaries: FloatArray, whitePoint: WhitePoint, gamma: Double)

Creates a new RGB color space using a specified set of primaries and a specified white point.

Public methods

Boolean
equals(other: Any?)

FloatArray
fromLinear(r: Float, g: Float, b: Float)

Encodes an RGB value from linear space to this color space's "gamma space".

FloatArray

Encodes an RGB value from linear space to this color space's "gamma space".

FloatArray

Converts tristimulus values from the CIE XYZ space to this color space's color model.

FloatArray

Returns the inverse transform of this color space as a new array.

FloatArray
getInverseTransform(inverseTransform: FloatArray)

Copies the inverse transform of this color space in specified array.

Float
getMaxValue(component: Int)

Returns the maximum valid value for the specified component of this color space's color model.

Float
getMinValue(component: Int)

Returns the minimum valid value for the specified component of this color space's color model.

FloatArray

Returns the primaries of this color space as a new array of 6 floats.

FloatArray

Copies the primaries of this color space in specified array.

FloatArray

Returns the transform of this color space as a new array.

FloatArray

Copies the transform of this color space in specified array.

Int

FloatArray
toLinear(r: Float, g: Float, b: Float)

Decodes an RGB value to linear space.

FloatArray

Decodes an RGB value to linear space.

FloatArray

Converts a color value from this color space's model to tristimulus CIE XYZ values.

Inherited functions

Inherited extension functions

From androidx.ui.graphics.colorspace
ColorSpace
ColorSpace.adapt(whitePoint: WhitePoint, adaptation: Adaptation = Adaptation.Bradford)

Performs the chromatic adaptation of a color space from its native white point to the specified white point.

Connector
ColorSpace.connect(destination: ColorSpace = ColorSpaces.Srgb, intent: RenderIntent = RenderIntent.Perceptual)

Connects two color spaces to allow conversion from the source color space to the destination color space.

Properties

(Double) -> Double

Returns the electro-optical transfer function (EOTF) of this color space.

Boolean

Indicates whether this color space is the sRGB color space or equivalent to the sRGB color space.

Boolean

Returns whether this color space is a wide-gamut color space.

(Double) -> Double

Returns the opto-electronic transfer function (OETF) of this color space.

TransferParameters?

Returns the parameters used by the electro-optical and opto-electronic transfer functions.

WhitePoint

Inherited properties

Public constructors

<init>

Rgb(
    name: String,
    toXYZ: FloatArray,
    oetf: (Double) -> Double,
    eotf: (Double) -> Double)

Creates a new RGB color space using a 3x3 column-major transform matrix. The transform matrix must convert from the RGB space to the profile connection space CIE XYZ.

The range of the color space is imposed to be [0..1].

Parameters
name: String Name of the color space, cannot be null, its length must be >= 1
toXYZ: FloatArray 3x3 column-major transform matrix from RGB to the profile connection space CIE XYZ as an array of 9 floats, cannot be null
oetf: (Double) -> Double Opto-electronic transfer function, cannot be null
eotf: (Double) -> Double Electro-optical transfer function, cannot be null
Exceptions
IllegalArgumentException If any of the following conditions is met:

<init>

Rgb(
    name: String,
    primaries: FloatArray,
    whitePoint: WhitePoint,
    oetf: (Double) -> Double,
    eotf: (Double) -> Double,
    min: Float,
    max: Float)

Creates a new RGB color space using a specified set of primaries and a specified white point.

The primaries and white point can be specified in the CIE xyY space or in CIE XYZ. The length of the arrays depends on the chosen space:

| Spaces | Primaries length | White point length |
|--------|------------------|--------------------|
| xyY    | 6                | 2                  |
| XYZ    | 9                | 3                  |

When the primaries and/or white point are specified in xyY, the Y component does not need to be specified and is assumed to be 1.0. Only the xy components are required.

