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Rgb

public final class Rgb extends ColorSpace

java.lang.Object
   ↳ androidx.compose.ui.graphics.colorspace.ColorSpace
     ↳ androidx.compose.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:

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

Rgb(
    @NonNull String name,
    @NonNull float[] toXYZ,
    @NonNull TransferParameters function
)

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

Rgb(@NonNull String name, @NonNull float[] toXYZ, double gamma)

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

Rgb(
    @NonNull String name,
    @NonNull float[] primaries,
    @NonNull WhitePoint whitePoint,
    @NonNull TransferParameters function
)

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

Rgb(
    @NonNull String name,
    @NonNull float[] primaries,
    @NonNull WhitePoint whitePoint,
    double gamma
)

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

Rgb(
    @NonNull String name,
    @NonNull float[] toXYZ,
    @NonNull Function1<@NonNull Double, @NonNull Double> oetf,
    @NonNull Function1<@NonNull Double, @NonNull Double> eotf
)

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

Rgb(
    @NonNull String name,
    @NonNull float[] primaries,
    @NonNull WhitePoint whitePoint,
    @NonNull Function1<@NonNull Double, @NonNull Double> oetf,
    @NonNull Function1<@NonNull Double, @NonNull Double> eotf,
    float min,
    float max
)

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

Public methods

boolean
equals(Object other)
final @NonNull float[]
fromLinear(@NonNull float[] v)

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

final @NonNull float[]
fromLinear(float r, float g, float b)

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

@NonNull float[]
fromXyz(@NonNull float[] v)

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

final @NonNull Function1<@NonNull Double, @NonNull Double>

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

final @NonNull float[]

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

final @NonNull float[]
getInverseTransform(@NonNull float[] inverseTransform)

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

float
getMaxValue(int component)

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

float
getMinValue(int component)

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

final @NonNull Function1<@NonNull Double, @NonNull Double>

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

final @NonNull float[]

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

final @NonNull float[]
getPrimaries(@NonNull float[] primaries)

Copies the primaries of this color space in specified array.

final TransferParameters

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

final @NonNull float[]

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

final @NonNull float[]
getTransform(@NonNull float[] transform)

Copies the transform of this color space in specified array.

final @NonNull WhitePoint
int
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.

final @NonNull float[]
toLinear(@NonNull float[] v)

Decodes an RGB value to linear space.

final @NonNull float[]
toLinear(float r, float g, float b)

Decodes an RGB value to linear space.

@NonNull float[]
toXyz(@NonNull float[] v)

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

Inherited methods

From androidx.compose.ui.graphics.colorspace.ColorSpace
final @NonNull float[]
fromXyz(float x, float y, float z)

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

final int

Returns the number of components that form a color value according to this color space's color model.

final @NonNull ColorModel

The color model of this color space.

final @NonNull String

Returns the name of this color space.

@NonNull String

Returns a string representation of the object.

final @NonNull float[]
toXyz(float r, float g, float b)

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

Public constructors

Rgb

public Rgb(
    @NonNull String name,
    @NonNull float[] toXYZ,
    @NonNull TransferParameters function
)

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
@NonNull String name

Name of the color space, cannot be null, its length must be >= 1

@NonNull float[] toXYZ

3x3 column-major transform matrix from RGB to the profile connection space CIE XYZ as an array of 9 floats, cannot be null

@NonNull TransferParameters function

Parameters for the transfer functions

Throws
kotlin.IllegalArgumentException

If any of the following conditions is met:

  • The name is null or has a length of 0.

  • Gamma is negative.

Rgb

public Rgb(@NonNull String name, @NonNull float[] toXYZ, double gamma)

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
@NonNull String name

Name of the color space, cannot be null, its length must be >= 1

@NonNull float[] toXYZ

3x3 column-major transform matrix from RGB to the profile connection space CIE XYZ as an array of 9 floats, cannot be null

double gamma

Gamma to use as the transfer function

Throws
kotlin.IllegalArgumentException

If any of the following conditions is met:

  • The name is null or has a length of 0.