Parameters
name: String Name of the color space, cannot be null, its length must be >= 1
primaries: FloatArray RGB primaries as an array of 6 (xy) or 9 (XYZ) floats
whitePoint: WhitePoint Reference white as an array of 2 (xy) or 3 (XYZ) floats
oetf: (Double) -> Double Opto-electronic transfer function, cannot be null
eotf: (Double) -> Double Electro-optical transfer function, cannot be null
min: Float The minimum valid value in this color space's RGB range
max: Float The maximum valid value in this color space's RGB range
Exceptions
IllegalArgumentException If any of the following conditions is met:

<init>

Rgb(
    name: String,
    toXYZ: FloatArray,
    function: TransferParameters)

Creates a new RGB color space using a 3x3 column-major transform matrix. The transform matrix must convert from the RGB space to the profile connection space CIE XYZ.

The range of the color space is imposed to be [0..1].

Parameters
name: String Name of the color space, cannot be null, its length must be >= 1
toXYZ: FloatArray 3x3 column-major transform matrix from RGB to the profile connection space CIE XYZ as an array of 9 floats, cannot be null
function: TransferParameters Parameters for the transfer functions
Exceptions
IllegalArgumentException If any of the following conditions is met:

<init>

Rgb(
    name: String,
    primaries: FloatArray,
    whitePoint: WhitePoint,
    function: TransferParameters)

Creates a new RGB color space using a specified set of primaries and a specified white point.

The primaries and white point can be specified in the CIE xyY space or in CIE XYZ. The length of the arrays depends on the chosen space:

| Spaces | Primaries length | White point length |
|--------|------------------|--------------------|
| xyY    | 6                | 2                  |
| XYZ    | 9                | 3                  |

When the primaries and/or white point are specified in xyY, the Y component does not need to be specified and is assumed to be 1.0. Only the xy components are required.

Parameters
name: String Name of the color space, cannot be null, its length must be >= 1
primaries: FloatArray RGB primaries as an array of 6 (xy) or 9 (XYZ) floats
whitePoint: WhitePoint Reference white as an array of 2 (xy) or 3 (XYZ) floats
function: TransferParameters Parameters for the transfer functions
Exceptions
IllegalArgumentException If any of the following conditions is met:

<init>

Rgb(
    name: String,
    toXYZ: FloatArray,
    gamma: Double)

Creates a new RGB color space using a 3x3 column-major transform matrix. The transform matrix must convert from the RGB space to the profile connection space CIE XYZ.

The range of the color space is imposed to be [0..1].

Parameters
name: String Name of the color space, cannot be null, its length must be >= 1
toXYZ: FloatArray 3x3 column-major transform matrix from RGB to the profile connection space CIE XYZ as an array of 9 floats, cannot be null
gamma: Double Gamma to use as the transfer function
Exceptions
IllegalArgumentException If any of the following conditions is met:

See Also

<init>

Rgb(
    name: String,
    primaries: FloatArray,
    whitePoint: WhitePoint,
    gamma: Double)

Creates a new RGB color space using a specified set of primaries and a specified white point.

The primaries and white point can be specified in the CIE xyY space or in CIE XYZ. The length of the arrays depends on the chosen space:

| Spaces | Primaries length | White point length |
|--------|------------------|--------------------|
| xyY    | 6                | 2                  |
| XYZ    | 9                | 3                  |

When the primaries and/or white point are specified in xyY, the Y component does not need to be specified and is assumed to be 1.0. Only the xy components are required.

Parameters
name: String Name of the color space, cannot be null, its length must be >= 1
primaries: FloatArray RGB primaries as an array of 6 (xy) or 9 (XYZ) floats
whitePoint: WhitePoint Reference white as an array of 2 (xy) or 3 (XYZ) floats
gamma: Double Gamma to use as the transfer function
Exceptions
IllegalArgumentException If any of the following conditions is met:

See Also

Public methods

equals

fun equals(other: Any?): Boolean

fromLinear

fun fromLinear(
    r: Float,
    g: Float,
    b: Float
): FloatArray

Encodes an RGB value from linear space to this color space's "gamma space". This is achieved by applying this color space's opto-electronic transfer function to the supplied values.

Refer to the documentation of Rgb for more information about transfer functions and their use for encoding and decoding RGB values.

Parameters
r: Float The red component to encode from linear space
g: Float The green component to encode from linear space
b: Float The blue component to encode from linear space
Return
A new array of 3 floats containing non-linear RGB values

See Also

fromLinear

fun fromLinear(v: FloatArray): FloatArray

Encodes an RGB value from linear space to this color space's "gamma space". This is achieved by applying this color space's opto-electronic transfer function to the first 3 values of the supplied array. The result is stored back in the input array.

Refer to the documentation of Rgb for more information about transfer functions and their use for encoding and decoding RGB values.

Parameters
v: FloatArray A non-null array of linear RGB values, its length must be at least 3
Return
A new array of 3 floats containing non-linear RGB values

See Also

fromXyz

fun fromXyz(v: FloatArray): FloatArray

Converts tristimulus values from the CIE XYZ space to this color space's color model. The resulting value is passed back in the specified array.

The specified array's length must be at least equal to to the number of color components as returned by ColorModel.componentCount, and its first 3 values must be the XYZ components to convert from.

Parameters
v: FloatArray An array of color components containing the XYZ values to convert from, and large enough to hold the number of components of this color space's model
Return
The array passed in parameter

See Also

getInverseTransform

fun getInverseTransform(): FloatArray

Returns the inverse transform of this color space as a new array. The inverse transform is used to convert from XYZ to RGB (with the same white point as this color space). To connect color spaces, you must first adapt them to the same white point.

It is recommended to use ColorSpace.connect to convert between color spaces.

Return
A new array of 9 floats

See Also

getInverseTransform

fun getInverseTransform(inverseTransform: FloatArray): FloatArray

Copies the inverse transform of this color space in specified array. The inverse transform is used to convert from XYZ to RGB (with the same white point as this color space). To connect color spaces, you must first adapt them to the same white point.

It is recommended to use ColorSpace.connect to convert between color spaces.

Parameters
inverseTransform: FloatArray The destination array, cannot be null, its length must be >= 9
Return
The destination array passed as a parameter

See Also

getMaxValue

fun getMaxValue(component: Int): Float

Returns the maximum valid value for the specified component of this color space's color model.

Parameters
component: Int The index of the component
Return
A floating point value greater than getMinValue

getMinValue

fun getMinValue(component: Int): Float

Returns the minimum valid value for the specified component of this color space's color model.

Parameters
component: Int The index of the component
Return
A floating point value less than getMaxValue

getPrimaries

fun getPrimaries(): FloatArray

Returns the primaries of this color space as a new array of 6 floats. The Y component is assumed to be 1 and is therefore not copied into the destination. The x and y components of the first primary are written in the array at positions 0 and 1 respectively.

Return
A new non-null array of 2 floats

See Also

getPrimaries

fun getPrimaries(primaries: FloatArray): FloatArray

Copies the primaries of this color space in specified array. The Y component is assumed to be 1 and is therefore not copied into the destination. The x and y components of the first primary are written in the array at positions 0 and 1 respectively.

Parameters
primaries: FloatArray The destination array, cannot be null, its length must be >= 6
Return
The destination array passed as a parameter

See Also

getTransform

fun getTransform(): FloatArray

Returns the transform of this color space as a new array. The transform is used to convert from RGB to XYZ (with the same white point as this color space). To connect color spaces, you must first adapt them to the same white point.

It is recommended to use ColorSpace.connect to convert between color spaces.

Return
A new array of 9 floats

getTransform

fun getTransform(transform: FloatArray): FloatArray

Copies the transform of this color space in specified array. The transform is used to convert from RGB to XYZ (with the same white point as this color space). To connect color spaces, you must first adapt them to the same white point.

It is recommended to use ColorSpace.connect to convert between color spaces.

Parameters
transform: FloatArray The destination array, cannot be null, its length must be >= 9
Return
The destination array passed as a parameter

hashCode

fun hashCode(): Int

toLinear

fun toLinear(
    r: Float,
    g: Float,
    b: Float
): FloatArray

Decodes an RGB value to linear space. This is achieved by applying this color space's electro-optical transfer function to the supplied values.