  • Gamma is negative.

See also
get

Rgb

public Rgb(
    @NonNull String name,
    @NonNull float[] primaries,
    @NonNull WhitePoint whitePoint,
    @NonNull TransferParameters function
)

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
@NonNull String name

Name of the color space, cannot be null, its length must be >= 1

@NonNull float[] primaries

RGB primaries as an array of 6 (xy) or 9 (XYZ) floats

@NonNull WhitePoint whitePoint

Reference white as an array of 2 (xy) or 3 (XYZ) floats

@NonNull TransferParameters function

Parameters for the transfer functions

Throws
kotlin.IllegalArgumentException

If any of the following conditions is met:

  • The name is null or has a length of 0.

  • The primaries array is null or has a length that is neither 6 or 9.

  • The white point array is null or has a length that is neither 2 or 3.

  • The transfer parameters are invalid.

Rgb

public Rgb(
    @NonNull String name,
    @NonNull float[] primaries,
    @NonNull WhitePoint whitePoint,
    double gamma
)

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
@NonNull String name

Name of the color space, cannot be null, its length must be >= 1

@NonNull float[] primaries

RGB primaries as an array of 6 (xy) or 9 (XYZ) floats

@NonNull WhitePoint whitePoint

Reference white as an array of 2 (xy) or 3 (XYZ) floats

double gamma

Gamma to use as the transfer function

Throws
kotlin.IllegalArgumentException

If any of the following conditions is met:

  • The name is null or has a length of 0.

  • The primaries array is null or has a length that is neither 6 or 9.

  • The white point array is null or has a length that is neither 2 or 3.

  • Gamma is negative.

See also
get

Rgb

public Rgb(
    @NonNull String name,
    @NonNull float[] toXYZ,
    @NonNull Function1<@NonNull Double, @NonNull Double> oetf,
    @NonNull Function1<@NonNull Double, @NonNull Double> eotf
)

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
@NonNull String name

Name of the color space, cannot be null, its length must be >= 1

@NonNull float[] toXYZ

3x3 column-major transform matrix from RGB to the profile connection space CIE XYZ as an array of 9 floats, cannot be null

@NonNull Function1<@NonNull Double, @NonNull Double> oetf

Opto-electronic transfer function, cannot be null

@NonNull Function1<@NonNull Double, @NonNull Double> eotf

Electro-optical transfer function, cannot be null

Throws
kotlin.IllegalArgumentException

If any of the following conditions is met:

  • The name is null or has a length of 0.

  • The OETF is null or the EOTF is null.

  • The minimum valid value is >= the maximum valid value.

Rgb

public Rgb(
    @NonNull String name,
    @NonNull float[] primaries,
    @NonNull WhitePoint whitePoint,
    @NonNull Function1<@NonNull Double, @NonNull Double> oetf,
    @NonNull Function1<@NonNull Double, @NonNull Double> eotf,
    float min,
    float max
)

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
@NonNull String name

Name of the color space, cannot be null, its length must be >= 1

@NonNull float[] primaries

RGB primaries as an array of 6 (xy) or 9 (XYZ) floats

@NonNull WhitePoint whitePoint

Reference white as an array of 2 (xy) or 3 (XYZ) floats

@NonNull Function1<@NonNull Double, @NonNull Double> oetf

Opto-electronic transfer function, cannot be null

@NonNull Function1<@NonNull Double, @NonNull Double> eotf

Electro-optical transfer function, cannot be null

float min

The minimum valid value in this color space's RGB range

float max

The maximum valid value in this color space's RGB range

Throws
kotlin.IllegalArgumentException

If any of the following conditions is met:

  • The name is null or has a length of 0.

  • The primaries array is null or has a length that is neither 6 or 9.

  • The white point array is null or has a length that is neither 2 or 3.

  • The OETF is null or the EOTF is null.

  • The minimum valid value is >= the maximum valid value.