Refer to the documentation of Rgb for more information about transfer functions and their use for encoding and decoding RGB values.

Parameters
r: Float The red component to decode to linear space
g: Float The green component to decode to linear space
b: Float The blue component to decode to linear space
Return
A new array of 3 floats containing linear RGB values

See Also

toLinear

fun toLinear(v: FloatArray): FloatArray

Decodes an RGB value to linear space. This is achieved by applying this color space's electro-optical transfer function to the first 3 values of the supplied array. The result is stored back in the input array.

Refer to the documentation of Rgb for more information about transfer functions and their use for encoding and decoding RGB values.

Parameters
v: FloatArray A non-null array of non-linear RGB values, its length must be at least 3
Return
The specified array

See Also

toXyz

fun toXyz(v: FloatArray): FloatArray

Converts a color value from this color space's model to tristimulus CIE XYZ values. If the color model of this color space is not RGB, it is assumed that the target CIE XYZ space uses a D50 standard illuminant.

The specified array's length must be at least equal to to the number of color components as returned by ColorModel.componentCount.

Parameters
v: FloatArray An array of color components containing the color space's color value to convert to XYZ, and large enough to hold the resulting tristimulus XYZ values
Return
The array passed in parameter

See Also

Properties

eotf

val eotf: (Double) -> Double

Returns the electro-optical transfer function (EOTF) of this color space. The inverse function is the opto-electronic transfer function (OETF) returned by oetf. These functions are defined to satisfy the following equality for x in [0..1]:

    OETF(EOTF(x) = EOTF(OETF(x)) = x

For RGB colors, this function can be used to convert from "gamma space" (gamma encoded) to linear space. The terms gamma space and gamma encoded are frequently used because many EOTFs can be closely approximated using a simple power function of the form x^γ (the approximation of the sRGB EOTF uses γ = 2.2 for instance).

Return
A transfer function that converts from "gamma space" to linear space

isSrgb

val isSrgb: Boolean

Indicates whether this color space is the sRGB color space or equivalent to the sRGB color space.

A color space is considered sRGB if it meets all the following conditions:

Its primaries are within 1e-3 of the true sRGB primaries.

Its white point is within 1e-3 of the CIE standard illuminant D65.

  • Its opto-electronic transfer function is not linear.
  • Its electro-optical transfer function is not linear.
  • Its transfer functions yield values within 1e-3 of ColorSpaces.Srgb.
  • Its range is [0..1].

This method always returns true for ColorSpaces.Srgb.

Return
True if this color space is the sRGB color space (or a close approximation), false otherwise

isWideGamut

val isWideGamut: Boolean

Returns whether this color space is a wide-gamut color space. An RGB color space is wide-gamut if its gamut entirely contains the sRGB gamut and if the area of its gamut is 90% of greater than the area of the NTSC gamut.

Return
True if this color space is a wide-gamut color space, false otherwise

oetf

val oetf: (Double) -> Double

Returns the opto-electronic transfer function (OETF) of this color space. The inverse function is the electro-optical transfer function (EOTF) returned by eotf. These functions are defined to satisfy the following equality for x ∈ [0..1]:

    OETF(EOTF(x) = EOTF(OETF(x)) = x

For RGB colors, this function can be used to convert from linear space to "gamma space" (gamma encoded). The terms gamma space and gamma encoded are frequently used because many OETFs can be closely approximated using a simple power function of the form x^γ (the approximation of the sRGB OETF uses γ = 2.2 for instance).

Return
A transfer function that converts from linear space to "gamma space"

transferParameters

val transferParameters: TransferParameters?

Returns the parameters used by the electro-optical and opto-electronic transfer functions. If the transfer functions do not match the ICC parametric curves defined in ICC.1:2004-10 (section 10.15), this method returns null.

See TransferParameters for a full description of the transfer functions.

Return
An instance of TransferParameters or null if this color space's transfer functions do not match the equation defined in TransferParameters

whitePoint

val whitePoint: WhitePoint