Public methods

equals

public boolean equals(Object other)

fromLinear

public final @NonNull float[] fromLinear(@NonNull float[] v)

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
@NonNull float[] v

A non-null array of linear RGB values, its length must be at least 3

Returns
@NonNull float[]

v, containing non-linear RGB values

See also
fromLinear
toLinear

fromLinear

public final @NonNull float[] fromLinear(float r, float g, float b)

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
float r

The red component to encode from linear space

float g

The green component to encode from linear space

float b

The blue component to encode from linear space

Returns
@NonNull float[]

A new array of 3 floats containing non-linear RGB values

See also
fromLinear
toLinear

fromXyz

public @NonNull float[] fromXyz(@NonNull float[] v)

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
@NonNull float[] v

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. The minimum size is 3, but most color spaces have 4 components.

Returns
@NonNull float[]

The array passed in parameter v.

See also
fromXyz
toXyz

getEotf

public final @NonNull Function1<@NonNull Double, @NonNull DoublegetEotf()

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).

Returns
@NonNull Function1<@NonNull Double, @NonNull Double>

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

getInverseTransform

public final @NonNull float[] getInverseTransform()

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.

Returns
@NonNull float[]

A new array of 9 floats

See also
getTransform

getInverseTransform

public final @NonNull float[] getInverseTransform(@NonNull float[] inverseTransform)

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
@NonNull float[] inverseTransform

The destination array, cannot be null, its length must be >= 9

Returns
@NonNull float[]

The inverseTransform array passed as a parameter, modified to contain the inverse transform of this color space.

See also
getTransform

getMaxValue

public float getMaxValue(int component)

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

Parameters
int component

The index of the component, from 0 to 3, inclusive

Returns
float

A floating point value greater than getMinValue

getMinValue

public float getMinValue(int component)

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

Parameters
int component

The index of the component, from 0 to 3, inclusive.

Returns
float

A floating point value less than getMaxValue

getOetf

public final @NonNull Function1<@NonNull Double, @NonNull DoublegetOetf()

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).

Returns
@NonNull Function1<@NonNull Double, @NonNull Double>

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

getPrimaries

public final @NonNull float[] getPrimaries()

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.

Returns
@NonNull float[]

A new non-null array of 2 floats

See also
whitePoint

getPrimaries

public final @NonNull float[] getPrimaries(@NonNull float[] primaries)

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
@NonNull float[] primaries

The destination array, cannot be null, its length must be >= 6

Returns
@NonNull float[]

primaries array, modified to contain the primaries of this color space.

See also
getPrimaries

getTransferParameters

public final TransferParameters getTransferParameters()

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.

Returns
TransferParameters

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

getTransform

public final @NonNull float[] getTransform()

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.

Returns
@NonNull float[]

A new array of 9 floats

getTransform

public final @NonNull float[] getTransform(@NonNull float[] transform)

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
@NonNull float[] transform

The destination array, cannot be null, its length must be >= 9

Returns
@NonNull float[]

transform, modified to contain the transform for this color space.

getWhitePoint

public final @NonNull WhitePoint getWhitePoint()

hashCode

public int hashCode()

isSrgb

public boolean isSrgb()

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.

This method always returns true for ColorSpaces.Srgb.

Returns
boolean

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

isWideGamut

public boolean isWideGamut()

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.

Returns
boolean

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

toLinear

public final @NonNull float[] toLinear(@NonNull float[] v)

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
@NonNull float[] v

A non-null array of non-linear RGB values, its length must be at least 3

Returns
@NonNull float[]

v, containing linear RGB values

See also
toLinear
fromLinear

toLinear

public final @NonNull float[] toLinear(float r, float g, float b)

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
float r

The red component to decode to linear space

float g

The green component to decode to linear space

float b

The blue component to decode to linear space

Returns
@NonNull float[]

A new array of 3 floats containing linear RGB values

See also
toLinear
fromLinear

toXyz

public @NonNull float[] toXyz(@NonNull float[] v)

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
@NonNull float[] v

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, at least 3 values.

Returns
@NonNull float[]

The array passed in parameter v.

See also
toXyz
fromXyz